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Editor Work2022 Vol. 30, No. 3
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2022, 30(3): 599-608.
Abstract
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The successive implementation of national strategic deployments(e.g., the Western Development) and the gradual launch of some giant engineering(e.g., Sichuan-Tibet Railway) have been increasing the engineering activities on the Tibetan Plateau. Affected by rapid uplift, the tectonic movement in the plateau is active and the engineering geological conditions are complex. Reasonable site selection becomes the key for safe construction and operation of giant engineering. In this paper, the distance from the Holocene active fault and the relief amplitude are selected as evaluation factors, and the membership method is used to classify the engineering geological stability of the Tibetan Plateau. The results show that the whole region can be divided into five zones based on the engineering geological stability, namely poor, relatively poor, medium, relatively good and good. And the corresponding proportions in the regional land area are 22.48%, 18.01%, 28.79%, 22.72% and 8.00%, respectively. By interpreting the giant engineering and their disturbance disasters in the Tibetan Plateau, a total of 2176 giant engineering projects(e.g., railways, highways, hydropower stations, mines) are identified. And 6562 disturbance disasters are identified and mainly distributed in the poor and relatively poor zones. They take accounts of 69.66% in the total. Preliminary analysis shows that the result of engineering geological stability zoning has great significance for guiding the site selection of giant engineering in the Tibetan Plateau. Engineering disturbance disasters mainly occur in the high occurrence areas of nature disasters. The slope-cutting disturbance disasters mainly occur in the areas where landslides, thick colluvial slopes and strong unloading slopes exist. The main types of reservoir-induced disasters are landslide revival and slump in loose deposits, and the number of these disasters decreases rapidly after water storage.
The successive implementation of national strategic deployments(e.g., the Western Development) and the gradual launch of some giant engineering(e.g., Sichuan-Tibet Railway) have been increasing the engineering activities on the Tibetan Plateau. Affected by rapid uplift, the tectonic movement in the plateau is active and the engineering geological conditions are complex. Reasonable site selection becomes the key for safe construction and operation of giant engineering. In this paper, the distance from the Holocene active fault and the relief amplitude are selected as evaluation factors, and the membership method is used to classify the engineering geological stability of the Tibetan Plateau. The results show that the whole region can be divided into five zones based on the engineering geological stability, namely poor, relatively poor, medium, relatively good and good. And the corresponding proportions in the regional land area are 22.48%, 18.01%, 28.79%, 22.72% and 8.00%, respectively. By interpreting the giant engineering and their disturbance disasters in the Tibetan Plateau, a total of 2176 giant engineering projects(e.g., railways, highways, hydropower stations, mines) are identified. And 6562 disturbance disasters are identified and mainly distributed in the poor and relatively poor zones. They take accounts of 69.66% in the total. Preliminary analysis shows that the result of engineering geological stability zoning has great significance for guiding the site selection of giant engineering in the Tibetan Plateau. Engineering disturbance disasters mainly occur in the high occurrence areas of nature disasters. The slope-cutting disturbance disasters mainly occur in the areas where landslides, thick colluvial slopes and strong unloading slopes exist. The main types of reservoir-induced disasters are landslide revival and slump in loose deposits, and the number of these disasters decreases rapidly after water storage.
2022, 30(3): 609-620.
The reservoir-induced landslide is an important form of the impact of major engineering on geological environment and one of the frontier hot spots of research in engineering geology disciplines. Jinsha River Basin is located in the alpine gorge region at the eastern margin of the Tibetan Plateau, and has fragile geological environment and abundant hydro energy resources. It is one of the most densely built areas for hydropower plants and has 25 levels of cascade hydropower stations planned. However, the spatio-temporal effect of reservoir storage on reservoir bank reconstruction is still unclear. We took Xiluodu hydropower station as an example and study the distribution pattern of reservoir-induced landslides in the Jinsha River Basin. We use the multi-period remote sensing images from 2013 to 2020 to interpret the reservoir-induced landslides within the Xiluodu reservoir area. We finally acquire a total of 433 landslides. On this basis, we analyse the trend of the number and area of reservoir-induced landslides with impounding time. Subsequently, we statistically analyse the distribution of reservoir-induced landslides in relation to using the frequency ratio method. The six factors are elevation, slope, slope direction, engineering geological rock group, fracture and distance from dead water level. The assessment on susceptibility of each single factor was also carried out, and the reliability of the assessment results was verified by using the AUC method. And based on the evaluation results, four factors were selected to evaluate the susceptibility of reservoir-induced landslides. The four factors are elevation, distance from the fracture, slope and distance from the dead water level. The study concludes that:(1)Reservoir-induced landslides mainly occur during the initial 3-4 years of impounding, after which the number and area of landslides gradually decrease and the bank slope exogenetic reconstruction gradually stabilizes. (2)The range of slope and aspect that are liable to induce landslides are 30°~60°and SE, W, NW direction respectively. Landslide development is more favorable in the range of 400~3200 m from the fracture and 100~200 m from the reservoir area. (3)The AUC is 0.912, which proved that the evaluation result is highly reliable. (4)The main control factors of reservoir-induced landslide are the elevation and distance from the dead water level. The extremely high susceptibility area and high susceptibility area are mainly located within 400 m from the reservoir area and below 1 km in elevation. In this paper, a database of reservoir-induced landslides is established for the first time using multi-period remote sensing images, and the research results can provide support for the planning and construction of hydropower plants and disaster prevention and mitigation.
The reservoir-induced landslide is an important form of the impact of major engineering on geological environment and one of the frontier hot spots of research in engineering geology disciplines. Jinsha River Basin is located in the alpine gorge region at the eastern margin of the Tibetan Plateau, and has fragile geological environment and abundant hydro energy resources. It is one of the most densely built areas for hydropower plants and has 25 levels of cascade hydropower stations planned. However, the spatio-temporal effect of reservoir storage on reservoir bank reconstruction is still unclear. We took Xiluodu hydropower station as an example and study the distribution pattern of reservoir-induced landslides in the Jinsha River Basin. We use the multi-period remote sensing images from 2013 to 2020 to interpret the reservoir-induced landslides within the Xiluodu reservoir area. We finally acquire a total of 433 landslides. On this basis, we analyse the trend of the number and area of reservoir-induced landslides with impounding time. Subsequently, we statistically analyse the distribution of reservoir-induced landslides in relation to using the frequency ratio method. The six factors are elevation, slope, slope direction, engineering geological rock group, fracture and distance from dead water level. The assessment on susceptibility of each single factor was also carried out, and the reliability of the assessment results was verified by using the AUC method. And based on the evaluation results, four factors were selected to evaluate the susceptibility of reservoir-induced landslides. The four factors are elevation, distance from the fracture, slope and distance from the dead water level. The study concludes that:(1)Reservoir-induced landslides mainly occur during the initial 3-4 years of impounding, after which the number and area of landslides gradually decrease and the bank slope exogenetic reconstruction gradually stabilizes. (2)The range of slope and aspect that are liable to induce landslides are 30°~60°and SE, W, NW direction respectively. Landslide development is more favorable in the range of 400~3200 m from the fracture and 100~200 m from the reservoir area. (3)The AUC is 0.912, which proved that the evaluation result is highly reliable. (4)The main control factors of reservoir-induced landslide are the elevation and distance from the dead water level. The extremely high susceptibility area and high susceptibility area are mainly located within 400 m from the reservoir area and below 1 km in elevation. In this paper, a database of reservoir-induced landslides is established for the first time using multi-period remote sensing images, and the research results can provide support for the planning and construction of hydropower plants and disaster prevention and mitigation.
2022, 30(3): 621-634.
Rockburst is one of the main risks in the process of underground tunnel construction in high geostress area, which is characterized by sudden occurrence and high harmfulness. The quantitative prediction of rockburst damage degree is of great guiding significance to the design and construction of underground engineering in high in-situ stress area. By collecting a large number of characteristic parameters of typical rockburst tunnels at home and abroad and conducting statistical analysis, this paper establishes a quantitative rockburst risk prediction model that can predict the maximum depth of rockburst pit. At the same time, combined with the laboratory test, rock strength damage criterion and multiple linear regression inversion method for geostress field, the rockburst risk of Sejila Tunnel of one railway is quantitatively predicted, and the rockburst risk is compared and analyzed with similar engineering cases of Bayu tunnel in China. The conclusions are as follows: (1)The rockburst prediction model based on the linear statistical relationship between the depth of rockburst tunnel and the stress intensity ratio can realize the quantitative prediction and evaluation of rockburst risk. (2)The geostress field of Sejila Tunnel is obviously controlled by tectonic action, and the geostress along the whole line is generally high. In addition, the hard rock section along the tunnel accounts for a large proportion and the rockburst tendency is high, so the rockburst risk of high geostress is prominent. (3)It is predicted that the rock burst risk section of medium grade or above in Sejila Tunnel can reach 12 188 m, accounting for 32.1% of the total length of the tunnel. The rock burst will mainly occur in the section of weakly weathered granite, diorite and gneiss with large burial depth. (4)The predicted maximum pit depth of Sejila Tunnel is 3.42 m, which is less than the measured maximum pit depth(3.5 m) of the already connected Bayu tunnel. Under reasonable construction and prevention and control measures, the rock burst risk of Sejila Tunnel is generally controllable.
Rockburst is one of the main risks in the process of underground tunnel construction in high geostress area, which is characterized by sudden occurrence and high harmfulness. The quantitative prediction of rockburst damage degree is of great guiding significance to the design and construction of underground engineering in high in-situ stress area. By collecting a large number of characteristic parameters of typical rockburst tunnels at home and abroad and conducting statistical analysis, this paper establishes a quantitative rockburst risk prediction model that can predict the maximum depth of rockburst pit. At the same time, combined with the laboratory test, rock strength damage criterion and multiple linear regression inversion method for geostress field, the rockburst risk of Sejila Tunnel of one railway is quantitatively predicted, and the rockburst risk is compared and analyzed with similar engineering cases of Bayu tunnel in China. The conclusions are as follows: (1)The rockburst prediction model based on the linear statistical relationship between the depth of rockburst tunnel and the stress intensity ratio can realize the quantitative prediction and evaluation of rockburst risk. (2)The geostress field of Sejila Tunnel is obviously controlled by tectonic action, and the geostress along the whole line is generally high. In addition, the hard rock section along the tunnel accounts for a large proportion and the rockburst tendency is high, so the rockburst risk of high geostress is prominent. (3)It is predicted that the rock burst risk section of medium grade or above in Sejila Tunnel can reach 12 188 m, accounting for 32.1% of the total length of the tunnel. The rock burst will mainly occur in the section of weakly weathered granite, diorite and gneiss with large burial depth. (4)The predicted maximum pit depth of Sejila Tunnel is 3.42 m, which is less than the measured maximum pit depth(3.5 m) of the already connected Bayu tunnel. Under reasonable construction and prevention and control measures, the rock burst risk of Sejila Tunnel is generally controllable.
2022, 30(3): 635-647.
The geological hazard risk assessment is guiding significance to local disaster prevention and mitigation. Taking the Lancang River major hydropower engineering area as the research area, this study was based on the remote sensing interpretation and field surveys, and 9 impact factors(the elevation, slope, aspect, difference vegetation index(NDVI), distance to reservoir area, engineering geological rock group, fault zone density, average annual rainfall and peak acceleration of earthquake) were selected to evaluate the risk assessment based on weighted information model. Then, population density, hydropower station, road, land cover type and GDP are taken as the disaster bearing bodies to carry out vulnerability evaluation. Finally, the risk matrix of geological disaster is constructed, and the risk and vulnerability information is integrated to complete the risk evaluation of geological disaster. The evaluation results show that: the extremely high and high risk areas are mainly distributed in the vicinity of Wunonglong reservoir and its upstream hydropower station, and the regions with relatively intensive human activities on both sides of the downstream reservoir, while the medium risk areas are mainly distributed in the two sides of Wunonglong reservoir and the whole region of Wunonglong Toba Hydropower Station, scattered in the downstream. The low risk area is mainly distributed in the middle mountain valley. This study accurately evaluates the risk of geological hazards, which can provide scientific basis and technical guidance for the risk planning of geological hazards in Lancang River Basin.
