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Editor Work2023 Vol. 31, No. 3
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2023, 31(3): 689-705.
Abstract
Red beds serves as the widely distributed and unique-characterized disaster-prone strata. Its catastrophe research is one of the cutting-edge topics in the field of engineering geology. The scale of the red beds distribution area in China is tremendous, and its disasters are prominent. It is mainly manifested in the three major types of geological hazards, engineering diseases, and ecological damage. They make the sustainable economic and social development of the red beds area facing unprecedented disaster hazards and risks. They seriously threaten the implementation of major national strategies. However, it is difficult to adapt to the major challenges caused by the disaster theory and prevention and control technology of traditional red beds, which need to be solved urgently. Therefore, in this study, we clarify the overview of red beds around home and abroad through detailed investigations, in-depth thinking, and systematic sorting out. Then, we analyse the current status and development trends of the basic research of red beds disaster, and clarifying the three major international cutting-edge scientific issues. The three key scientific issues that need to be resolved in the basic research of red beds are proposed. Simultaneously, the main research ideas, contents, and solutions are explained. These thoughts are supporting problems such as red beds geological genes, cause mechanisms, toughness coordination prevention and control of the disaster. It can ensure the efficient implementation of major national strategies in the red beds area, ensure the safety of human settlement, the construction of ecological civilization, and the sustainable development of social economy. Furthermore, it can lead the world red beds catastrophic research.
Red beds serves as the widely distributed and unique-characterized disaster-prone strata. Its catastrophe research is one of the cutting-edge topics in the field of engineering geology. The scale of the red beds distribution area in China is tremendous, and its disasters are prominent. It is mainly manifested in the three major types of geological hazards, engineering diseases, and ecological damage. They make the sustainable economic and social development of the red beds area facing unprecedented disaster hazards and risks. They seriously threaten the implementation of major national strategies. However, it is difficult to adapt to the major challenges caused by the disaster theory and prevention and control technology of traditional red beds, which need to be solved urgently. Therefore, in this study, we clarify the overview of red beds around home and abroad through detailed investigations, in-depth thinking, and systematic sorting out. Then, we analyse the current status and development trends of the basic research of red beds disaster, and clarifying the three major international cutting-edge scientific issues. The three key scientific issues that need to be resolved in the basic research of red beds are proposed. Simultaneously, the main research ideas, contents, and solutions are explained. These thoughts are supporting problems such as red beds geological genes, cause mechanisms, toughness coordination prevention and control of the disaster. It can ensure the efficient implementation of major national strategies in the red beds area, ensure the safety of human settlement, the construction of ecological civilization, and the sustainable development of social economy. Furthermore, it can lead the world red beds catastrophic research.
2023, 31(3): 706-717.
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Geological hazards are numerous and widely distributed in China. Thus the disaster prevention strategy of "double-control of point and zone" would inevitably become a way forward. How to effectively obtain the dynamic change information of geological bodies at a wide scale and the refined geological information of major geological bodies is a significant way to achieve "double-control of point and zone". Based on the construction of China's real scene 3D view, this article proposes to further construct the cooperative observation system of "Space-Air-Ground-Interior" landslides by relying on the opportunity of Real 3D China Construction. Through the Space-Air-Ground-Internal collaborative observation technology, the dynamic observation and perception capabilities of all-space and all-elements among relevant areas, including"ground and underground", "above water and underwater", "indoor and outdoor", "disaster causing body and disaster bearing body" can be achieved, by which the landslides prevention ability and level would be significantly promoted. In addition to building the Space-Air-Ground-Interior landslides collaborative observation system, this article focuses on the high-resolution nap-of-the-object photogrammetry technology, the rapid mapping technology of underwater topography based on multibeam bathymetry, and the rapid underwater terrain mapping technology based on multibeam bathymetry, and rapid fine mapping technology based on SLAM for closed space forms such as buildings and caves. The real scene 3D view is a digital virtual space that reflects and expresses the real, three-dimensional and sequential reflection and expression of human production, life and ecological space. Through the construction of landslide 'Space-Air-Ground-Internal' integrated collaborative observation technology can further improve China's landslide disaster prevention and control capabilities.
Geological hazards are numerous and widely distributed in China. Thus the disaster prevention strategy of "double-control of point and zone" would inevitably become a way forward. How to effectively obtain the dynamic change information of geological bodies at a wide scale and the refined geological information of major geological bodies is a significant way to achieve "double-control of point and zone". Based on the construction of China's real scene 3D view, this article proposes to further construct the cooperative observation system of "Space-Air-Ground-Interior" landslides by relying on the opportunity of Real 3D China Construction. Through the Space-Air-Ground-Internal collaborative observation technology, the dynamic observation and perception capabilities of all-space and all-elements among relevant areas, including"ground and underground", "above water and underwater", "indoor and outdoor", "disaster causing body and disaster bearing body" can be achieved, by which the landslides prevention ability and level would be significantly promoted. In addition to building the Space-Air-Ground-Interior landslides collaborative observation system, this article focuses on the high-resolution nap-of-the-object photogrammetry technology, the rapid mapping technology of underwater topography based on multibeam bathymetry, and the rapid underwater terrain mapping technology based on multibeam bathymetry, and rapid fine mapping technology based on SLAM for closed space forms such as buildings and caves. The real scene 3D view is a digital virtual space that reflects and expresses the real, three-dimensional and sequential reflection and expression of human production, life and ecological space. Through the construction of landslide 'Space-Air-Ground-Internal' integrated collaborative observation technology can further improve China's landslide disaster prevention and control capabilities.
2023, 31(3): 718-735.
The Ya'an to Nyingchi section of the Sichuan-Tibet traffic corridor is located in the southeast of the Qinghai-Tibet Plateau. The project region is characterized by complex geological conditions,strong river cutting,fragile geological environment,active neotectonic movement,high mountains,deep valleys and poor slope stability. It is one of the areas with the most developed and serious hazards of collapses and landslides in China. In order to guarantee the smooth construction and safe operation of the related project in the corridor,this study takes the first order watershed on both sides of the line as the boundary,and obtains a total of 4509 collapses and landslides in the Ya'an-Nyingchi section of the Sichuan-Tibet traffic corridor through remote sensing interpretation and field investigation. On this basis,a total of nine factors,including elevation,slope,aspect,engineering geological strata,fault,river,road,peak ground acceleration and rainfall are selected to analyze the spatial distribution law and development characteristics of disasters. Then it establishes a coupling model of frequency ratio method and logistic regression method to evaluate the hazard of collapses and landslides for the major traffic corridor project in plateau mountainous area. The study results show that: (1)The areal density of collapses and landslides in various counties along the corridor shows a spatial decreasing trend from west to east. (2)The conditions conducive to disasters occurrence include elevation of 1~4 km,slope gradient steeper than 20°,aspects of S,SW and W,rock groups of soft,hard and very hard,within 6.4 km of fault,within 3.2 km of river,within 800 m of road,peak ground acceleration of 0.20g and average annual rainfall more than 1100 mm. (3)The hazard of study area is divided into five grades: very low hazard(18.64%),low hazard(26.18%),medium hazard(24.75%),high hazard(19.82%),and very high hazard(10.61%),where the very high hazard and high hazard areas are mainly distributed near the faults and in the areas with steep slopes. (4)The AUC value of the coupling model reaches 0.737,which is better than that of the single frequency ratio model 0.712,indicating that the evaluation result of the coupling model has higher accuracy. This study can provide an important reference for disaster prevention and mitigation in the planning,construction and future operation of the related project in Sichuan-Tibet traffic corridor.
The Ya'an to Nyingchi section of the Sichuan-Tibet traffic corridor is located in the southeast of the Qinghai-Tibet Plateau. The project region is characterized by complex geological conditions,strong river cutting,fragile geological environment,active neotectonic movement,high mountains,deep valleys and poor slope stability. It is one of the areas with the most developed and serious hazards of collapses and landslides in China. In order to guarantee the smooth construction and safe operation of the related project in the corridor,this study takes the first order watershed on both sides of the line as the boundary,and obtains a total of 4509 collapses and landslides in the Ya'an-Nyingchi section of the Sichuan-Tibet traffic corridor through remote sensing interpretation and field investigation. On this basis,a total of nine factors,including elevation,slope,aspect,engineering geological strata,fault,river,road,peak ground acceleration and rainfall are selected to analyze the spatial distribution law and development characteristics of disasters. Then it establishes a coupling model of frequency ratio method and logistic regression method to evaluate the hazard of collapses and landslides for the major traffic corridor project in plateau mountainous area. The study results show that: (1)The areal density of collapses and landslides in various counties along the corridor shows a spatial decreasing trend from west to east. (2)The conditions conducive to disasters occurrence include elevation of 1~4 km,slope gradient steeper than 20°,aspects of S,SW and W,rock groups of soft,hard and very hard,within 6.4 km of fault,within 3.2 km of river,within 800 m of road,peak ground acceleration of 0.20g and average annual rainfall more than 1100 mm. (3)The hazard of study area is divided into five grades: very low hazard(18.64%),low hazard(26.18%),medium hazard(24.75%),high hazard(19.82%),and very high hazard(10.61%),where the very high hazard and high hazard areas are mainly distributed near the faults and in the areas with steep slopes. (4)The AUC value of the coupling model reaches 0.737,which is better than that of the single frequency ratio model 0.712,indicating that the evaluation result of the coupling model has higher accuracy. This study can provide an important reference for disaster prevention and mitigation in the planning,construction and future operation of the related project in Sichuan-Tibet traffic corridor.
2023, 31(3): 736-749.
A series of deep and large active fault zones are widely developed in the eastern margin of the Qinghai-Tibet Plateau,which strongly controls the regional stress field. Here we determine the in-situ stress field under the influence of active faults in the eastern margin of the Qinghai-Tibet Plateau by numerical simulation inversion of an extensive collection of 1181 groups of in-situ stress data collected from 178 points. The result show that an obvious non-uniformity is the most significant characteristic in the Qinghai-Tibet Plateau. The stress value decreases gradually from west to east. The potential of rock burst and large deformation at the depth of 100~2000 m in the eastern margin of the Qinghai-Tibet Plateau is also analyzed by ArcGIS. Rock burst is concentrated within the secondary plate while the large deformation mainly occurs at the boundary. The area of rock burst does not change with depth basically,however,large deformation gradually increases and develops to the interior of the secondary plate. The potential of rock burst and deformation changes regularly with the buried depth. Finally,two engineering cases of Erlang Mountain tunnel and Shuangjiangkou Hydropower station are presented to discussed the applicability of the prediction of rock burst and large deformation potential. The results indicate that the underground geohzards potential in the eastern margin of Qinghai-Tibet Plateau predicted in this study is basically consistent with the rock burst tendency based on the strength-stress ratio and the rock burst phenomenon in the two cases.
A series of deep and large active fault zones are widely developed in the eastern margin of the Qinghai-Tibet Plateau,which strongly controls the regional stress field. Here we determine the in-situ stress field under the influence of active faults in the eastern margin of the Qinghai-Tibet Plateau by numerical simulation inversion of an extensive collection of 1181 groups of in-situ stress data collected from 178 points. The result show that an obvious non-uniformity is the most significant characteristic in the Qinghai-Tibet Plateau. The stress value decreases gradually from west to east. The potential of rock burst and large deformation at the depth of 100~2000 m in the eastern margin of the Qinghai-Tibet Plateau is also analyzed by ArcGIS. Rock burst is concentrated within the secondary plate while the large deformation mainly occurs at the boundary. The area of rock burst does not change with depth basically,however,large deformation gradually increases and develops to the interior of the secondary plate. The potential of rock burst and deformation changes regularly with the buried depth. Finally,two engineering cases of Erlang Mountain tunnel and Shuangjiangkou Hydropower station are presented to discussed the applicability of the prediction of rock burst and large deformation potential. The results indicate that the underground geohzards potential in the eastern margin of Qinghai-Tibet Plateau predicted in this study is basically consistent with the rock burst tendency based on the strength-stress ratio and the rock burst phenomenon in the two cases.
