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Editor Work2013 Vol. 21, No. 2
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2013, 21(2): 171-181.
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Usually, the earthquake-induced damage to underground structures is lighter than that to above-ground structures. But, under the condition of strong earthquakes and faults, the earthquake-induced damage to underground structures is still considerably serious. On May 12, 2008,Wenchuan earthquake with a magnitude of Ms 8.0 in Sichuan province, China caused tremendous damage to underground structures, especially the tunnels of railways and roads that traverse active faults. Dengjiaping tunnel of Cheng-Lan Railway(Chengdu to Lanzhou, in China) traverses the central fault belt in Longmenshan zone with complex geological conditions and developed active faults. This study uses dynamic module of 3 Dimensional Discrete Element Code(3DEC) and acceleration histories of Wenchuan earthquake in Qingping station to investigate the dynamic response process of Dengjiaping tunnel under the combined effects of strong earthquake and fault. Verified by comparing the ground motion of field survey and modeling results, the modeling results have high reliability. The modeling results show that the combined effects of strong earthquake and fault disturb the initial field stress distribution and cause the stress accumulation and stress concentration of tunnel surrounding rock near faulting zone. The high stress concentration results in fault gradual rupture and tunnel gradual failure, which can be qualitatively divided into 5 stages: 1)elastic stress accumulation, 2)local rupture beginning, 3)rupture growth at high speed, 4)spontaneous rupture growth, 5)gradual stability state. This study is helpful to understand the dynamic response process of tunnel surrounding rock under the combined effect of strong earthquakes and faults, and has considerable significance for tunnel safety estimation.
Usually, the earthquake-induced damage to underground structures is lighter than that to above-ground structures. But, under the condition of strong earthquakes and faults, the earthquake-induced damage to underground structures is still considerably serious. On May 12, 2008,Wenchuan earthquake with a magnitude of Ms 8.0 in Sichuan province, China caused tremendous damage to underground structures, especially the tunnels of railways and roads that traverse active faults. Dengjiaping tunnel of Cheng-Lan Railway(Chengdu to Lanzhou, in China) traverses the central fault belt in Longmenshan zone with complex geological conditions and developed active faults. This study uses dynamic module of 3 Dimensional Discrete Element Code(3DEC) and acceleration histories of Wenchuan earthquake in Qingping station to investigate the dynamic response process of Dengjiaping tunnel under the combined effects of strong earthquake and fault. Verified by comparing the ground motion of field survey and modeling results, the modeling results have high reliability. The modeling results show that the combined effects of strong earthquake and fault disturb the initial field stress distribution and cause the stress accumulation and stress concentration of tunnel surrounding rock near faulting zone. The high stress concentration results in fault gradual rupture and tunnel gradual failure, which can be qualitatively divided into 5 stages: 1)elastic stress accumulation, 2)local rupture beginning, 3)rupture growth at high speed, 4)spontaneous rupture growth, 5)gradual stability state. This study is helpful to understand the dynamic response process of tunnel surrounding rock under the combined effect of strong earthquakes and faults, and has considerable significance for tunnel safety estimation.
2013, 21(2): 182-189.
Based on the similarity model material, the trifarious FBG strain sensor which is suitable for model test is developed. It overcomes the shortages of traditional fiber strain sensors. It simplifies the mechanics transferring process. The finite element method is adopted to emphatically analyze the effect of colloid elastic modulus to strain transfer characteristics of the FBG strain sensor. Then the colloid with elastic modulus 300MPa is selected in the experiment. The strain transferring coefficient of the sensor is 0.662, and the sensitivity is 0.794pm -1.The FBG strain sensors are used in tunnel excavation model test to explore the strain distributing situation in surrounding rock by supporting-step-excavation method, supporting-whole-section-excavation method and non-support and whole-section excavation method. The monitoring results of the FBG strain sensors show that surrounding rock is more stable when the supporting-step-excavation method is adopted. The experiment provides reliable data support for research different excavation method and supporting method of the tunnel.
Based on the similarity model material, the trifarious FBG strain sensor which is suitable for model test is developed. It overcomes the shortages of traditional fiber strain sensors. It simplifies the mechanics transferring process. The finite element method is adopted to emphatically analyze the effect of colloid elastic modulus to strain transfer characteristics of the FBG strain sensor. Then the colloid with elastic modulus 300MPa is selected in the experiment. The strain transferring coefficient of the sensor is 0.662, and the sensitivity is 0.794pm -1.The FBG strain sensors are used in tunnel excavation model test to explore the strain distributing situation in surrounding rock by supporting-step-excavation method, supporting-whole-section-excavation method and non-support and whole-section excavation method. The monitoring results of the FBG strain sensors show that surrounding rock is more stable when the supporting-step-excavation method is adopted. The experiment provides reliable data support for research different excavation method and supporting method of the tunnel.
2013, 21(2): 190-198.