The geological hazard risk assessment is guiding significance to local disaster prevention and mitigation. Taking the Lancang River major hydropower engineering area as the research area, this study was based on the remote sensing interpretation and field surveys, and 9 impact factors(the elevation, slope, aspect, difference vegetation index(NDVI), distance to reservoir area, engineering geological rock group, fault zone density, average annual rainfall and peak acceleration of earthquake) were selected to evaluate the risk assessment based on weighted information model. Then, population density, hydropower station, road, land cover type and GDP are taken as the disaster bearing bodies to carry out vulnerability evaluation. Finally, the risk matrix of geological disaster is constructed, and the risk and vulnerability information is integrated to complete the risk evaluation of geological disaster. The evaluation results show that: the extremely high and high risk areas are mainly distributed in the vicinity of Wunonglong reservoir and its upstream hydropower station, and the regions with relatively intensive human activities on both sides of the downstream reservoir, while the medium risk areas are mainly distributed in the two sides of Wunonglong reservoir and the whole region of Wunonglong Toba Hydropower Station, scattered in the downstream. The low risk area is mainly distributed in the middle mountain valley. This study accurately evaluates the risk of geological hazards, which can provide scientific basis and technical guidance for the risk planning of geological hazards in Lancang River Basin.
2022, 30(3): 648-655.
This paper is based on the latest remote sensing data of domestic gaogao-1 satellite(hereinafter referred to as GF-1) and collects ETM data in 1990, 2000 and 2010 to assist remote sensing interpretation. It finds out the distribution of major projects within 280 000 km2 in the area adjacent to Southeast Asia. The major engineering activities in the study area are mainly hydropower(water conservancy) projects and transportation projects. Additionally there are also some mine engineering activities. The latest development and distribution of landslides disturbed by major projects are interpreted. There are as many as 1373 landslides that pose a direct threat to the living environment in the area. They include 625 induced by hydropower projects, 723 induced by traffic projects and 22 induced by mining projects. The correlation analysis with the geological environment shows that the major engineering disturbance landslides in the area are mostly developed on the sunny slope with frequent human activities at an altitude of 1000~3000 m and a slope of more than 25°, and the lithology is mainly soft rock, hard rock and engineering geological rock group with alternating soft and hard rocks.
This paper is based on the latest remote sensing data of domestic gaogao-1 satellite(hereinafter referred to as GF-1) and collects ETM data in 1990, 2000 and 2010 to assist remote sensing interpretation. It finds out the distribution of major projects within 280 000 km2 in the area adjacent to Southeast Asia. The major engineering activities in the study area are mainly hydropower(water conservancy) projects and transportation projects. Additionally there are also some mine engineering activities. The latest development and distribution of landslides disturbed by major projects are interpreted. There are as many as 1373 landslides that pose a direct threat to the living environment in the area. They include 625 induced by hydropower projects, 723 induced by traffic projects and 22 induced by mining projects. The correlation analysis with the geological environment shows that the major engineering disturbance landslides in the area are mostly developed on the sunny slope with frequent human activities at an altitude of 1000~3000 m and a slope of more than 25°, and the lithology is mainly soft rock, hard rock and engineering geological rock group with alternating soft and hard rocks.
2022, 30(3): 656-671.
The Himalayas is featured by developed tectonic faults, frequent seismic activities, intense neotectonics movement, and abnormal activity of endogenic and exogenic dynamic geological processes. The geological hazards caused by highway construction in plateaus and canyons are extremely developed and poses a great harm to the safe operation of highways in the region. In this study, field investigation and theoretical analysis were carried out to investigate the development pattern of disturbed geological hazards, damage characteristics of protective structures and formation mechanism of road slopes in the Himalayas. According to the slope material composition and stratigraphic structure type, the classification method of highway slope types was put forward and four failure patterns of highway slope were proposed. Spatial statistical method was applied to investigate the characteristics and mechanisms of the geological hazards. It was found that the formation and distribution of road slope hazards in canyons are closely related to regional fault structures, seismic intensity, geotechnical structure types, and climatic and environmental conditions. A few quantitative numerical indicators were further presented to illustrate their relationships. On top of that, the coupling mechanism of endogenic and exogenic geological processes of geological hazards evolution in the Himalayan region was discussed. It is concluded that the relaxation effect of slope rock mass and landslide was induced by the differential uplift and river undercutting and the results of the coupled endogenic and exogenic geological dynamics. On the time scale of road engineering, climate variation is the most active exogenic dynamic geological processes in the region at present. In terms of slope geological hazard protection, there are many uncertainties in the stability of hazard protection projects. In the survey, 10% of the hazard prevention projects showed different degrees of deformation and damage. Through the analysis of the damage characteristics of the protective structure, the reasons for the difference between the protective effect of the protective structure and the stability of the structure itself in the slope disaster protection were clarified. It is suggested that the selection and optimization of the protective structures need to consider the slope engineering geological characteristics, geohazards types, movement paths, failure modes and the engineering compatibility, et al., and adopt multiple protective measures for optimal combination to minimize the occurrence of geohazards and its potential impacts.
The Himalayas is featured by developed tectonic faults, frequent seismic activities, intense neotectonics movement, and abnormal activity of endogenic and exogenic dynamic geological processes. The geological hazards caused by highway construction in plateaus and canyons are extremely developed and poses a great harm to the safe operation of highways in the region. In this study, field investigation and theoretical analysis were carried out to investigate the development pattern of disturbed geological hazards, damage characteristics of protective structures and formation mechanism of road slopes in the Himalayas. According to the slope material composition and stratigraphic structure type, the classification method of highway slope types was put forward and four failure patterns of highway slope were proposed. Spatial statistical method was applied to investigate the characteristics and mechanisms of the geological hazards. It was found that the formation and distribution of road slope hazards in canyons are closely related to regional fault structures, seismic intensity, geotechnical structure types, and climatic and environmental conditions. A few quantitative numerical indicators were further presented to illustrate their relationships. On top of that, the coupling mechanism of endogenic and exogenic geological processes of geological hazards evolution in the Himalayan region was discussed. It is concluded that the relaxation effect of slope rock mass and landslide was induced by the differential uplift and river undercutting and the results of the coupled endogenic and exogenic geological dynamics. On the time scale of road engineering, climate variation is the most active exogenic dynamic geological processes in the region at present. In terms of slope geological hazard protection, there are many uncertainties in the stability of hazard protection projects. In the survey, 10% of the hazard prevention projects showed different degrees of deformation and damage. Through the analysis of the damage characteristics of the protective structure, the reasons for the difference between the protective effect of the protective structure and the stability of the structure itself in the slope disaster protection were clarified. It is suggested that the selection and optimization of the protective structures need to consider the slope engineering geological characteristics, geohazards types, movement paths, failure modes and the engineering compatibility, et al., and adopt multiple protective measures for optimal combination to minimize the occurrence of geohazards and its potential impacts.
2022, 30(3): 672-687.
This paper aims to explore the causal factors and road engineering disturbance effect of landslides in the Bailong River Basin. We collected 2730 landslides through fieldwork and data collection. Several factors were extracted by GIS spatial analysis and remote sensing interpretation, including topography, geological structure, human activities, et al. The influence of factors on the landslides was analyzed based on the Information Value Model. We clustered landslides with the spatially constrained multivariate clustering method according to the geographic location and characteristics of factors. The importance of factors in clusters was obtained by the random forest algorithm. The disturbance effect of road engineering on landslides was analyzed. Results show that the landslides were affected by various factors including altitude, slope, aspect, rainfall, lithology, fault distance, vegetation coverage, land use, and road engineering disturbance. Landslides can be clustered into four clusters. The importance of factors that cause landslides is different among the clusters. "The multi-year average rainfall" is more important in Cluster A, located in the middle reaches of the Bailong River."Elevation" is the most important for Cluster B, located in the upper reaches of the Bailong River."The distance from the fault" is more important for Cluster C, located in the northeast direction of Tanchang."The distance from the road" plays a more important role in Cluster D, located in the lower reaches of the Bailong River. The disturbance effect of road engineering is less important in areas with a fragile geological environment, but is more important in areas with better geological environment conditions.
This paper aims to explore the causal factors and road engineering disturbance effect of landslides in the Bailong River Basin. We collected 2730 landslides through fieldwork and data collection. Several factors were extracted by GIS spatial analysis and remote sensing interpretation, including topography, geological structure, human activities, et al. The influence of factors on the landslides was analyzed based on the Information Value Model. We clustered landslides with the spatially constrained multivariate clustering method according to the geographic location and characteristics of factors. The importance of factors in clusters was obtained by the random forest algorithm. The disturbance effect of road engineering on landslides was analyzed. Results show that the landslides were affected by various factors including altitude, slope, aspect, rainfall, lithology, fault distance, vegetation coverage, land use, and road engineering disturbance. Landslides can be clustered into four clusters. The importance of factors that cause landslides is different among the clusters. "The multi-year average rainfall" is more important in Cluster A, located in the middle reaches of the Bailong River."Elevation" is the most important for Cluster B, located in the upper reaches of the Bailong River."The distance from the fault" is more important for Cluster C, located in the northeast direction of Tanchang."The distance from the road" plays a more important role in Cluster D, located in the lower reaches of the Bailong River. The disturbance effect of road engineering is less important in areas with a fragile geological environment, but is more important in areas with better geological environment conditions.
2022, 30(3): 688-695.
This paper proposes the concept of hydrogeological structure of deep-incised river valleys. It aims to effectively prevent and control the hydrogeological problems that may be encountered in the construction and operation of water conservancy and hydropower projects. The proposal of this concept is guided by the theory of rock engineering geomechanics and is based on the understanding of rock mass structure and hydrogeological structure. In China, most of the hydropower projects are built in deep-incised river valleys in western areas. With regard to the geological and environmental features in the areas, this paper summarizes four types of deep-incised river valleys including bank slope type, river-paralleling type, river-crossing type and regional type. It also summarizes their corresponding characteristics. In addition, this paper also preliminarily expounds the control mechanism of these types of valleys on the engineering hydrogeological problems during the construction of hydropower projects.
This paper proposes the concept of hydrogeological structure of deep-incised river valleys. It aims to effectively prevent and control the hydrogeological problems that may be encountered in the construction and operation of water conservancy and hydropower projects. The proposal of this concept is guided by the theory of rock engineering geomechanics and is based on the understanding of rock mass structure and hydrogeological structure. In China, most of the hydropower projects are built in deep-incised river valleys in western areas. With regard to the geological and environmental features in the areas, this paper summarizes four types of deep-incised river valleys including bank slope type, river-paralleling type, river-crossing type and regional type. It also summarizes their corresponding characteristics. In addition, this paper also preliminarily expounds the control mechanism of these types of valleys on the engineering hydrogeological problems during the construction of hydropower projects.
2022, 30(3): 696-707.