2023, 31(3): 750-761.
The exploration shows that the grained cutting band with certain thickness and extension length is widely developed in the quartz diorite on both sides of the dam site of Ye Batan Hydropower Station. This kind of cutting band not only reduces the integrity of rock mass, but also deteriorates the quality of foundation rock mass. According to its manifestation and developmental characteristics, it is called "compressional fracture zone". Based on the field investigation, this paper describes in detail the typical compression fracture zone newly revealed during the construction period. The development and distribution characteristics of the compression fracture zone are revealed. The study shows that the compression fracture zone develops in both strong and weak unloading zones and deeper areas. It is mainly distributed in the medium elevation of the left bank. The compressional fracture zone in the dam site of Ye Batan Hydropower Station is formed by tectonics. It appears as a clastic debris strip with a clear boundary and a certain thickness and extension, which is developed in fresh, complete and hard rock mass with obvious boundary. It may be formed by tectonic forces and generally attached to faults or structural planes of larger length. Its extent is limited and its occurrence is unstable. Most of the cleavage lithification in the zone, and part of the grains can be observed in directional arrangement, with zonal characteristics, no obvious dislocation distance. All these belong to the characteristics of rock mass extrusion deformation under the condition of high ground stress. At the same time, the compressional fracture zone is easily affected by the later transformation, and weathering, rust dyeing and muddy bands can be observed in some extrusion fracture zones. They are mainly distributed in the clamping or confining area of faults(long structural planes), the end of the fault(long structural planes), or the side of the long structural planes.
The exploration shows that the grained cutting band with certain thickness and extension length is widely developed in the quartz diorite on both sides of the dam site of Ye Batan Hydropower Station. This kind of cutting band not only reduces the integrity of rock mass, but also deteriorates the quality of foundation rock mass. According to its manifestation and developmental characteristics, it is called "compressional fracture zone". Based on the field investigation, this paper describes in detail the typical compression fracture zone newly revealed during the construction period. The development and distribution characteristics of the compression fracture zone are revealed. The study shows that the compression fracture zone develops in both strong and weak unloading zones and deeper areas. It is mainly distributed in the medium elevation of the left bank. The compressional fracture zone in the dam site of Ye Batan Hydropower Station is formed by tectonics. It appears as a clastic debris strip with a clear boundary and a certain thickness and extension, which is developed in fresh, complete and hard rock mass with obvious boundary. It may be formed by tectonic forces and generally attached to faults or structural planes of larger length. Its extent is limited and its occurrence is unstable. Most of the cleavage lithification in the zone, and part of the grains can be observed in directional arrangement, with zonal characteristics, no obvious dislocation distance. All these belong to the characteristics of rock mass extrusion deformation under the condition of high ground stress. At the same time, the compressional fracture zone is easily affected by the later transformation, and weathering, rust dyeing and muddy bands can be observed in some extrusion fracture zones. They are mainly distributed in the clamping or confining area of faults(long structural planes), the end of the fault(long structural planes), or the side of the long structural planes.
2023, 31(3): 762-779.
With the increasingly active engineering construction in mountainous areas these years, the giant remote gully disaster chain induced by landslide-debris flow transformation has attracted widespread attention for its superb motility and huge destructive power. Compared with the single hazard of landslide, the transformed debris flow has significantly increased in disaster scale, movement form, affected scope, and construction damage degree. Therefore, scientifically understanding the process and mechanism of landslide-induced debris flow is important to reduce the risk of remote gully disaster chain from the beginning, and subsequently, choose suitable mitigation measures. This study systematically reviews the concept, conditions, and mechanism of landslide-induced debris flow based on recent research achievements in the world. First, the concept of landslide-debris flow transformation is clarified by comparing it with the phenomenon of high-speed and long-runout landslides. Subsequently, we sort out the transformation conditions of landslide-induced debris flow from three perspectives of solid material, water source, and topography. We find the landslide can transform into debris flow only if it is satisfied with a combination of both three conditions. We further sort out the static and dynamic indicators that are used to classify landslides and debris flows from the microscopic scale. The results indicate a combination of both static and dynamic indicators may be the suitable choice to quantitatively the transformation process. Based on a large number of cases of landslide-induced debris flow, we also summarize two modes of landslide-debris flow transformation, which fall into static and dynamic transformation. The physical mechanisms are further discussed. Finally, we propose three key scientific challenges for landslide-debris flow transformation study: (1)Scientific and quantitative characterization of landslide-debris flow transformation processes; (2)Mechanism of the phase change when coupled solid, liquid, and gas in disaster; and (3)Critical conditions of landslide-debris flow transformation based on physical mechanisms. We further point out the relevant theories and methods for transformation mechanism study, and their feasibility in quantitatively characterizing the physical mechanism analysis of landslide-debris flow transformation process is also discussed.
With the increasingly active engineering construction in mountainous areas these years, the giant remote gully disaster chain induced by landslide-debris flow transformation has attracted widespread attention for its superb motility and huge destructive power. Compared with the single hazard of landslide, the transformed debris flow has significantly increased in disaster scale, movement form, affected scope, and construction damage degree. Therefore, scientifically understanding the process and mechanism of landslide-induced debris flow is important to reduce the risk of remote gully disaster chain from the beginning, and subsequently, choose suitable mitigation measures. This study systematically reviews the concept, conditions, and mechanism of landslide-induced debris flow based on recent research achievements in the world. First, the concept of landslide-debris flow transformation is clarified by comparing it with the phenomenon of high-speed and long-runout landslides. Subsequently, we sort out the transformation conditions of landslide-induced debris flow from three perspectives of solid material, water source, and topography. We find the landslide can transform into debris flow only if it is satisfied with a combination of both three conditions. We further sort out the static and dynamic indicators that are used to classify landslides and debris flows from the microscopic scale. The results indicate a combination of both static and dynamic indicators may be the suitable choice to quantitatively the transformation process. Based on a large number of cases of landslide-induced debris flow, we also summarize two modes of landslide-debris flow transformation, which fall into static and dynamic transformation. The physical mechanisms are further discussed. Finally, we propose three key scientific challenges for landslide-debris flow transformation study: (1)Scientific and quantitative characterization of landslide-debris flow transformation processes; (2)Mechanism of the phase change when coupled solid, liquid, and gas in disaster; and (3)Critical conditions of landslide-debris flow transformation based on physical mechanisms. We further point out the relevant theories and methods for transformation mechanism study, and their feasibility in quantitatively characterizing the physical mechanism analysis of landslide-debris flow transformation process is also discussed.
2023, 31(3): 780-795.
The significant seasonal changing of surface coverage makes it is difficult to maintain the InSAR interferometric coherence with a long temporal baseline in the cold mountain region. It causes a negative effect in the identification of geohazard in such region. Here, we propose a geohazard identification method based on InSAR seasonal coherence variation in the cold mountain region. First, the InSAR time series interferograms and coherence are obtained. Then, according to the InSAR coherence variation, each year is divided into summer season, transition season and winter season. Second, according to the characteristic of the coherence of the transition season interferometric pairs, they can be added into summer season or winter season groups. Then, the time series InSAR deformation in summer season and winter season are extracted based on Stacking-InSAR technique, respectively. It is noted that some long temporal baseline InSAR interferometric pairs with a high coherence also are introduced into InSAR time series analysis. Finally, the Stacking-InSAR deformation in summer season and winter season are jointly used to detect the geohazard in the cold mountain region. In this study, the Eastern Himalayan Syntaxis is set as study area, and the proposed method is adopted to detect the geohazard in this area. And it is found that only 16% geohazards can be identified by both the summer and winter InSAR results, which indicates that different geohazards in summer and winter. In addition, the proposed method detects more 28% geohazards than the result of traditional Stacking-InSAR technology using all interferograms. Therefore, the proposed method can accurately and effectively detect geohazard in the cold mountain region. It can provide a help to the reduction and prevention of geohazard in such region.
The significant seasonal changing of surface coverage makes it is difficult to maintain the InSAR interferometric coherence with a long temporal baseline in the cold mountain region. It causes a negative effect in the identification of geohazard in such region. Here, we propose a geohazard identification method based on InSAR seasonal coherence variation in the cold mountain region. First, the InSAR time series interferograms and coherence are obtained. Then, according to the InSAR coherence variation, each year is divided into summer season, transition season and winter season. Second, according to the characteristic of the coherence of the transition season interferometric pairs, they can be added into summer season or winter season groups. Then, the time series InSAR deformation in summer season and winter season are extracted based on Stacking-InSAR technique, respectively. It is noted that some long temporal baseline InSAR interferometric pairs with a high coherence also are introduced into InSAR time series analysis. Finally, the Stacking-InSAR deformation in summer season and winter season are jointly used to detect the geohazard in the cold mountain region. In this study, the Eastern Himalayan Syntaxis is set as study area, and the proposed method is adopted to detect the geohazard in this area. And it is found that only 16% geohazards can be identified by both the summer and winter InSAR results, which indicates that different geohazards in summer and winter. In addition, the proposed method detects more 28% geohazards than the result of traditional Stacking-InSAR technology using all interferograms. Therefore, the proposed method can accurately and effectively detect geohazard in the cold mountain region. It can provide a help to the reduction and prevention of geohazard in such region.
2023, 31(3): 796-814.
Mélange is a rock mass containing foreign or in situ blocks in a fine-grained fractured matrix and is often characterized by diverse material composition, complex geological structure and widely varying engineering properties. The internal heterogeneity and spatial variability of the mélange in lithological composition and mechanical properties would have a significant influence on siting and stability of the engineering project. Nowadays, engineering and geological hazards occur frequently in mélange areas. In order to satisfy the demand for rapid and safe construction of engineering projects in this region, the engineering mechanical properties of mélange need to be clarified urgently. This paper systematically reviews the literature on the mechanical properties of mélange. The non-homogeneous properties of the mélange are used as the entry point for this paper. First, the reasons for the formation of inhomogeneity of mélange are summarized. On this basis, the current classification methods of mélange are generalized. Second, the current methods describing the inhomogeneous properties of mélange are analyzed. The influencing factors and prediction methods on inhomogeneous mechanical properties of mélange rocks are also discussed. Finally, the mechanical properties of mélange rock masses in an engineering context are summarized. In the future studies need to be focused on the following three areas: quantitative classification methods hased on the mechanical properties of mélange, the mechanics of mélange under the influence of multiple factors, and the relationship between the geometric distribution and mechanical properties of mélange at a engineering scale. This paper can be useful for clarifying the mechanical properties of mélange rocks and reducing the engineering risks in this type of area.
Mélange is a rock mass containing foreign or in situ blocks in a fine-grained fractured matrix and is often characterized by diverse material composition, complex geological structure and widely varying engineering properties. The internal heterogeneity and spatial variability of the mélange in lithological composition and mechanical properties would have a significant influence on siting and stability of the engineering project. Nowadays, engineering and geological hazards occur frequently in mélange areas. In order to satisfy the demand for rapid and safe construction of engineering projects in this region, the engineering mechanical properties of mélange need to be clarified urgently. This paper systematically reviews the literature on the mechanical properties of mélange. The non-homogeneous properties of the mélange are used as the entry point for this paper. First, the reasons for the formation of inhomogeneity of mélange are summarized. On this basis, the current classification methods of mélange are generalized. Second, the current methods describing the inhomogeneous properties of mélange are analyzed. The influencing factors and prediction methods on inhomogeneous mechanical properties of mélange rocks are also discussed. Finally, the mechanical properties of mélange rock masses in an engineering context are summarized. In the future studies need to be focused on the following three areas: quantitative classification methods hased on the mechanical properties of mélange, the mechanics of mélange under the influence of multiple factors, and the relationship between the geometric distribution and mechanical properties of mélange at a engineering scale. This paper can be useful for clarifying the mechanical properties of mélange rocks and reducing the engineering risks in this type of area.
