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Editor Work2021 Vol. 29, No. 2
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2021, 29(2): 275-288.
Abstract
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The Sichuan-Tibet railway corridor has high crustal stress, temperature and water pressure. The soft rock is a difficult problem that cannot be ignored. However, the distribution characteristics and engineering effects of the soft rock have not been deeply studied. This paper is based on the geological map of railway corridor, rock mass structure investigation and rebound test as well as microanalysis. It finds that suture zones had obvious control effect on the formation of soft rocks. The paper has the following findings. (1)There are Jinshajiang, Lancangjiang, Nujiang and Yarlung Zangbo suture zones along Sichuan-Tibet railway corridor. Under the influence of the special tectonic activity pattern, temperature and pressure conditions in the suture zone, the soft rocks such as schist, slate, mylonite, cataclasite and damaged rock zones are mainly distributed in the suture zone and on both sides of the boundary faults. (2)The tectonic damage, deformation and metamorphism of rock mass were caused by the plate splitting and converging movement, which led to the deterioration of rock mechanical properties and form soft rocks in the area. (3)The large deformation risk of railway tunnel engineering is higher in the soft rock section controlled by suture zone. Water and mud inrush will be easy to occur when the tunnel engineering passes through tectonic soft rocks near the active bound faults of suture zone. Besides, mountain hazards in suture zones mainly occur in soft rock area with intense river erosion. These findings can provide scientific basis for the prediction and prevention of engineering geological problems of soft rocks along Sichuan-Tibet railway corridor, and also lay foundation for the research of deformation mechanism and engineering prevention technology of soft rock under plate collision and compression.
The Sichuan-Tibet railway corridor has high crustal stress, temperature and water pressure. The soft rock is a difficult problem that cannot be ignored. However, the distribution characteristics and engineering effects of the soft rock have not been deeply studied. This paper is based on the geological map of railway corridor, rock mass structure investigation and rebound test as well as microanalysis. It finds that suture zones had obvious control effect on the formation of soft rocks. The paper has the following findings. (1)There are Jinshajiang, Lancangjiang, Nujiang and Yarlung Zangbo suture zones along Sichuan-Tibet railway corridor. Under the influence of the special tectonic activity pattern, temperature and pressure conditions in the suture zone, the soft rocks such as schist, slate, mylonite, cataclasite and damaged rock zones are mainly distributed in the suture zone and on both sides of the boundary faults. (2)The tectonic damage, deformation and metamorphism of rock mass were caused by the plate splitting and converging movement, which led to the deterioration of rock mechanical properties and form soft rocks in the area. (3)The large deformation risk of railway tunnel engineering is higher in the soft rock section controlled by suture zone. Water and mud inrush will be easy to occur when the tunnel engineering passes through tectonic soft rocks near the active bound faults of suture zone. Besides, mountain hazards in suture zones mainly occur in soft rock area with intense river erosion. These findings can provide scientific basis for the prediction and prevention of engineering geological problems of soft rocks along Sichuan-Tibet railway corridor, and also lay foundation for the research of deformation mechanism and engineering prevention technology of soft rock under plate collision and compression.
2021, 29(2): 289-306.
The strong and complex movement of active fault zones inevitably causes different degrees of damage to the crustal rock mass. These damages can significantly affect the processes of earthquake rupture, geomorphic evolution, geological disaster, and engineering rock mass. However, the tectonic damage of crustal rock mass around large active faults is still not well understood. The concept of the tectonic damage of crustal rock mass is firstly proposed. The tectonic damage is irreversible, accumulative, heterogeneous, and healable. We measure tectonic discontinuities of the outcrops in the six major fault zones on the eastern margin of the Tibetan Plateau. They are the Xianshuihe fault zone, the Longmenshan fault zone, the Anninghe fault zone, the Daliangshan fault zone, the Zemuhe fault zone, and the Xiaojiang fault zone. The crustal rock mass outside fault core can be divided into a damage zone and wall rock according to the intensity of tectonic discontinuities. This intensity is a quantitative index of tectonic damage. Then we analyze the spatial pattern, the characteristics of damage, and the influence factors of the tectonic damage of crustal rock mass. The main conclusions are as follows: (1)Damage degree shows a decrease with perpendicular distance from the main fault trace. High damage areas alternate with low damage areas in the damage zone. The widest damage zone is 3100 m; (2)The rock mass in damage zone and wall rock is damaged in brittle regime at high strain rate and low strain rate, respectively. And the orientations of tectonic discontinuities in damage zone show a strong correlation with recent crustal stress field; (4)The cumulative displacement that characterizes the development stage of faults determines the scale of the damage zone, and the local variations are mainly controlled by fault geometry and lithology; (5)A new conceptual model based on cumulative displacement, fault geometry, lithology, and depth is proposed to explain the pattern of the tectonic damage of crustal rock mass around the active fault zone. This study can provide evidences for constraining the structure of crustal rock masses in seismic dynamics, tectonic geomorphology, geological disaster, and engineering, and help to deepen the understanding of the crustal rock mass of active fault zones.
The strong and complex movement of active fault zones inevitably causes different degrees of damage to the crustal rock mass. These damages can significantly affect the processes of earthquake rupture, geomorphic evolution, geological disaster, and engineering rock mass. However, the tectonic damage of crustal rock mass around large active faults is still not well understood. The concept of the tectonic damage of crustal rock mass is firstly proposed. The tectonic damage is irreversible, accumulative, heterogeneous, and healable. We measure tectonic discontinuities of the outcrops in the six major fault zones on the eastern margin of the Tibetan Plateau. They are the Xianshuihe fault zone, the Longmenshan fault zone, the Anninghe fault zone, the Daliangshan fault zone, the Zemuhe fault zone, and the Xiaojiang fault zone. The crustal rock mass outside fault core can be divided into a damage zone and wall rock according to the intensity of tectonic discontinuities. This intensity is a quantitative index of tectonic damage. Then we analyze the spatial pattern, the characteristics of damage, and the influence factors of the tectonic damage of crustal rock mass. The main conclusions are as follows: (1)Damage degree shows a decrease with perpendicular distance from the main fault trace. High damage areas alternate with low damage areas in the damage zone. The widest damage zone is 3100 m; (2)The rock mass in damage zone and wall rock is damaged in brittle regime at high strain rate and low strain rate, respectively. And the orientations of tectonic discontinuities in damage zone show a strong correlation with recent crustal stress field; (4)The cumulative displacement that characterizes the development stage of faults determines the scale of the damage zone, and the local variations are mainly controlled by fault geometry and lithology; (5)A new conceptual model based on cumulative displacement, fault geometry, lithology, and depth is proposed to explain the pattern of the tectonic damage of crustal rock mass around the active fault zone. This study can provide evidences for constraining the structure of crustal rock masses in seismic dynamics, tectonic geomorphology, geological disaster, and engineering, and help to deepen the understanding of the crustal rock mass of active fault zones.
2021, 29(2): 307-325.
With the western development, sub-sections of the line traffic engineering from Ya'an to Nyingchi is being planned and constructed one after another. The planned route of Sichuan-Tibet Railway has to span seven great rivers and eight grand mountains, where the terrain elevation difference is very significant. The analysis shows that under the special geological background of high altitude, large elevation difference, strong tectonic movement, rapid crustal uplift and rapid river cutting, the study area presents"three high and two strong" geological characteristics. They include the high-intensity earthquake, the high in-situ stress, the high ground temperature, and the strongly developed diverse geological disasters, and the strongly developed deep and large active faults. Under the action of external dynamic geology and the action of in ternal dynamic geology, the surface geological problems such as glacier debris flow, high-level collapse landslide, debris slope, rock pile, ice lake break and chain hazard are formed in the study area. Under the action of internal dynamic geology, the tunnel may encounter deep geological problems such as deep active fault, high intensity earthquake, high ground stress(rock burst and large deformation of soft rock), high ground temperature and so on. In view of different engineering geological problems, we analyze the engineering hazards. At the same time, through the geological route selection in the planning and design stage, we use reasonable engineering settings to avoid or reduce engineering risks. We suggest that in the construction and operation stage, the advance detection, prediction, monitoring and early warning of geological risk be strengthened, and scientific and reasonable engineering measures be adopted to ensure that the geological risk can be controlled. This paper can provide scientific support for the planning and construction of line engineering in the traffic corridor.
With the western development, sub-sections of the line traffic engineering from Ya'an to Nyingchi is being planned and constructed one after another. The planned route of Sichuan-Tibet Railway has to span seven great rivers and eight grand mountains, where the terrain elevation difference is very significant. The analysis shows that under the special geological background of high altitude, large elevation difference, strong tectonic movement, rapid crustal uplift and rapid river cutting, the study area presents"three high and two strong" geological characteristics. They include the high-intensity earthquake, the high in-situ stress, the high ground temperature, and the strongly developed diverse geological disasters, and the strongly developed deep and large active faults. Under the action of external dynamic geology and the action of in ternal dynamic geology, the surface geological problems such as glacier debris flow, high-level collapse landslide, debris slope, rock pile, ice lake break and chain hazard are formed in the study area. Under the action of internal dynamic geology, the tunnel may encounter deep geological problems such as deep active fault, high intensity earthquake, high ground stress(rock burst and large deformation of soft rock), high ground temperature and so on. In view of different engineering geological problems, we analyze the engineering hazards. At the same time, through the geological route selection in the planning and design stage, we use reasonable engineering settings to avoid or reduce engineering risks. We suggest that in the construction and operation stage, the advance detection, prediction, monitoring and early warning of geological risk be strengthened, and scientific and reasonable engineering measures be adopted to ensure that the geological risk can be controlled. This paper can provide scientific support for the planning and construction of line engineering in the traffic corridor.