This paper examines the variation characteristics of principal stress, lateral pressure coefficient and stress accumulation level with depth in the five tectonic stress zones(i.e., the Bayankala Mountain, Longmenshan-Songpan, Motuo-changdu, Sichuan-Yunnan and southwestern Yunnan stress zones) within the southeastern Tibetan Plateau. It uses the statistical regression analysis based on an extensive collection of 900 groups of in-situ stress data. The stress direction characteristics were also analyzed based on a combined analysis of focal mechanism with the orientation of the maximum horizontal in-situ stress. The results show that: (1)In the Bayankala Mountain, Longmenshan-Songpan and Motuo-changdu stress zones, the stress gradients are relatively large, and the deep stress is dominated by the horizontal component; while, in the Sichuan-Yunnan and southwestern Yunnan stress zones, the stress gradients are relatively small, and the deep stress is dominated by the vertical component; showing a stress pattern of "strong in north and weak in south". (2)The ratio of average differential stress to average effective stress(μm), which is a parameter measuring the stress accumulation level, is relatively high in the Bayankala Mountain, Longmenshan-Songpan and Sichuan-Yunnan stress zones, suggesting a state closer to the limit equilibrium of friction, and thus a higher probability of earthquake. (3)The dominant direction of the maximum horizontal stress of the southeastern Tibet Plateau rotates clockwise around the eastern Himalayan syntaxis, which is consistent with the GPS velocity field and the dominant direction of the maximum horizontal stress derived from the focal mechanism in the middle and upper crust. Based on these results, we preliminarily concluded that the stress pattern of "strong in north and weak in south" may be owing to the dominances of block lateral extrusions in north and lower crustal flows in south. Finally, using rock burst risk as an index, the stability of major underground projects in each stress zone was evaluated based on the stress state. The results show that: the rockburst risks within 0~2 km buried depth in the southeastern Tibetan Plateau are mainly low, moderate and high and that extremely high rock burst risk only exists in local areas. Furthermore, the buried depths of the same rock burst risk level at different stress zones have obvious differences.
This paper examines the variation characteristics of principal stress, lateral pressure coefficient and stress accumulation level with depth in the five tectonic stress zones(i.e., the Bayankala Mountain, Longmenshan-Songpan, Motuo-changdu, Sichuan-Yunnan and southwestern Yunnan stress zones) within the southeastern Tibetan Plateau. It uses the statistical regression analysis based on an extensive collection of 900 groups of in-situ stress data. The stress direction characteristics were also analyzed based on a combined analysis of focal mechanism with the orientation of the maximum horizontal in-situ stress. The results show that: (1)In the Bayankala Mountain, Longmenshan-Songpan and Motuo-changdu stress zones, the stress gradients are relatively large, and the deep stress is dominated by the horizontal component; while, in the Sichuan-Yunnan and southwestern Yunnan stress zones, the stress gradients are relatively small, and the deep stress is dominated by the vertical component; showing a stress pattern of "strong in north and weak in south". (2)The ratio of average differential stress to average effective stress(μm), which is a parameter measuring the stress accumulation level, is relatively high in the Bayankala Mountain, Longmenshan-Songpan and Sichuan-Yunnan stress zones, suggesting a state closer to the limit equilibrium of friction, and thus a higher probability of earthquake. (3)The dominant direction of the maximum horizontal stress of the southeastern Tibet Plateau rotates clockwise around the eastern Himalayan syntaxis, which is consistent with the GPS velocity field and the dominant direction of the maximum horizontal stress derived from the focal mechanism in the middle and upper crust. Based on these results, we preliminarily concluded that the stress pattern of "strong in north and weak in south" may be owing to the dominances of block lateral extrusions in north and lower crustal flows in south. Finally, using rock burst risk as an index, the stability of major underground projects in each stress zone was evaluated based on the stress state. The results show that: the rockburst risks within 0~2 km buried depth in the southeastern Tibetan Plateau are mainly low, moderate and high and that extremely high rock burst risk only exists in local areas. Furthermore, the buried depths of the same rock burst risk level at different stress zones have obvious differences.
2022, 30(3): 708-719.
The Qinghai-Tibet Plateau is characterized by complex geological structure that has many unfavorable geological phenomena such as suture zones, faults and hot spring outcroppings. The phenomena tend to produce local sources of abnormal high heat. The transport line runs across the Qinghai-Tibet Plateau and is influenced by coupled effects of obvious geothermal anomalies and large buried depth. Thus the railway is vulnerable to the threat of high geothermal disaster. In this study, geothermal distribution in the Qinghai-Tibet Plateau is first analyzed. Then, the high geothermal risks of some typical deep and long tunnels of the transport line are quantitatively assessed. The results show that the distribution of ground temperature over the Qinghai-Tibet Plateau varies both spatially and temporally. Generally, the ground temperature in the Qinghai-Tibet Plateau is higher in south and east than in north and west, and has been increasing in the past 50 years. Typical tunnels, such as the Zheduoshan tunnel and the Layue tunnel, are subject to high geothermal risks of different degrees. The risk of high geothermal in the Layue tunnel is higher than that in the Zheduoshan tunnel. The distribution of high risk area along tunnel is related to buried depth and geological structure. In geothermal anomaly areas, special geological structure is the main cause of high geothermal. Furthermore, the controllability of high geothermal risk is evaluated by comparing with domestic and foreign tunnels having similar engineering geology backgrounds. It is concluded that, with reasonable engineering measures, the high geothermal risks of the Zheduoshan and Layue tunnel of the transport line are generally controllable. Nevertheless, it is still needed to strengthen the scientific and comprehensive control of high geothermal risk during the whole life cycle of the transport line.
The Qinghai-Tibet Plateau is characterized by complex geological structure that has many unfavorable geological phenomena such as suture zones, faults and hot spring outcroppings. The phenomena tend to produce local sources of abnormal high heat. The transport line runs across the Qinghai-Tibet Plateau and is influenced by coupled effects of obvious geothermal anomalies and large buried depth. Thus the railway is vulnerable to the threat of high geothermal disaster. In this study, geothermal distribution in the Qinghai-Tibet Plateau is first analyzed. Then, the high geothermal risks of some typical deep and long tunnels of the transport line are quantitatively assessed. The results show that the distribution of ground temperature over the Qinghai-Tibet Plateau varies both spatially and temporally. Generally, the ground temperature in the Qinghai-Tibet Plateau is higher in south and east than in north and west, and has been increasing in the past 50 years. Typical tunnels, such as the Zheduoshan tunnel and the Layue tunnel, are subject to high geothermal risks of different degrees. The risk of high geothermal in the Layue tunnel is higher than that in the Zheduoshan tunnel. The distribution of high risk area along tunnel is related to buried depth and geological structure. In geothermal anomaly areas, special geological structure is the main cause of high geothermal. Furthermore, the controllability of high geothermal risk is evaluated by comparing with domestic and foreign tunnels having similar engineering geology backgrounds. It is concluded that, with reasonable engineering measures, the high geothermal risks of the Zheduoshan and Layue tunnel of the transport line are generally controllable. Nevertheless, it is still needed to strengthen the scientific and comprehensive control of high geothermal risk during the whole life cycle of the transport line.
2022, 30(3): 720-728.
River incision is an important geological force for geomorphic evolution of deep valley. River incision and side erosion processes often influence the stability state and slope evolution of the slope on both sides of the valley. At present, little research results are available on the spatial distribution characteristics of slope rock mass and their quantitative relationship under the action of river incision. To some extent, this restricts the development of stability prediction of slope rock mass and susceptibility assessment of geological hazards in deep valley area. Based on the above background, this paper studies the spatial distribution characteristics of channel steepness index(ksn) and rock mass quality index in the study area. It uses on-site investigation, statistics, Matlab, Topotoolbox, ArcGIS, Origin and other tools and examines the BQ system of rock mass quality evaluation, the river hydraulic erosion model, the relavant relationships and internal mechanisms in the deep-cut valley area(Lancang-Jinsha River) and G214 Zuogong-Tiger Leaping Gorge section of the Qinghai-Tibet Plateau. The results show that the Pearson correlation coefficients of rock mass with fracture density, ksn and engineering rock group are 0.52, 0.67 and-0.11 respectively. The correlation degree between rock mass quality and ksn is the highest. Based on the shape extraction of cross section and analysis of stress characteristic area of valley slope, it is found that the characteristic distribution area of rock mass studied in this paper is mainly the slope section which responds sensitively to river downcutting in real time, i.e. the section strongly affected by river incision. Based on the research results, this paper suggests that ksn should be considered and used as an important evaluation index in evaluating the susceptibility of collapse disasters by characterizing river incision.
River incision is an important geological force for geomorphic evolution of deep valley. River incision and side erosion processes often influence the stability state and slope evolution of the slope on both sides of the valley. At present, little research results are available on the spatial distribution characteristics of slope rock mass and their quantitative relationship under the action of river incision. To some extent, this restricts the development of stability prediction of slope rock mass and susceptibility assessment of geological hazards in deep valley area. Based on the above background, this paper studies the spatial distribution characteristics of channel steepness index(ksn) and rock mass quality index in the study area. It uses on-site investigation, statistics, Matlab, Topotoolbox, ArcGIS, Origin and other tools and examines the BQ system of rock mass quality evaluation, the river hydraulic erosion model, the relavant relationships and internal mechanisms in the deep-cut valley area(Lancang-Jinsha River) and G214 Zuogong-Tiger Leaping Gorge section of the Qinghai-Tibet Plateau. The results show that the Pearson correlation coefficients of rock mass with fracture density, ksn and engineering rock group are 0.52, 0.67 and-0.11 respectively. The correlation degree between rock mass quality and ksn is the highest. Based on the shape extraction of cross section and analysis of stress characteristic area of valley slope, it is found that the characteristic distribution area of rock mass studied in this paper is mainly the slope section which responds sensitively to river downcutting in real time, i.e. the section strongly affected by river incision. Based on the research results, this paper suggests that ksn should be considered and used as an important evaluation index in evaluating the susceptibility of collapse disasters by characterizing river incision.
2022, 30(3): 729-739.
At 17:00 on June 1st, 2022, following the Lushan Earthquake in 2013, an MS6.1 earthquake occurred again in Lushan County, Ya'an City, Sichuan Province after 9 years. Earthquake is one of the most important factors that trigger geological hazards in mountainous areas, which usually leads to a large number of casualties and property losses. Rapidly and accurately obtaining the spatial distribution of earthquake-induced geological hazards is crucial for post-earthquake emergency rescue and temporary resettlement planning. Based on the global earthquake-induced landslide database, this paper employed Deep Forest algorithm to establish a near real-time prediction model for the spatial distribution probability of earthquake-induced landslides. The model was applied to the rapid prediction of geological hazards induced by the "6.1" Lushan Earthquake, and the prediction results of the spatial distribution probability of geological hazards were obtained within 1 hour after the earthquake. Meanwhile, we arrived at the seismic zone as soon as possible to conduct emergency investigation and model verification of geological hazards. The survey indicates that the geological hazards induced by this earthquake mainly consist of small collapses and landslides. The high-risk areas are mainly distributed in the intersection region of the northern Lushan County and the western Baoxing County. The number of geological hazards in the upper fault is significantly higher than that in the lower fault. Comparing the prediction results with the field survey in the basin of Baoxing Donghe, it can be concluded that the accuracy of the model is more than 80%. In particular, all large-scale landslides exactly occurred in the high-risk areas predicted by the model. The results confirm that the model enables to make up for the lack of timeliness of post-earthquake field investigation and remote sensing data acquisition and provides scientific support for emergency rescue.
At 17:00 on June 1st, 2022, following the Lushan Earthquake in 2013, an MS6.1 earthquake occurred again in Lushan County, Ya'an City, Sichuan Province after 9 years. Earthquake is one of the most important factors that trigger geological hazards in mountainous areas, which usually leads to a large number of casualties and property losses. Rapidly and accurately obtaining the spatial distribution of earthquake-induced geological hazards is crucial for post-earthquake emergency rescue and temporary resettlement planning. Based on the global earthquake-induced landslide database, this paper employed Deep Forest algorithm to establish a near real-time prediction model for the spatial distribution probability of earthquake-induced landslides. The model was applied to the rapid prediction of geological hazards induced by the "6.1" Lushan Earthquake, and the prediction results of the spatial distribution probability of geological hazards were obtained within 1 hour after the earthquake. Meanwhile, we arrived at the seismic zone as soon as possible to conduct emergency investigation and model verification of geological hazards. The survey indicates that the geological hazards induced by this earthquake mainly consist of small collapses and landslides. The high-risk areas are mainly distributed in the intersection region of the northern Lushan County and the western Baoxing County. The number of geological hazards in the upper fault is significantly higher than that in the lower fault. Comparing the prediction results with the field survey in the basin of Baoxing Donghe, it can be concluded that the accuracy of the model is more than 80%. In particular, all large-scale landslides exactly occurred in the high-risk areas predicted by the model. The results confirm that the model enables to make up for the lack of timeliness of post-earthquake field investigation and remote sensing data acquisition and provides scientific support for emergency rescue.