Fast classification of surrounding rock mass during construction period is the key measure for construction security and engineering quality. This paper combines the surrounding rock mass classification work during tunnel group construction in Jihuang and Ningji expressway. It proposes a new classification system as a kind of improved national standard BQ classification method. The system is based on many field tests and indoor experiments. The quick field testing method of each classification index is presented. Furthermore, the new classification system is used to cope with the surrounding rock classification in-situ. The classification results are served as the training samples of the evolutionary support vector regression(SVR)algorithm in order to establish the intelligent classification model. Finally, the intelligent model is transferred to an elementary function mathematical model according to SVR theory for the purpose of convenience application. The accuracy of this mathematical classification model is verified by classification examples of tunnel group. Thus, the system offers a new simple fast classification method for surrounding rock mass during tunnel construction period.
Fast classification of surrounding rock mass during construction period is the key measure for construction security and engineering quality. This paper combines the surrounding rock mass classification work during tunnel group construction in Jihuang and Ningji expressway. It proposes a new classification system as a kind of improved national standard BQ classification method. The system is based on many field tests and indoor experiments. The quick field testing method of each classification index is presented. Furthermore, the new classification system is used to cope with the surrounding rock classification in-situ. The classification results are served as the training samples of the evolutionary support vector regression(SVR)algorithm in order to establish the intelligent classification model. Finally, the intelligent model is transferred to an elementary function mathematical model according to SVR theory for the purpose of convenience application. The accuracy of this mathematical classification model is verified by classification examples of tunnel group. Thus, the system offers a new simple fast classification method for surrounding rock mass during tunnel construction period.
2013, 21(2): 199-205.
This paper investigates the P-wave velocity, the engineering quality and the basic quality of rock mass of 10 tunnels at the Sanhekou dam site on Ziwu River. The results show that the high wave speed occupies a large area(more than 70%).The velocity distribution has partition shapes. This shape was particularly obvious in the medium height of the left bank and the high medium of the right bank. The velocity increases as the tunnel depths increase.the low velocity length increases as the tunnel elevation increases. The rock mass quality has the similar variation characteristics to those of the velocity. The high quality value increases as the tunnel depth increases and the tunnel depth showing high quality value increases as the tunnel elevation increase. In local areas similar characteristics can be found in both medium high and high elevations. The P-wave velocity can reflect the engineering quality of rock mass especially for the rock mass having the low value(2000m s-1) and the high value(4000m s-1) of the P-wave velocity. The rock mass having the value between 2000m s-1 to 4000m s-1should combine other index. The correlation between the P-wave velocity and the basic quality of rock mass can illustrate the denotation on the basic quality of rock mass. Preliminary evaluation of the rock mass can be carried out with the correlation between the P-wave velocity and the rock mass and test selectivity to raise reconnaissance efficiency.
This paper investigates the P-wave velocity, the engineering quality and the basic quality of rock mass of 10 tunnels at the Sanhekou dam site on Ziwu River. The results show that the high wave speed occupies a large area(more than 70%).The velocity distribution has partition shapes. This shape was particularly obvious in the medium height of the left bank and the high medium of the right bank. The velocity increases as the tunnel depths increase.the low velocity length increases as the tunnel elevation increases. The rock mass quality has the similar variation characteristics to those of the velocity. The high quality value increases as the tunnel depth increases and the tunnel depth showing high quality value increases as the tunnel elevation increase. In local areas similar characteristics can be found in both medium high and high elevations. The P-wave velocity can reflect the engineering quality of rock mass especially for the rock mass having the low value(2000m s-1) and the high value(4000m s-1) of the P-wave velocity. The rock mass having the value between 2000m s-1 to 4000m s-1should combine other index. The correlation between the P-wave velocity and the basic quality of rock mass can illustrate the denotation on the basic quality of rock mass. Preliminary evaluation of the rock mass can be carried out with the correlation between the P-wave velocity and the rock mass and test selectivity to raise reconnaissance efficiency.
2013, 21(2): 206-215.
The main granite mass surrounding the underground cavern groups of Dagangshan hydropower station have many diabase dikes ().Their types, trends, shapes and scales are different. They run through and interpenetrate the granite body (4-12).
These dikes have broken rocks, low strength, long adhesion fault along the boundaries. They become remarkable weak structure zones of the entire underground caverns, and bring greater difficulties and risks to the excavation and support. Investigations are carried to clearly understand the development characteristics and influence scope of diabase dikes for better guiding in-site construction. The investigations include the following works. Firstly, dike strikes, extension sizes, morphologic features, internal structure and material composition in different elevations are examined in detail. Then, the regional geological structure and evaluative rule are applied to analyze the diabase disks' invasion and the effect process of magmatic hydrothermal activity. Finally, based on systematic geological survey and evaluative rule analysis, the stability of dominant diabase dikes are evaluated reasonably and some significant supporting methods are recommended. In addition, a useful discussion is given about material sectional characteristics of diabase dikes and association between alteration-degree and forming sequence.
The main granite mass surrounding the underground cavern groups of Dagangshan hydropower station have many diabase dikes ().Their types, trends, shapes and scales are different. They run through and interpenetrate the granite body (4-12).