2021, 29(2): 326-341.
The Sichuan-Tibet Railway is the most challenging railway project ever in the world. The project region is characterized by various adverse geological conditions including active tectonic movement, intensive mega faults, abrupt topographic relief and frequent geological disasters. Therefore, the construction of this project is challenged by complex geological disaster risks from both ground surface and underground. This study comprehensively and quantitatively analyzes the ground surface and underground geological risks along the Sichuan-Tibet Railway, and further evaluates their consequential influences on the project so as to support its feasibility study. The risk analysis utilizes abundant spatial-temporal data, and various approaches including three-dimensional structure modeling, numerical modeling, statistical modeling, dynamic modeling, time series modeling and spatial distribution modeling. The results show that there are three areas concentrated with high ground surface geological hazards risk along the Sichuan-Tibet railway, namely the Xianshuihe fault zone, the Jinshajiang fault zone and the eastern Himalayan syntaxis area. However, ground surface engineering risks of this project are significantly reduced, because its underground tunnels are over 80% of the total railway line length. The universal quantitative risk assessment models are developed for major underground engineering geological risks, including fault activities, rock bursts and large deformations. For several major tunnels such as the Yigong tunnel, risks of typical individual underground geological hazards(e.g. rock burst and large deformation) as well as the integrated risk, are quantitatively evaluated. The results show that both surface and subsurface engineering risks are significant and can threaten the safety of project. This study provides a scientific and technical support for the feasibility study of the Sichuan-Tibet Railway, and is also expected to be a reference for major engineering geological risk control for similar line engineering projects around the world.
The Sichuan-Tibet Railway is the most challenging railway project ever in the world. The project region is characterized by various adverse geological conditions including active tectonic movement, intensive mega faults, abrupt topographic relief and frequent geological disasters. Therefore, the construction of this project is challenged by complex geological disaster risks from both ground surface and underground. This study comprehensively and quantitatively analyzes the ground surface and underground geological risks along the Sichuan-Tibet Railway, and further evaluates their consequential influences on the project so as to support its feasibility study. The risk analysis utilizes abundant spatial-temporal data, and various approaches including three-dimensional structure modeling, numerical modeling, statistical modeling, dynamic modeling, time series modeling and spatial distribution modeling. The results show that there are three areas concentrated with high ground surface geological hazards risk along the Sichuan-Tibet railway, namely the Xianshuihe fault zone, the Jinshajiang fault zone and the eastern Himalayan syntaxis area. However, ground surface engineering risks of this project are significantly reduced, because its underground tunnels are over 80% of the total railway line length. The universal quantitative risk assessment models are developed for major underground engineering geological risks, including fault activities, rock bursts and large deformations. For several major tunnels such as the Yigong tunnel, risks of typical individual underground geological hazards(e.g. rock burst and large deformation) as well as the integrated risk, are quantitatively evaluated. The results show that both surface and subsurface engineering risks are significant and can threaten the safety of project. This study provides a scientific and technical support for the feasibility study of the Sichuan-Tibet Railway, and is also expected to be a reference for major engineering geological risk control for similar line engineering projects around the world.
2021, 29(2): 342-352.
Climate warming and engineering actions impact and accelerate permafrost degradation, resulting in significant changes of engineering stability in permafrost regions. This article mainly discusses the relationship between climate warming and engineering stability from the view of permafrost changes and engineering hazards under the impacts of climate warming and engineering. We summarize the changes in active layer thickness and permafrost temperature under climate warming and in permafrost table and temperature under the embankment of Qinghai-Tibet Highway and Railway and their subgrade deformation. Especially, we summarize the engineering measures of preventing permafrost thaw under the embankment in Qinghai-Tibet Plateau and discuss the role of these measures of cooling underlying permafrost under the future climate warming and its impact on the engineering serviceability. The results show that the Plateau permafrost has undergone remarkable degradation during the past decades and engineering thermal impacts accelerated permafrost degradation under the embankment, resulting in engineering instability. Qinghai-Tibet Railway used some measures of cooling the underlying permafrost, which can adapt to climate warming of 1.0 ℃. Under the future climate warming of 1.5 ℃, reinforcement measures of Qinghai-Tibet Railway is required and has to be planned as soon as possible.
Climate warming and engineering actions impact and accelerate permafrost degradation, resulting in significant changes of engineering stability in permafrost regions. This article mainly discusses the relationship between climate warming and engineering stability from the view of permafrost changes and engineering hazards under the impacts of climate warming and engineering. We summarize the changes in active layer thickness and permafrost temperature under climate warming and in permafrost table and temperature under the embankment of Qinghai-Tibet Highway and Railway and their subgrade deformation. Especially, we summarize the engineering measures of preventing permafrost thaw under the embankment in Qinghai-Tibet Plateau and discuss the role of these measures of cooling underlying permafrost under the future climate warming and its impact on the engineering serviceability. The results show that the Plateau permafrost has undergone remarkable degradation during the past decades and engineering thermal impacts accelerated permafrost degradation under the embankment, resulting in engineering instability. Qinghai-Tibet Railway used some measures of cooling the underlying permafrost, which can adapt to climate warming of 1.0 ℃. Under the future climate warming of 1.5 ℃, reinforcement measures of Qinghai-Tibet Railway is required and has to be planned as soon as possible.
2021, 29(2): 353-364.
The proposed Luolong railway station is located on the Chada large-scale accumulation. This accumulation is geometrically characterized by three-level platforms from crown to toe, featured by boulders, rock blocks and gravel soil, especially coarse boulders cover the whole slope surface. However, there are many opinions on its formation. This paper ascertains the spatial distribution characteristics and material composition(including grain and lithology) of the Chada accumulation through on-site investigation, geological drilling, three-dimensional oblique photography of drones and satellite images. In addition, the paper determines the age of black silty soil below the valley section of accumulation using C-14 dating method. Preliminary analysis indicates that the deeper soil of the large-scale accumulation(above 3780 m elevation including the second and third platforms) belongs to the origin of early morainal process, the deeper soil of the large-scale accumulation(below 3780 m elevation) is formed by the river alluvium, the coarse boulders on the whole surface of deposit are presumed to be the resultant of high-elevation rockfall, and the rock blocks located on the surface of the second platform should result from the failure of the left ridge in the later period. According to the current geomorphological characteristics, the paper analyzes the five formation stages of the Chada large-scale accumulation. The results provide a basis for the stability evaluation of the accumulation.
The proposed Luolong railway station is located on the Chada large-scale accumulation. This accumulation is geometrically characterized by three-level platforms from crown to toe, featured by boulders, rock blocks and gravel soil, especially coarse boulders cover the whole slope surface. However, there are many opinions on its formation. This paper ascertains the spatial distribution characteristics and material composition(including grain and lithology) of the Chada accumulation through on-site investigation, geological drilling, three-dimensional oblique photography of drones and satellite images. In addition, the paper determines the age of black silty soil below the valley section of accumulation using C-14 dating method. Preliminary analysis indicates that the deeper soil of the large-scale accumulation(above 3780 m elevation including the second and third platforms) belongs to the origin of early morainal process, the deeper soil of the large-scale accumulation(below 3780 m elevation) is formed by the river alluvium, the coarse boulders on the whole surface of deposit are presumed to be the resultant of high-elevation rockfall, and the rock blocks located on the surface of the second platform should result from the failure of the left ridge in the later period. According to the current geomorphological characteristics, the paper analyzes the five formation stages of the Chada large-scale accumulation. The results provide a basis for the stability evaluation of the accumulation.
2021, 29(2): 365-374.
Under the comprehensive influences of tectonics, weathering, and acidification of acid rain, the rock mass along the Sichuan-Tibet Railway has extensive deep shattered zones. When the rock masses are excavated due to constructions, a series of deep and cataclastic rock slopes can be formed. These slopes are highly susceptible to collapse as well as overall instability, which is hard to be reinforced by the traditional safety netting system(SNS). This study proposes a new composite structure for slope protection, anchored flexible system, replacing bolts of SNS with prestressed anchor cables to constrain the surface displacement of the cataclastic rock slope while simultaneously stabilizing the slope body. Here, we conduct 1 ︰ 10 large-scale indoor model tests to explore the stress-strain characteristics, the coordinated loading mechanism, and the design method of the anchored flexible systems for cataclastic rock slope protection under heavy rainfall conditions. Model test reveals the coordinated loading between both prestressed anchor cables and nets in anchored flexible systems when the cataclastic rock slope deformation happens. The stress of the flexible nets has significant impacts on the working state of the prestressed anchor cable, and it can form an obvious re-tension, which should be fully taken into account in the design.