2022, 30(3): 740-750.
A debris flow hazard triggered by rainstorm occurred in Zhuozhui Gully,Xiajijiehaizi Gully and Zechawa Gully,Jiuzhaigou County,where is the epicenter of the Jiuzhaigou Earthquake on June 20,2019. About 2.79×104m3,3.7×104m3 and 2.67×104m3 solid materials rushed out of the three gullies respectively,caused damage to retaining walls and debris dams,buried part of the scenic road,disrupted traffic temporarily,and had no casualty. This paper identified the cause and mechanism of the debris flow disaster preliminarily,according to the field survey and remote sensing interpretation after the disaster. Cause of disaster is as follows. The earthquake-induced landslide produces a large number of new loose solid material sources and the original gully slope debris(including old debris flow debris) under the action of heavy rainfall to form debris flow. So the debris flows are the results of the earthquake and rainfall. Based on the investigation and analysis of longitudinal profile and typical cross section of gully before and after the debris flow,we find that the mechanisms of debris flow disaster mainly include the follows. (1)The debris flow erodes the old debris flow deposits,at the same time induces the landslide along the bank,so as enhances the debris flow scale and impact force and other dynamic parameters; (2)The channel jam and the landslide slide into the channel and lead to debris flow blockage. Cascade outburst occurs under the action of the subsequent debris flow,and then increase the dynamic parameters such as the peak flow rate and impact force of debris flow. Under the action of the two mechanisms,the parameters such as debris flow size and impact force can exceed the planning and design indexes of the prevention and control project,which leads to the destruction of the prevention and control project and the burying of the road. Therefore,it is suggested that the risk assessment of debris flow and the rationality and reliability of prevention and control engineering planning and design in Jiuzhaigou scenic area under the combined action of earthquake and heavy rainfall should be fully considered to ensure the safety of the scenic area.
A debris flow hazard triggered by rainstorm occurred in Zhuozhui Gully,Xiajijiehaizi Gully and Zechawa Gully,Jiuzhaigou County,where is the epicenter of the Jiuzhaigou Earthquake on June 20,2019. About 2.79×104m3,3.7×104m3 and 2.67×104m3 solid materials rushed out of the three gullies respectively,caused damage to retaining walls and debris dams,buried part of the scenic road,disrupted traffic temporarily,and had no casualty. This paper identified the cause and mechanism of the debris flow disaster preliminarily,according to the field survey and remote sensing interpretation after the disaster. Cause of disaster is as follows. The earthquake-induced landslide produces a large number of new loose solid material sources and the original gully slope debris(including old debris flow debris) under the action of heavy rainfall to form debris flow. So the debris flows are the results of the earthquake and rainfall. Based on the investigation and analysis of longitudinal profile and typical cross section of gully before and after the debris flow,we find that the mechanisms of debris flow disaster mainly include the follows. (1)The debris flow erodes the old debris flow deposits,at the same time induces the landslide along the bank,so as enhances the debris flow scale and impact force and other dynamic parameters; (2)The channel jam and the landslide slide into the channel and lead to debris flow blockage. Cascade outburst occurs under the action of the subsequent debris flow,and then increase the dynamic parameters such as the peak flow rate and impact force of debris flow. Under the action of the two mechanisms,the parameters such as debris flow size and impact force can exceed the planning and design indexes of the prevention and control project,which leads to the destruction of the prevention and control project and the burying of the road. Therefore,it is suggested that the risk assessment of debris flow and the rationality and reliability of prevention and control engineering planning and design in Jiuzhaigou scenic area under the combined action of earthquake and heavy rainfall should be fully considered to ensure the safety of the scenic area.
2022, 30(3): 751-759.
There was intensive rockburst risk during the excavation of China Jinping Underground Laboratory(CJPL-Ⅱ)expansion project. Therefore,we established an optimization layout method of fixed microsesmic(MS)sensor array for adjacent short tunnels with same excavation direction,as well as dynamic MS sensor array for opposite expansion excavation at one-side. Meanwhile,we proposed an optimization principle of rockburst warning frequency based on the degree of rockburst risk. The rockburst control measures corresponding to CJPL-II enlarging excavation is given too. The real-time monitoring,dynamic warning and prevention on rockbursts during CJPL-II anisotropic excavation is realized based on these proposed methods. The rockburst warning is in good agreement with the actual situation and the CJPL-II enlarging excavation project is successfully completed. We analyzed the difference of temporal and spatial evolution laws of MS activity between each CJPL-II enlarging excavation segments. The results show that the MS activity of the new tunnel is more active than that of the expansion excavation section,and the rockburst risk is also higher. The size of excavation section,depth of excavation and structural plane affect the degree and spatial characteristics of MS activity during enlarging excavation. This study can provide reference for the safety construction of similar deep projects.
There was intensive rockburst risk during the excavation of China Jinping Underground Laboratory(CJPL-Ⅱ)expansion project. Therefore,we established an optimization layout method of fixed microsesmic(MS)sensor array for adjacent short tunnels with same excavation direction,as well as dynamic MS sensor array for opposite expansion excavation at one-side. Meanwhile,we proposed an optimization principle of rockburst warning frequency based on the degree of rockburst risk. The rockburst control measures corresponding to CJPL-II enlarging excavation is given too. The real-time monitoring,dynamic warning and prevention on rockbursts during CJPL-II anisotropic excavation is realized based on these proposed methods. The rockburst warning is in good agreement with the actual situation and the CJPL-II enlarging excavation project is successfully completed. We analyzed the difference of temporal and spatial evolution laws of MS activity between each CJPL-II enlarging excavation segments. The results show that the MS activity of the new tunnel is more active than that of the expansion excavation section,and the rockburst risk is also higher. The size of excavation section,depth of excavation and structural plane affect the degree and spatial characteristics of MS activity during enlarging excavation. This study can provide reference for the safety construction of similar deep projects.
2022, 30(3): 760-771.
In addition to the regional geological background, heavy rainfall triggering, unsaturated soil mechanical analysis and numerical simulation of stability analysis, it is necessary to find out the main reasons for the differences between the occurrence and distribution of super large and medium to small size loess landslides, from the aspects of small and medium-sized geological structure and sedimentary phase variation. Taking the Zeketai Gallenpute Landslide of 22.75 million cubic meters in May 2002 as an example, the author adopted the methods of sedimentary phase change analysis, high-density electrical exploration, interpretation of medium and small-scale geological structure and comparison of hydrogeological conditions. The mechanism of the reactivation of the large-scale old landslide is revealed as follows. It appeared before Dec. 1985, initiated in one earthquake and triggered by heavy rainfall and the change of hydrogeological conditions under the fault control of the super large landslide. It is expected that the new model of loess landslide presented in this paper can provide a basis for the analysis of the overall stability of the super large Gallente landslide at different stages, and the regulation of the provincial highway S316 passing through it and supporting by the shallow bedrock at its lower section.
In addition to the regional geological background, heavy rainfall triggering, unsaturated soil mechanical analysis and numerical simulation of stability analysis, it is necessary to find out the main reasons for the differences between the occurrence and distribution of super large and medium to small size loess landslides, from the aspects of small and medium-sized geological structure and sedimentary phase variation. Taking the Zeketai Gallenpute Landslide of 22.75 million cubic meters in May 2002 as an example, the author adopted the methods of sedimentary phase change analysis, high-density electrical exploration, interpretation of medium and small-scale geological structure and comparison of hydrogeological conditions. The mechanism of the reactivation of the large-scale old landslide is revealed as follows. It appeared before Dec. 1985, initiated in one earthquake and triggered by heavy rainfall and the change of hydrogeological conditions under the fault control of the super large landslide. It is expected that the new model of loess landslide presented in this paper can provide a basis for the analysis of the overall stability of the super large Gallente landslide at different stages, and the regulation of the provincial highway S316 passing through it and supporting by the shallow bedrock at its lower section.
2022, 30(3): 772-783.
The strength of foundation in island frozen soil decreases sharply as the frozen soil thaws,which leads to uneven settlement of the subgrade. Hence,we propose a new raft structure for the highway in island frozen soil area in this paper. In order to study the bearing characteristics of the new raft foundation,the freeze-thaw cycle,ramp load tests and numerical simulation method are applied on the new raft foundation model. We analyze the bearing characteristics of the new raft foundation and how the freeze-thaw cycle affects the deformation and the stress distribution of foundation model and the strain of the new raft structure. The results show that the bearing effect of the new raft greatly alleviates the foundation deformation and reduces the foundation stress within a certain depth,which indicates that the raft exists as a "reinforced structure" of the foundation. The larger stiffness of the new raft allows the load to be transmitted to the periphery,reducing the foundation reaction force at the center of the raft. The strain of the new raft presents a U-shaped distribution with large in the middle and small on both sides. Meantime,the longitudinal strain is higher than the transverse strain,indicating that the deformation is transmitted more along the longitudinal direction of the raft. The soil structure is seriously damaged by the freeze-thaw cycle,resulting in a significant increase in settlement of foundation. The raft-soil system shares the upper load,and the raft strain increases while the soil strength decreases. Besides,the increase of stress in a certain depth range of the foundation caused by freeze-thaw cycle is consistent with the depth range of freeze-thaw cycle action,and the degree of influence becomes more obviously with the increase of the load level. In addition,the numerical simulation results are in good agreement with the experimental results,which indicates that the numerical simulation method can be used to analyze the mechanical characteristics of the new raft foundation in island frozen soil area.
The strength of foundation in island frozen soil decreases sharply as the frozen soil thaws,which leads to uneven settlement of the subgrade. Hence,we propose a new raft structure for the highway in island frozen soil area in this paper. In order to study the bearing characteristics of the new raft foundation,the freeze-thaw cycle,ramp load tests and numerical simulation method are applied on the new raft foundation model. We analyze the bearing characteristics of the new raft foundation and how the freeze-thaw cycle affects the deformation and the stress distribution of foundation model and the strain of the new raft structure. The results show that the bearing effect of the new raft greatly alleviates the foundation deformation and reduces the foundation stress within a certain depth,which indicates that the raft exists as a "reinforced structure" of the foundation. The larger stiffness of the new raft allows the load to be transmitted to the periphery,reducing the foundation reaction force at the center of the raft. The strain of the new raft presents a U-shaped distribution with large in the middle and small on both sides. Meantime,the longitudinal strain is higher than the transverse strain,indicating that the deformation is transmitted more along the longitudinal direction of the raft. The soil structure is seriously damaged by the freeze-thaw cycle,resulting in a significant increase in settlement of foundation. The raft-soil system shares the upper load,and the raft strain increases while the soil strength decreases. Besides,the increase of stress in a certain depth range of the foundation caused by freeze-thaw cycle is consistent with the depth range of freeze-thaw cycle action,and the degree of influence becomes more obviously with the increase of the load level. In addition,the numerical simulation results are in good agreement with the experimental results,which indicates that the numerical simulation method can be used to analyze the mechanical characteristics of the new raft foundation in island frozen soil area.
2022, 30(3): 784-793.