2023, 31(3): 815-829.
Rock avalanches are characterized by huge volume,high velocity and long runout and greatly threaten human lives and construction of major projects of the mountain areas in China. Fragmentation of rock avalanches is a universal and critical phenomenon,which is one of the prerequisites for the formation of the special internal structures in deposit and even considered as the possible mechanism for the hypermobility of rock avalanches. The fragmentation of rock avalanches has become a highlighted scientific issue in the field of landslide dynamics,since is currently great controversy as whether fragmentation promotes or hinders the mobility of failure mass. The substantial point of this controversy is how the fragmentation process contributes to the runout of the sliding mass when fragmentation itself consuming energy. This article reviews studies on sedimentological characteristics induced by fragmentation process in rock avalanches,including inverse grading,jigsaw structure,retaining of source stratigraphy and local shear band. The implication of fragmentation related deposit characteristics for rock avalanche dynamics is conducted based on those studies. The research progress of the influencing factors of fragmentation process and the friction-weaken mechanisms of rock fragmentation are further discussed. Finally,the controversial issue of energy consumption/friction-weaken induced by fragmentation process is summarized. Then we propose some key issues for future research on the mechanism of fragmentation in rock avalanches.
Rock avalanches are characterized by huge volume,high velocity and long runout and greatly threaten human lives and construction of major projects of the mountain areas in China. Fragmentation of rock avalanches is a universal and critical phenomenon,which is one of the prerequisites for the formation of the special internal structures in deposit and even considered as the possible mechanism for the hypermobility of rock avalanches. The fragmentation of rock avalanches has become a highlighted scientific issue in the field of landslide dynamics,since is currently great controversy as whether fragmentation promotes or hinders the mobility of failure mass. The substantial point of this controversy is how the fragmentation process contributes to the runout of the sliding mass when fragmentation itself consuming energy. This article reviews studies on sedimentological characteristics induced by fragmentation process in rock avalanches,including inverse grading,jigsaw structure,retaining of source stratigraphy and local shear band. The implication of fragmentation related deposit characteristics for rock avalanche dynamics is conducted based on those studies. The research progress of the influencing factors of fragmentation process and the friction-weaken mechanisms of rock fragmentation are further discussed. Finally,the controversial issue of energy consumption/friction-weaken induced by fragmentation process is summarized. Then we propose some key issues for future research on the mechanism of fragmentation in rock avalanches.
2023, 31(3): 830-842.
This paper aims to comprehensively interpret and judge the stable state or disaster of the surrounding rock of the tunnel constructed by deep-buried drilling and blasting method. First of all,we propose the methods of microseismic event classification and surrounding rock damage grade classification based on the source parameter space. Second,we construct a time series of multiple microseismic parameters. The comparison reveals the microseismic characteristics of the three states of surrounding rock stability,collapse and rockburst during blasting construction. Finally,we propose a comprehensive judgment method for the stability of the surrounding rock in the construction of deep-buried tunnels by drilling and blasting. This method is suitable for the judgment of the stable state of surrounding rock,landslides and rockburst disasters during the blasting construction of deep-buried tunnels. On this basis,we combine with geological conditions to determine the disaster risk level. The research results show that the three states of surrounding rock (i.e. stability,collapse and rockburst) during the construction of the drilling and blasting method have unique characteristics and laws in the source parameter space and the microseismic time series trend. In the stable stage of surrounding rock,a strong stress adjustment occurs only in a short time after blasting. In the abnormal stage of surrounding rock stability,the microseismic event continues to be active for a long time after blasting,and the cumulative energy,cumulative event number,and cumulative apparent volume curve increase rapidly,and the energy index curve declines rapidly. The research results can provide an important reference for the surrounding rock stability judgment,disaster early warning and prevention and control scheme of deep-buried tunnel constructed by drilling and blasting method,as well as for other similar projects.
This paper aims to comprehensively interpret and judge the stable state or disaster of the surrounding rock of the tunnel constructed by deep-buried drilling and blasting method. First of all,we propose the methods of microseismic event classification and surrounding rock damage grade classification based on the source parameter space. Second,we construct a time series of multiple microseismic parameters. The comparison reveals the microseismic characteristics of the three states of surrounding rock stability,collapse and rockburst during blasting construction. Finally,we propose a comprehensive judgment method for the stability of the surrounding rock in the construction of deep-buried tunnels by drilling and blasting. This method is suitable for the judgment of the stable state of surrounding rock,landslides and rockburst disasters during the blasting construction of deep-buried tunnels. On this basis,we combine with geological conditions to determine the disaster risk level. The research results show that the three states of surrounding rock (i.e. stability,collapse and rockburst) during the construction of the drilling and blasting method have unique characteristics and laws in the source parameter space and the microseismic time series trend. In the stable stage of surrounding rock,a strong stress adjustment occurs only in a short time after blasting. In the abnormal stage of surrounding rock stability,the microseismic event continues to be active for a long time after blasting,and the cumulative energy,cumulative event number,and cumulative apparent volume curve increase rapidly,and the energy index curve declines rapidly. The research results can provide an important reference for the surrounding rock stability judgment,disaster early warning and prevention and control scheme of deep-buried tunnel constructed by drilling and blasting method,as well as for other similar projects.
2023, 31(3): 843-853.
Brittleness plays an important role in rock fracture mode and damage evolution. In this paper,uniaxial compression tests were carried out on 6 kinds of brittle rocks with different lithology from a railway tunnels. Based on the analysis of stress-strain process,failure mode and energy evolution characteristics,a calculation method of brittleness index was established by comprehensively considering the pre-peak elastic energy accumulation rate,post-peak energy dissipation degree and dissipation rate. Furthermore,the damage variable was characterized by energy dissipation,and the feasibility and rationality of establishing brittleness evaluation index from the perspective of damage evolution were discussed. The results show that: (1)The stress-strain curves of different rocks show different degrees of brittle drop after the peak. (2)Based on the brittleness index established in this paper,the brittleness degree is in the order of gabbro,metasandstone,quartz schist,coarse-grained granite,slate and marble. (3)The damage evolution process of brittle rock based on energy dissipation presents an "S" shaped development trend,which can be divided into five stages: initial damage,damage maintenance,damage stable development,damage accelerated development and damage mitigation to termination,which can well reflect the whole process of micro-crack pressure sealing,initiation and development,expansion and penetration until macroscopic failure in rock.
Brittleness plays an important role in rock fracture mode and damage evolution. In this paper,uniaxial compression tests were carried out on 6 kinds of brittle rocks with different lithology from a railway tunnels. Based on the analysis of stress-strain process,failure mode and energy evolution characteristics,a calculation method of brittleness index was established by comprehensively considering the pre-peak elastic energy accumulation rate,post-peak energy dissipation degree and dissipation rate. Furthermore,the damage variable was characterized by energy dissipation,and the feasibility and rationality of establishing brittleness evaluation index from the perspective of damage evolution were discussed. The results show that: (1)The stress-strain curves of different rocks show different degrees of brittle drop after the peak. (2)Based on the brittleness index established in this paper,the brittleness degree is in the order of gabbro,metasandstone,quartz schist,coarse-grained granite,slate and marble. (3)The damage evolution process of brittle rock based on energy dissipation presents an "S" shaped development trend,which can be divided into five stages: initial damage,damage maintenance,damage stable development,damage accelerated development and damage mitigation to termination,which can well reflect the whole process of micro-crack pressure sealing,initiation and development,expansion and penetration until macroscopic failure in rock.
2023, 31(3): 854-867.
The engineering projects of deep buried tunnels in different positions of tectonic active zone in previous research indicate that the stability of deep tunnels is deeply relevant to in-situ stress. To analyse the influence mechanism of in-situ stress state on rock burst proneness of deep-buried-curved tunnel in Qinghai-Tibet Plateau and its adjacent region,three-dimensional finite element numerical simulation is done to explore the combine action of the angle φ between the maximum horizontal principal stress orientation and tunnel axis,and lateral pressure coefficient KH on the distribution of strain energy density and rock burst proneness. The results conclude that whenφ is about 45°,the change of φhas the greatest influence on the proneness of rock burst. When the maximum horizontal principal stress orientation is perpendicular to the tunnel axis,the change of KH has the most significant effect on strain energy density of surrounding rock. When the maximum horizontal principal stress orientation is parallel to the tunnel axis,the change of KH has the least influence on strain energy density of surrounding rock. The multivariate regression equation is verified by a number of typical deep buried tunnels in the Qinghai-Tibet Plateau and the surrounding area. The multiple regression equation can be applied to quickly evaluate the influence of φ and KH on tunnel stability serving the tunnel planning and design efficiently.
The engineering projects of deep buried tunnels in different positions of tectonic active zone in previous research indicate that the stability of deep tunnels is deeply relevant to in-situ stress. To analyse the influence mechanism of in-situ stress state on rock burst proneness of deep-buried-curved tunnel in Qinghai-Tibet Plateau and its adjacent region,three-dimensional finite element numerical simulation is done to explore the combine action of the angle φ between the maximum horizontal principal stress orientation and tunnel axis,and lateral pressure coefficient KH on the distribution of strain energy density and rock burst proneness. The results conclude that whenφ is about 45°,the change of φhas the greatest influence on the proneness of rock burst. When the maximum horizontal principal stress orientation is perpendicular to the tunnel axis,the change of KH has the most significant effect on strain energy density of surrounding rock. When the maximum horizontal principal stress orientation is parallel to the tunnel axis,the change of KH has the least influence on strain energy density of surrounding rock. The multivariate regression equation is verified by a number of typical deep buried tunnels in the Qinghai-Tibet Plateau and the surrounding area. The multiple regression equation can be applied to quickly evaluate the influence of φ and KH on tunnel stability serving the tunnel planning and design efficiently.
2023, 31(3): 868-879.
The traditional landslide depth detection methods only determine the depth in some sparse points,and cannot accurately reflect the depth distribution of the whole landslide. The cost is high. In this paper,we develop a landslide depth inversion method based on the ascending and descending InSAR deformation field. And the main process includes: first,the ascending and descending InSAR deformation fields are extracted based on the time series InSAR technique. Second,according to the spatial geometric relationship between the satellite line-of-sight and the landslide,the two-dimensional deformation fields along the slope and normal directions of the landslide surface are calculated. Third,a landslide depth inversion model is constructed based on two-dimensional slope deformation under the constraint of mass conservation criterion. Finally,we estimate the landslide depth based on the developed landslide depth inversion model. We conduct a case study of an ancient landslide in Taoping Village,Li County in Sichuan Province. The InSAR results show that the moving area of the landslide is about 2.9 km2. When the rheological parameter is set as 0.7,the estimated landslide depth is 9~33m,and the landslide volume is about 3.49×107 m3. The inversion result is consistent with the result of previous study,which proves the reliability of the theory and method developed in this paper. The proposed method can obtain continuous depth over the landslide,and can more directly reflect the risk area of the landslide. It can provide data support for the landslide disaster impact analysis and prevention.