Under the comprehensive influences of tectonics, weathering, and acidification of acid rain, the rock mass along the Sichuan-Tibet Railway has extensive deep shattered zones. When the rock masses are excavated due to constructions, a series of deep and cataclastic rock slopes can be formed. These slopes are highly susceptible to collapse as well as overall instability, which is hard to be reinforced by the traditional safety netting system(SNS). This study proposes a new composite structure for slope protection, anchored flexible system, replacing bolts of SNS with prestressed anchor cables to constrain the surface displacement of the cataclastic rock slope while simultaneously stabilizing the slope body. Here, we conduct 1 ︰ 10 large-scale indoor model tests to explore the stress-strain characteristics, the coordinated loading mechanism, and the design method of the anchored flexible systems for cataclastic rock slope protection under heavy rainfall conditions. Model test reveals the coordinated loading between both prestressed anchor cables and nets in anchored flexible systems when the cataclastic rock slope deformation happens. The stress of the flexible nets has significant impacts on the working state of the prestressed anchor cable, and it can form an obvious re-tension, which should be fully taken into account in the design.
2021, 29(2): 375-382.
With the extension of China's railway to the western mountainous areas such as the Qinghai-Tibet Plateau, there are more and more deep buried tunnels. High in-situ stress has become a kind of complex geological condition which controls the route selection scheme. If it is possible to quantitatively assess the in-situ stress state of the tunnel site before lifting, then the risk control is the most active in the stage of route selection. We have measured a lot of in-situ stress data along the Lalin section of Sichuan-Tibet railway. The structure of in-situ stress in the study area is mainly reverse stress regime and strike-slip stress regime. The direction of in-situ stress is distributed between N19°W~N30°E. The average transition depth of in-situ stress state is about 500 m. Less than that depth, the maximum horizontal in-situ stress has disordered change with buried depth. But the maximum value does not exceed the maximum stress level. More than that depth, the maximum horizontal stress can be estimated approximately by Helm formula. This is the most important rule of in-situ stress with depth. Based on this: If the buried depth of the tunnel is less than the transition depth, the supporting structure and construction method should be dynamically adjusted during the construction period. Because this is conducive to control the risk of high in-situ stress. If the buried depth of the tunnel is more than the transition depth, the in-situ stress of tunnel site can be estimated by Helm formula. According to the understanding, we can use the method of route selection to choose the better scheme of economy and technology. Finally, the route selection program of high in-situ stress area is established. The paper gives useful ideas for solving the problem of lack of quantitative evaluation method of in-situ stress in railway scheme selection stage.
With the extension of China's railway to the western mountainous areas such as the Qinghai-Tibet Plateau, there are more and more deep buried tunnels. High in-situ stress has become a kind of complex geological condition which controls the route selection scheme. If it is possible to quantitatively assess the in-situ stress state of the tunnel site before lifting, then the risk control is the most active in the stage of route selection. We have measured a lot of in-situ stress data along the Lalin section of Sichuan-Tibet railway. The structure of in-situ stress in the study area is mainly reverse stress regime and strike-slip stress regime. The direction of in-situ stress is distributed between N19°W~N30°E. The average transition depth of in-situ stress state is about 500 m. Less than that depth, the maximum horizontal in-situ stress has disordered change with buried depth. But the maximum value does not exceed the maximum stress level. More than that depth, the maximum horizontal stress can be estimated approximately by Helm formula. This is the most important rule of in-situ stress with depth. Based on this: If the buried depth of the tunnel is less than the transition depth, the supporting structure and construction method should be dynamically adjusted during the construction period. Because this is conducive to control the risk of high in-situ stress. If the buried depth of the tunnel is more than the transition depth, the in-situ stress of tunnel site can be estimated by Helm formula. According to the understanding, we can use the method of route selection to choose the better scheme of economy and technology. Finally, the route selection program of high in-situ stress area is established. The paper gives useful ideas for solving the problem of lack of quantitative evaluation method of in-situ stress in railway scheme selection stage.
2021, 29(2): 383-393.
Karst geothermal system is one of the most important geothermal types. The particularity of karst media makes geothermal groundwater easier to be influenced by the shallow circulating cold groundwater during its formation, as a result, differs the genetic mechanism of karst geothermal system from others. In present research, the karst geothermal system of Tongluoshan anticline at the margin of Sichuan Basin is taken as an example to reveal the potential misunderstanding of geothermal groundwater genesis caused by the mixing of cold and hot water. A comprehensive approach using of hydrogeochemistry and isotope coupled with field survey is performed to get insight into the mixing process of cold and hot water at the discharge zone of geothermal system. The effects of the mixing on the understanding of geothermal system are deeply discussed. A conceptual model of karst geothermal groundwater system with cold-hot water mixing was established. The results show that the mixing effect of cold and hot water is extremely strong at the discharge zone of geothermal system. The mixing ratio of cold water can be up to 73% ~89% in Tongluoshan geothermal system. The mixing of cold and hot water would potentially destroy the information of thermal groundwater for geothermal system, resulting in underestimating the recharge elevation and reservoir temperature. This underestimation reaches to 78% and 45% for recharge elevation and reservoir temperature, respectively, in Tongluoshan geothermal system. The true model of Tongluoshan karst geothermal groundwater system is recognized by eliminating the effects of cold and hot water mixing. The geothermal system is recharged by precipitation in the exposed karst mountain area at an elevation of 2100~2400 m at the north. Recharged water is heated by the terrestrial heat flow during its deep circulation. The reservoir temperature of carbonate aquifers of lower Triassic Jialingjiang formation(T1j) and middle Triassic Leikoupo formation(T2l) is estimated ranging from 128~172 ℃. Thermal groundwater is controlled by the karst and geological structure of anticline, and flows from the northeast to the southwest. Thermal water mixes with the local shallow circulating cold water during its discharge. As a result, the temperature of exposed thermal water declines to 38~62 ℃.
Karst geothermal system is one of the most important geothermal types. The particularity of karst media makes geothermal groundwater easier to be influenced by the shallow circulating cold groundwater during its formation, as a result, differs the genetic mechanism of karst geothermal system from others. In present research, the karst geothermal system of Tongluoshan anticline at the margin of Sichuan Basin is taken as an example to reveal the potential misunderstanding of geothermal groundwater genesis caused by the mixing of cold and hot water. A comprehensive approach using of hydrogeochemistry and isotope coupled with field survey is performed to get insight into the mixing process of cold and hot water at the discharge zone of geothermal system. The effects of the mixing on the understanding of geothermal system are deeply discussed. A conceptual model of karst geothermal groundwater system with cold-hot water mixing was established. The results show that the mixing effect of cold and hot water is extremely strong at the discharge zone of geothermal system. The mixing ratio of cold water can be up to 73% ~89% in Tongluoshan geothermal system. The mixing of cold and hot water would potentially destroy the information of thermal groundwater for geothermal system, resulting in underestimating the recharge elevation and reservoir temperature. This underestimation reaches to 78% and 45% for recharge elevation and reservoir temperature, respectively, in Tongluoshan geothermal system. The true model of Tongluoshan karst geothermal groundwater system is recognized by eliminating the effects of cold and hot water mixing. The geothermal system is recharged by precipitation in the exposed karst mountain area at an elevation of 2100~2400 m at the north. Recharged water is heated by the terrestrial heat flow during its deep circulation. The reservoir temperature of carbonate aquifers of lower Triassic Jialingjiang formation(T1j) and middle Triassic Leikoupo formation(T2l) is estimated ranging from 128~172 ℃. Thermal groundwater is controlled by the karst and geological structure of anticline, and flows from the northeast to the southwest. Thermal water mixes with the local shallow circulating cold water during its discharge. As a result, the temperature of exposed thermal water declines to 38~62 ℃.
2021, 29(2): 394-403.
Sejila Mountain is close to the core area of the eastern Himalayan tectonic junction. The tectonic stress level is high due to the block uplift and compression. The in-situ stress field background is complex. Yet the scientific research and engineering practice work in area are relatively less. In order to study the characteristics of present in-situ stress field in the traffic corridor area, we carried out deep hole in-situ stress measurement, data statistics and regression analysis. The 12 deep holes were set up. The maximum test depth was 1410.2 m. The measured data of 108 sections were obtained by the method of hydraulic fracturing. The results show the follows. The direction and magnitude of the maximum horizontal principal stress are basically consistent with the regional ground stress background level. The dominant direction is NE-NEE. The maximum horizontal principal stress gradient coefficient is 2.5~4.3 MPa Per 100 meters, slightly higher than the regional background level. The relationship among the three principal stresses in the field is as follows: maximum horizontal principal stress>minimum horizontal principal stress>vertical principal stress. Through the statistics and analysis of the obtained in-situ stress, it is roughly divided into three sections, with the distance away from the core area of the Eastern Himalayan tectonic knot. The tectonic stress tends to weaken to the southwest. The regression formula of the maximum horizontal principal stress varying with depth in different sections of the field is obtained by using the least square method of statistical analysis. We estimate the in-situ stress value near the measuring depth level. The present in-situ stress field of Sejila Mountain traffic corridor obtained by in-situ stress measurement and research are of great significance for engineering route selection and survey design. The research methods of deep holes in-situ stress measurement, regional tectonic origin analysis, in-situ stress characteristics segmentation, characteristic depth division of linear distribution, can provide an important reference for the follow-up research work of in-situ stress in similar mountain areas.