The Jiala barrier lake threatens the population,urban facilities,and ecological environment. It is in an uninhabited area and thus difficult to investigate and study its formation mechanism. In March 2019,we conducted a barrier lake site investigation. The topography,lithology of the remaining dammed body,and the surge damage phenomenon were investigated,combined with the grain size and material composition of the dammed body to reveal the formation process and damage mechanism. The results showed that the deposits of Sedongpu gully on the left bank of Yarlung Zangbo River rushed into the river channel three times and formed the barrier lake. The breach took place twice on October 19 and 31,2018, with the breach discharge of 32000m3 ·s-1 and 19000m3 ·s-1 respectively. The barrier body volume caused by the first two activities reaches 65 million m3,with the height of 85m. And when the breach occurred,the lake water storage reached 600 million m3. The barrier body volume induced by the third activity is about 10 million m3 with the height of 67m. When water storage was 326 million m3,the second breach occurred. It reveals that the dammed body derived from accumulated moraine which has high water content and ice blocks,suggesting a unique failure mechanism and flood characteristics like debris flow accumulation. The damming events in the Yarlung Zangbo River occurred frequently. This study can provide a reference for the disaster response of the barrier lake in this region.
The Jiala barrier lake threatens the population,urban facilities,and ecological environment. It is in an uninhabited area and thus difficult to investigate and study its formation mechanism. In March 2019,we conducted a barrier lake site investigation. The topography,lithology of the remaining dammed body,and the surge damage phenomenon were investigated,combined with the grain size and material composition of the dammed body to reveal the formation process and damage mechanism. The results showed that the deposits of Sedongpu gully on the left bank of Yarlung Zangbo River rushed into the river channel three times and formed the barrier lake. The breach took place twice on October 19 and 31,2018, with the breach discharge of 32000m3 ·s-1 and 19000m3 ·s-1 respectively. The barrier body volume caused by the first two activities reaches 65 million m3,with the height of 85m. And when the breach occurred,the lake water storage reached 600 million m3. The barrier body volume induced by the third activity is about 10 million m3 with the height of 67m. When water storage was 326 million m3,the second breach occurred. It reveals that the dammed body derived from accumulated moraine which has high water content and ice blocks,suggesting a unique failure mechanism and flood characteristics like debris flow accumulation. The damming events in the Yarlung Zangbo River occurred frequently. This study can provide a reference for the disaster response of the barrier lake in this region.
2022, 30(3): 803-816.
Monitoring the deformation of infrastructure reliably is essential for assessing its structural health. This paper is based on 46 scene ascending orbit and 45 scene descending orbit Sentinel-1A radar images,and obtains the surface deformation rate and time series displacement of Zhongchuan International Airport from March 27,2017 to March 23,2020 and March 20,2017 to March 28,2020 using SBASInSAR and PSInSAR techniques at the same time. Four kinds of monitoring results are evaluated by means of internal and external inspection. Combined with the mean value of coherence coefficient,histogram statistics,deformation rate variance and its standard deviation,the most ideal deformation result is selected to analyze the causes of land deformation at Zhongchuan International Airport from human and natural factors. The results show that the deformation results of the four kinds of data are generally consistent. The variance and standard deviation of monitoring points from different orbit mode data are similar when the same time series InSAR technique is adopted. The deformation results of the same orbit mode data are slightly different when different time series InSAR techniques are used. The monitoring result of SBASInSAR is more robust than that of PSInSAR. Among the scattered subsidence areas in Zhongchuan International Airport,the deformation in the southwest corner is the most significant,and the maximum vertical subsidence rate of it can reach 11 mm·a-1. The ground deformation of Zhongchuan International Airport is related to human factors such as road network and internal expansion. The stratigraphic boundary is not directly related to the internal deformation of the airport,and the land subsidence area is closely related to lithology. While further promoting the construction of Zhongchuan International Airport,the negative impact of excessive human activities should be avoided. The research results are expected to provide guidance and relevant information for land use planning and disaster prevention and control of Zhongchuan International Airport.
Monitoring the deformation of infrastructure reliably is essential for assessing its structural health. This paper is based on 46 scene ascending orbit and 45 scene descending orbit Sentinel-1A radar images,and obtains the surface deformation rate and time series displacement of Zhongchuan International Airport from March 27,2017 to March 23,2020 and March 20,2017 to March 28,2020 using SBASInSAR and PSInSAR techniques at the same time. Four kinds of monitoring results are evaluated by means of internal and external inspection. Combined with the mean value of coherence coefficient,histogram statistics,deformation rate variance and its standard deviation,the most ideal deformation result is selected to analyze the causes of land deformation at Zhongchuan International Airport from human and natural factors. The results show that the deformation results of the four kinds of data are generally consistent. The variance and standard deviation of monitoring points from different orbit mode data are similar when the same time series InSAR technique is adopted. The deformation results of the same orbit mode data are slightly different when different time series InSAR techniques are used. The monitoring result of SBASInSAR is more robust than that of PSInSAR. Among the scattered subsidence areas in Zhongchuan International Airport,the deformation in the southwest corner is the most significant,and the maximum vertical subsidence rate of it can reach 11 mm·a-1. The ground deformation of Zhongchuan International Airport is related to human factors such as road network and internal expansion. The stratigraphic boundary is not directly related to the internal deformation of the airport,and the land subsidence area is closely related to lithology. While further promoting the construction of Zhongchuan International Airport,the negative impact of excessive human activities should be avoided. The research results are expected to provide guidance and relevant information for land use planning and disaster prevention and control of Zhongchuan International Airport.
2022, 30(3): 817-828.
The Batang-Dege section in the upstream of Jinsha River is located in the east of Qinghai-Tibet Plateau,where the geology,terrain and landform are extremely complex and the landslide hazards are developed well. The analysis of the regional landslide disasters susceptibility is significant to the landslide disaster prevention and mitigation. Taking the Batang-Dege section in the upstream of Jinsha River as the research area. It is based on the landslide record and field surveys. The 11 impact factors include the elevation,slope,aspect,curvature,relief amplitude,degree of surface cutting,surface roughness,stratum lithology,fault,road and water system. They are used to construct a landslide susceptibility evaluation system by analyzing the distribution law and influencing factors. The Pearson coefficient is calculated to remove the high-correlation impact factors. The frequency ratio method is used to analyze the relationship between each factor and the landslide development quantitatively. The frequency ratio model is applied to selecting non-landslide samples and the ensemble learning model is used to evaluate landslide susceptibility. According to the index of susceptibility,the search area is divided into five levels including extreme-highly susceptible area,highly susceptible area,moderately susceptible area,low susceptible area,and extreme-low susceptible area. As shown in the susceptibility divisional graph and ROC curve,the extreme-highly susceptible and highly susceptible area areas are mainly distributed along the banks of Jinsha River and ravines. The area under curve of success ratio of the Random Forest model is 0.84,the number of disasters located in extreme-highly and highly susceptible areas accounted for 84.8 percent of the total landslides. The area under curve of success ratio of the Gradient Boost Tree model is 0.79,the number of disasters located in extreme-highly and highly susceptible areas accounted for 79.3 percent of the total landslides. By the value of AUC and the distribution of historical disasters,it can be observed in the research area that the Random Forest model has better evaluation accuracy and higher prediction ability in landslide susceptibility evaluation than the Gradient Boost Tree model.
The Batang-Dege section in the upstream of Jinsha River is located in the east of Qinghai-Tibet Plateau,where the geology,terrain and landform are extremely complex and the landslide hazards are developed well. The analysis of the regional landslide disasters susceptibility is significant to the landslide disaster prevention and mitigation. Taking the Batang-Dege section in the upstream of Jinsha River as the research area. It is based on the landslide record and field surveys. The 11 impact factors include the elevation,slope,aspect,curvature,relief amplitude,degree of surface cutting,surface roughness,stratum lithology,fault,road and water system. They are used to construct a landslide susceptibility evaluation system by analyzing the distribution law and influencing factors. The Pearson coefficient is calculated to remove the high-correlation impact factors. The frequency ratio method is used to analyze the relationship between each factor and the landslide development quantitatively. The frequency ratio model is applied to selecting non-landslide samples and the ensemble learning model is used to evaluate landslide susceptibility. According to the index of susceptibility,the search area is divided into five levels including extreme-highly susceptible area,highly susceptible area,moderately susceptible area,low susceptible area,and extreme-low susceptible area. As shown in the susceptibility divisional graph and ROC curve,the extreme-highly susceptible and highly susceptible area areas are mainly distributed along the banks of Jinsha River and ravines. The area under curve of success ratio of the Random Forest model is 0.84,the number of disasters located in extreme-highly and highly susceptible areas accounted for 84.8 percent of the total landslides. The area under curve of success ratio of the Gradient Boost Tree model is 0.79,the number of disasters located in extreme-highly and highly susceptible areas accounted for 79.3 percent of the total landslides. By the value of AUC and the distribution of historical disasters,it can be observed in the research area that the Random Forest model has better evaluation accuracy and higher prediction ability in landslide susceptibility evaluation than the Gradient Boost Tree model.
2022, 30(3): 829-842.
Tongren City of Qinghai Province is located in the northeast corner of the Qinghai-Tibet Plateau,and located in the junction of the West Qinling orogenic belt and the North Qilian orogenic belt. Since the Miocene,the study area has experienced several times of intermittent geological upthrow and planation,the river valley has been strongly eroded. Under the coupling effect of internal and external stresses,there are many large-extra ancient landslides on banks of Longwu River. In recent years,affected by global warming,there are obvious signs of deformation in five ancient landslides in this area,sone old cracks have been expanded obviously,many new cracks have appeared. In this paper,the Longwuxishan ancient landslide group on the left bank of Longwu River in Tongren City is taken as the research object. The paper analyzes the development and distribution,deformation characteristics,revitalization mechanism and movement characteristics of the Xishan ancient landslide group with the help of field investigation,drilling,laboratory experiment and numerical simulation. The results indicate that:(1)The strong uplift of neotectonics and the incised valley of the Longwu River are the main controlling factors for the formation of ancient landslides; (2)Field investigation found that the recent deformation of the Xishan ancient landslide group is mainly concentrated on the No. 5,No. 7,No. 9,No. 10,No. 11 and No. 12 landslides. There are many terracettes and tension fissures on the slope surface; (3)Rainfall is the controlling factor for the revitalization of ancient Longwuxishan landslide group,the deformation failure mode is sliding and fracturing; (4)The numerical simulation result shows that the distance of landslide migration is mainly from 50 m to 75 m,the average thickness of the accumulation area is from 12 m to 18 m. At present,Xishan ancient landslide group is becoming a serious threat to the safety of Tongren County.
Tongren City of Qinghai Province is located in the northeast corner of the Qinghai-Tibet Plateau,and located in the junction of the West Qinling orogenic belt and the North Qilian orogenic belt. Since the Miocene,the study area has experienced several times of intermittent geological upthrow and planation,the river valley has been strongly eroded. Under the coupling effect of internal and external stresses,there are many large-extra ancient landslides on banks of Longwu River. In recent years,affected by global warming,there are obvious signs of deformation in five ancient landslides in this area,sone old cracks have been expanded obviously,many new cracks have appeared. In this paper,the Longwuxishan ancient landslide group on the left bank of Longwu River in Tongren City is taken as the research object. The paper analyzes the development and distribution,deformation characteristics,revitalization mechanism and movement characteristics of the Xishan ancient landslide group with the help of field investigation,drilling,laboratory experiment and numerical simulation. The results indicate that:(1)The strong uplift of neotectonics and the incised valley of the Longwu River are the main controlling factors for the formation of ancient landslides; (2)Field investigation found that the recent deformation of the Xishan ancient landslide group is mainly concentrated on the No. 5,No. 7,No. 9,No. 10,No. 11 and No. 12 landslides. There are many terracettes and tension fissures on the slope surface; (3)Rainfall is the controlling factor for the revitalization of ancient Longwuxishan landslide group,the deformation failure mode is sliding and fracturing; (4)The numerical simulation result shows that the distance of landslide migration is mainly from 50 m to 75 m,the average thickness of the accumulation area is from 12 m to 18 m. At present,Xishan ancient landslide group is becoming a serious threat to the safety of Tongren County.
2022, 30(3): 852-862.