These dikes have broken rocks, low strength, long adhesion fault along the boundaries. They become remarkable weak structure zones of the entire underground caverns, and bring greater difficulties and risks to the excavation and support. Investigations are carried to clearly understand the development characteristics and influence scope of diabase dikes for better guiding in-site construction. The investigations include the following works. Firstly, dike strikes, extension sizes, morphologic features, internal structure and material composition in different elevations are examined in detail. Then, the regional geological structure and evaluative rule are applied to analyze the diabase disks' invasion and the effect process of magmatic hydrothermal activity. Finally, based on systematic geological survey and evaluative rule analysis, the stability of dominant diabase dikes are evaluated reasonably and some significant supporting methods are recommended. In addition, a useful discussion is given about material sectional characteristics of diabase dikes and association between alteration-degree and forming sequence.
2013, 21(2): 216-221.
This paper takes the extended project of Yantan hydropower station as an example. It analyzes the Discrete Smooth Interpolation method. At the same time, it applies the 3D model to the underground construction in Yantan Hydropower Station. The examination shows good results in display, modeling analysis and 3D numerical calculation.
This paper takes the extended project of Yantan hydropower station as an example. It analyzes the Discrete Smooth Interpolation method. At the same time, it applies the 3D model to the underground construction in Yantan Hydropower Station. The examination shows good results in display, modeling analysis and 3D numerical calculation.
2013, 21(2): 222-227.
The exploitation of shallow geothermal energy is the energy exchange process relating to the geotechnical medium. In the view of geotechnical engineering application, this paper briefly elaborates the present domestic and international research about geotechnical-related issues during shallow geothermal energy exploitation. It points out the existing problems and the development orientation. Furthermore, it presents three key scientific issues. They are heat and moisture migration mechanism of soil in heat transfer process, effect of geological structure on heat transfer and effect of heat transfer on mechanical properties of soil. The paper also analyzes their detailed research contents. It points out the great theoretical and practical significance for understanding effect of shallow geothermal energy exploitation on mechanical behavior, rational development and utilization of shallow geothermal energy, and the energy sustainable development.
The exploitation of shallow geothermal energy is the energy exchange process relating to the geotechnical medium. In the view of geotechnical engineering application, this paper briefly elaborates the present domestic and international research about geotechnical-related issues during shallow geothermal energy exploitation. It points out the existing problems and the development orientation. Furthermore, it presents three key scientific issues. They are heat and moisture migration mechanism of soil in heat transfer process, effect of geological structure on heat transfer and effect of heat transfer on mechanical properties of soil. The paper also analyzes their detailed research contents. It points out the great theoretical and practical significance for understanding effect of shallow geothermal energy exploitation on mechanical behavior, rational development and utilization of shallow geothermal energy, and the energy sustainable development.
2013, 21(2): 228-235.
Earthquake is one of the main factors of the generation of a landslide. This paper takes the Daguangbao rockslide triggered by the Ms 8.0 Wenchuan earthquake for example. Based on site investigation, the physical model experiments and numerical model are built to simulate the deformation and failure process of the rockslide. The results of model test match the results of numerical simulation well. The results show that failure model of slide was that the toe and the middle of the slide was shear failure and the top of the slide was tension failure. The tension cracks of slope and the shear oblique layer on the bottom composed the slide boundary. Through the research of acceleration and velocity response, the calculated also resulted that the structural plane played a controlling role in the dynamic response of the rock slope.
Earthquake is one of the main factors of the generation of a landslide. This paper takes the Daguangbao rockslide triggered by the Ms 8.0 Wenchuan earthquake for example. Based on site investigation, the physical model experiments and numerical model are built to simulate the deformation and failure process of the rockslide. The results of model test match the results of numerical simulation well. The results show that failure model of slide was that the toe and the middle of the slide was shear failure and the top of the slide was tension failure. The tension cracks of slope and the shear oblique layer on the bottom composed the slide boundary. Through the research of acceleration and velocity response, the calculated also resulted that the structural plane played a controlling role in the dynamic response of the rock slope.
2013, 21(2): 236-242.
Perilous rock collapse is one of the main types of geological disasters in mountain areas. The root cause leading to perilous rock instability is the crack growth of main control structural surface. Using the theory of linear elastic fracture mechanics analysis methods, the approximate analytical formula to calculate stress intensity factor(SIF) of perilous rock under gravity is established by introducing the stress concentration coefficient method. The SIF can be used for unstable rock control structure surface and cracks collinear. Based on ABAQUS J-integral and Displacement extrapolation method, the progress of perilous rock crack tip stress intensity factor is derived. Instance computational analysis shows that the two numerical results are close to the approximate analytical results, which can verify the reasonableness of calculating perilous rock SIF by ABAQUS.Finally, simulation is given for the impact on stress intensity factor by crack angle and the width of the free surface change. Using ABAQUS to analysis unstable rock, and drawing the trend graph of the stress intensity factor under the influence of various factors can be used to speculate that the instability of the critical condition of the unstable rock.
Perilous rock collapse is one of the main types of geological disasters in mountain areas. The root cause leading to perilous rock instability is the crack growth of main control structural surface. Using the theory of linear elastic fracture mechanics analysis methods, the approximate analytical formula to calculate stress intensity factor(SIF) of perilous rock under gravity is established by introducing the stress concentration coefficient method. The SIF can be used for unstable rock control structure surface and cracks collinear. Based on ABAQUS J-integral and Displacement extrapolation method, the progress of perilous rock crack tip stress intensity factor is derived. Instance computational analysis shows that the two numerical results are close to the approximate analytical results, which can verify the reasonableness of calculating perilous rock SIF by ABAQUS.Finally, simulation is given for the impact on stress intensity factor by crack angle and the width of the free surface change. Using ABAQUS to analysis unstable rock, and drawing the trend graph of the stress intensity factor under the influence of various factors can be used to speculate that the instability of the critical condition of the unstable rock.