Sejila Mountain is close to the core area of the eastern Himalayan tectonic junction. The tectonic stress level is high due to the block uplift and compression. The in-situ stress field background is complex. Yet the scientific research and engineering practice work in area are relatively less. In order to study the characteristics of present in-situ stress field in the traffic corridor area, we carried out deep hole in-situ stress measurement, data statistics and regression analysis. The 12 deep holes were set up. The maximum test depth was 1410.2 m. The measured data of 108 sections were obtained by the method of hydraulic fracturing. The results show the follows. The direction and magnitude of the maximum horizontal principal stress are basically consistent with the regional ground stress background level. The dominant direction is NE-NEE. The maximum horizontal principal stress gradient coefficient is 2.5~4.3 MPa Per 100 meters, slightly higher than the regional background level. The relationship among the three principal stresses in the field is as follows: maximum horizontal principal stress>minimum horizontal principal stress>vertical principal stress. Through the statistics and analysis of the obtained in-situ stress, it is roughly divided into three sections, with the distance away from the core area of the Eastern Himalayan tectonic knot. The tectonic stress tends to weaken to the southwest. The regression formula of the maximum horizontal principal stress varying with depth in different sections of the field is obtained by using the least square method of statistical analysis. We estimate the in-situ stress value near the measuring depth level. The present in-situ stress field of Sejila Mountain traffic corridor obtained by in-situ stress measurement and research are of great significance for engineering route selection and survey design. The research methods of deep holes in-situ stress measurement, regional tectonic origin analysis, in-situ stress characteristics segmentation, characteristic depth division of linear distribution, can provide an important reference for the follow-up research work of in-situ stress in similar mountain areas.
2021, 29(2): 404-415.
Snow avalanche is one of the most common geological disasters ubiquitously distributed in the Qinghai-Tibet Plateau. Snow avalanche susceptibility mapping is critical for disaster prevention and mitigation of major engineering construction such as the Sichuan-Tibet Railway. This paper exemplifies the Parlung-Tsangpo catchment in south-eastern Tibet, collects 381 channelled snow avalanches that fell below the timberline through field surveys and remote sensing interpretation. First of all, 18 influence factors are selected and quantitatively extracted by using GIS, remote sensing, et al. Then, Principal Component Analysis(PCA)method is performed to obtain the key predisposing factors and assign weight coefficient to each factor. Thereafter, the Weighted Information Value Method(PCA-Ⅰ) and Weighted Certainty Factor Method(PCA-CF) are conducted to map snow avalanche susceptibility. Finally, the performance of two models is compared and evaluated based on ROC(receiver operating characteristic) curve and AUC(area under receiver). The results show that the susceptibility assessment is very sensitive to climate, macro-topography, micro-topography, and inhibition factors. Among them, the climate explained 30.61% of the data variation; topography explained 21.23% of the data variation. The PCA-Ⅰ model gives the susceptibility zoning index in the range of [-2.41, 1.365], and the PCA-CF model gives the susceptibility zoning index ranging in[-0.549, 0.424]. In addition, the susceptibility map of the PCA-Ⅰ model has a significant abnormal area in downstream at the Tongmai section. Thus, the zoning index of the PCA-CF model is more reasonable than that of the PCA-Ⅰ model. The overall results suggest that the high snow avalanche prone areas are mainly distributed at Ranwu-Yupu section along the National Road 318 around in the upper narrow valley section of Parlung-Tsangpo river, the ridges of the mountains on both sides of the middle and lower reaches, and the narrow valley sections of the tributaries.
Snow avalanche is one of the most common geological disasters ubiquitously distributed in the Qinghai-Tibet Plateau. Snow avalanche susceptibility mapping is critical for disaster prevention and mitigation of major engineering construction such as the Sichuan-Tibet Railway. This paper exemplifies the Parlung-Tsangpo catchment in south-eastern Tibet, collects 381 channelled snow avalanches that fell below the timberline through field surveys and remote sensing interpretation. First of all, 18 influence factors are selected and quantitatively extracted by using GIS, remote sensing, et al. Then, Principal Component Analysis(PCA)method is performed to obtain the key predisposing factors and assign weight coefficient to each factor. Thereafter, the Weighted Information Value Method(PCA-Ⅰ) and Weighted Certainty Factor Method(PCA-CF) are conducted to map snow avalanche susceptibility. Finally, the performance of two models is compared and evaluated based on ROC(receiver operating characteristic) curve and AUC(area under receiver). The results show that the susceptibility assessment is very sensitive to climate, macro-topography, micro-topography, and inhibition factors. Among them, the climate explained 30.61% of the data variation; topography explained 21.23% of the data variation. The PCA-Ⅰ model gives the susceptibility zoning index in the range of [-2.41, 1.365], and the PCA-CF model gives the susceptibility zoning index ranging in[-0.549, 0.424]. In addition, the susceptibility map of the PCA-Ⅰ model has a significant abnormal area in downstream at the Tongmai section. Thus, the zoning index of the PCA-CF model is more reasonable than that of the PCA-Ⅰ model. The overall results suggest that the high snow avalanche prone areas are mainly distributed at Ranwu-Yupu section along the National Road 318 around in the upper narrow valley section of Parlung-Tsangpo river, the ridges of the mountains on both sides of the middle and lower reaches, and the narrow valley sections of the tributaries.
2021, 29(2): 426-434.
A railway tunnel in southeast Tibet has a length of 42.3 km and is located in the southeast of Qinghai-Tibet Plateau. It has high altitudes, large relative elevation differences, dense mountain tops with glaciers, harsh natural environments, and frequent extreme weather. Therefore, the conventional geophysical methods and equipment cannot meet the accuracy and efficiency requirements of tunnel surveys. In order to solve the problem of no geophysical data coverage for long tunnels under the restriction of terrain conditions, this research uses a helicopter to carry an airborne object detection system. It is based on the Versatile time domain electromagnetic(VTEM), Z-axis Tipper Electromagnetic(ZTEM), and the airborne magnetic method developed by Geotech, It is the first time achieved full coverage of geophysical data for a long tunnel under the extremely harsh climatic conditions of Qinghai-Tibet Plateau. and we carry out a fusion and comparative analysis of the tunnel-related aerial geophysical results, ground geophysical results and deep hole drilling actual reveals. The conclusions are drawn as follows: (1)The application of aerial geophysical prospecting to a railway tunnel in southeastern Tibet can fill in the blank of no survey data available for tunnel engineering and efficiently provide a basis for route selection, design and construction of linear projects in difficult and dangerous mountainous areas on the plateau; (2)Through the interpretation of the spatial distribution of resistivity and magnetic susceptibility obtained by aeronautical electrical method and aeromagnetic method, a comprehensive analysis and interpretation of the stratum lithology, structure and joint dense zone along the tunnel can be realized; (3)The airborne electromagnetic method can better reflect the low-resistance anomaly areas and resistivity change zones such as stratigraphic boundaries, faulted structures, and dense joints. The results are in good agreement with the ground geophysical prospecting and deep hole drilling. The detection and interpretation results of the aviation electromagnetic method are highly reliable, and the detection effect and ability are effective for the survey of long tunnels; (4)Through multi-source geophysical prospecting fusion and comparative interpretation, the interpretation accuracy of aerial geophysical prospecting results can be further improved and applied to tunnel survey design.
A railway tunnel in southeast Tibet has a length of 42.3 km and is located in the southeast of Qinghai-Tibet Plateau. It has high altitudes, large relative elevation differences, dense mountain tops with glaciers, harsh natural environments, and frequent extreme weather. Therefore, the conventional geophysical methods and equipment cannot meet the accuracy and efficiency requirements of tunnel surveys. In order to solve the problem of no geophysical data coverage for long tunnels under the restriction of terrain conditions, this research uses a helicopter to carry an airborne object detection system. It is based on the Versatile time domain electromagnetic(VTEM), Z-axis Tipper Electromagnetic(ZTEM), and the airborne magnetic method developed by Geotech, It is the first time achieved full coverage of geophysical data for a long tunnel under the extremely harsh climatic conditions of Qinghai-Tibet Plateau. and we carry out a fusion and comparative analysis of the tunnel-related aerial geophysical results, ground geophysical results and deep hole drilling actual reveals. The conclusions are drawn as follows: (1)The application of aerial geophysical prospecting to a railway tunnel in southeastern Tibet can fill in the blank of no survey data available for tunnel engineering and efficiently provide a basis for route selection, design and construction of linear projects in difficult and dangerous mountainous areas on the plateau; (2)Through the interpretation of the spatial distribution of resistivity and magnetic susceptibility obtained by aeronautical electrical method and aeromagnetic method, a comprehensive analysis and interpretation of the stratum lithology, structure and joint dense zone along the tunnel can be realized; (3)The airborne electromagnetic method can better reflect the low-resistance anomaly areas and resistivity change zones such as stratigraphic boundaries, faulted structures, and dense joints. The results are in good agreement with the ground geophysical prospecting and deep hole drilling. The detection and interpretation results of the aviation electromagnetic method are highly reliable, and the detection effect and ability are effective for the survey of long tunnels; (4)Through multi-source geophysical prospecting fusion and comparative interpretation, the interpretation accuracy of aerial geophysical prospecting results can be further improved and applied to tunnel survey design.