The traditional landslide depth detection methods only determine the depth in some sparse points,and cannot accurately reflect the depth distribution of the whole landslide. The cost is high. In this paper,we develop a landslide depth inversion method based on the ascending and descending InSAR deformation field. And the main process includes: first,the ascending and descending InSAR deformation fields are extracted based on the time series InSAR technique. Second,according to the spatial geometric relationship between the satellite line-of-sight and the landslide,the two-dimensional deformation fields along the slope and normal directions of the landslide surface are calculated. Third,a landslide depth inversion model is constructed based on two-dimensional slope deformation under the constraint of mass conservation criterion. Finally,we estimate the landslide depth based on the developed landslide depth inversion model. We conduct a case study of an ancient landslide in Taoping Village,Li County in Sichuan Province. The InSAR results show that the moving area of the landslide is about 2.9 km2. When the rheological parameter is set as 0.7,the estimated landslide depth is 9~33m,and the landslide volume is about 3.49×107 m3. The inversion result is consistent with the result of previous study,which proves the reliability of the theory and method developed in this paper. The proposed method can obtain continuous depth over the landslide,and can more directly reflect the risk area of the landslide. It can provide data support for the landslide disaster impact analysis and prevention.
2023, 31(3): 880-892.
As a typical kind of structural rock mass,columnar jointed rock mass has the characteristics of well-developed columnar joints network and poor rock mass integrity. These characteristics lead to significant mechanical and seepage anisotropy. Based on the formation mechanism analyses of columnar joint,current research achievements on the mechanical and seepage anisotropy of columnar jointed rock mass are systematically summarized from the following four aspects of field tests,physical model tests,numerical tests and theoretical analyses. Then the deficiencies of the employed methods and results of present researches are analysed and the future research direction on the mechanical and seepage anisotropy of columnar jointed rock mass is discussed. From the discussions,it is concluded that the future research should focus on the mechanical and seepage anisotropy of columnar jointed rock mass under unloading condition by combining physical model tests with a new method for columnar joint rock mass specimen preparation that can take the formation mechanism of columnar joint into account.
As a typical kind of structural rock mass,columnar jointed rock mass has the characteristics of well-developed columnar joints network and poor rock mass integrity. These characteristics lead to significant mechanical and seepage anisotropy. Based on the formation mechanism analyses of columnar joint,current research achievements on the mechanical and seepage anisotropy of columnar jointed rock mass are systematically summarized from the following four aspects of field tests,physical model tests,numerical tests and theoretical analyses. Then the deficiencies of the employed methods and results of present researches are analysed and the future research direction on the mechanical and seepage anisotropy of columnar jointed rock mass is discussed. From the discussions,it is concluded that the future research should focus on the mechanical and seepage anisotropy of columnar jointed rock mass under unloading condition by combining physical model tests with a new method for columnar joint rock mass specimen preparation that can take the formation mechanism of columnar joint into account.
2023, 31(3): 893-904.
The vertical distribution of flow velocity in debris flow section is the key to study the flow,impact force and sediment entrainment process. However,in the field measurement of debris flow and flume test,the commonly used stratified current meter only collects the velocity data of a small number of sampling points in the section due to the limitation of the arrangement of measuring devices,which makes it difficult for the linear distribution model based on the regression of measured results to accurately describe the velocity distribution law of debris flow. The paper uses a large-scale flume test of debris flow and a smoothed particle hydrodynamics(SPH)numerical model based on HBP constitutive,and inverts the three-dimensional dynamic process of debris flow. Large amounts of particle velocity data are analyzed and processed by hierarchical statistical algorithm. The vertical distribution characteristics of velocity in the section are obtained. A nonlinear vertical distribution model of flow velocity of debris flow based on logarithmic function is proposed. In order to verify the accuracy of the proposed model,several sets of flume test data are used for comparative analysis. The results show that the proposed logarithmic distribution model can fit the velocity profile more accurately than the traditional linear distribution model,and has better robustness in terms of model parameter sensitivity.
The vertical distribution of flow velocity in debris flow section is the key to study the flow,impact force and sediment entrainment process. However,in the field measurement of debris flow and flume test,the commonly used stratified current meter only collects the velocity data of a small number of sampling points in the section due to the limitation of the arrangement of measuring devices,which makes it difficult for the linear distribution model based on the regression of measured results to accurately describe the velocity distribution law of debris flow. The paper uses a large-scale flume test of debris flow and a smoothed particle hydrodynamics(SPH)numerical model based on HBP constitutive,and inverts the three-dimensional dynamic process of debris flow. Large amounts of particle velocity data are analyzed and processed by hierarchical statistical algorithm. The vertical distribution characteristics of velocity in the section are obtained. A nonlinear vertical distribution model of flow velocity of debris flow based on logarithmic function is proposed. In order to verify the accuracy of the proposed model,several sets of flume test data are used for comparative analysis. The results show that the proposed logarithmic distribution model can fit the velocity profile more accurately than the traditional linear distribution model,and has better robustness in terms of model parameter sensitivity.
2023, 31(3): 905-915.
The Meigu River Basin is located in the transition zone between the Yunnan-Guizhou Plateau and the southwestern Sichuan Mountains in the eastern edge of the Qinghai-Tibet Plateau,where landslides are the most intensive in the world. The giant and super large-scale landslides are widely distributed. They are numerous,have complex mechanisms and can be serious harmful in the region due to the types of special landform evolution. They have become a major safety hazard for road safety,rural revitalization and urban construction in river valleys. Therefore,some scientific responses are urgently needed to deal with them. On the basis of many years of ancient landslide research in China and abroad,the authors summarize the research progress with temporal and spatial distribution of ancient landslides in Meigu River Basin,the response of landslides to tectonic landforms,the disaster-pregnancy mechanism of landslide,and the pattern of landslide-induced disaster and the main controlling factors. Combined with the actual needs of disaster prevention and mitigation of landslides,three key scientific issues in the disaster-pregnancy patterns of ancient landslides under the control of tectonic landforms in the Meigu River Basin are proposed. (1)The disaster-pregnancy and disaster-control pattern of landslides caused by different developmental coincident tectonic landforms; (2)The disaster-pregnancy patterns of large-scale landslides due to coincident tectonic landforms in the tectonic uplifting differences area; (3)Establishment of the corresponding relationship among faults,folds,ancient earthquakes and paleoclimate change and landslide development,to reveal the genetic mechanism of ancient landslides in Meigu River Basin. The solution of the above key scientific problems would play a positive guiding role in the study of ancient landslides and disaster prevention and mitigation in the southwestern mountainous area.
The Meigu River Basin is located in the transition zone between the Yunnan-Guizhou Plateau and the southwestern Sichuan Mountains in the eastern edge of the Qinghai-Tibet Plateau,where landslides are the most intensive in the world. The giant and super large-scale landslides are widely distributed. They are numerous,have complex mechanisms and can be serious harmful in the region due to the types of special landform evolution. They have become a major safety hazard for road safety,rural revitalization and urban construction in river valleys. Therefore,some scientific responses are urgently needed to deal with them. On the basis of many years of ancient landslide research in China and abroad,the authors summarize the research progress with temporal and spatial distribution of ancient landslides in Meigu River Basin,the response of landslides to tectonic landforms,the disaster-pregnancy mechanism of landslide,and the pattern of landslide-induced disaster and the main controlling factors. Combined with the actual needs of disaster prevention and mitigation of landslides,three key scientific issues in the disaster-pregnancy patterns of ancient landslides under the control of tectonic landforms in the Meigu River Basin are proposed. (1)The disaster-pregnancy and disaster-control pattern of landslides caused by different developmental coincident tectonic landforms; (2)The disaster-pregnancy patterns of large-scale landslides due to coincident tectonic landforms in the tectonic uplifting differences area; (3)Establishment of the corresponding relationship among faults,folds,ancient earthquakes and paleoclimate change and landslide development,to reveal the genetic mechanism of ancient landslides in Meigu River Basin. The solution of the above key scientific problems would play a positive guiding role in the study of ancient landslides and disaster prevention and mitigation in the southwestern mountainous area.
2023, 31(3): 916-923.
The Sichuan-Tibet traffic corridor passes through the frozen soil area of the Qinghai-Tibet Plateau. During its life cycle,the slope protection projects would inevitably and adversely be affected by frozen soil. Some prevention and control projects nearby were damaged during the freeze-thaw cycles. To mitigate the adverse effects,we proposed a new anchor cable. The new anchor cable was mainly composed of the disc spring system and yield device. We made and tested 7 groups of yield sets with different lengths,different contact methods and different outer diameters. And we found some samples that could provide sufficient yield force and stroke. Then we proposed a calculation method for the key parameters of the yield set. We developed a yield device which consists of 4 yield sets. Each yield set could provide resistance force 120~135 kN. The total initial yield strength was 420~450 kN. The yield stroke can reach more than 100 mm. We performed the tension test of the disc spring anchor cable in the laboratory. The laboratory test results showed that the growth of the force was reduced by 60% during the frost heave process. And the loss of the force was reduced by about 40% during the melting process. We analyzed the working principle of disc springs on the basis of experiments. We combined the yielding device and the disc spring to form a new anchor cable and tested it under tension. The laboratory tests showed that it could adjust the prestress in both directions effectively. After the end of the yield stroke,we carried out the ultimate bearing capacity tests of the anchor cables. The ultimate bearing capacity of the anchor cable was 1050 kN. The initial yield force and the stroke of the anchor cable could be extended as needed. The performance of the new anchor cable was better than similar products in the market. It could be used for landslide protection in seasonal frozen soil areas along the Sichuan-Tibet traffic corridor.
The Sichuan-Tibet traffic corridor passes through the frozen soil area of the Qinghai-Tibet Plateau. During its life cycle,the slope protection projects would inevitably and adversely be affected by frozen soil. Some prevention and control projects nearby were damaged during the freeze-thaw cycles. To mitigate the adverse effects,we proposed a new anchor cable. The new anchor cable was mainly composed of the disc spring system and yield device. We made and tested 7 groups of yield sets with different lengths,different contact methods and different outer diameters. And we found some samples that could provide sufficient yield force and stroke. Then we proposed a calculation method for the key parameters of the yield set. We developed a yield device which consists of 4 yield sets. Each yield set could provide resistance force 120~135 kN. The total initial yield strength was 420~450 kN. The yield stroke can reach more than 100 mm. We performed the tension test of the disc spring anchor cable in the laboratory. The laboratory test results showed that the growth of the force was reduced by 60% during the frost heave process. And the loss of the force was reduced by about 40% during the melting process. We analyzed the working principle of disc springs on the basis of experiments. We combined the yielding device and the disc spring to form a new anchor cable and tested it under tension. The laboratory tests showed that it could adjust the prestress in both directions effectively. After the end of the yield stroke,we carried out the ultimate bearing capacity tests of the anchor cables. The ultimate bearing capacity of the anchor cable was 1050 kN. The initial yield force and the stroke of the anchor cable could be extended as needed. The performance of the new anchor cable was better than similar products in the market. It could be used for landslide protection in seasonal frozen soil areas along the Sichuan-Tibet traffic corridor.
2023, 31(3): 924-931.
Similar material is the key factor to replicate the rock avalanche dam-forming and dam-breaking process in laboratory experiments. Few rock similar materials can be used to model this process at present. Therefore,we choose seven raw materials to prepare similar materials to conduct proportion experiments. These materials include(a) barite and calcium carbonate sand as aggregate,(b)gypsum and sodium silicate as binder,(c)sodium carboxymethyl cellulose,glycerol and water as auxiliary additives. The control variable method is used to study the influence of five factors on the physical and mechanical properties of similar materials. The factors include the ratio of aggregate and binder,the ratio of barite and calcium carbonate sand,the ratio of sodium silicate and gypsum,sodium carboxymethyl cellulose content and water content. The mechanism of sodium silicate controlling the water stability of similar materials is preliminarily explored. The results show that: the ratio of aggregate and binder controls elastic modulus,the ratio of barite and quartz sand has the great effect on the angle of internal friction,the ratio of sodium silicate and gypsum controls water stability,sodium carboxymethyl cellulose controls the angle of internal friction,water content controls cohesion and compressive strength. Sodium silicate plays a role of chemical cementation,filling and skeleton in improving the water stability of materials,which is the key factor to control the water stability of similar materials. Based on the experimental results and theoretical analysis,the similar materials with low strength,and good water stability are prepared. The obtained similar materials can be used to conduct the physical test when the similarity ratio is approximately 1︰400-1︰800.