Typical large deformation geological hazards of soft rock occurred frequently during tunneling in Yangjiaping Tunnel,including extrusion at the tunnel wall and severe damage of the primary and secondary support. This paper uses the combined method of the engineering geological investigation with field monitoring and measurement,laboratory rock mechanics test,numerical simulation and microscopic analysis. It reveals the formation mechanism of large deformation of Yangjiaping Tunnel. The field monitoring results show that there might be a close relationship between the large deformation phenomena and tunnel seepage. Furthermore,the laboratory test results show that the longitudinal wave velocity of phyllite are attenuated by 2.04% ~5.85% after immersion. After being fully immersed in water for 28 days,the uniaxial compressive strength and elastic modulus of the phyllite decreased by 59.56% and 69.68%. The water-rock interaction results in certain damage of the phyllite structure. Meanwhile,we use the X-Ray Diffraction to detect the mineral composition,and to reveal the microscopic reasons for the reduction of the surrounding rock strength after water-rock interaction. The results from in situ stress tests and inversion analysis indicate that as a result of high tectonic stress and low rock strength,92.08% of Yangjiaping Tunnel is in a state of high to extremely high geostress. In addition,the engineering mechanical properties of the high-steep thin layered phyllite stratum and water-rock interaction are the main reasons for the large deformations in the Yangjiaping Tunnel.
Typical large deformation geological hazards of soft rock occurred frequently during tunneling in Yangjiaping Tunnel,including extrusion at the tunnel wall and severe damage of the primary and secondary support. This paper uses the combined method of the engineering geological investigation with field monitoring and measurement,laboratory rock mechanics test,numerical simulation and microscopic analysis. It reveals the formation mechanism of large deformation of Yangjiaping Tunnel. The field monitoring results show that there might be a close relationship between the large deformation phenomena and tunnel seepage. Furthermore,the laboratory test results show that the longitudinal wave velocity of phyllite are attenuated by 2.04% ~5.85% after immersion. After being fully immersed in water for 28 days,the uniaxial compressive strength and elastic modulus of the phyllite decreased by 59.56% and 69.68%. The water-rock interaction results in certain damage of the phyllite structure. Meanwhile,we use the X-Ray Diffraction to detect the mineral composition,and to reveal the microscopic reasons for the reduction of the surrounding rock strength after water-rock interaction. The results from in situ stress tests and inversion analysis indicate that as a result of high tectonic stress and low rock strength,92.08% of Yangjiaping Tunnel is in a state of high to extremely high geostress. In addition,the engineering mechanical properties of the high-steep thin layered phyllite stratum and water-rock interaction are the main reasons for the large deformations in the Yangjiaping Tunnel.
2022, 30(3): 863-873.
Stress determination of deep-buried super-long tunnel has attracted more and more attention from scientists and engineers. How to determine the stress state especially for deep and complex geological conditions with high efficiency and accuracy has become a major concern in tunnel engineering and underground excavation. We developed an intergrated stress determination method for the stress determination of deep-buried super-long tunnel during engineering design and excavation. The method includes in-situ stress orientation and magnitude estimation based on multi-source data and stress recheck after excavation. For in-situ stress determination,we utilized the hydraulic fracturing in-situ stress measurements to obtain the stress magnitude and orientation of Taoziya tunnel in one deep borehole ZK3 before excavation. We analyzed the regional stress state using multi-source data by combining geomechanical trace analysis,Anderson's faulting theory,focal mechanics and stress inversion based on focal mechanism and stress database of China Mainland. We are based on the limited number of in-situ stress measurements in survey and design stage and regional multi-source data and used the modified Sheorey model combined with Hoek-Brown criterion to predict the initial stress along the designed tunnel axis. Finally,we rechecked the predicted stresses by hydraulic fracturing in-situ stress measurements of 4 boreholes in Taoziya tunnel during the tunnel construction. Results show that the preferred principal stress orientation is around N15°W~N40°W which is consistent with the regional stress orientation obtained from multi-source data except for the focal mechanics results. The stress orientation in shallow depth may be influence by topography and deviates from deep crustal stress. The relationship between three principal stresses is SH≥Sv>Sh,which indicates that the stress regime is in favor of reverse faulting and strike-slip faulting. The predicted stress magnitudes are in the range of field measurements and database data near the borehole. The predicted magnitudes of horizontal maximum and minimum principal stresses are around 9.8 MPa and 6.6 MPa at the buried depth of 300 m,respectively,and 16 MPa and 10 MPa at the buried depth of 600 m,respectively. In the deepest buried depth,the predicted maximum and minimum horizontal principal stresses are around 24 and 16 MPa,respectively. The stress recheck in 4 boreholes along the tunnel axis indicates that the predicted stresses using modified Sheorey model are consistent with these stress measurement results in general. Local influence of lithology changes and fault fracture zone may lead to some excepts such as local bias and deviation of stress magnitude. The integrated stress prediction and recheck approach developed in this paper can ensure the efficiency and reliability of stress prediction results and reduce the cost for in-situ stress measurement in survey and design stage. And this method can also provide powerful evidence and data support for timely change of tunnel excavation scheme and budget adjustment,which is of great importance for successful completion of the project cost control.
Stress determination of deep-buried super-long tunnel has attracted more and more attention from scientists and engineers. How to determine the stress state especially for deep and complex geological conditions with high efficiency and accuracy has become a major concern in tunnel engineering and underground excavation. We developed an intergrated stress determination method for the stress determination of deep-buried super-long tunnel during engineering design and excavation. The method includes in-situ stress orientation and magnitude estimation based on multi-source data and stress recheck after excavation. For in-situ stress determination,we utilized the hydraulic fracturing in-situ stress measurements to obtain the stress magnitude and orientation of Taoziya tunnel in one deep borehole ZK3 before excavation. We analyzed the regional stress state using multi-source data by combining geomechanical trace analysis,Anderson's faulting theory,focal mechanics and stress inversion based on focal mechanism and stress database of China Mainland. We are based on the limited number of in-situ stress measurements in survey and design stage and regional multi-source data and used the modified Sheorey model combined with Hoek-Brown criterion to predict the initial stress along the designed tunnel axis. Finally,we rechecked the predicted stresses by hydraulic fracturing in-situ stress measurements of 4 boreholes in Taoziya tunnel during the tunnel construction. Results show that the preferred principal stress orientation is around N15°W~N40°W which is consistent with the regional stress orientation obtained from multi-source data except for the focal mechanics results. The stress orientation in shallow depth may be influence by topography and deviates from deep crustal stress. The relationship between three principal stresses is SH≥Sv>Sh,which indicates that the stress regime is in favor of reverse faulting and strike-slip faulting. The predicted stress magnitudes are in the range of field measurements and database data near the borehole. The predicted magnitudes of horizontal maximum and minimum principal stresses are around 9.8 MPa and 6.6 MPa at the buried depth of 300 m,respectively,and 16 MPa and 10 MPa at the buried depth of 600 m,respectively. In the deepest buried depth,the predicted maximum and minimum horizontal principal stresses are around 24 and 16 MPa,respectively. The stress recheck in 4 boreholes along the tunnel axis indicates that the predicted stresses using modified Sheorey model are consistent with these stress measurement results in general. Local influence of lithology changes and fault fracture zone may lead to some excepts such as local bias and deviation of stress magnitude. The integrated stress prediction and recheck approach developed in this paper can ensure the efficiency and reliability of stress prediction results and reduce the cost for in-situ stress measurement in survey and design stage. And this method can also provide powerful evidence and data support for timely change of tunnel excavation scheme and budget adjustment,which is of great importance for successful completion of the project cost control.
2022, 30(3): 874-883.
The metal sulfide oxidation in the waste rock results in a serious exceeding standard of acidity, SO42- and heavy metals in surface water and groundwater. Previous studies on the oxidation mechanism of metal sulfide mostly focus on the laboratory experiment of a single mineral. However, the field situation is complex and inconsistent with the experiment. This paper analyzes the composition of rock samples(ore and waste rock) and hydrochemistry, trace elements, and 87Sr/86Sr in water samples from river, groundwater, and leachate of abandoned tailings pond. The paper discusses the influence and mechanisms of a lead-zinc mine waste rock on the actual water environment. The results show that the oxidation of metal sulfide caused serious pollution to the water environment. The river water is acidified, where the pH is as low as 2.38, the concentration of SO42- and Zn, Pb, Ni, Mn, and Cd exceed the drinking water limit most seriously. The concentration is negatively correlated with pH. The main cause of river acidification is the oxidation of pyrite and pyrrhotite. They contribute most of SO42- to the river. The sphalerite not only contributes a part of SO42- to the river, but also is the main source of heavy metals. The ion concentrations in groundwater are lower than that of river water, and the pH is neutral. The pH of groundwater is higher than that of river water, which is mainly due to the dilution of groundwater in lateral mountains. The neutralization effect of silicate and carbonate on acid in the process of river water flow has great enlightenment value for the treatment of acid water. The understanding of the mechanism is of great significance for the prevention and control of waste rock pollution to water and soil environment. This study is of great significance for the prevention and control of waste rock on water pollution.
The metal sulfide oxidation in the waste rock results in a serious exceeding standard of acidity, SO42- and heavy metals in surface water and groundwater. Previous studies on the oxidation mechanism of metal sulfide mostly focus on the laboratory experiment of a single mineral. However, the field situation is complex and inconsistent with the experiment. This paper analyzes the composition of rock samples(ore and waste rock) and hydrochemistry, trace elements, and 87Sr/86Sr in water samples from river, groundwater, and leachate of abandoned tailings pond. The paper discusses the influence and mechanisms of a lead-zinc mine waste rock on the actual water environment. The results show that the oxidation of metal sulfide caused serious pollution to the water environment. The river water is acidified, where the pH is as low as 2.38, the concentration of SO42- and Zn, Pb, Ni, Mn, and Cd exceed the drinking water limit most seriously. The concentration is negatively correlated with pH. The main cause of river acidification is the oxidation of pyrite and pyrrhotite. They contribute most of SO42- to the river. The sphalerite not only contributes a part of SO42- to the river, but also is the main source of heavy metals. The ion concentrations in groundwater are lower than that of river water, and the pH is neutral. The pH of groundwater is higher than that of river water, which is mainly due to the dilution of groundwater in lateral mountains. The neutralization effect of silicate and carbonate on acid in the process of river water flow has great enlightenment value for the treatment of acid water. The understanding of the mechanism is of great significance for the prevention and control of waste rock pollution to water and soil environment. This study is of great significance for the prevention and control of waste rock on water pollution.
CHARACTERISTICS AND EVOLUTION PROCESSES OF SEDIMENTS IN BARRIER LAKE TRIGGERED BY "DIEXI EARTHQUAKE"
2022, 30(3): 884-895.
The Diexi earthquake of 7.5 magnitudein 1933 is located at the upstream area of Minjiang River,the east of the Tibetan Plateau. It caused that the rocks at the two sides of the Minjiang River collapsed and blocked Minjiang River,and formed a barrier lake entitled "Diexi Xiaohaizi". After the barrier lake formed,the soil and sand from Songping Valley entered and sunk into the barrier lake successively. It formed gilbert-type fan delta showing threefold subdivision into topset,foreset,and bottomset strata. Songping valley had at least two catastrophic flood events happened according to the landform of the sedimentary bodies and the sedimentary facies characteristics. The study on the deposit characters and causes of Songping ditch accumulation body is combined with flow energy method in dynamics to back calculation. It supplied a new method and thoughts for learning the mountainous geological environment and the occurrence frequency and damage degree of the geological hazard evolution and so on events.
The Diexi earthquake of 7.5 magnitudein 1933 is located at the upstream area of Minjiang River,the east of the Tibetan Plateau. It caused that the rocks at the two sides of the Minjiang River collapsed and blocked Minjiang River,and formed a barrier lake entitled "Diexi Xiaohaizi". After the barrier lake formed,the soil and sand from Songping Valley entered and sunk into the barrier lake successively. It formed gilbert-type fan delta showing threefold subdivision into topset,foreset,and bottomset strata. Songping valley had at least two catastrophic flood events happened according to the landform of the sedimentary bodies and the sedimentary facies characteristics. The study on the deposit characters and causes of Songping ditch accumulation body is combined with flow energy method in dynamics to back calculation. It supplied a new method and thoughts for learning the mountainous geological environment and the occurrence frequency and damage degree of the geological hazard evolution and so on events.