2021, 29(2): 435-444.
Frequent mountain disasters in southeastern Tibet serve as a key and challenging problem in the planning and construction of Sichuan-Tibet Railway, as the railway crosses the Chalong-Longbaqu gully in this area with a bridge project near the mouth of the gully. In order to evaluate the influence of mountain disasters in Chalong-Longbaqu gully on bridge engineering, this paper first studies the scale-frequency, potential development trend and disaster performance of debris flow, avalanche, landslide, collapse and other mountain disasters in Chalong-Longbaqu gully. It uses comprehensive technical methods including on-site investigation, high-precision remote sensing interpretation, multi-spectral remote sensing surface displacement monitoring, accumulation geochronology analysis and engineering analogy. Generally speaking, the main effects of mountain disasters such as ice avalanches, rock avalanches and landslides are to provide material sources for subsequent debris flows. It finds that the mountain disasters in Chalong-Longbaqu are relatively inactive. Afterwards, considering that the high ice avalanche debris flow to occur in the source material of 6.75 million cubic meter at the No. 1 Glacier in the upstream of Chalong-Longbaqu gully under extreme conditions, this paper simulates elaborately the whole process of avalanche debris flow with Massflow. With energy consumed by the ice avalanche debris flow through shoveling, collision and friction along the way, the flow velocity near Chalong-Longbaqu Bridge is 34m ·s-1, and the flow depth is 24m, which is lower than the clearance of the bridge(43.5m). On this basis, the disaster risk of high ice avalanche debris flow to bridge work is evaluated, which provides a basis for the engineering setting and protective measures of Chalong-Longbaqu Bridge.
Frequent mountain disasters in southeastern Tibet serve as a key and challenging problem in the planning and construction of Sichuan-Tibet Railway, as the railway crosses the Chalong-Longbaqu gully in this area with a bridge project near the mouth of the gully. In order to evaluate the influence of mountain disasters in Chalong-Longbaqu gully on bridge engineering, this paper first studies the scale-frequency, potential development trend and disaster performance of debris flow, avalanche, landslide, collapse and other mountain disasters in Chalong-Longbaqu gully. It uses comprehensive technical methods including on-site investigation, high-precision remote sensing interpretation, multi-spectral remote sensing surface displacement monitoring, accumulation geochronology analysis and engineering analogy. Generally speaking, the main effects of mountain disasters such as ice avalanches, rock avalanches and landslides are to provide material sources for subsequent debris flows. It finds that the mountain disasters in Chalong-Longbaqu are relatively inactive. Afterwards, considering that the high ice avalanche debris flow to occur in the source material of 6.75 million cubic meter at the No. 1 Glacier in the upstream of Chalong-Longbaqu gully under extreme conditions, this paper simulates elaborately the whole process of avalanche debris flow with Massflow. With energy consumed by the ice avalanche debris flow through shoveling, collision and friction along the way, the flow velocity near Chalong-Longbaqu Bridge is 34m ·s-1, and the flow depth is 24m, which is lower than the clearance of the bridge(43.5m). On this basis, the disaster risk of high ice avalanche debris flow to bridge work is evaluated, which provides a basis for the engineering setting and protective measures of Chalong-Longbaqu Bridge.
2021, 29(2): 445-453.
Remote sensing provides a new perspective and an important method for lithology identification. The Kangyu tunnel of the Sichuan-Tibet Railway locates near the Yongba area of the Salween River Canyon in Hengduan Mountain, southeast Tibet, has a total length of 20.235km and a maximum buried depth of 1314m. This paper is based on the current situation of complex topography and geomorphology, harsh environment, hard to reach personnel, and lack of geological data in this area, and comprehensively identify the lithologies using high-resolution, multi-spectral and hyper-spectral remote sensing data. Based on visual interpretation of high-resolution remote sensing images, this paper uses a comprehensive processing scheme of multi-spectral and hyper-spectral remote sensing data for effectively extracting lithology information, such as spectral angle matching(SAM), minimum noise separation transforms(MNF), and typical band combinations. It effectively enhances, extracts, and automatically classifies the remote sensing information combined with the rich band information of GF-5 hyperspectral data. Combined with field investigation, the paper newly identifies the NW-trending carbonate strata of the Middle Jurassic Sankara formation(J2s)in this region. In addition, this paper refines the boundaries of several stratigraphic units such as the Paleogene Zongbai Group(E2z). More than 10 original stratigraphic boundaries have been revised, and the methods used in our paper for rock identification can act as a remote sensing interpretation technical model for rapid identification of plateau geomorphological fluctuation areas and effective acquisition of lithology information. This contribution can provide important basic data for planning, route selection and design of the railway. It is also hoped that this work with examples of applications can be useful to other workers for lithological remote sensing.
Remote sensing provides a new perspective and an important method for lithology identification. The Kangyu tunnel of the Sichuan-Tibet Railway locates near the Yongba area of the Salween River Canyon in Hengduan Mountain, southeast Tibet, has a total length of 20.235km and a maximum buried depth of 1314m. This paper is based on the current situation of complex topography and geomorphology, harsh environment, hard to reach personnel, and lack of geological data in this area, and comprehensively identify the lithologies using high-resolution, multi-spectral and hyper-spectral remote sensing data. Based on visual interpretation of high-resolution remote sensing images, this paper uses a comprehensive processing scheme of multi-spectral and hyper-spectral remote sensing data for effectively extracting lithology information, such as spectral angle matching(SAM), minimum noise separation transforms(MNF), and typical band combinations. It effectively enhances, extracts, and automatically classifies the remote sensing information combined with the rich band information of GF-5 hyperspectral data. Combined with field investigation, the paper newly identifies the NW-trending carbonate strata of the Middle Jurassic Sankara formation(J2s)in this region. In addition, this paper refines the boundaries of several stratigraphic units such as the Paleogene Zongbai Group(E2z). More than 10 original stratigraphic boundaries have been revised, and the methods used in our paper for rock identification can act as a remote sensing interpretation technical model for rapid identification of plateau geomorphological fluctuation areas and effective acquisition of lithology information. This contribution can provide important basic data for planning, route selection and design of the railway. It is also hoped that this work with examples of applications can be useful to other workers for lithological remote sensing.
2021, 29(2): 454-465.
Chada valley is located in the lower reaches of the Dongcuo river in Lajiu Township, Luolong County, Southeast Tibet. It is a typical U-shaped valley with high and steep bank slopes on both sides. The high slope of Chada No.1 is located on the southeast side of the proposed railway station. The elevation of the slope is 3700~5328m, and a large amount of loose materials such as stones, gravel and breccias are piled up along and under the slope. The conglomerate(E2z) scarp is outcropped on the top of the slope, with a height of 300~500m, and the horizontal distance from the proposed railway station is about 2.6km. Due to the complicated geological conditions of the slope and the unknown origin of the debris, it is very important to carry out the risk assessment of the high slope for the engineering suitability assessment. This paper uses remote sensing analysis, UAV aerial survey, drilling, geophysical exploration and field investigation to identify the slope structure. The slope is divided into three sections according to the topographic and structural features: rocky slopes and escarpments at the top, the upper debris and the lower debris. In addition, we interprete the potential dangerous rocks. We calculate and analyze the stability of dangerous rocks and slope debris, and simulate the movement distance of rockfall. The results show that large-scale dangerous rocks at the top of the slope remain stable, while small scale dangerous rocks at the bottom of the slope have lower stability and even unstable under extreme conditions. The upper and lower debris are stable under various working conditions, and the shallow surface may creep locally under the conditions of rainfall and earthquake. The rockfall movement only stays on the upper debris platform. The furthest surface boulder is 440m away from the line, and these do not reach the line position. The geological hazard formed by the high slope of No. 1 Chada is controllable to the proposed railway station.
Chada valley is located in the lower reaches of the Dongcuo river in Lajiu Township, Luolong County, Southeast Tibet. It is a typical U-shaped valley with high and steep bank slopes on both sides. The high slope of Chada No.1 is located on the southeast side of the proposed railway station. The elevation of the slope is 3700~5328m, and a large amount of loose materials such as stones, gravel and breccias are piled up along and under the slope. The conglomerate(E2z) scarp is outcropped on the top of the slope, with a height of 300~500m, and the horizontal distance from the proposed railway station is about 2.6km. Due to the complicated geological conditions of the slope and the unknown origin of the debris, it is very important to carry out the risk assessment of the high slope for the engineering suitability assessment. This paper uses remote sensing analysis, UAV aerial survey, drilling, geophysical exploration and field investigation to identify the slope structure. The slope is divided into three sections according to the topographic and structural features: rocky slopes and escarpments at the top, the upper debris and the lower debris. In addition, we interprete the potential dangerous rocks. We calculate and analyze the stability of dangerous rocks and slope debris, and simulate the movement distance of rockfall. The results show that large-scale dangerous rocks at the top of the slope remain stable, while small scale dangerous rocks at the bottom of the slope have lower stability and even unstable under extreme conditions. The upper and lower debris are stable under various working conditions, and the shallow surface may creep locally under the conditions of rainfall and earthquake. The rockfall movement only stays on the upper debris platform. The furthest surface boulder is 440m away from the line, and these do not reach the line position. The geological hazard formed by the high slope of No. 1 Chada is controllable to the proposed railway station.