2013, 21(2): 243-249.
The accumulation body group is an aggregate of accumulations. It can be seen everywhere along the upper reaches of Jinsha river. It is a big problem to limit the progress of hydropower development at this area. This paper examines the problem using a project of a hydropower station at upper reaches of Jinsha river. This place is strongly affected by geological structure and climate. The ancient accumulation body group lies on the right bank of the upper reaches of Jinsha river. Its size is almost three million tons and its geological structure and origin can not be certain. It is located just only about one kilometer distance to the hydropower station. So it will be a big problem of the hydropower project. Three methods are applied to analyze the problem in this paper. They are topographic feature analysis, rock structure theory, and analogy analysis. Finally, four results are achieved.(1)on the basis of topographic feature, the accumulation group can be divided into four domains.(2)Comprehensive topographic and geological structure feature analysis results are achieved that river blocking had happened at this area.(3)the product period of domain Ⅰ is earlier than the other domains. However, the river blocking was not happened during the period of domain I production. The production of domain Ⅰ just made the river diversion.(4)the structure of domain Ⅱ have a separation grade feature from up to down. This is a typical character belong to debris flow. So the conclusion is that the domain Ⅱ was come from anti-shore. The true river blocking was happened after the domain Ⅱ production.
The accumulation body group is an aggregate of accumulations. It can be seen everywhere along the upper reaches of Jinsha river. It is a big problem to limit the progress of hydropower development at this area. This paper examines the problem using a project of a hydropower station at upper reaches of Jinsha river. This place is strongly affected by geological structure and climate. The ancient accumulation body group lies on the right bank of the upper reaches of Jinsha river. Its size is almost three million tons and its geological structure and origin can not be certain. It is located just only about one kilometer distance to the hydropower station. So it will be a big problem of the hydropower project. Three methods are applied to analyze the problem in this paper. They are topographic feature analysis, rock structure theory, and analogy analysis. Finally, four results are achieved.(1)on the basis of topographic feature, the accumulation group can be divided into four domains.(2)Comprehensive topographic and geological structure feature analysis results are achieved that river blocking had happened at this area.(3)the product period of domain Ⅰ is earlier than the other domains. However, the river blocking was not happened during the period of domain I production. The production of domain Ⅰ just made the river diversion.(4)the structure of domain Ⅱ have a separation grade feature from up to down. This is a typical character belong to debris flow. So the conclusion is that the domain Ⅱ was come from anti-shore. The true river blocking was happened after the domain Ⅱ production.
2013, 21(2): 250-259.
Yakaze landslide is a large unconsolidated soil slope, located in Danba County, Sichuan. The landslide has serious deformation and its possible instability can cause serious disaster consequences. The highly precise GPS monitoring is selected for the landslide. This paper explains the application of GPS monitoring to the selection of landslide points, and data processing methods. Over a long series of GPS monitoring from 2007,it is concluded that this landslide has deformed seriously. The total shift rate of the points on the main body of landslide is 0.6～0.9m per year. On the other hand, site survey results show the surface fissures and sere vegetation at the same time, which Indicates that the landslide deformation is serious. The GPS monitoring result is combined with the surface features (i.e., the surface fissure and the sere vegetation).It is found that rainfall and the river erosion and scour of the Daduhe river determine the activity of the landslide, the serious deformation of the landslide and the serious geologic hazards. Preventive measures are proposed as well. It is suggested to strengthen the monitoring and early warning forecast work. This paper also points out that during the monitoring period, the effects of Wenchuan Earthquake on May 12, 2008 and human engineering activities were monitored on the impact of landslide.
Yakaze landslide is a large unconsolidated soil slope, located in Danba County, Sichuan. The landslide has serious deformation and its possible instability can cause serious disaster consequences. The highly precise GPS monitoring is selected for the landslide. This paper explains the application of GPS monitoring to the selection of landslide points, and data processing methods. Over a long series of GPS monitoring from 2007,it is concluded that this landslide has deformed seriously. The total shift rate of the points on the main body of landslide is 0.6～0.9m per year. On the other hand, site survey results show the surface fissures and sere vegetation at the same time, which Indicates that the landslide deformation is serious. The GPS monitoring result is combined with the surface features (i.e., the surface fissure and the sere vegetation).It is found that rainfall and the river erosion and scour of the Daduhe river determine the activity of the landslide, the serious deformation of the landslide and the serious geologic hazards. Preventive measures are proposed as well. It is suggested to strengthen the monitoring and early warning forecast work. This paper also points out that during the monitoring period, the effects of Wenchuan Earthquake on May 12, 2008 and human engineering activities were monitored on the impact of landslide.
2013, 21(2): 260-268.
