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Editor Work2009 Vol. 17, No. 4
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2009, 17(4): 433-444.
Abstract
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A large scale of mountain collapse occurred in Jiwei mountain, Wulong county. Chongqing City on June 5, 2009. Its volume is of 5106 m3. The limestone rock mass was cut by a set of discontinuities into a shape of building blocks, and slipped down along a low angle dip inter-bedded shale plane. The high speed moving mass blocked the valley. The valley was 200 m wide and 50 deep. The debris accumulated in the valley. It is of 30 m thick in general and 2200 m long. The debris destroyed 12 houses, killed 10 people, buried 64 people, and injured 8 people. Based on site investigation, the remote sensing, three dimension laser scanning technologies, this paper provides a detailed description on the landslide. It then gives the analysis on the mechanism of the landslide. The results show that the causes of the Jiweishan landslide are complex geological settings, long term loading stress, karst effect and the underground mining activities. The triggering factor is the failure of a relatively small key rock block in front of the main landslide body. The key block had been functioned as a barrier or shear key to make the main landslide body stable. There will be a big attribution if such case can be studied further. It can provide the significant experience on dealing with this kind of landslide and how to provide advice on early warning and remediation project on similar cases in south western China under such complex geological setting.
A large scale of mountain collapse occurred in Jiwei mountain, Wulong county. Chongqing City on June 5, 2009. Its volume is of 5106 m3. The limestone rock mass was cut by a set of discontinuities into a shape of building blocks, and slipped down along a low angle dip inter-bedded shale plane. The high speed moving mass blocked the valley. The valley was 200 m wide and 50 deep. The debris accumulated in the valley. It is of 30 m thick in general and 2200 m long. The debris destroyed 12 houses, killed 10 people, buried 64 people, and injured 8 people. Based on site investigation, the remote sensing, three dimension laser scanning technologies, this paper provides a detailed description on the landslide. It then gives the analysis on the mechanism of the landslide. The results show that the causes of the Jiweishan landslide are complex geological settings, long term loading stress, karst effect and the underground mining activities. The triggering factor is the failure of a relatively small key rock block in front of the main landslide body. The key block had been functioned as a barrier or shear key to make the main landslide body stable. There will be a big attribution if such case can be studied further. It can provide the significant experience on dealing with this kind of landslide and how to provide advice on early warning and remediation project on similar cases in south western China under such complex geological setting.
2009, 17(4): 445-448.
A large rock fall in Houziyan, Shunhe, Hanyuan happened on 23:30 pm, August 6, 2009, completely damming Daduhe River for 4.5 hours, forming a ten kilometer long dammed reservoir and inundating road S306. Sichuan Bureau of land and mineral resources invited expert group headed by Prof. Huang Runqiu to have a field investigation on August 7. Based on the analysis of the topography, texture of the slope and induced factors and with help of Laser scanning, the expert group provided a scheme for removing risk rockmass step by step, No. A rock block about 10000 m3 was successfully removed by exploding at 19: 10 of August 8, which provide a base for new S306 and recovery of the old S306.
A large rock fall in Houziyan, Shunhe, Hanyuan happened on 23:30 pm, August 6, 2009, completely damming Daduhe River for 4.5 hours, forming a ten kilometer long dammed reservoir and inundating road S306. Sichuan Bureau of land and mineral resources invited expert group headed by Prof. Huang Runqiu to have a field investigation on August 7. Based on the analysis of the topography, texture of the slope and induced factors and with help of Laser scanning, the expert group provided a scheme for removing risk rockmass step by step, No. A rock block about 10000 m3 was successfully removed by exploding at 19: 10 of August 8, which provide a base for new S306 and recovery of the old S306.
2009, 17(4): 449-454.
The 1920 Haiyuan Earthquake caused a great number of loess landslides, and resulted in more than 100,000 deaths. This paper investigates the Dangjiacha landslide, a typical rapid and long run-out landslide located in Xiji County triggered by Haiyuan earthquake. Representative soils on sliding surface were collected for soil tests. By using the advanced DPRI ring shear apparatus, a series of ring shear tests were carried out to study the initiation mechanism of Dangjiacha landslide under the seismic wave loading of EL-Centro Earthquake. This Earthquake occurred on May 18, 1940 in United States. The ring shear test results show that when the earthquake happened, the sliding surface liquefaction occurred on potential sliding surface of landslide. It was an important reason for taking place of rapid and long run-out landslide. Meanwhile, a large shear displacement (2.03 m) and a high pore water pressure (104 kPa) could be generated and a high velocity could be got for the sliding mass, which supplied a necessary condition for the generation of rapid and long run-out landslide.