2021, 29(2): 466-477.
The Kangding segment of the Sichuan-Tibet Railway passes through the Xianshuihe active structural system, where a series of significant engineering geological problems exist such as intensive earthquake and active faults, high-level slippage flow, unstable high and steep bank slopes, high geostress, rockburst and large deformation, high geo-temperature and high stress water inrush. This segment possesses the greatest seismic and geological risks. and it is difficult to find proper reference. Based on the selecting process for ten years, we have chosen the feasible and safe plan of the Sandaoqiao station, Zheduoshan crop and Zheduoshan Mountain tunnel. In this study, through a systematic geological line selection in the Xianshuihe structural belt, we sum up the geological line selection should follow the order of regional stability line selection, engineering geological disasters over ground line selection, "very difficult" engineering geological problems in underground engineering geological line selection, integrated geological line selection, cross line selection etc. Based on the fundamental line selection, structure, lithology and groundwater should be considered. Giving priority to give way and then passing through are suggested in the deep and large fault. Considering the effects of lithology, defective engineering rock mass(soluble rock, alteration rock and structural soft rock) should be avoided and the hard engineering rock mass is preferred. Considering groundwater, karst groundwater area should shorten the length of horizontal circulating band, groundwater rich area should build line in side and high areas and discharge groundwater along slope, geothermal anomaly area should choose low temperature gallery. This achievement can provide a reference for the constructions of the Jinshajiang suture and Jiali structural belt of the Sichuan-Tibet railway and planed Yunnan-Tibet railway.
The Kangding segment of the Sichuan-Tibet Railway passes through the Xianshuihe active structural system, where a series of significant engineering geological problems exist such as intensive earthquake and active faults, high-level slippage flow, unstable high and steep bank slopes, high geostress, rockburst and large deformation, high geo-temperature and high stress water inrush. This segment possesses the greatest seismic and geological risks. and it is difficult to find proper reference. Based on the selecting process for ten years, we have chosen the feasible and safe plan of the Sandaoqiao station, Zheduoshan crop and Zheduoshan Mountain tunnel. In this study, through a systematic geological line selection in the Xianshuihe structural belt, we sum up the geological line selection should follow the order of regional stability line selection, engineering geological disasters over ground line selection, "very difficult" engineering geological problems in underground engineering geological line selection, integrated geological line selection, cross line selection etc. Based on the fundamental line selection, structure, lithology and groundwater should be considered. Giving priority to give way and then passing through are suggested in the deep and large fault. Considering the effects of lithology, defective engineering rock mass(soluble rock, alteration rock and structural soft rock) should be avoided and the hard engineering rock mass is preferred. Considering groundwater, karst groundwater area should shorten the length of horizontal circulating band, groundwater rich area should build line in side and high areas and discharge groundwater along slope, geothermal anomaly area should choose low temperature gallery. This achievement can provide a reference for the constructions of the Jinshajiang suture and Jiali structural belt of the Sichuan-Tibet railway and planed Yunnan-Tibet railway.
2021, 29(2): 478-485.
Debris flow is one of the most developed disaster types in the Tibetan Plateau, and poses a certain threat to the construction of Sichuan-Tibet Railway and the safety of life and property due to its sudden outbreak, violent movement process, and strong destructive characteristics. Geological hazard assessment is part of the effective measures in the management and prevention of disaster prevention and mitigation. For reasonably quantifying the spatial distribution characteristics of debris flow hazard along the railway line, the paper takes the Zire-Bomi section of the Sichuan-Tibet Railway within Linzhi City as the experimental area. We apply the Bayesian optimization algorithm based random forest(TBOR) and gradient boosting tree model(TBOG)to quantify the debris flow hazard values of the route section and identify the hazard levels. The input information of the two models includes 172 historical hazard points and 11 feature parameters. The output information is the outbreak probability of debris flow for each prediction unit. Lastly, the ROC-AUC method is employed to test the evaluation outcomes of the two prediction algorithms. The findings reveal that in the TBOR and TBOG models, the overall debris flow hazard level of the Zire-Bomi line section of the Sichuan-Tibet Railway is relatively high. The proportion of hazard zones inside the high-higher hazard interval of the two models reaches 56.439% and 66.580% respectively, corresponding to the highest hazard point densities of 12.577/(102km2) and 12.940/(102km2)respectively. Compared to the ROC-AUC values derived from the TBOG model, the TBOR model computes 0.89, which is higher than that of TBOR at 0.83. Therefore, the TBOR model has better prediction accuracy. The research findings can provide necessary reference for the construction of disaster prevention and mitigation protection projects along Sichuan-Tibet Railway and the hazard evaluation of other line sections.
Debris flow is one of the most developed disaster types in the Tibetan Plateau, and poses a certain threat to the construction of Sichuan-Tibet Railway and the safety of life and property due to its sudden outbreak, violent movement process, and strong destructive characteristics. Geological hazard assessment is part of the effective measures in the management and prevention of disaster prevention and mitigation. For reasonably quantifying the spatial distribution characteristics of debris flow hazard along the railway line, the paper takes the Zire-Bomi section of the Sichuan-Tibet Railway within Linzhi City as the experimental area. We apply the Bayesian optimization algorithm based random forest(TBOR) and gradient boosting tree model(TBOG)to quantify the debris flow hazard values of the route section and identify the hazard levels. The input information of the two models includes 172 historical hazard points and 11 feature parameters. The output information is the outbreak probability of debris flow for each prediction unit. Lastly, the ROC-AUC method is employed to test the evaluation outcomes of the two prediction algorithms. The findings reveal that in the TBOR and TBOG models, the overall debris flow hazard level of the Zire-Bomi line section of the Sichuan-Tibet Railway is relatively high. The proportion of hazard zones inside the high-higher hazard interval of the two models reaches 56.439% and 66.580% respectively, corresponding to the highest hazard point densities of 12.577/(102km2) and 12.940/(102km2)respectively. Compared to the ROC-AUC values derived from the TBOG model, the TBOR model computes 0.89, which is higher than that of TBOR at 0.83. Therefore, the TBOR model has better prediction accuracy. The research findings can provide necessary reference for the construction of disaster prevention and mitigation protection projects along Sichuan-Tibet Railway and the hazard evaluation of other line sections.
2021, 29(2): 486-494.
The Quaternary deep overburden is developed in a proposed airport site on the southern margin of the Qinghai-Tibet Plateau, and induces a great restriction on the construction of the project. Drilling data shows that the deep overburden is generally distributed in the entire field area with a thickness of more than 30m, and the maximum hole depth of 105m has not been exposed. Vertically, the deep overburden can be divided into four layers from top to bottom: Holocene debris flow accumulation layer(Q4sef), Holocene alluvial accumulation layer(Q4al+pl), Holocene lacustrine accumulation layer(Q4l) and Late Pleistocene Alluvial accumulation layer(Q3al+pl). Among them, the debris flow is mainly composed of breccia and gravel, with a maximum thickness of about 13m, distributed on the west side of the research site; the Holocene alluvial strata is composed of complex materials, mostly silty fine sand and round gravel, without obvious layering rules, with a maximum thickness of about 7m; the lacustrine sedimentary silty clay is plastic-flow plastic, with sand in some parts, and the maximum thickness is about 43m; the late Pleistocene alluvial strata are dominated by fine sand and medium-coarse sand, with pebbles and gravels locally, and the thickness is greater than 42m. The analysis shows that the cause of the deep overburden is closely related to the rapid uplift of the Himalayas since the Late Pleistocene and the interglacial climate, while the surface overburden is closely related to the warming and the short-term alternate climate of cold and warm of the Qinghai-Tibet Plateau climate since the Holocene. The test results reveal that the physical and mechanical properties of the deep overburden are obviously different, and there are major engineering geological problems including uneven settlement, seepage failure, slope stability, and foundation damage induced by freezing and thawing.
The Quaternary deep overburden is developed in a proposed airport site on the southern margin of the Qinghai-Tibet Plateau, and induces a great restriction on the construction of the project. Drilling data shows that the deep overburden is generally distributed in the entire field area with a thickness of more than 30m, and the maximum hole depth of 105m has not been exposed. Vertically, the deep overburden can be divided into four layers from top to bottom: Holocene debris flow accumulation layer(Q4sef), Holocene alluvial accumulation layer(Q4al+pl), Holocene lacustrine accumulation layer(Q4l) and Late Pleistocene Alluvial accumulation layer(Q3al+pl). Among them, the debris flow is mainly composed of breccia and gravel, with a maximum thickness of about 13m, distributed on the west side of the research site; the Holocene alluvial strata is composed of complex materials, mostly silty fine sand and round gravel, without obvious layering rules, with a maximum thickness of about 7m; the lacustrine sedimentary silty clay is plastic-flow plastic, with sand in some parts, and the maximum thickness is about 43m; the late Pleistocene alluvial strata are dominated by fine sand and medium-coarse sand, with pebbles and gravels locally, and the thickness is greater than 42m. The analysis shows that the cause of the deep overburden is closely related to the rapid uplift of the Himalayas since the Late Pleistocene and the interglacial climate, while the surface overburden is closely related to the warming and the short-term alternate climate of cold and warm of the Qinghai-Tibet Plateau climate since the Holocene. The test results reveal that the physical and mechanical properties of the deep overburden are obviously different, and there are major engineering geological problems including uneven settlement, seepage failure, slope stability, and foundation damage induced by freezing and thawing.