A large debris flow disaster was triggered by a heavy rainfall in Hongchun valley, Yingxiu town on August 14, 2010.The debris flow carried out a lot of loose sediments and the total amount is about 80.5104m3.This debris flow led to serious secondary disasters including Minjiang river was blocked, Yingxiu town was flooded, the 213 highway was interrupted, the roadbed and bridge pier of a ramp bridge was destroyed. According to survey, a large number of loose sediments was distributed in the groove before the disaster., the valley was clogged seriously. So the outbreak of debris flow was inevitable in the condition of strong rainfall. To prevent the occurrence of debris flow again, a detailed investigation was carried out around Hongchun valley. The results showed that there were still many loose sediments of about 310.14104m3.Among unstable reserves, the loose sediments were about 98.4104m3.Large-scale debris flow disasters were extremely easy to outbreak in condition of strong rainfall. This paper introduces the debris characteristics, and analyzes its risk and development trend. Furthermore, it formulates the management roadmap of debris flows and puts forward the concept of the whole basin comprehensive treatment. In order to control debris flow disaster happening again, reinforcing management and loose sediment retaining measures are carried out in the middle and upper reaches of the valley. Solid groove bed and platoon guide measures are constructed in the downstream. After the completion of project, during two heavy rainfalls in July and August, 2011,there was not any solid loose sediments into Minjiang river and the treatment project was fine, which can reflect that the whole basin comprehensive treatment design concept has good effect for preventing giant debris flow.
A large debris flow disaster was triggered by a heavy rainfall in Hongchun valley, Yingxiu town on August 14, 2010.The debris flow carried out a lot of loose sediments and the total amount is about 80.5104m3.This debris flow led to serious secondary disasters including Minjiang river was blocked, Yingxiu town was flooded, the 213 highway was interrupted, the roadbed and bridge pier of a ramp bridge was destroyed. According to survey, a large number of loose sediments was distributed in the groove before the disaster., the valley was clogged seriously. So the outbreak of debris flow was inevitable in the condition of strong rainfall. To prevent the occurrence of debris flow again, a detailed investigation was carried out around Hongchun valley. The results showed that there were still many loose sediments of about 310.14104m3.Among unstable reserves, the loose sediments were about 98.4104m3.Large-scale debris flow disasters were extremely easy to outbreak in condition of strong rainfall. This paper introduces the debris characteristics, and analyzes its risk and development trend. Furthermore, it formulates the management roadmap of debris flows and puts forward the concept of the whole basin comprehensive treatment. In order to control debris flow disaster happening again, reinforcing management and loose sediment retaining measures are carried out in the middle and upper reaches of the valley. Solid groove bed and platoon guide measures are constructed in the downstream. After the completion of project, during two heavy rainfalls in July and August, 2011,there was not any solid loose sediments into Minjiang river and the treatment project was fine, which can reflect that the whole basin comprehensive treatment design concept has good effect for preventing giant debris flow.
2013, 21(2): 269-281.
The Wenchuan M 8.0 earthquake on May 12, 2008 caused thousands of rock falls and landslides. The Daguangbao landslide in Anxian County is the largest landslide site. Its failed slope volume is up to 1billion m3.Its formation mechanism and kinematics attract a wide attention of scholars at domestic and abroad. Based on a series survey of the landslide field measurement and laboratory experiments, this paper presents some new understandings of the landslide as follows.(1)the landslide is a wedge and trough shaped fall. The bottom Sinianperiod dolomitite layer functioned as the main surface of rupture. The early X-tectonic fractures that orthogonal to the layer functioned as a side surface of rupture. The intersection line of two control planes tends to 64with dip angle 12.(2)the Huangdongzi valley in front of landslide is the outlet of the surface rupture. The landslide rapidly slipped into the valley. The moving mass was obstructed and braked by the valley slope on its left side. The upper part of landslide mass passed over the left valley slope and developed a debris flow.(3)the rupture plan of the landslide is along a layer of Sinian dolomite rock mass. It experienced strong karstification and became a band layer of sand-soil. This sand-soil layer during the strong vibration changed its performance caused by the suddenly increase of excess pore pressure. Even then, it developed into a fluidal structure layer. This may be the main formation mechanism of this huge landslide. Daguangbao landslide may be the new model of mountain collapse that caused by earthquake. The research on the analysis of the evolution and the stability of the slope has an important meaning.
The Wenchuan M 8.0 earthquake on May 12, 2008 caused thousands of rock falls and landslides. The Daguangbao landslide in Anxian County is the largest landslide site. Its failed slope volume is up to 1billion m3.Its formation mechanism and kinematics attract a wide attention of scholars at domestic and abroad. Based on a series survey of the landslide field measurement and laboratory experiments, this paper presents some new understandings of the landslide as follows.(1)the landslide is a wedge and trough shaped fall. The bottom Sinianperiod dolomitite layer functioned as the main surface of rupture. The early X-tectonic fractures that orthogonal to the layer functioned as a side surface of rupture. The intersection line of two control planes tends to 64with dip angle 12.(2)the Huangdongzi valley in front of landslide is the outlet of the surface rupture. The landslide rapidly slipped into the valley. The moving mass was obstructed and braked by the valley slope on its left side. The upper part of landslide mass passed over the left valley slope and developed a debris flow.(3)the rupture plan of the landslide is along a layer of Sinian dolomite rock mass. It experienced strong karstification and became a band layer of sand-soil. This sand-soil layer during the strong vibration changed its performance caused by the suddenly increase of excess pore pressure. Even then, it developed into a fluidal structure layer. This may be the main formation mechanism of this huge landslide. Daguangbao landslide may be the new model of mountain collapse that caused by earthquake. The research on the analysis of the evolution and the stability of the slope has an important meaning.