The 1920 Haiyuan Earthquake caused a great number of loess landslides, and resulted in more than 100,000 deaths. This paper investigates the Dangjiacha landslide, a typical rapid and long run-out landslide located in Xiji County triggered by Haiyuan earthquake. Representative soils on sliding surface were collected for soil tests. By using the advanced DPRI ring shear apparatus, a series of ring shear tests were carried out to study the initiation mechanism of Dangjiacha landslide under the seismic wave loading of EL-Centro Earthquake. This Earthquake occurred on May 18, 1940 in United States. The ring shear test results show that when the earthquake happened, the sliding surface liquefaction occurred on potential sliding surface of landslide. It was an important reason for taking place of rapid and long run-out landslide. Meanwhile, a large shear displacement (2.03 m) and a high pore water pressure (104 kPa) could be generated and a high velocity could be got for the sliding mass, which supplied a necessary condition for the generation of rapid and long run-out landslide.
2009, 17(4): 455-462.
Field geological investigations after earthquakes show that the effect of vertical seismic force is very evident, whereas only the effect of horizontal seismic force is concerned in conventional analysis of dynamic response of slopes. Collapsing and sliding responses of slope near epicenter and its running out process triggered by single and combined actions with time difference, local condtions and spatial heterogeneity of P and S seismic waves are elaborated. The formation mechanism and key controlling factors of the slope collapsing and sliding are confirmed. The result of numerical simulation shows that the slope collapsing and sliding are triggered by the combined action of seismic P- and S-waves, i.e. the coupled effect of vertical periodic tension and compression and horizontal periodic shearing. For the vertical tension of P-wave is dominant, tension and shear fractures would appear in slope body. On the other hand, combined action between periodic tension and compression of P-wave and periodic shearing of S-wave is the key controlling factor inducing slope collapsing and sliding on the conditions of known seismic tectonics, structure and tectonics of slope mass, weathering degree of rock mass and physical and mechanical parameters of slope body. At the same time, slope topography is the key controlling factor leading to collision and debris flow of slope mass fractured in latter process. It is of great theoretical and practical value in studying collapsing and sliding of slope triggered by seismic loads.
Field geological investigations after earthquakes show that the effect of vertical seismic force is very evident, whereas only the effect of horizontal seismic force is concerned in conventional analysis of dynamic response of slopes. Collapsing and sliding responses of slope near epicenter and its running out process triggered by single and combined actions with time difference, local condtions and spatial heterogeneity of P and S seismic waves are elaborated. The formation mechanism and key controlling factors of the slope collapsing and sliding are confirmed. The result of numerical simulation shows that the slope collapsing and sliding are triggered by the combined action of seismic P- and S-waves, i.e. the coupled effect of vertical periodic tension and compression and horizontal periodic shearing. For the vertical tension of P-wave is dominant, tension and shear fractures would appear in slope body. On the other hand, combined action between periodic tension and compression of P-wave and periodic shearing of S-wave is the key controlling factor inducing slope collapsing and sliding on the conditions of known seismic tectonics, structure and tectonics of slope mass, weathering degree of rock mass and physical and mechanical parameters of slope body. At the same time, slope topography is the key controlling factor leading to collision and debris flow of slope mass fractured in latter process. It is of great theoretical and practical value in studying collapsing and sliding of slope triggered by seismic loads.
2009, 17(4): 463-468.
This is a summary speech for the 3th China national geoengineering conference co-organized by 4 Chinese societies in geoengineering in Chengdu, June 11~18, 2009.
The conference has shown the following 4 features in the research of geoengineering in the recent years: (1) Fundamental researches have been enhanced. A series of progresses have been made in tests of problematic soils, the dynamics of rock and soil has become a new hotspot after Wenchuan earthquake, and the theoretical exploration for the basic behaviors of rock and soil has attracted more attention, (2) Engineering induced geohazards has been emphasized in research, (3) New techniques have been developed rapidly, and (4) education, training, standardization in geoengineering have been widely concerned.