2021, 29(2): 495-507.
The unstable rock mass develop in the intersection section of Qinghai-Tibet Railway, G109 National Highway and Beijing-Tibet Expressway, which pose a great threat to the construction and safe operation of traffic engineering. The geological background, development characteristics and deformation failure mechanism of the unstable rock mass are systematically analyzed in order to find out the instability conditions, the main controlling factors and to evaluate the stability. Using block theory and discrete element method, the stability and dynamic response of dangerous rock mass under dead weight condition and seismic load are studied respectively. The study shows that the unstable rock mass can be divided into three parts: the integral collapse source at the top, the fissure zone in the middle and the accumulation area of the block stone in the lower. and there are four groups of dominant structural planes. The calculation results show that the dangerous rock block is basically stable under the condition of dead weight. The unstable modes of dangerous rock mass under the action of seismic load are shear sliding, fracture and fall. Short-time violent earthquakes intensified the accumulation of internal damage in the unstable rock mass. To ensure safety, it is suggested to carry out targeted prevention and control, monitoring and early warning.
The unstable rock mass develop in the intersection section of Qinghai-Tibet Railway, G109 National Highway and Beijing-Tibet Expressway, which pose a great threat to the construction and safe operation of traffic engineering. The geological background, development characteristics and deformation failure mechanism of the unstable rock mass are systematically analyzed in order to find out the instability conditions, the main controlling factors and to evaluate the stability. Using block theory and discrete element method, the stability and dynamic response of dangerous rock mass under dead weight condition and seismic load are studied respectively. The study shows that the unstable rock mass can be divided into three parts: the integral collapse source at the top, the fissure zone in the middle and the accumulation area of the block stone in the lower. and there are four groups of dominant structural planes. The calculation results show that the dangerous rock block is basically stable under the condition of dead weight. The unstable modes of dangerous rock mass under the action of seismic load are shear sliding, fracture and fall. Short-time violent earthquakes intensified the accumulation of internal damage in the unstable rock mass. To ensure safety, it is suggested to carry out targeted prevention and control, monitoring and early warning.
2021, 29(2): 508-515.
Based on the consideration of the temperature and the number of cycles on the internal structure damage of the granite sample, we studied the mechanical properties and acoustic emission response characteristics of the granite after high temperature-rapid cooling cycles by the uniaxial compression test and the acoustic emission monitoring test. The results show the follows. As the temperature and number of cycles applied to the granite increase, the uniaxial compressive strength of the granite continued to decrease, and the peak strain corresponding to the uniaxial compressive strength increased accordingly. There was a clear difference in the intensity and distribution characteristics of the acoustic emission signal of granite between the normal temperature and the high temperature treatment. As the temperature applied to the granite increased, the maximum acoustic emission count rate and the cumulative ring count of the acoustic emission increased first and then decreased. With the increase of the number of heating-cooling cycles for granite, the maximum value of AE count rate and cumulative AE ring count tended to decrease, while the intensity of AE signal tended to increase.
Based on the consideration of the temperature and the number of cycles on the internal structure damage of the granite sample, we studied the mechanical properties and acoustic emission response characteristics of the granite after high temperature-rapid cooling cycles by the uniaxial compression test and the acoustic emission monitoring test. The results show the follows. As the temperature and number of cycles applied to the granite increase, the uniaxial compressive strength of the granite continued to decrease, and the peak strain corresponding to the uniaxial compressive strength increased accordingly. There was a clear difference in the intensity and distribution characteristics of the acoustic emission signal of granite between the normal temperature and the high temperature treatment. As the temperature applied to the granite increased, the maximum acoustic emission count rate and the cumulative ring count of the acoustic emission increased first and then decreased. With the increase of the number of heating-cooling cycles for granite, the maximum value of AE count rate and cumulative AE ring count tended to decrease, while the intensity of AE signal tended to increase.
2021, 29(2): 516-525.
Based on the background of Xi'an Metro Line 6 section tunnel with shallow excavation construction through the ground fissure site, and considering the particularity of the ground fissure site, the construction optimization method based on the traditional CRD method was constructed. The three-dimensional finite element numerical calculation was carried out to simulate the excavation process of traditional CRD and optimized CRD method. Combined with in-situ monitoring test data, the surface settlement deformation of the ground fissure site and the stress deformation characteristics of the metro tunnel were analyzed. The results show that the surface settlement deformation is anti-s-shaped, which can be roughly divided into three stages: small deformation before excavation, rapid settlement deformation during excavation and stable deformation after excavation. The closer the monitoring points are to the tunnel face, the higher the ground settlement. Compared with the traditional CRD method, the optimized CRD method can increase appropriately the number of locking feet and waist bolts, improve the concrete strength of primary support properly, and so as to simplify the temporary support, expand the construction surface of the lower stage, facilitate the removal of temporary support, and improve the speed of the closure of the initial support and the removal of the temporary middle diaphragm. The construction speed of the optimized CRD method is 1.37 times faster than that of the traditional CRD method. The maximum surface settlement is reduced by 52.96%, the influence range is reduced by 22.17%, and the settlement of the tunnel roof is reduced by 54.53%. The optimized CRD method has the advantages of rapid construction speed, lower influence range, easily controlled surface and structure settlement, which can not only improve engineering benefit, but also guarantee the construction safety and the reliability of the tunnel construction. The research results can provide a scientific reference for the underground excavation construction of metro tunnel through ground fissure site in Xi'an city and other areas.
Based on the background of Xi'an Metro Line 6 section tunnel with shallow excavation construction through the ground fissure site, and considering the particularity of the ground fissure site, the construction optimization method based on the traditional CRD method was constructed. The three-dimensional finite element numerical calculation was carried out to simulate the excavation process of traditional CRD and optimized CRD method. Combined with in-situ monitoring test data, the surface settlement deformation of the ground fissure site and the stress deformation characteristics of the metro tunnel were analyzed. The results show that the surface settlement deformation is anti-s-shaped, which can be roughly divided into three stages: small deformation before excavation, rapid settlement deformation during excavation and stable deformation after excavation. The closer the monitoring points are to the tunnel face, the higher the ground settlement. Compared with the traditional CRD method, the optimized CRD method can increase appropriately the number of locking feet and waist bolts, improve the concrete strength of primary support properly, and so as to simplify the temporary support, expand the construction surface of the lower stage, facilitate the removal of temporary support, and improve the speed of the closure of the initial support and the removal of the temporary middle diaphragm. The construction speed of the optimized CRD method is 1.37 times faster than that of the traditional CRD method. The maximum surface settlement is reduced by 52.96%, the influence range is reduced by 22.17%, and the settlement of the tunnel roof is reduced by 54.53%. The optimized CRD method has the advantages of rapid construction speed, lower influence range, easily controlled surface and structure settlement, which can not only improve engineering benefit, but also guarantee the construction safety and the reliability of the tunnel construction. The research results can provide a scientific reference for the underground excavation construction of metro tunnel through ground fissure site in Xi'an city and other areas.
2021, 29(2): 526-535.
Thousands of coseismic landslides were induced by the Jiuzhaigou MS7.0 earthquake on August 8th 2017, Sichuan, China. Thus, a tremendous volume of loose debris are extremely prone to convert into landslides and debris flow under rainfall. Therefore, it is necessary to conduct landslide susceptibility assessment in Jiuzhaigou Scenic area. Based on a large set of pre-and post-earthquake high-resolution satellite images and field investigation, a polygon-based interpretation of the coseismic landslides is carried out. In total, 1047 landslides are identified, covering an area of 3.88 km2. The relationship between the spatial distribution of landslides and its influencing factors is analyzed. Nine factors including tectonic, topographic, geological and other factors are selected to evaluate the landslide susceptibility by certainty factor model and logistic regression model, as well as coupled model. The result shows that slope, aspect, elevation and lithology are the main factors controlling the spatial distribution of landslides. The susceptibility of landslide is divided into low(60.72%), moderate(24.18%), high(9.89%) and extremely high areas(5.21%). The high and extremely high areas covering an area of 99 km2 including Tiger Lake and Panda Lake are distributed along the valleys. The assessment result of the coupled model is more reasonable than that of the single model and can be used as scientific reference for prevention of landslide hazard and segmented opening time of scenic area.
Thousands of coseismic landslides were induced by the Jiuzhaigou MS7.0 earthquake on August 8th 2017, Sichuan, China. Thus, a tremendous volume of loose debris are extremely prone to convert into landslides and debris flow under rainfall. Therefore, it is necessary to conduct landslide susceptibility assessment in Jiuzhaigou Scenic area. Based on a large set of pre-and post-earthquake high-resolution satellite images and field investigation, a polygon-based interpretation of the coseismic landslides is carried out. In total, 1047 landslides are identified, covering an area of 3.88 km2. The relationship between the spatial distribution of landslides and its influencing factors is analyzed. Nine factors including tectonic, topographic, geological and other factors are selected to evaluate the landslide susceptibility by certainty factor model and logistic regression model, as well as coupled model. The result shows that slope, aspect, elevation and lithology are the main factors controlling the spatial distribution of landslides. The susceptibility of landslide is divided into low(60.72%), moderate(24.18%), high(9.89%) and extremely high areas(5.21%). The high and extremely high areas covering an area of 99 km2 including Tiger Lake and Panda Lake are distributed along the valleys. The assessment result of the coupled model is more reasonable than that of the single model and can be used as scientific reference for prevention of landslide hazard and segmented opening time of scenic area.