Similar material is the key factor to replicate the rock avalanche dam-forming and dam-breaking process in laboratory experiments. Few rock similar materials can be used to model this process at present. Therefore,we choose seven raw materials to prepare similar materials to conduct proportion experiments. These materials include(a) barite and calcium carbonate sand as aggregate,(b)gypsum and sodium silicate as binder,(c)sodium carboxymethyl cellulose,glycerol and water as auxiliary additives. The control variable method is used to study the influence of five factors on the physical and mechanical properties of similar materials. The factors include the ratio of aggregate and binder,the ratio of barite and calcium carbonate sand,the ratio of sodium silicate and gypsum,sodium carboxymethyl cellulose content and water content. The mechanism of sodium silicate controlling the water stability of similar materials is preliminarily explored. The results show that: the ratio of aggregate and binder controls elastic modulus,the ratio of barite and quartz sand has the great effect on the angle of internal friction,the ratio of sodium silicate and gypsum controls water stability,sodium carboxymethyl cellulose controls the angle of internal friction,water content controls cohesion and compressive strength. Sodium silicate plays a role of chemical cementation,filling and skeleton in improving the water stability of materials,which is the key factor to control the water stability of similar materials. Based on the experimental results and theoretical analysis,the similar materials with low strength,and good water stability are prepared. The obtained similar materials can be used to conduct the physical test when the similarity ratio is approximately 1︰400-1︰800.
2023, 31(3): 932-948.
Data of surface morphology and underground structure(morphological structure) in the course of slope disaster are necessary in slope stability evaluation and disaster prevention. The "space-ground-interior" multi-source date joint analysis is an effective method for morphological structure research based on aerial telemetry,ground survey,internal real exploration and inversion. Morphological and structural investigation of the Shidaguan oversize toppling body(1388×104m3),located on the anti-inclined slope of metamorphic rocks on the right bank of Minjiang River,was carried out by unmanned aerial vehicle(UAV)aerial survey,artificial ground survey,surface displacement monitoring(GNSS),drilling,exploration well and electrical resistivity tomography(ERT). The results show that the upper reaches(north side) of the Shidaguan toppling body are characterized by the collapse of debris and soil at the leading edge,multi-stage tension cracking at the middle and rear ends,and lateral margin en echelon shear,but the swelling and lateral cracking of completely weathered phyllite at the lower reaches(south side),with the maximum displacement of the upper reaches up to 24 times that of the lower reaches. The toppling fracture zone is step-shaped in the toppling direction,with a thickness of 0.8~10.3m and a buried depth of 35~75m,increasing from upstream to downstream. Further investigation of macroscopic and microscopic material structure shows that the shear slip in the upstream fracture zone is mainly marked by the secondary shear zone and the scratches,and the insitu weathering of the rock and reverse bend in the downstream fracture zone is the main characteristic. It is further found that the upper reaches of the Shidaguan toppling body belong to the traditional mode of "rock toppling→rear pull crack→base break→integral slip". The toppling of the downstream is inhibited by the blocking of mountain in the leading edge,the compressive stress of the front part is concentrated,and the basal body breaks and slippage occur after the shear failure of the extrusion part. Hence a new model of "rock toppling→rear pull crack and pressure stress concentration at the front→base fracture→front bulge,lateral crack,and back warping shear→integral slip" is proposed. The methods and results of the morphological structure survey are helpful to the analysis of catastrophic processes of similar slopes.
Data of surface morphology and underground structure(morphological structure) in the course of slope disaster are necessary in slope stability evaluation and disaster prevention. The "space-ground-interior" multi-source date joint analysis is an effective method for morphological structure research based on aerial telemetry,ground survey,internal real exploration and inversion. Morphological and structural investigation of the Shidaguan oversize toppling body(1388×104m3),located on the anti-inclined slope of metamorphic rocks on the right bank of Minjiang River,was carried out by unmanned aerial vehicle(UAV)aerial survey,artificial ground survey,surface displacement monitoring(GNSS),drilling,exploration well and electrical resistivity tomography(ERT). The results show that the upper reaches(north side) of the Shidaguan toppling body are characterized by the collapse of debris and soil at the leading edge,multi-stage tension cracking at the middle and rear ends,and lateral margin en echelon shear,but the swelling and lateral cracking of completely weathered phyllite at the lower reaches(south side),with the maximum displacement of the upper reaches up to 24 times that of the lower reaches. The toppling fracture zone is step-shaped in the toppling direction,with a thickness of 0.8~10.3m and a buried depth of 35~75m,increasing from upstream to downstream. Further investigation of macroscopic and microscopic material structure shows that the shear slip in the upstream fracture zone is mainly marked by the secondary shear zone and the scratches,and the insitu weathering of the rock and reverse bend in the downstream fracture zone is the main characteristic. It is further found that the upper reaches of the Shidaguan toppling body belong to the traditional mode of "rock toppling→rear pull crack→base break→integral slip". The toppling of the downstream is inhibited by the blocking of mountain in the leading edge,the compressive stress of the front part is concentrated,and the basal body breaks and slippage occur after the shear failure of the extrusion part. Hence a new model of "rock toppling→rear pull crack and pressure stress concentration at the front→base fracture→front bulge,lateral crack,and back warping shear→integral slip" is proposed. The methods and results of the morphological structure survey are helpful to the analysis of catastrophic processes of similar slopes.
2023, 31(3): 949-958.
The establishment of mathematical model based on slope monitoring data is an important method for slope deformation and stability analysis. Grey prediction, support vector machine(SVM) and related improvement models are the hot spots in slope deformation prediction. However, the form and application scope of single prediction model limit the utilization of monitoring data, resulting in low model accuracy and poor applicability. On the one hand, the inherent defects of the grey prediction model are difficult to be eliminated, and the dependence on historical data is strong, which leads to this model not suitable for many slope engineering. Although the SVM model shows great advantages in nonlinear fitting, its prediction accuracy for future trends is low. Aiming at the large error of a single prediction model, we propose an optimally combined PSO-SVR-NGM model based on the entropy weight method. The new model combines the high-precision variable-weight buffer NGM(1, 1, k, c)model and the PSO-SVR model. It can make up for the shortcomings of the single prediction model and improve prediction accuracy. We first improve the unbiased NGM(1, 1, k, c)model, through introducing the variable weight buffer operator λ and the background value weight coefficients η, κ to construct a new three-parameter variable weight buffer NGM(1, 1, k, c)model. And we use the improved particle swarm algorithm(PSO)to search and determine the best parameter combination, so that it can meet the requirements of fitting and prediction accuracy at the same time. The improved PSO integrates the maximum grey correlation degree and the minimum average relative error to reconstruct its fitness function. The support vector regression(SVR) is a kind of SVM. We also use PSO to search the best parameters of SVR model to achieve better modeling results. After obtaining these two high-precision models, we use the entropy method to weight the improved variable weight buffer NGM(1, 1, k, c)model and PSO-SVR model to establish a combined model. We use three slope projects with different deformation characteristics to verify the effectiveness of the combined model, by calculating and comparing average relative error(MRE), root mean square error(RMSE) and coefficient of determination(R2) of single model and combined model. The results show that, in contrast with single prediction model, the proposed combined model has lower error, higher fitting and prediction accuracy, better correlation with the original displacement data, can more truly reflect the slope deformation law, which make it has stronger engineering applicability. It is also found that the combined model combines the advantages of these single models, and make full use of the known monitoring information. Through a lot of research, we find that the combined model has strong applicability to displacement data with certain trend, which may be related to the single model selected. With the improvement of data processing technology and the optimization of models, the combined prediction model that considering various influencing factors of slope deformation will become the research direction in the future. At the same time, we find that the proposal and development of the combined model also promote the optimization and improvement of the single model, they complement each other and provide good ideas for solving practical landslide engineering problems.
The establishment of mathematical model based on slope monitoring data is an important method for slope deformation and stability analysis. Grey prediction, support vector machine(SVM) and related improvement models are the hot spots in slope deformation prediction. However, the form and application scope of single prediction model limit the utilization of monitoring data, resulting in low model accuracy and poor applicability. On the one hand, the inherent defects of the grey prediction model are difficult to be eliminated, and the dependence on historical data is strong, which leads to this model not suitable for many slope engineering. Although the SVM model shows great advantages in nonlinear fitting, its prediction accuracy for future trends is low. Aiming at the large error of a single prediction model, we propose an optimally combined PSO-SVR-NGM model based on the entropy weight method. The new model combines the high-precision variable-weight buffer NGM(1, 1, k, c)model and the PSO-SVR model. It can make up for the shortcomings of the single prediction model and improve prediction accuracy. We first improve the unbiased NGM(1, 1, k, c)model, through introducing the variable weight buffer operator λ and the background value weight coefficients η, κ to construct a new three-parameter variable weight buffer NGM(1, 1, k, c)model. And we use the improved particle swarm algorithm(PSO)to search and determine the best parameter combination, so that it can meet the requirements of fitting and prediction accuracy at the same time. The improved PSO integrates the maximum grey correlation degree and the minimum average relative error to reconstruct its fitness function. The support vector regression(SVR) is a kind of SVM. We also use PSO to search the best parameters of SVR model to achieve better modeling results. After obtaining these two high-precision models, we use the entropy method to weight the improved variable weight buffer NGM(1, 1, k, c)model and PSO-SVR model to establish a combined model. We use three slope projects with different deformation characteristics to verify the effectiveness of the combined model, by calculating and comparing average relative error(MRE), root mean square error(RMSE) and coefficient of determination(R2) of single model and combined model. The results show that, in contrast with single prediction model, the proposed combined model has lower error, higher fitting and prediction accuracy, better correlation with the original displacement data, can more truly reflect the slope deformation law, which make it has stronger engineering applicability. It is also found that the combined model combines the advantages of these single models, and make full use of the known monitoring information. Through a lot of research, we find that the combined model has strong applicability to displacement data with certain trend, which may be related to the single model selected. With the improvement of data processing technology and the optimization of models, the combined prediction model that considering various influencing factors of slope deformation will become the research direction in the future. At the same time, we find that the proposal and development of the combined model also promote the optimization and improvement of the single model, they complement each other and provide good ideas for solving practical landslide engineering problems.
FAST MODELING METHOD OF MULTI-ATTRIBUTE 3D GEOLOGICAL MODEL AND APPLICATION IN HIGH GEOSTRESS TUNNEL
2023, 31(3): 959-967.
In order to raise the efficiency of 3D geological modeling method on complex geological conditions, based on Indicator Kriging, this paper realized the fast construction of 3D geological model under complex geological conditions. Through the 3D geological model, the lithology distribution in space can be accurately characterized. By secondary development, the integration of 3D geological model and numerical model under complex geological conditions is realized. Taking the prediction of rockburst disaster in tunnel with high geostress and surrounding rock classification modification as examples, the attribute analysis of 3D geological model is carried out. Finally, combined with the geostress attribute model and the stress distribution of tunnel surrounding rock obtained from excavation simulation, the grade and area of rock burst in a tunnel are analyzed. The results show that medium to strong rockburst may occur when the tunnel crosses through hard rock.