2022, 30(3): 896-907.
The deformation and failure patterns of the surrounding rocks of tunnels in mixed ground composed of soft and hard strata are complex at different depths. Under the gravity stress operated in extensional basins,the lateral pressure coefficient is generally small and basically within 1.0. This paper takes the TBM excavation of circular caverns in horizontal and vertical superimposed mixed ground as an example. It uses the finite difference numerical simulation software FLAC3D to study the displacement,principal stress and failure characteristics of different superimposed mixed ground along the tunnel axis under different depths in extensional basins. The results show that the deformation of surrounding rock mainly occurs in soft rock. With the increase of depth,the stability of hard rock becomes worse,especially the displacement of the top arch in working face increases obviously. When the buried depth is more than 800 m,the large deformation as nodal segments of soft rock along the tunnel axis begins to appear. With the increase of depth,the difference in principal stress between soft rock and hard rock becomes smaller. The larger the depth is,the larger the distribution range of plastic zone is. The tensile failure is the main deformation in small depth,while the shear failure is the main deformation in large depth. The transition depth(critical depth) of the two states is about 800 m. Therefore,the limit value of deep burial in extensional basin is theoretically verified.
The deformation and failure patterns of the surrounding rocks of tunnels in mixed ground composed of soft and hard strata are complex at different depths. Under the gravity stress operated in extensional basins,the lateral pressure coefficient is generally small and basically within 1.0. This paper takes the TBM excavation of circular caverns in horizontal and vertical superimposed mixed ground as an example. It uses the finite difference numerical simulation software FLAC3D to study the displacement,principal stress and failure characteristics of different superimposed mixed ground along the tunnel axis under different depths in extensional basins. The results show that the deformation of surrounding rock mainly occurs in soft rock. With the increase of depth,the stability of hard rock becomes worse,especially the displacement of the top arch in working face increases obviously. When the buried depth is more than 800 m,the large deformation as nodal segments of soft rock along the tunnel axis begins to appear. With the increase of depth,the difference in principal stress between soft rock and hard rock becomes smaller. The larger the depth is,the larger the distribution range of plastic zone is. The tensile failure is the main deformation in small depth,while the shear failure is the main deformation in large depth. The transition depth(critical depth) of the two states is about 800 m. Therefore,the limit value of deep burial in extensional basin is theoretically verified.
2022, 30(3): 908-919.
The Kangding to Litang section of CZ Railway is located in the eastern edge of Qinghai-Tibet Plateau. The region is characterized by varied landforms,complicated geological structures and widely developed landslide disasters,which causes a serious threat to the planning,construction and future safe operation of the Kangding to Litang section of CZ Railway. Therefore,12 impact factors were chosen to be the evaluation indices. They include elevation,aspect,plane curvature,profile curvature,topographic relief,surface cutting degree,topographic wetness index,normalized difference vegetation index,stratum lithology,distance to fault,distance to river and distance to road. The landslide spatial database was constructed,and the deep learning convolutional neural network(CNN)model was used to evaluate the landslide susceptibility. According to the susceptibility index,the study area was classified into the following five grades: landslide extremely high-prone area(13.76%),landslide high-prone area(14.00%),landslide moderate-prone area(15.86%),landslide low-prone area(18.17%) and landslide extremely low-prone area(38.21%). The prediction performance was compared with the artificial neural network(ANN)model. The results show that the AUC value of the area under the ROC curve of the CNN model is 0.87,which is better than 0.84 of the ANN model,and the frequency ratio of the extremely high-prone areas is higher than the ANN model,so the CNN model has a higher predictive ability in this study area. The landslide extremely high-prone area and high-prone area are mainly distributed in the areas with relatively developed river,and the zones are distributed in the 2 km range along both sides of the Yalong River and other rivers. The results of landslide susceptibility well reflect the development and distribution of landslide hazards in the study area,which can provide a scientific basis for the construction of CZ railway and the work of disaster prevention and mitigation in the future safe operation.
The Kangding to Litang section of CZ Railway is located in the eastern edge of Qinghai-Tibet Plateau. The region is characterized by varied landforms,complicated geological structures and widely developed landslide disasters,which causes a serious threat to the planning,construction and future safe operation of the Kangding to Litang section of CZ Railway. Therefore,12 impact factors were chosen to be the evaluation indices. They include elevation,aspect,plane curvature,profile curvature,topographic relief,surface cutting degree,topographic wetness index,normalized difference vegetation index,stratum lithology,distance to fault,distance to river and distance to road. The landslide spatial database was constructed,and the deep learning convolutional neural network(CNN)model was used to evaluate the landslide susceptibility. According to the susceptibility index,the study area was classified into the following five grades: landslide extremely high-prone area(13.76%),landslide high-prone area(14.00%),landslide moderate-prone area(15.86%),landslide low-prone area(18.17%) and landslide extremely low-prone area(38.21%). The prediction performance was compared with the artificial neural network(ANN)model. The results show that the AUC value of the area under the ROC curve of the CNN model is 0.87,which is better than 0.84 of the ANN model,and the frequency ratio of the extremely high-prone areas is higher than the ANN model,so the CNN model has a higher predictive ability in this study area. The landslide extremely high-prone area and high-prone area are mainly distributed in the areas with relatively developed river,and the zones are distributed in the 2 km range along both sides of the Yalong River and other rivers. The results of landslide susceptibility well reflect the development and distribution of landslide hazards in the study area,which can provide a scientific basis for the construction of CZ railway and the work of disaster prevention and mitigation in the future safe operation.
2022, 30(3): 920-930.
The Bailong River Diversion Project is a proposed major strategic project in China,and the Daigusi Reservoir is the water source hub of this project. The Daigusi Reservoir and its surrounding areas(the study area of this paper) are surrounded by many active faults and frequent major earthquakes. Therefore,a reliable seismic hazard assessment for this study area is urgently needed to protect the area's engineering construction and operation. Because traditional seismic assessment methods lack solid physical basis,we adopt a new method based on earthquake physical prediction to evaluate the seismic hazard of the study area. The results of this study show that the seismic hazard of the study area in the next 100 years mainly originates from the next MS8.5 landmark earthquake in the Haiyuan seismic zone. Based on the seismicity,seismogenic potential and distribution characteristics of faults,we pre-judge the possible seismogenic faults and epicenters of this landmark earthquake; using the seismic intensity decay relationship,we calculate the seismic intensity generated from this earthquake with different epicenters. To ensure the long-term safety of the water source hub of Daigusi Reservoir associated with Bailong River Diversion Project,we suggest that the seismic intensity of the study area should not be less than 8 degrees.
The Bailong River Diversion Project is a proposed major strategic project in China,and the Daigusi Reservoir is the water source hub of this project. The Daigusi Reservoir and its surrounding areas(the study area of this paper) are surrounded by many active faults and frequent major earthquakes. Therefore,a reliable seismic hazard assessment for this study area is urgently needed to protect the area's engineering construction and operation. Because traditional seismic assessment methods lack solid physical basis,we adopt a new method based on earthquake physical prediction to evaluate the seismic hazard of the study area. The results of this study show that the seismic hazard of the study area in the next 100 years mainly originates from the next MS8.5 landmark earthquake in the Haiyuan seismic zone. Based on the seismicity,seismogenic potential and distribution characteristics of faults,we pre-judge the possible seismogenic faults and epicenters of this landmark earthquake; using the seismic intensity decay relationship,we calculate the seismic intensity generated from this earthquake with different epicenters. To ensure the long-term safety of the water source hub of Daigusi Reservoir associated with Bailong River Diversion Project,we suggest that the seismic intensity of the study area should not be less than 8 degrees.
2022, 30(3): 931-943.
On July 20,2021,an extreme rainstorm in Henan province triggered mountain torrents and geological disasters in four cities(Xingyang,Gongyi,Xinmi,and Dengfeng) in the western area of Zhengzhou city,Henan province of China,which caused 251 deaths and missing people. The victims are distributed in 140 villages and communities of 44 towns. The disasters have the characteristics of group-occurring,dispersion,and relatively agglomeration. The mountain torrents and geological disasters were scattered and complex,and the watershed disaster chain and regional disaster groups coexisted. The disaster chain of mountain torrents showed the effects of spatial relevancy,time continuity,dynamic conversion,and disaster amplification. In order to reveal the cause of the mountain torrents and geological disasters,we summarized its spatio-temporal distribution characteristics and analyzed its triggering factors. We discussed the cause of a typical mountain torrent disaster chain,which is an outburst of subgrade blocking water in waterlogging from Xingmentangnao embankment in the upper reach of Suohe river,flash flood of Wangzongdian Village,and damming water of Haigouzhai in Cuimiao Village. We also investigated the geomechanical model of the translational landslide of Nantou Community in Wangzongdian Village,and the relationship between its stability and mechanical parameters. We suggest an early warning and response criterion of mountain torrent and geological hazards,i. e.,if the current process or daily rainfall reaches 200 mm,and the rainfall forecast exceeds 40 mm in the next one hour or 100 mm in three hours,a red alert response must be initiated. The research results can provide decision-making support for prevention and emergency response of mountain torrent and geological hazards in the western area of Zhengzhou city in the future,and can also provide a reference for disaster risk reduction of urban and rural communities in similar regions.
On July 20,2021,an extreme rainstorm in Henan province triggered mountain torrents and geological disasters in four cities(Xingyang,Gongyi,Xinmi,and Dengfeng) in the western area of Zhengzhou city,Henan province of China,which caused 251 deaths and missing people. The victims are distributed in 140 villages and communities of 44 towns. The disasters have the characteristics of group-occurring,dispersion,and relatively agglomeration. The mountain torrents and geological disasters were scattered and complex,and the watershed disaster chain and regional disaster groups coexisted. The disaster chain of mountain torrents showed the effects of spatial relevancy,time continuity,dynamic conversion,and disaster amplification. In order to reveal the cause of the mountain torrents and geological disasters,we summarized its spatio-temporal distribution characteristics and analyzed its triggering factors. We discussed the cause of a typical mountain torrent disaster chain,which is an outburst of subgrade blocking water in waterlogging from Xingmentangnao embankment in the upper reach of Suohe river,flash flood of Wangzongdian Village,and damming water of Haigouzhai in Cuimiao Village. We also investigated the geomechanical model of the translational landslide of Nantou Community in Wangzongdian Village,and the relationship between its stability and mechanical parameters. We suggest an early warning and response criterion of mountain torrent and geological hazards,i. e.,if the current process or daily rainfall reaches 200 mm,and the rainfall forecast exceeds 40 mm in the next one hour or 100 mm in three hours,a red alert response must be initiated. The research results can provide decision-making support for prevention and emergency response of mountain torrent and geological hazards in the western area of Zhengzhou city in the future,and can also provide a reference for disaster risk reduction of urban and rural communities in similar regions.
2022, 30(3): 944-955.