2013, 21(2): 282-288.
Rapid loess flowslides induced by irrigation often occur in the loess irrigation area, which have resulted in serious damages to farmlands, residential houses and loss of lives. A typical case of the Gaolou flowslide in Guanzhong irrigation area, Shaanxi Province of China, was investigated. Laboratory tests suggest that the loess flowslide had a loose structure and that the saturated water content was higher than the liquid limit. As the loess slope started to fail, the saturated loess of the sliding zone quickly fluidized and then flowed on the relative dry-hard path because the loess structure was damaged by the shear force to produce a high excess pore pressure in the lower portion of the displaced mass. Excess pore pressure was produced between the displaced mass and the ground surface because of pore pressure dissipation on the dry ground. So the shearing zone was within the lower portion of the displaced mass other than on the ground surface, which made part of the displaced mass cohere on the ground as observed at the site. The triaxial tests for the loess specimens suggest that fluidization occurred at the source area in the beginning and maintains in the moving process, which produced a quick and long run-out flow. The modified Sassa K.simulation model for landslide motion is applied to simulate the motion scenarios of this case. And the simulated results fit the actual ones of site investigation.
Rapid loess flowslides induced by irrigation often occur in the loess irrigation area, which have resulted in serious damages to farmlands, residential houses and loss of lives. A typical case of the Gaolou flowslide in Guanzhong irrigation area, Shaanxi Province of China, was investigated. Laboratory tests suggest that the loess flowslide had a loose structure and that the saturated water content was higher than the liquid limit. As the loess slope started to fail, the saturated loess of the sliding zone quickly fluidized and then flowed on the relative dry-hard path because the loess structure was damaged by the shear force to produce a high excess pore pressure in the lower portion of the displaced mass. Excess pore pressure was produced between the displaced mass and the ground surface because of pore pressure dissipation on the dry ground. So the shearing zone was within the lower portion of the displaced mass other than on the ground surface, which made part of the displaced mass cohere on the ground as observed at the site. The triaxial tests for the loess specimens suggest that fluidization occurred at the source area in the beginning and maintains in the moving process, which produced a quick and long run-out flow. The modified Sassa K.simulation model for landslide motion is applied to simulate the motion scenarios of this case. And the simulated results fit the actual ones of site investigation.
2013, 21(2): 289-296.
Many kinds of complex rockfall geological disasters are induced by the mining at the upstream side of the Yangshui river basin in Guizhou province. The cracking-topple model of failure is taken as an example in this article. Based on the analysis of slope structure, the process of the rockfall developing is studied. It includes the exerted force, the compression and the dilatancy in rock mass. During the study, the spacing-stress-analysis theory of rock mechanics is used. The DEM simulation is used to verifying the deformation behavior and failure mode. The conclusion can be drawn as follow. The rockfall is triggered by the Phosphate mining. Then the stress-strain adjustment and deformation of the rock mass are caused so that the rock mass dilatancy leads to instability of rock dumping, and then cause collapse. The process of load and deformation can be divided into four phases as follows. The discontinuities are stretched and cut through. The compressed rock mass deformed. The rock mass gets dilatancy. And the rock mass gets failure. The adjustments of the stress and strain, the deformation and the cracks influence each other.
Many kinds of complex rockfall geological disasters are induced by the mining at the upstream side of the Yangshui river basin in Guizhou province. The cracking-topple model of failure is taken as an example in this article. Based on the analysis of slope structure, the process of the rockfall developing is studied. It includes the exerted force, the compression and the dilatancy in rock mass. During the study, the spacing-stress-analysis theory of rock mechanics is used. The DEM simulation is used to verifying the deformation behavior and failure mode. The conclusion can be drawn as follow. The rockfall is triggered by the Phosphate mining. Then the stress-strain adjustment and deformation of the rock mass are caused so that the rock mass dilatancy leads to instability of rock dumping, and then cause collapse. The process of load and deformation can be divided into four phases as follows. The discontinuities are stretched and cut through. The compressed rock mass deformed. The rock mass gets dilatancy. And the rock mass gets failure. The adjustments of the stress and strain, the deformation and the cracks influence each other.
2013, 21(2): 297-303.
This paper analyzes the geological hazards induced by typhoon in Wenzhou. The landslide with arbor was most typical. Physical model experiments well reappear the the slope deformation-failure process caused by typhoon. The connection of failure phenomena between bare and arbor slope was analyzed after the induction and summarization on the characteristics of deformation and failure. Then a comprehensive analysis is made. The deformation and failure mechanism of typhoon landside is initially obtained. The results show that the slope is more likely to be damaged coupling typhoon with arbor after soil is softened by stronger rainfall. The main actions of typhoon to slope are the rain wash and softening caused by rainstorm with dynamic effect of gale, which is significantly different from general landside. When arbor roots are above the sliding zone, the roots go against the stability of slope under typhoon calamity. Soil mass failure may be caused in slope front areas. A phenomenon of wind liquefaction is found in the model testing. The reason is that soil liquefaction is formed with the cyclic loading of fluctuating wind to soil around root. It aggravates the wind throw of trees, makes the slope destruction complicated. Therefore, the deformation and failure mechanism of typhoon landslide is summarized asthe rain washsoil softeningwind actionarbor swingingsoil looseningcrack developmentfront soil failurelandslide formation.