In order to raise the efficiency of 3D geological modeling method on complex geological conditions, based on Indicator Kriging, this paper realized the fast construction of 3D geological model under complex geological conditions. Through the 3D geological model, the lithology distribution in space can be accurately characterized. By secondary development, the integration of 3D geological model and numerical model under complex geological conditions is realized. Taking the prediction of rockburst disaster in tunnel with high geostress and surrounding rock classification modification as examples, the attribute analysis of 3D geological model is carried out. Finally, combined with the geostress attribute model and the stress distribution of tunnel surrounding rock obtained from excavation simulation, the grade and area of rock burst in a tunnel are analyzed. The results show that medium to strong rockburst may occur when the tunnel crosses through hard rock.
2023, 31(3): 968-980.
To reveal the meso-mechanism of crack coalescence, this paper uses particle flow code(PFC) to simulate uniaxial compression test of gypsum specimens containing double parallel pre-existing flaws. The paper classifies the crack coalescence types in the specimens with different geometry of double pre-existing flaws, and analyzes the force chain and particle displacement field around the pre-existing flaws. It is found that the relative position of pre-existing flaws can affect the contact force distribution and particle displacement filed around the pre-existing flaws, and then affect the crack propagation path. When the two pre-existing flaws are nearly coplanar, there is a concentration of contact force in the rock bridge area. Micro-tensile cracks first appear in the rock bridge area and gradually evolve into macro-shear band with the loading. These micro-tensile cracks lead to type Ⅰ coalescence. When the rock bridge inclination angle is large and the two pre-existing flaws do not overlap, the contact force concentration in the rock bridge area increases. Vertical micro-tensile cracks first appear in the rock bridge area. Macro-cracks evolving from micro-tensile cracks connect pre-existing flaw tips, resulting in the type Ⅱ or Ⅶb coalescence. When the tips of two pre-existing flaws are partially overlapped, the compressive contact force concentration at the overlapped tips is smaller than that at the non overlapped tips due to the stress shielding effect, which leads to the wing cracks becoming the main cracks leading to coalescence. When the two pre-existing flaws overlap in the vertical direction, the contact force between the two pre-existing flaws on the same side tips is concentrated, resulting in tensile cracks caused by compression. Tensile cracks induced by compression connect the tips of the pre-existing flaws on the same side, forming type Ⅴ coalescence. The results show that the number of micro-cracks in the samples with type Ⅱ, Ⅴ and Ⅶb coalescence increases step by step, which indicates that the propagation of macro-cracks in these three coalescence types are caused by the sudden release of strain energy.
To reveal the meso-mechanism of crack coalescence, this paper uses particle flow code(PFC) to simulate uniaxial compression test of gypsum specimens containing double parallel pre-existing flaws. The paper classifies the crack coalescence types in the specimens with different geometry of double pre-existing flaws, and analyzes the force chain and particle displacement field around the pre-existing flaws. It is found that the relative position of pre-existing flaws can affect the contact force distribution and particle displacement filed around the pre-existing flaws, and then affect the crack propagation path. When the two pre-existing flaws are nearly coplanar, there is a concentration of contact force in the rock bridge area. Micro-tensile cracks first appear in the rock bridge area and gradually evolve into macro-shear band with the loading. These micro-tensile cracks lead to type Ⅰ coalescence. When the rock bridge inclination angle is large and the two pre-existing flaws do not overlap, the contact force concentration in the rock bridge area increases. Vertical micro-tensile cracks first appear in the rock bridge area. Macro-cracks evolving from micro-tensile cracks connect pre-existing flaw tips, resulting in the type Ⅱ or Ⅶb coalescence. When the tips of two pre-existing flaws are partially overlapped, the compressive contact force concentration at the overlapped tips is smaller than that at the non overlapped tips due to the stress shielding effect, which leads to the wing cracks becoming the main cracks leading to coalescence. When the two pre-existing flaws overlap in the vertical direction, the contact force between the two pre-existing flaws on the same side tips is concentrated, resulting in tensile cracks caused by compression. Tensile cracks induced by compression connect the tips of the pre-existing flaws on the same side, forming type Ⅴ coalescence. The results show that the number of micro-cracks in the samples with type Ⅱ, Ⅴ and Ⅶb coalescence increases step by step, which indicates that the propagation of macro-cracks in these three coalescence types are caused by the sudden release of strain energy.
2023, 31(3): 981-998.
Melange is a special geological body composed of mixed accumulation of rock blocks with different compositions, ages and sources, which is formed at the boundary of plate subduction and collision. The rock mass has the characteristics of complex structure, rapid spatial change, easy alteration and large differences in mechanical properties. It is widely distributed in the Qinghai-Tibet Plateau of China. Due to the complex geological environment of the Qinghai-Tibet Plateau, the melange belt is often prone to geological disasters, which has a great impact on human life and property and engineering construction. Therefore, this paper analyzes the genetic mechanism and geological characteristics of the melange, and summarizes the distribution, geological characteristics and typical geological disasters of the melange belt in the Qinghai-Tibet Plateau. On this basis, the research direction of the problems existing in the study of geological hazards in the melange belt of the Qinghai-Tibet Plateau is put forward. The research results can provide a reference for the study of geological hazards in the melange belt of the Qinghai-Tibet Plateau.
Melange is a special geological body composed of mixed accumulation of rock blocks with different compositions, ages and sources, which is formed at the boundary of plate subduction and collision. The rock mass has the characteristics of complex structure, rapid spatial change, easy alteration and large differences in mechanical properties. It is widely distributed in the Qinghai-Tibet Plateau of China. Due to the complex geological environment of the Qinghai-Tibet Plateau, the melange belt is often prone to geological disasters, which has a great impact on human life and property and engineering construction. Therefore, this paper analyzes the genetic mechanism and geological characteristics of the melange, and summarizes the distribution, geological characteristics and typical geological disasters of the melange belt in the Qinghai-Tibet Plateau. On this basis, the research direction of the problems existing in the study of geological hazards in the melange belt of the Qinghai-Tibet Plateau is put forward. The research results can provide a reference for the study of geological hazards in the melange belt of the Qinghai-Tibet Plateau.
2023, 31(3): 999-1017.
Complex friction heating processes and effects exist between the basal facies and the substrates of rock avalanches. A series of friction heating induced phenomenon and corresponding weakening mechanisms consequently occur. The friction heating of rock avalanches has become one of the most crucial scientific problems in the field of landslide dynamics for decades. In this study, a general review of the study history on friction heating of rock avalanches is firstly given. The term frictionite is described in detail. Next, the state of art of friction heating induced weakening mechanisms along with newly reported cases are reviewed in terms of: thermal melting, thermal pressurization, thermal decomposition and thermal moisture. Then the authors propose several problems to which attention and efforts should be paid in future study: (1)precise discovery and judgement of more field evidence referring to friction heating induced weakening on rock avalanches; (2)quantified real-time dynamic monitoring and illustration of experimental parameters and (3)establishing multi-processes, multi-field coupling study of friction heating induced weakening mechanisms on rock avalanches. Finally, the future development of friction heating induced weakening mechanisms of rock avalanches was proposed.
Complex friction heating processes and effects exist between the basal facies and the substrates of rock avalanches. A series of friction heating induced phenomenon and corresponding weakening mechanisms consequently occur. The friction heating of rock avalanches has become one of the most crucial scientific problems in the field of landslide dynamics for decades. In this study, a general review of the study history on friction heating of rock avalanches is firstly given. The term frictionite is described in detail. Next, the state of art of friction heating induced weakening mechanisms along with newly reported cases are reviewed in terms of: thermal melting, thermal pressurization, thermal decomposition and thermal moisture. Then the authors propose several problems to which attention and efforts should be paid in future study: (1)precise discovery and judgement of more field evidence referring to friction heating induced weakening on rock avalanches; (2)quantified real-time dynamic monitoring and illustration of experimental parameters and (3)establishing multi-processes, multi-field coupling study of friction heating induced weakening mechanisms on rock avalanches. Finally, the future development of friction heating induced weakening mechanisms of rock avalanches was proposed.
2023, 31(3): 1018-1026.
Machala coal strata is one of the main coal stratums in the coal-bearing belt of Changdu. In order to clarify the influence of weathering on the pore structure characteristics of Machala coal formation in Tibet,in this paper we took different types of weathered rocks from the Early Carboniferous Machala Formation section in Tibet as the research object,and investigated the microscopic pore structure and its complexity by using nitrogen adsorption test and fractal theory. The test results show that the sorption and desorption isotherms of the rocks show an inverse "S" shape and the pore structure shows a homogeneous trend. The relative pressure(P/P0)can be divided into three stages: less than 0.1,0.1~0.45 and more than 0.45 according to the rising trend of the sorption and desorption curve. The pore structure of the rock samples is concentrated in the range of 1~5 nm,among which the pore volume of muddy clastic limestone,chalky mudstone,siltstone,mudstone and limestone is larger in the range of 1~2 nm,and the specific surface area and pore volume of the coal seam are lower compared with those of the adjacent rock layers. The fractal dimension of macropores is significantly higher than that of micropores,and the complexity of pore structure is higher. The fractal dimension of pores in coal seams and carbonaceous mudstone is lower compared with other types of rocks. The results of the study can be used for the development and disaster prevention in the Changdu area.
Machala coal strata is one of the main coal stratums in the coal-bearing belt of Changdu. In order to clarify the influence of weathering on the pore structure characteristics of Machala coal formation in Tibet,in this paper we took different types of weathered rocks from the Early Carboniferous Machala Formation section in Tibet as the research object,and investigated the microscopic pore structure and its complexity by using nitrogen adsorption test and fractal theory. The test results show that the sorption and desorption isotherms of the rocks show an inverse "S" shape and the pore structure shows a homogeneous trend. The relative pressure(P/P0)can be divided into three stages: less than 0.1,0.1~0.45 and more than 0.45 according to the rising trend of the sorption and desorption curve. The pore structure of the rock samples is concentrated in the range of 1~5 nm,among which the pore volume of muddy clastic limestone,chalky mudstone,siltstone,mudstone and limestone is larger in the range of 1~2 nm,and the specific surface area and pore volume of the coal seam are lower compared with those of the adjacent rock layers. The fractal dimension of macropores is significantly higher than that of micropores,and the complexity of pore structure is higher. The fractal dimension of pores in coal seams and carbonaceous mudstone is lower compared with other types of rocks. The results of the study can be used for the development and disaster prevention in the Changdu area.
2023, 31(3): 1027-1037.
In order to explore the influence of black shale bedding on its mechanical characteristics and energy dissipation process,this paper uses the black shale of Longmaxi Formation as the research object,obtains the characteristic stresses,volume strain and crack strain under different confining pressures and bedding dip angles with indoor conventional triaxial compression tests and analyses the crack strain and energy evolution mechanism according to the principle of energy balance. The research shows that the characteristic stress and characteristic stress ratio show a "V"-shaped trend with the increase of the bedding surface inclination under the same confining pressure value. As the confining pressure increases,the energy density of the dissipated energy mutation point gradually increases. The dissipation ratio presents a "V"-shaped trend with the increase of axial crack strain. Before and after the failure of the rock samples,there is a certain conversion relationship between elastic strain energy and dissipation energy with the bedding. The research results provide a reference for further exploring the influence of black shale bedding effects on its mechanical characteristics and energy evolution mechanism.