Landslides occur in a large number of places in Fujian Province,China,so it is an important measure to carry out regional landslides warning,and the scientificity and effectiveness of the warning model is the key. Due to the complex of landslide mechanism,limited data accumulation,and insufficient big data method,etc. traditional regional landslides warning models have many problems,such as limited warning accuracy and lack of refinement. Based on the geological and meteorological big data in the past decade,using the random forest algorithm,the regional landslides warning model in Fujian Province was studied in this paper. Then,the case verification was carried out. (1)The building method of regional landslide training sample set was optimized,and the regional landslides training set of Fujian Province was constructed,which included 26 input characteristics and 1 output characteristic,covered nearly nine years in Fujian Province(2010~2018)total sample size of 15589(3562 positive samples and 12027 negative samples). (2)Based on the random forest algorithm,the training sample set was trained,optimized and stored. The model was trained with the five-fold cross-validation method,and model parameters were optimized with the Bayesian optimization algorithm. Then,the accuracy value,ROC curve and AUC value were used to verify the model accuracy and generalization ability. Finally,the optimized model had good accuracy and generalization ability(the accuracy value was 94.3%,and AUC was 0.954). (3)The actual landslides on June 22 and 28,2021 were selected to verify the new warning model. Then,verified result was that the hit ratio of new warning model were 100% in both June 22 and 28. Compared with the warning results of the original explicit statistical model,the hit ratio of the new model is 6 times(on June 22)or equivalent(on June 28)to that of the original model,and the landslide density in the warning area of the new model is 1.6 to 1.7 times to that of the original model. Therefore,the new model based on random forest has obvious advantages,which is the new model warning result has higher hit rate and smaller warning area. In other words,the new model can achieve a more accurate warning. In the follow-up,new landslides in the study area will be tracked to verify and modify the model.
Landslides occur in a large number of places in Fujian Province,China,so it is an important measure to carry out regional landslides warning,and the scientificity and effectiveness of the warning model is the key. Due to the complex of landslide mechanism,limited data accumulation,and insufficient big data method,etc. traditional regional landslides warning models have many problems,such as limited warning accuracy and lack of refinement. Based on the geological and meteorological big data in the past decade,using the random forest algorithm,the regional landslides warning model in Fujian Province was studied in this paper. Then,the case verification was carried out. (1)The building method of regional landslide training sample set was optimized,and the regional landslides training set of Fujian Province was constructed,which included 26 input characteristics and 1 output characteristic,covered nearly nine years in Fujian Province(2010~2018)total sample size of 15589(3562 positive samples and 12027 negative samples). (2)Based on the random forest algorithm,the training sample set was trained,optimized and stored. The model was trained with the five-fold cross-validation method,and model parameters were optimized with the Bayesian optimization algorithm. Then,the accuracy value,ROC curve and AUC value were used to verify the model accuracy and generalization ability. Finally,the optimized model had good accuracy and generalization ability(the accuracy value was 94.3%,and AUC was 0.954). (3)The actual landslides on June 22 and 28,2021 were selected to verify the new warning model. Then,verified result was that the hit ratio of new warning model were 100% in both June 22 and 28. Compared with the warning results of the original explicit statistical model,the hit ratio of the new model is 6 times(on June 22)or equivalent(on June 28)to that of the original model,and the landslide density in the warning area of the new model is 1.6 to 1.7 times to that of the original model. Therefore,the new model based on random forest has obvious advantages,which is the new model warning result has higher hit rate and smaller warning area. In other words,the new model can achieve a more accurate warning. In the follow-up,new landslides in the study area will be tracked to verify and modify the model.
2022, 30(3): 956-965.
Hydraulic fracturing is the key technology in the exploitation of unconventional resources,such as shale gas. Depth of the shale reservoir in the southwestern area of Sichuan Basin has breached 4000 m and some blocks even are approaching 5000 m. There are great differences in the exploitation of such reservoirs due to the challenge in situ conditions in the deep subsurface. Brittleness of the reservoir rock under the in situ conditions plays very important role in the hydraulic fracturing of the reservoir. Shale samples were collected from the borehole and in situ conditions were recorded on the drilling site. The standard rock specimens were prepared,having a height to diameter ratio of 2.0 and a diameter of 50 mm. Triaxial compression experiments under in situ conditions were carried out in the laboratory to obtain the complete stress-strain curves. Brittleness index based on the complete stress-strain curves under in situ conditions were used here for the evaluation of brittleness of the reservoir rocks. Brittleness of four sub-layers of the Longmaxi shale and underlying Wufeng shale were estimated using the brittleness index under in-situ conditions. Results of the brittleness values of the reservoir rocks were studied and the comparison with the fracturing results of the real reservoirs is carried out. The results of brittleness evaluation under in situ conditions agree well with the fracturing operation on the drilling site.
Hydraulic fracturing is the key technology in the exploitation of unconventional resources,such as shale gas. Depth of the shale reservoir in the southwestern area of Sichuan Basin has breached 4000 m and some blocks even are approaching 5000 m. There are great differences in the exploitation of such reservoirs due to the challenge in situ conditions in the deep subsurface. Brittleness of the reservoir rock under the in situ conditions plays very important role in the hydraulic fracturing of the reservoir. Shale samples were collected from the borehole and in situ conditions were recorded on the drilling site. The standard rock specimens were prepared,having a height to diameter ratio of 2.0 and a diameter of 50 mm. Triaxial compression experiments under in situ conditions were carried out in the laboratory to obtain the complete stress-strain curves. Brittleness index based on the complete stress-strain curves under in situ conditions were used here for the evaluation of brittleness of the reservoir rocks. Brittleness of four sub-layers of the Longmaxi shale and underlying Wufeng shale were estimated using the brittleness index under in-situ conditions. Results of the brittleness values of the reservoir rocks were studied and the comparison with the fracturing results of the real reservoirs is carried out. The results of brittleness evaluation under in situ conditions agree well with the fracturing operation on the drilling site.
2022, 30(3): 966-974.
In rock engineering,alteration usually causes various engineering geological problems. The microscopic characteristics and physical and mechanical properties of altered rocks in a deep buried long tunnel in northern Xinjiang were studied,and numerical simulations were performed for the altered rock tunnel section. The results show that the rock alteration type of the tunnel surrounding rock is chloritization of black mica and clayification of potassium feldspar. The concept of alteration index is proposed using the chlorite content and clay mineral content in the altered rock. The macroscopic characteristics of the altered rock are combined to classify the alteration degree. As the degree of alteration increases,the water absorption,and porosity of the rock subsequently become larger,and the bulk density,saturated uniaxial compressive strength,elastic modulus,and deformation modulus decrease substantially. The engineering example simulation found that the displacement of tunnel surrounding rock is increased significantly with the enhancement of rock alteration,revealing that the alteration effect has a great influence on the deformation and damage of surrounding rock. The research results have a certain reference value for similar projects in eroded rock areas.
In rock engineering,alteration usually causes various engineering geological problems. The microscopic characteristics and physical and mechanical properties of altered rocks in a deep buried long tunnel in northern Xinjiang were studied,and numerical simulations were performed for the altered rock tunnel section. The results show that the rock alteration type of the tunnel surrounding rock is chloritization of black mica and clayification of potassium feldspar. The concept of alteration index is proposed using the chlorite content and clay mineral content in the altered rock. The macroscopic characteristics of the altered rock are combined to classify the alteration degree. As the degree of alteration increases,the water absorption,and porosity of the rock subsequently become larger,and the bulk density,saturated uniaxial compressive strength,elastic modulus,and deformation modulus decrease substantially. The engineering example simulation found that the displacement of tunnel surrounding rock is increased significantly with the enhancement of rock alteration,revealing that the alteration effect has a great influence on the deformation and damage of surrounding rock. The research results have a certain reference value for similar projects in eroded rock areas.
2022, 30(3): 975-986.
In rock engineering,the shear behavior of jointed rocks mainly depends on the surface characteristics of joints. It has been found that rock joint surfaces can be decomposed into a first-order waviness and a second-order unevenness,which play different roles in the shear behavior. To quantitatively estimate their influences,we first used wavelet analysis to decompose granite joints and red sandstone joints,then counted the wavelength and undulation angle of the waviness and unevenness. A reasonable parameter research scheme was designed to investigate the shear characteristics of the two types of joints. Based on the 3D printing technology,rock-like samples were prepared,and laboratory direct shear tests and two-dimensional particle flow code(PFC2D)numerical simulations were conducted. To reliably replicate the mechanical behavior of jointed rocks,the parallel bond contact model was used to mimic the rock sample. The smooth-joint contact model was used to reproduce the rock joints with undulation angles of 4°,8°,12°,16°,and 20°. The meso-failure mode and shear mechanical properties of jointed rocks during the shear process were analyzed. The influence of the undulation angle and normal stress was revealed. The specific results and conclusions are as follows.(1)The unevenness model is less likely to crack under low normal stress. Under high stress,for the waviness and unevenness models with a larger undulation angle,the cracks gradually propagate to the deep part of the sample. For the waviness model under low normal stress and unevenness model under high stress,the cracks are mainly parallel to the shear direction. For the waviness model under high normal stress,the cracks far from the undulation toe are almost perpendicular to the uphill slope,while the cracks near the toe are almost parallel to the shear direction.(2)The tensile cracks dominate,accompanied by a small amount of shear cracks,the amount of cracks increases with the increasing normal stress. Fewer cracks were identified under low normal stresses. In the case of high normal stress,the number of cracks increases sharply. In addition,the shear strength of the waviness is higher than that of the unevenness with the same undulation angle and under the same normal stress.(3)The undulation angle and normal stress are the key factors determining the shear strength,and the influence of wavelength is negligible. The predicted empirical formula for shear strength of joints was established,which considers the undulation angle θ, the normal stress σn, and the uniaxial compressive strength \begin{document}$J C S: \tau=\sigma_{\mathrm{n}} \tan \left[a+b \ln \left(\frac{J C S}{\sigma_{\mathrm{n}}}\right)+c\left(\theta \cdot \frac{l_{b}}{l}\right)+\phi_{b}\right] $\end{document} \begin{document}$J C S: \tau=\sigma_{\mathrm{n}} \tan \left[a+b \ln \left(\frac{J C S}{\sigma_{\mathrm{n}}}\right)+c\left(\theta \cdot \frac{l_{b}}{l}\right)+\phi_{b}\right] $\end{document}
2022, 30(3): 987-997.
Grouting to plug water is a common technical measure for the prevention and control of water disaster in underground engineering and mines. However,the current research on the mechanism of grout propagation and the mining effect lags the practical requirement,which restricts the scientific and effective implementation of grouting engineering. Based on the theory of "deflection effect" of groundwater in fractures,this paper traces the study on the propagation in fractured rock masses,and proposes a scientific hypothesis of the "deflection effect" for the propagation of grouting in fractured rock masses with flowing water in deep underground mines. Two key scientific problems that should be solved for further study are proposed: the mechanism of grout deflection propagation in fractured rock masses,and the mechanism of failure and permeability change of "grouted-rock" composite formed by bias grouting flow. Combined with the research trend,an interdisciplinary comprehensive research method is proposed. It is recommended that future research should take the typical grouting project as the background to study the hydrogeological structure of deep mines and the spatial-temporal evolution of mining,focusing on revealing the deflection mechanism of grout propagation and its influencing factors under dynamic water conditions of fractured rock masses,establishing a mathematical model of grout deflection propagation and an evaluation method for the permeability change due to mining. The result will provide an important scientific basis for the prevention and control of water disaster and safe production in deep mines.
Grouting to plug water is a common technical measure for the prevention and control of water disaster in underground engineering and mines. However,the current research on the mechanism of grout propagation and the mining effect lags the practical requirement,which restricts the scientific and effective implementation of grouting engineering. Based on the theory of "deflection effect" of groundwater in fractures,this paper traces the study on the propagation in fractured rock masses,and proposes a scientific hypothesis of the "deflection effect" for the propagation of grouting in fractured rock masses with flowing water in deep underground mines. Two key scientific problems that should be solved for further study are proposed: the mechanism of grout deflection propagation in fractured rock masses,and the mechanism of failure and permeability change of "grouted-rock" composite formed by bias grouting flow. Combined with the research trend,an interdisciplinary comprehensive research method is proposed. It is recommended that future research should take the typical grouting project as the background to study the hydrogeological structure of deep mines and the spatial-temporal evolution of mining,focusing on revealing the deflection mechanism of grout propagation and its influencing factors under dynamic water conditions of fractured rock masses,establishing a mathematical model of grout deflection propagation and an evaluation method for the permeability change due to mining. The result will provide an important scientific basis for the prevention and control of water disaster and safe production in deep mines.
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