This paper analyzes the geological hazards induced by typhoon in Wenzhou. The landslide with arbor was most typical. Physical model experiments well reappear the the slope deformation-failure process caused by typhoon. The connection of failure phenomena between bare and arbor slope was analyzed after the induction and summarization on the characteristics of deformation and failure. Then a comprehensive analysis is made. The deformation and failure mechanism of typhoon landside is initially obtained. The results show that the slope is more likely to be damaged coupling typhoon with arbor after soil is softened by stronger rainfall. The main actions of typhoon to slope are the rain wash and softening caused by rainstorm with dynamic effect of gale, which is significantly different from general landside. When arbor roots are above the sliding zone, the roots go against the stability of slope under typhoon calamity. Soil mass failure may be caused in slope front areas. A phenomenon of wind liquefaction is found in the model testing. The reason is that soil liquefaction is formed with the cyclic loading of fluctuating wind to soil around root. It aggravates the wind throw of trees, makes the slope destruction complicated. Therefore, the deformation and failure mechanism of typhoon landslide is summarized asthe rain washsoil softeningwind actionarbor swingingsoil looseningcrack developmentfront soil failurelandslide formation.
2013, 21(2): 304-310.
High rock slope with laminated structure is inclined to generate toppling deformation. Plenty of large size landslides in mountain areas occurred in the toppling rock mass slope. Therefore, it is important for landslides stability evaluation to study on the mechanism of topplinglandslide process. In this paper, the Yangtai landslide is taken as a case to study the toppling-landslide process. Based on the engineering geological survey of the Yangtai landslide, the failure process and triggering factors are studied by combination of qualitative analysis, discrete element and limited element methods. The results indicate that the failure process of the Yangtai landslide include rock mass unloading, toppling deformation, sliding, and secondary landslide.
High rock slope with laminated structure is inclined to generate toppling deformation. Plenty of large size landslides in mountain areas occurred in the toppling rock mass slope. Therefore, it is important for landslides stability evaluation to study on the mechanism of topplinglandslide process. In this paper, the Yangtai landslide is taken as a case to study the toppling-landslide process. Based on the engineering geological survey of the Yangtai landslide, the failure process and triggering factors are studied by combination of qualitative analysis, discrete element and limited element methods. The results indicate that the failure process of the Yangtai landslide include rock mass unloading, toppling deformation, sliding, and secondary landslide.
2013, 21(2): 311-316.
Mechanical behaves of coarse grained soil is greatly influenced by the content of coarse gravels. The shear characteristics of four groups of strong weathered basalt coarse grained soils are investigated under different coarse gravel contents on large-scale direct shear apparatus to obtain the strength and deformation parameters in this paper. Based on the theory of discrete element method(DEM),four direct shear samples under vertical pressure of 100kPa are carried out using the parallel bond model(PBM)with multiplicity coarse gravel content. The parameters are calibrated. Then we simulate the relationship among shear stress, shear deformation and vertical deformation. The simulation also simultaneously analyzes the particle movement and force in order to settle the mechanism for the fact that coarse content affects shearing properties. Results show that the inherence for shear strength increasing with the increase of coarse gravel content at the same vertical stress is due to the increase of particle stiffness and the increase of friction coefficient. The peak of stress-strain curve can be well simulated by the PBM.But the soften segment cannot be well fitted. Simulation of shear-vertical displacement curve does not fit perfectly to the testing value. The effects of coarse particles on the peak force chains were significantly evident than those of fine particles during the shearing process. It is considered that the vortex area is the thickness of shear band, approximately 1/3-1/5 of the height of shear box.
Mechanical behaves of coarse grained soil is greatly influenced by the content of coarse gravels. The shear characteristics of four groups of strong weathered basalt coarse grained soils are investigated under different coarse gravel contents on large-scale direct shear apparatus to obtain the strength and deformation parameters in this paper. Based on the theory of discrete element method(DEM),four direct shear samples under vertical pressure of 100kPa are carried out using the parallel bond model(PBM)with multiplicity coarse gravel content. The parameters are calibrated. Then we simulate the relationship among shear stress, shear deformation and vertical deformation. The simulation also simultaneously analyzes the particle movement and force in order to settle the mechanism for the fact that coarse content affects shearing properties. Results show that the inherence for shear strength increasing with the increase of coarse gravel content at the same vertical stress is due to the increase of particle stiffness and the increase of friction coefficient. The peak of stress-strain curve can be well simulated by the PBM.But the soften segment cannot be well fitted. Simulation of shear-vertical displacement curve does not fit perfectly to the testing value. The effects of coarse particles on the peak force chains were significantly evident than those of fine particles during the shearing process. It is considered that the vortex area is the thickness of shear band, approximately 1/3-1/5 of the height of shear box.