In order to explore the influence of black shale bedding on its mechanical characteristics and energy dissipation process,this paper uses the black shale of Longmaxi Formation as the research object,obtains the characteristic stresses,volume strain and crack strain under different confining pressures and bedding dip angles with indoor conventional triaxial compression tests and analyses the crack strain and energy evolution mechanism according to the principle of energy balance. The research shows that the characteristic stress and characteristic stress ratio show a "V"-shaped trend with the increase of the bedding surface inclination under the same confining pressure value. As the confining pressure increases,the energy density of the dissipated energy mutation point gradually increases. The dissipation ratio presents a "V"-shaped trend with the increase of axial crack strain. Before and after the failure of the rock samples,there is a certain conversion relationship between elastic strain energy and dissipation energy with the bedding. The research results provide a reference for further exploring the influence of black shale bedding effects on its mechanical characteristics and energy evolution mechanism.
2023, 31(3): 1038-1048.
The Lucaogou shale oil reservoir in the Jimusar Depression is a typical continental shale oil reservoir in China. The reservoir presents a typical thin interlayer feature with rapid changes in lithofacies and strong heterogeneities,resulting in difficult reservoir stimulations. In particular,the heterogeneities of mechanical parameters of the Lucaogou Formation reservoir and its impact on hydraulic fractures should be further studied. In this paper,high-density sampling and mechanical testing on drilling core samples of the Lucaogou Formation are conducted. The heterogeneities of mechanical parameters are revealed,and the heterogeneities of the mechanical parameters on the evolution processes of hydraulic fractures are investigated. The results show that:(1)the mechanical parameters of the Lucaogou Formation are vertically highly heterogeneous,presenting obvious thin interlayers; (2)the variation of the in-situ stress and the breakdown pressure of the Lucaogou Formation are dramatic,which may affects the cross-layer propagation of hydraulic fractures; and (3)the heterogeneities of mechanical parameters greatly influences the vertical expansion of hydraulic fractures. Increasing the injection rate and the viscosity of fracturing fluids can effectively promote the cross-layer expansion of hydraulic fractures. This study provides an important theoretical basis for the effective development of the Lucaogou shale oil reservoir,and the results can help optimize the fracturing technologies of the Lucaogou formation.
The Lucaogou shale oil reservoir in the Jimusar Depression is a typical continental shale oil reservoir in China. The reservoir presents a typical thin interlayer feature with rapid changes in lithofacies and strong heterogeneities,resulting in difficult reservoir stimulations. In particular,the heterogeneities of mechanical parameters of the Lucaogou Formation reservoir and its impact on hydraulic fractures should be further studied. In this paper,high-density sampling and mechanical testing on drilling core samples of the Lucaogou Formation are conducted. The heterogeneities of mechanical parameters are revealed,and the heterogeneities of the mechanical parameters on the evolution processes of hydraulic fractures are investigated. The results show that:(1)the mechanical parameters of the Lucaogou Formation are vertically highly heterogeneous,presenting obvious thin interlayers; (2)the variation of the in-situ stress and the breakdown pressure of the Lucaogou Formation are dramatic,which may affects the cross-layer propagation of hydraulic fractures; and (3)the heterogeneities of mechanical parameters greatly influences the vertical expansion of hydraulic fractures. Increasing the injection rate and the viscosity of fracturing fluids can effectively promote the cross-layer expansion of hydraulic fractures. This study provides an important theoretical basis for the effective development of the Lucaogou shale oil reservoir,and the results can help optimize the fracturing technologies of the Lucaogou formation.
2023, 31(3): 1049-1058.
In order to study the mechanical properties of reinforced calcareous sand,a series of large-scale triaxial consolidation drainage tests were performed on reinforced and unreinforced calcareous sand. The testing variables included confining pressures,types of reinforcing materials and number of reinforcement layers. The study methods were as follows: First,the stress-strain relationships,volume strain-axial strain relationships and grain-size distribution curves after the tests of calcareous sand specimens were obtained by the consolidated-drained triaxial compression tests and sieve analyses. Second,the influences of reinforcement on the strength,deformation and particle breakage of calcareous sand were analyzed by these test results. Finally,the rule of particles breakage was obtained by correlating the particle breakage with the input energy. The study results indicated that the strength of reinforced calcareous sand is much higher than unreinforced calcareous sand,and the reinforcement effect increases with the number of reinforcement layers and the 2% elongation secant stiffness of the reinforcement material,but decreases with confining pressure. The reinforced materials can also effectively inhibit the dilatancy of calcareous sand,and the more the number of reinforcement layers,the more obvious the inhibitory effect. In addition,the relationship between particle breakage and input energy is unique regardless of the reinforcement conditions,and the degree of particle breakage increased with the input energy.
In order to study the mechanical properties of reinforced calcareous sand,a series of large-scale triaxial consolidation drainage tests were performed on reinforced and unreinforced calcareous sand. The testing variables included confining pressures,types of reinforcing materials and number of reinforcement layers. The study methods were as follows: First,the stress-strain relationships,volume strain-axial strain relationships and grain-size distribution curves after the tests of calcareous sand specimens were obtained by the consolidated-drained triaxial compression tests and sieve analyses. Second,the influences of reinforcement on the strength,deformation and particle breakage of calcareous sand were analyzed by these test results. Finally,the rule of particles breakage was obtained by correlating the particle breakage with the input energy. The study results indicated that the strength of reinforced calcareous sand is much higher than unreinforced calcareous sand,and the reinforcement effect increases with the number of reinforcement layers and the 2% elongation secant stiffness of the reinforcement material,but decreases with confining pressure. The reinforced materials can also effectively inhibit the dilatancy of calcareous sand,and the more the number of reinforcement layers,the more obvious the inhibitory effect. In addition,the relationship between particle breakage and input energy is unique regardless of the reinforcement conditions,and the degree of particle breakage increased with the input energy.
2023, 31(3): 1059-1072.
Fibre yarn is formed by loosening,carding and cutting waste synthetic textile polyester fabric. A certain proportion of fibre yarn was added to plain loess,which formed fibre yarn reinforced loess. The uniaxial compression test and triaxial shear test of fiber reinforced loess were carried out using servo hydraulic loading double chamber high pressure triaxial apparatus. The compressive deformation and stress-strain characteristics of fiber yarn reinforced loess were systematically analyzed. The results showed that with the increase of fiber yarn proportion in plain loess,the compressive deformation decreases. The yield pressure of fiber yarn reinforced loess was determined. The yield pressure increased with the increase of fiber yarn proportion in plain loess. According to the stress-strain relationship of fiber yarn reinforced loess in triaxial shear test,it was found that under the same consolidation pressure,with the increase of fiber yarn proportion in plain loess,the reflected shear stress also increased. With the increase of consolidation pressure,the shear stress increased with the increase of fiber yarn blending ratio. According to the stress-strain relationship of fiber yarn reinforced loess in triaxial shear test,a comprehensive index—fiber reinforced index Ir was constructed. The index Ir could reflect the actual reinforcement effect of liber yan reinforced loess. The cohesive force was hyperbolic with the increase of the index Ir. The internal friction angle kept constant with the increase of the index Ir. Based on modified Cambridge model,according to the difference of the index Ir,the isotropic compressive ball stress and critical state line with the change of fiber reinforced index Ir was determined. Taking plastic volume strain as hardening parameter,the elastoplastic constitutive model of fiber yarn reinforced loess was derived. After testing validation,it was proved that the constitutive model can reasonably describe the mechanical deformation characteristics of fiber yarn reinforced loess.
Fibre yarn is formed by loosening,carding and cutting waste synthetic textile polyester fabric. A certain proportion of fibre yarn was added to plain loess,which formed fibre yarn reinforced loess. The uniaxial compression test and triaxial shear test of fiber reinforced loess were carried out using servo hydraulic loading double chamber high pressure triaxial apparatus. The compressive deformation and stress-strain characteristics of fiber yarn reinforced loess were systematically analyzed. The results showed that with the increase of fiber yarn proportion in plain loess,the compressive deformation decreases. The yield pressure of fiber yarn reinforced loess was determined. The yield pressure increased with the increase of fiber yarn proportion in plain loess. According to the stress-strain relationship of fiber yarn reinforced loess in triaxial shear test,it was found that under the same consolidation pressure,with the increase of fiber yarn proportion in plain loess,the reflected shear stress also increased. With the increase of consolidation pressure,the shear stress increased with the increase of fiber yarn blending ratio. According to the stress-strain relationship of fiber yarn reinforced loess in triaxial shear test,a comprehensive index—fiber reinforced index Ir was constructed. The index Ir could reflect the actual reinforcement effect of liber yan reinforced loess. The cohesive force was hyperbolic with the increase of the index Ir. The internal friction angle kept constant with the increase of the index Ir. Based on modified Cambridge model,according to the difference of the index Ir,the isotropic compressive ball stress and critical state line with the change of fiber reinforced index Ir was determined. Taking plastic volume strain as hardening parameter,the elastoplastic constitutive model of fiber yarn reinforced loess was derived. After testing validation,it was proved that the constitutive model can reasonably describe the mechanical deformation characteristics of fiber yarn reinforced loess.
2023, 31(3): 1073-1083.
The Actively Heated Fiber Optic method is based on Fiber Bragg grating method(AHFO-FBG)technology and has become the latest research hotspots due to its advantages of small size, high temperature measurement accuracy, quasi-distributed measurement, anti-electromagnetic interference, and corrosion resistance. Research on the calibration method of this technology is very critical to improve the accuracy and applicability of moisture content measurement, but this content is not involved in the existing research. In this paper, the self-developed AHFO-FBG sensor is used to carry out a series of indoor calibration tests to determine the temperature change process of loess under various moisture contents. A comparative analysis of the moisture content measurement results of the ΔTmax method and the ΔTcum method is carried out in this paper. The influence of different heating time and different heating power on the calibration results of the ΔTmax method and the ΔTcum method is further explored. The results show that both ΔTmax method and the ΔTcum method can get good moisture content calibration results. The RMSE of the ΔTmax method is 0.001 m3·m-3 higher than that of the ΔTcum method, so the advantage of the ΔTcum method is not very significant. The ΔTmax and the ΔTcum method show that the longer the heating time, the error of the two methods to measure the moisture content can gradually increase. Under the same heating time, the ΔTcum method calculates the moisture content better than the ΔTmax method, and the shorter the heating time, the more obvious the phenomenon. Under the same heating power, the RMSE of ΔTmax method is small in the low power(5~10 W·m-1), and the RMSE of ΔTcum method is small in the high power(15~35 W·m-1). An appropriate increase in the heating power can help reduce the moisture content calibration error. The research results provide a basis for the AHFO-FBG technology to achieve accurate measurement and further application of soil moisture content.
The Actively Heated Fiber Optic method is based on Fiber Bragg grating method(AHFO-FBG)technology and has become the latest research hotspots due to its advantages of small size, high temperature measurement accuracy, quasi-distributed measurement, anti-electromagnetic interference, and corrosion resistance. Research on the calibration method of this technology is very critical to improve the accuracy and applicability of moisture content measurement, but this content is not involved in the existing research. In this paper, the self-developed AHFO-FBG sensor is used to carry out a series of indoor calibration tests to determine the temperature change process of loess under various moisture contents. A comparative analysis of the moisture content measurement results of the ΔTmax method and the ΔTcum method is carried out in this paper. The influence of different heating time and different heating power on the calibration results of the ΔTmax method and the ΔTcum method is further explored. The results show that both ΔTmax method and the ΔTcum method can get good moisture content calibration results. The RMSE of the ΔTmax method is 0.001 m3·m-3 higher than that of the ΔTcum method, so the advantage of the ΔTcum method is not very significant. The ΔTmax and the ΔTcum method show that the longer the heating time, the error of the two methods to measure the moisture content can gradually increase. Under the same heating time, the ΔTcum method calculates the moisture content better than the ΔTmax method, and the shorter the heating time, the more obvious the phenomenon. Under the same heating power, the RMSE of ΔTmax method is small in the low power(5~10 W·m-1), and the RMSE of ΔTcum method is small in the high power(15~35 W·m-1). An appropriate increase in the heating power can help reduce the moisture content calibration error. The research results provide a basis for the AHFO-FBG technology to achieve accurate measurement and further application of soil moisture content.