2021, 29(2): 536-544.
Karst ground collapse is the result of many factors, and has the characteristics of concealment and abruptness. In order to predict karst ground collapse quickly and accurately, this paper presents a karst ground collapse prediction model which is based on factor analysis, genetic algorithm(GA) and extreme learning machine(ELM). Firstly, we identify eight typical influencing factors in the karst area. Then, we extract five common factors by factor analysis. Finally, we input the common factors into GA-ELM model and predict karst ground collapse. The sample data contains 20 groups of actual case data, of which 12 groups as training sets and the other 8 groups as test sets. The conclusions are as follows: Factor analysis can not only simplify the ELM model network structure, but also improve the prediction accuracy under the same number of hidden layer of neuron nodes. In the case of a small number of samples, the prediction accuracy of the ELM model can be improved by increasing the number of hidden layer neuron nodes. Compared with the ELM model, the prediction accuracy of GA-ELM model is improved significantly, with stronger learning and prediction ability. The prediction method of karst ground collapse based on Factor Analysis-GA-ELM model is simple, accurate and efficient.
Karst ground collapse is the result of many factors, and has the characteristics of concealment and abruptness. In order to predict karst ground collapse quickly and accurately, this paper presents a karst ground collapse prediction model which is based on factor analysis, genetic algorithm(GA) and extreme learning machine(ELM). Firstly, we identify eight typical influencing factors in the karst area. Then, we extract five common factors by factor analysis. Finally, we input the common factors into GA-ELM model and predict karst ground collapse. The sample data contains 20 groups of actual case data, of which 12 groups as training sets and the other 8 groups as test sets. The conclusions are as follows: Factor analysis can not only simplify the ELM model network structure, but also improve the prediction accuracy under the same number of hidden layer of neuron nodes. In the case of a small number of samples, the prediction accuracy of the ELM model can be improved by increasing the number of hidden layer neuron nodes. Compared with the ELM model, the prediction accuracy of GA-ELM model is improved significantly, with stronger learning and prediction ability. The prediction method of karst ground collapse based on Factor Analysis-GA-ELM model is simple, accurate and efficient.
2021, 29(2): 545-553.
According to the clear segmental characteristics of the stress curve of red sandstone under impact load, a constitutive model with the nonlinear body, Maxwell body and damaged body in parallel is established based on the Zhu-Wang-Tang(Z-W-T)constitutive model. According to the mechanical properties of red sandstone, the Z-W-T model is simplified, and another rate-type damage constitutive equation is derived based on the Lemaitre equivalent strain hypothesis. The applicability of two new constitutive equations is discussed and the influence of each parameter on the fitting result of the experimental data is compared and analyzed. The results show that the nonlinear viscoelastic damage constitutive equation based on Weibull distribution can well characterize the dynamic mechanical properties of pre-peak stress and the whole stress curves at room temperature and freezing temperature. However, the damage constitutive equation based on Lemaitre's hypothesis of equivalent strain can only be used to solve the pre-peak stress of red sandstone, and has some limitations in the characterization of the whole stress curves.
According to the clear segmental characteristics of the stress curve of red sandstone under impact load, a constitutive model with the nonlinear body, Maxwell body and damaged body in parallel is established based on the Zhu-Wang-Tang(Z-W-T)constitutive model. According to the mechanical properties of red sandstone, the Z-W-T model is simplified, and another rate-type damage constitutive equation is derived based on the Lemaitre equivalent strain hypothesis. The applicability of two new constitutive equations is discussed and the influence of each parameter on the fitting result of the experimental data is compared and analyzed. The results show that the nonlinear viscoelastic damage constitutive equation based on Weibull distribution can well characterize the dynamic mechanical properties of pre-peak stress and the whole stress curves at room temperature and freezing temperature. However, the damage constitutive equation based on Lemaitre's hypothesis of equivalent strain can only be used to solve the pre-peak stress of red sandstone, and has some limitations in the characterization of the whole stress curves.
2021, 29(2): 554-563.
Rockfall hazard is a common type of geological hazard in mountain areas. It has significant meaning to research the character of rockfall for geological hazard investigation and risk assessment. A rockfall hazard occurred on 2018.9.15 during a project in Nepal. We investigated it at site and analyzed its genesis to find out the reason of the accident. The investigation results showed that"9.15 event" is a natural geological disaster and is not affected by human activities. The main cause of the accident is that the scope of rockfall from super high slope exceeded the scope which was predicted in the early stage. There are so many uncertainties in the rockfall movement. The movement pattern of rockfall has been predicted through the imprint analysis at site. According to impact point surface morphology, slope deposit material and geometrical characteristics, we calculate and analyze the motion trail and motion process of rockfall by the kinematics theory. In addition, combined with the scale of rockfall source area and the size, shape, mechanical properties of the rockfall blocks, we apply the Rocfall software to simulate and analyze the rockfall trail of super high slope. The Rocfall can calculate the energy of rockfall and provide the reliable basis for protection measures. The opening curtain type net has a good effect on preventing from high and steep slope rockfall disaster. This paper is useful to the investigation and prevention of dangerous rock of other similar height and steep slope, as reference.
Rockfall hazard is a common type of geological hazard in mountain areas. It has significant meaning to research the character of rockfall for geological hazard investigation and risk assessment. A rockfall hazard occurred on 2018.9.15 during a project in Nepal. We investigated it at site and analyzed its genesis to find out the reason of the accident. The investigation results showed that"9.15 event" is a natural geological disaster and is not affected by human activities. The main cause of the accident is that the scope of rockfall from super high slope exceeded the scope which was predicted in the early stage. There are so many uncertainties in the rockfall movement. The movement pattern of rockfall has been predicted through the imprint analysis at site. According to impact point surface morphology, slope deposit material and geometrical characteristics, we calculate and analyze the motion trail and motion process of rockfall by the kinematics theory. In addition, combined with the scale of rockfall source area and the size, shape, mechanical properties of the rockfall blocks, we apply the Rocfall software to simulate and analyze the rockfall trail of super high slope. The Rocfall can calculate the energy of rockfall and provide the reliable basis for protection measures. The opening curtain type net has a good effect on preventing from high and steep slope rockfall disaster. This paper is useful to the investigation and prevention of dangerous rock of other similar height and steep slope, as reference.
2021, 29(2): 564-574.
The deformation of overburden strata in goaf is a long-term process, seriously affecting the construction of tunnels that pass through the mining-induced subsidence zone. The Sangzhang tunnel is a typical case. Accurate predicting the influence of the residual deformation of goaf to Sangzhang tunnel is crucial to ensure its engineering safety. In this paper, a Boltzmann function is used to optimize the probability integral model of equivalent variable mining thickness, and a time function is introduced to put forward an improved model. We employ this modified model to predict the residual deformation of the four mining-induced subsidence zones in the Yangquan No.2 Mine, Shanxi Province, and then analyse the influence of the residual deformation of goaf to Sangzhang tunnel. The study indicates that the maximum residual settlement on the planned line of Sangzhang tunnel is 325 mm, appearing in the middle of the tunnel; the maximum residual lateral displacement is 168 mm, occurring near the start of the tunnel. As the axis of the Sangzhang tunnel intersects with the long axis of the mining-induced subsidence zone at a small angle, the tunnel shows a compound deformation trend of lateral movement, vertical settlement and axial torsion. Results in this paper can provide a scientific basis for the construction and deformation treatment of Sangzhang tunnel, and the adopted method can provide a theoretical support for the construction of tunnels that pass through mining-induced subsidence zones.
The deformation of overburden strata in goaf is a long-term process, seriously affecting the construction of tunnels that pass through the mining-induced subsidence zone. The Sangzhang tunnel is a typical case. Accurate predicting the influence of the residual deformation of goaf to Sangzhang tunnel is crucial to ensure its engineering safety. In this paper, a Boltzmann function is used to optimize the probability integral model of equivalent variable mining thickness, and a time function is introduced to put forward an improved model. We employ this modified model to predict the residual deformation of the four mining-induced subsidence zones in the Yangquan No.2 Mine, Shanxi Province, and then analyse the influence of the residual deformation of goaf to Sangzhang tunnel. The study indicates that the maximum residual settlement on the planned line of Sangzhang tunnel is 325 mm, appearing in the middle of the tunnel; the maximum residual lateral displacement is 168 mm, occurring near the start of the tunnel. As the axis of the Sangzhang tunnel intersects with the long axis of the mining-induced subsidence zone at a small angle, the tunnel shows a compound deformation trend of lateral movement, vertical settlement and axial torsion. Results in this paper can provide a scientific basis for the construction and deformation treatment of Sangzhang tunnel, and the adopted method can provide a theoretical support for the construction of tunnels that pass through mining-induced subsidence zones.
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