2013, 21(2): 317-323.
The change of loessial soil microstructure before and after damages is analyzed by observing different cross-sections of specimen with a scanning electron microscope and a polarizing microscope. The results show that at pre-loading, the loessial soil has granulometric bracket contact microstructure with quartz, feldspar, illite, kaolinite and other minerals distributed randomly and astatically. The uniaxial compression process of the loessial soil can be divided into three stages. The first stage is a compacted phase, when microcracks close up and macropores become microcracks. The second stage is an initial damage phase which begins prior to peak stress. The soil microstructure turns to a lightly cemented mosaic microporous structure with slippages produced between particles. The original and newborn small cracks get wider and longer. The third stage is a rapid damage development phase which occurs after peak stress. The pores and cracks are interconnected, and the minerals have a pronounced directional characteristic. On this basis, constitutive damage equations are established by applying statistical damage theory using the characteristic of loessial soil micro-unit strength following the Weibull stochastic distribution, and considering the moisture content and damage threshold of loessial soil. Verification is carried out by taking the results of loessial soil uniaxial compression tests. The comparison of calculated results with test results shows that this model can properly describe the complete stress-strain test curves for loessial soil deformation and failure.
The change of loessial soil microstructure before and after damages is analyzed by observing different cross-sections of specimen with a scanning electron microscope and a polarizing microscope. The results show that at pre-loading, the loessial soil has granulometric bracket contact microstructure with quartz, feldspar, illite, kaolinite and other minerals distributed randomly and astatically. The uniaxial compression process of the loessial soil can be divided into three stages. The first stage is a compacted phase, when microcracks close up and macropores become microcracks. The second stage is an initial damage phase which begins prior to peak stress. The soil microstructure turns to a lightly cemented mosaic microporous structure with slippages produced between particles. The original and newborn small cracks get wider and longer. The third stage is a rapid damage development phase which occurs after peak stress. The pores and cracks are interconnected, and the minerals have a pronounced directional characteristic. On this basis, constitutive damage equations are established by applying statistical damage theory using the characteristic of loessial soil micro-unit strength following the Weibull stochastic distribution, and considering the moisture content and damage threshold of loessial soil. Verification is carried out by taking the results of loessial soil uniaxial compression tests. The comparison of calculated results with test results shows that this model can properly describe the complete stress-strain test curves for loessial soil deformation and failure.
2013, 21(2): 324-329.
Solidification is one of the chemical methods for collapsible loess treatment. For better solidification effect, sodium silicate is modified by various methods. The mechanical strength of loess reinforced with compound modification sodium silicate is studied in this paper. The physical components such as chemical composition and mineral composition, microstructure are tested and analyzed by carrying out X-ray diffraction, scanning electron microscope and mercury porosimeter. The results show that the mechanical strength of reinforced loess is significantly improved. Diffraction intensity of parts of the mineral is increasing in the X-ray diffraction patterns. Low density amorphous phase peak groups still exists. The SEM images show that crack of gel films is reduced, and bonding relatively is tended to close. Surface area of pores is increased and mode pore diameters are reduced after sodium silicate is modified. The mechanism of loess reinforced with the compound modification sodium silicate is due to reinforcement of the bond strength of cement in microstructure and formation of three dimensional networks of frame.
Solidification is one of the chemical methods for collapsible loess treatment. For better solidification effect, sodium silicate is modified by various methods. The mechanical strength of loess reinforced with compound modification sodium silicate is studied in this paper. The physical components such as chemical composition and mineral composition, microstructure are tested and analyzed by carrying out X-ray diffraction, scanning electron microscope and mercury porosimeter. The results show that the mechanical strength of reinforced loess is significantly improved. Diffraction intensity of parts of the mineral is increasing in the X-ray diffraction patterns. Low density amorphous phase peak groups still exists. The SEM images show that crack of gel films is reduced, and bonding relatively is tended to close. Surface area of pores is increased and mode pore diameters are reduced after sodium silicate is modified. The mechanism of loess reinforced with the compound modification sodium silicate is due to reinforcement of the bond strength of cement in microstructure and formation of three dimensional networks of frame.
2013, 21(2): 330-335.
Using soft dredger fill in Tianjin Binhai New Area as materials, grey correlation analysis of structural strength of soft dredger is carried out after structural strength formed under different confining pressure, deviator pressure, and drainage condition. The results show that many factors can cause the growth of structural strength of soft dredger. The drainage is the critical influence factor. For the soft dredger fill with weaker initial structural strength, the influence of the confining pressure on the growth of structural strength is greater than that of deviator pressure. For the soft dredger fill has stronger initial structural strength, the influence of the deviator pressure is greater than confining pressure.
Using soft dredger fill in Tianjin Binhai New Area as materials, grey correlation analysis of structural strength of soft dredger is carried out after structural strength formed under different confining pressure, deviator pressure, and drainage condition. The results show that many factors can cause the growth of structural strength of soft dredger. The drainage is the critical influence factor. For the soft dredger fill with weaker initial structural strength, the influence of the confining pressure on the growth of structural strength is greater than that of deviator pressure. For the soft dredger fill has stronger initial structural strength, the influence of the deviator pressure is greater than confining pressure.
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