2023, 31(3): 1084-1096.
Shenhua multi-layered reservoir is the first GCS demonstration project in China. The gas absorption of its single reservoir increased dramatically. Under the original designed scheme, the cooled CO2 after compression was injected into the deep high-temperature aquifer, resulting in a sharp change in the fluid pressure, thermal stress and a large number of fractures in the first aquifer. The injectivity of the first layer was increased, but the storage capacity of the whole system was reduced, and it also brought the risk of leakage. A site-scale rock mass cracking module was developed, based on the TOUGH-FLAC, a three-dimensional multiphase multi-component THM coupling numerical simulation program, to study the comprehensive effect of CO2 injection scheme on the coupling characteristics and cracking characteristics of the target aquifer. Injection schemes including constant rate, first growth rate and then constant rate, intermittent constant rate, intermittent variable rate and secondary variable rate were designed, and the thermodynamic characteristics, multiphase flow characteristics and cracking of reservoir rock mass were calculated and analyzed. The results show that there are many cracks observed in the aquifer under the original designed scheme, and it is the reason of the injectivity increase. Continuous injection of CO2 causes a significant decrease in the effective stress in the aquifer rock mass and an increase in the permeability. The thermal stress under the constant rate scheme is the smallest. Among the designed injection schemes, the fracture observed in the reservoir under the constant rate injection scheme is the least.
Shenhua multi-layered reservoir is the first GCS demonstration project in China. The gas absorption of its single reservoir increased dramatically. Under the original designed scheme, the cooled CO2 after compression was injected into the deep high-temperature aquifer, resulting in a sharp change in the fluid pressure, thermal stress and a large number of fractures in the first aquifer. The injectivity of the first layer was increased, but the storage capacity of the whole system was reduced, and it also brought the risk of leakage. A site-scale rock mass cracking module was developed, based on the TOUGH-FLAC, a three-dimensional multiphase multi-component THM coupling numerical simulation program, to study the comprehensive effect of CO2 injection scheme on the coupling characteristics and cracking characteristics of the target aquifer. Injection schemes including constant rate, first growth rate and then constant rate, intermittent constant rate, intermittent variable rate and secondary variable rate were designed, and the thermodynamic characteristics, multiphase flow characteristics and cracking of reservoir rock mass were calculated and analyzed. The results show that there are many cracks observed in the aquifer under the original designed scheme, and it is the reason of the injectivity increase. Continuous injection of CO2 causes a significant decrease in the effective stress in the aquifer rock mass and an increase in the permeability. The thermal stress under the constant rate scheme is the smallest. Among the designed injection schemes, the fracture observed in the reservoir under the constant rate injection scheme is the least.
2023, 31(3): 1097-1104.
Land subsidence is one of the main geological disasters in China. It is necessary to evaluate and predict the development trend of land subsidence. In this paper, the hyperbolic subsidence model, exponential subsidence model and growth curve subsidence model are introduced into the measured subsidence mathematical model. Combined with the continuous deformation of different layers under the surface obtained by the full cross-section distributed fine monitoring system, the land subsidence prediction model based on the distributed optical fiber monitoring data is established. This new model can realize the potential evaluation of land subsidence. Taking the G06 optical fiber monitoring drilling results of Tianjin Binhai New Area as an example, the prediction results of three kinds of subsidence models are compared. The results show that: the land subsidence curve in Tianjin Binhai area presents nonlinear attenuation characteristics. From October 2017 to December 2019, the cumulative subsidence reached 52.4 mm, and the estimated limit subsidence was about 92.6 mm. There is still about 43.4% subsidence potential. There is still a large subsidence space, and it is expected to enter the stage of subsidence stability in 2050. The 3.4~18.4 m clayey silty sand and silty fine sand layers in this area have large subsidence amount. These layers are the main layers of land subsidence, namely "dominant layer". Although the current subsidence amount of 18.4~38.4 m silty clay and clayey silty sand layer is small, its residual subsidence is large and the subsidence duration is long, which is the "priority layer" for later monitoring.
Land subsidence is one of the main geological disasters in China. It is necessary to evaluate and predict the development trend of land subsidence. In this paper, the hyperbolic subsidence model, exponential subsidence model and growth curve subsidence model are introduced into the measured subsidence mathematical model. Combined with the continuous deformation of different layers under the surface obtained by the full cross-section distributed fine monitoring system, the land subsidence prediction model based on the distributed optical fiber monitoring data is established. This new model can realize the potential evaluation of land subsidence. Taking the G06 optical fiber monitoring drilling results of Tianjin Binhai New Area as an example, the prediction results of three kinds of subsidence models are compared. The results show that: the land subsidence curve in Tianjin Binhai area presents nonlinear attenuation characteristics. From October 2017 to December 2019, the cumulative subsidence reached 52.4 mm, and the estimated limit subsidence was about 92.6 mm. There is still about 43.4% subsidence potential. There is still a large subsidence space, and it is expected to enter the stage of subsidence stability in 2050. The 3.4~18.4 m clayey silty sand and silty fine sand layers in this area have large subsidence amount. These layers are the main layers of land subsidence, namely "dominant layer". Although the current subsidence amount of 18.4~38.4 m silty clay and clayey silty sand layer is small, its residual subsidence is large and the subsidence duration is long, which is the "priority layer" for later monitoring.
2023, 31(3): 1105-1115.
Shallow gas is a natural resource and also can bring about geological hazard. The disturbance of engineering unloading and the effect of formation pressure cause shallow gas evolution, resulting in damages to engineering works and accidents. This paper examines the shallow gas geological disasters occurred during the construction of Nali Bridge in Ningming Basin in Guangxi. In this context, the occurrence characteristics of ultra-shallow gas in the research area and its damage to engineering works are studied using geological drilling sampling method combined with geochemical experiments. Results show that:(1)Due to the frequent regional tectonic activities and fracture development, the thin silt, siltstone and silty mudstone sandwiched by the mudstone had a thickness of varying from 2 mm to 200 mm, with a measured porosity of about 25.6%, and the permeability of about 37.2~46.8 μm2. Shallow gas occurs in all kinds of reservoirs in the form of facies control, fracture control, shell control and their transition, showing the characteristics of independent, discontinuous and staggered distribution. (2)The deep and thick mudstone layer in the region with an organic carbon content(TOC) of 0.61% to 1.24% and abundant organic matter and high gas production capacity belongs to the source rock of shallow gas. The measured porosity of mudstone cap rock is 22.8% to 34%, with a permeability of (2.4~22.2)×10-3μm2 and ordinary sealing capacity. (3)Due to the geological occurrence characteristics of ultra-shallow natural gas in the area, it was hard to generate abnormal pressure within the range of engineering exploration and construction depth(10~100 m). Despite no occurrence of strong blowout accident during the construction of bridge cast-in-situ bored piles, it would cause gas invasion damage to the pile foundation concrete and affect pile body completeness. It is recommended to adopt advanced exhaust gas measures and to improve relevant technologies.
Shallow gas is a natural resource and also can bring about geological hazard. The disturbance of engineering unloading and the effect of formation pressure cause shallow gas evolution, resulting in damages to engineering works and accidents. This paper examines the shallow gas geological disasters occurred during the construction of Nali Bridge in Ningming Basin in Guangxi. In this context, the occurrence characteristics of ultra-shallow gas in the research area and its damage to engineering works are studied using geological drilling sampling method combined with geochemical experiments. Results show that:(1)Due to the frequent regional tectonic activities and fracture development, the thin silt, siltstone and silty mudstone sandwiched by the mudstone had a thickness of varying from 2 mm to 200 mm, with a measured porosity of about 25.6%, and the permeability of about 37.2~46.8 μm2. Shallow gas occurs in all kinds of reservoirs in the form of facies control, fracture control, shell control and their transition, showing the characteristics of independent, discontinuous and staggered distribution. (2)The deep and thick mudstone layer in the region with an organic carbon content(TOC) of 0.61% to 1.24% and abundant organic matter and high gas production capacity belongs to the source rock of shallow gas. The measured porosity of mudstone cap rock is 22.8% to 34%, with a permeability of (2.4~22.2)×10-3μm2 and ordinary sealing capacity. (3)Due to the geological occurrence characteristics of ultra-shallow natural gas in the area, it was hard to generate abnormal pressure within the range of engineering exploration and construction depth(10~100 m). Despite no occurrence of strong blowout accident during the construction of bridge cast-in-situ bored piles, it would cause gas invasion damage to the pile foundation concrete and affect pile body completeness. It is recommended to adopt advanced exhaust gas measures and to improve relevant technologies.
ROOF-RIPPING CONSTRUCTION TECHNOLOGY FOR LARGE CROSS-SECTIONAL TUNNEL IN SOFT AND WATER-RICH STRATUM
2023, 31(3): 1116-1123.
Roof-ripping construction for a large cross-sectional tunnel is a dangerous procedure under complex geological conditions. The spatial structure of the intersection is complex, the stress transformation is frequent, and the support strength is difficult to effectively restrain the surrounding rock deformation, which results in collapse accidents and threatens the construction safety. This paper aims to improve the safety of roof-lifting construction of large cross-sectional tunnel in soft and water-rich stratum. It is based on the construction of the inclined shaft into the main tunnel in Xi Shanying tunnel of Sanqing expressway. It develops a new structure of the combined support of the upper arch of portal frame and the strengthened portal frame at the intersection. It optimizes the supporting structure strength of the strengthened portal frame and roof-ripping construction technology. It studies the construction scheme, construction process and key points of vertical roof-lifting. The results show that the combined supporting structure reduces the over-excavation area and deformation of the surrounding rock, and strengthens the support strength and stability of the stress concentration area. The construction schedule of the proposed method takes only 20 days, which saves nearly one time compared with the traditional construction method, and the construction progress of the intersection from the inclined shaft into the main tunnel is accelerated by the rational organization of the process. The results of tunnel field monitoring show that the convergence deformation and stability control of the surrounding rock at the intersection of the tunnel during the roof-ripping construction meet the construction requirements. In summary, the technical principle of this method is simple and practical. The method can provide experience reference and technical guidance for the construction of large cross-sectional tunnels under similar engineering geological conditions.
Roof-ripping construction for a large cross-sectional tunnel is a dangerous procedure under complex geological conditions. The spatial structure of the intersection is complex, the stress transformation is frequent, and the support strength is difficult to effectively restrain the surrounding rock deformation, which results in collapse accidents and threatens the construction safety. This paper aims to improve the safety of roof-lifting construction of large cross-sectional tunnel in soft and water-rich stratum. It is based on the construction of the inclined shaft into the main tunnel in Xi Shanying tunnel of Sanqing expressway. It develops a new structure of the combined support of the upper arch of portal frame and the strengthened portal frame at the intersection. It optimizes the supporting structure strength of the strengthened portal frame and roof-ripping construction technology. It studies the construction scheme, construction process and key points of vertical roof-lifting. The results show that the combined supporting structure reduces the over-excavation area and deformation of the surrounding rock, and strengthens the support strength and stability of the stress concentration area. The construction schedule of the proposed method takes only 20 days, which saves nearly one time compared with the traditional construction method, and the construction progress of the intersection from the inclined shaft into the main tunnel is accelerated by the rational organization of the process. The results of tunnel field monitoring show that the convergence deformation and stability control of the surrounding rock at the intersection of the tunnel during the roof-ripping construction meet the construction requirements. In summary, the technical principle of this method is simple and practical. The method can provide experience reference and technical guidance for the construction of large cross-sectional tunnels under similar engineering geological conditions.
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