An expectation for the future development pointed out that the following aspects are to be emphasized: theoretical studies on basic properties and structure controlled behaviors of rock and soil under the condition with dynamics, coupled multiple physical and chemical field, high geostress and interaction between engineering and geoenvironment; solutions for special geo-engineering problems; techniques for testing, monitoring and reinforcement, etc.
This is a summary speech for the 3th China national geoengineering conference co-organized by 4 Chinese societies in geoengineering in Chengdu, June 11~18, 2009.
The conference has shown the following 4 features in the research of geoengineering in the recent years: (1) Fundamental researches have been enhanced. A series of progresses have been made in tests of problematic soils, the dynamics of rock and soil has become a new hotspot after Wenchuan earthquake, and the theoretical exploration for the basic behaviors of rock and soil has attracted more attention, (2) Engineering induced geohazards has been emphasized in research, (3) New techniques have been developed rapidly, and (4) education, training, standardization in geoengineering have been widely concerned.
An expectation for the future development pointed out that the following aspects are to be emphasized: theoretical studies on basic properties and structure controlled behaviors of rock and soil under the condition with dynamics, coupled multiple physical and chemical field, high geostress and interaction between engineering and geoenvironment; solutions for special geo-engineering problems; techniques for testing, monitoring and reinforcement, etc.
2009, 17(4): 469-475.
The excavation and stability of hundred meters high rock slopes in water conservancy project construction are of important technical issues . This paper bases on the abundant geological investigation of a construction site and examines the associated cut slope with height of 330 m in a large Hydroelectric Station in southwest China. The reactive deformation of the high rock slope with great sloping ratio is studied under the condition of complex geological conditions and high in-situ stresses. The study is systematical. The basic laws and special characteristics of the deformation responses are acquired and can be classified as follows: (1) During the slope excavation, there is a strong synchronism between the slope deformation and its excavation process. (2) The high slope deformation is mainly influenced by excavation. (3) The slope deformation generally is weakened as increase of the distance between the excavation plane and the monitoring position. Immediately after its formation, the cut slope had small deformation and the deformed depth was also shallow. After having been excavated for 12 to 18 months, the cut slope was stable. The findings are helpful to the design and construction of similar high cut slopes.
The excavation and stability of hundred meters high rock slopes in water conservancy project construction are of important technical issues . This paper bases on the abundant geological investigation of a construction site and examines the associated cut slope with height of 330 m in a large Hydroelectric Station in southwest China. The reactive deformation of the high rock slope with great sloping ratio is studied under the condition of complex geological conditions and high in-situ stresses. The study is systematical. The basic laws and special characteristics of the deformation responses are acquired and can be classified as follows: (1) During the slope excavation, there is a strong synchronism between the slope deformation and its excavation process. (2) The high slope deformation is mainly influenced by excavation. (3) The slope deformation generally is weakened as increase of the distance between the excavation plane and the monitoring position. Immediately after its formation, the cut slope had small deformation and the deformed depth was also shallow. After having been excavated for 12 to 18 months, the cut slope was stable. The findings are helpful to the design and construction of similar high cut slopes.
2009, 17(4): 476-482.
The primary deformation and failure mechanism of reservoir bank slopes with anti-dip rock mass are dominated by the geological structure, stratum lithology and inducing loading factors. The Longpan slope is located at the right embankment of Dale dam on Jinsha River. It consists of anti-dip alternate sandstone and slate strata. The thick riverbed sediments form a soft basement of the slope. This paper takes the Longpan slope as a case study and uses the discrete element method to simulate the deformation evolution process of the slope rock mass. Based on the viewpoint of time-dependent deformation, the strength reduction method is introduced to evaluate the factor of safety of the anti-dip rock slope. The numerical modeling result verifies that the geological mechanism is actually a deep-seated gravitational bending deformation. In accordance with the expansion way of the shear yielding zones, the progressive shear failure mechanism of the large-scale anti-dip rock masses with effects of interbedded strata and soft foundation is proposed in the paper. This mechanism is believed to have significance in the slope failure prevention.
The primary deformation and failure mechanism of reservoir bank slopes with anti-dip rock mass are dominated by the geological structure, stratum lithology and inducing loading factors. The Longpan slope is located at the right embankment of Dale dam on Jinsha River. It consists of anti-dip alternate sandstone and slate strata. The thick riverbed sediments form a soft basement of the slope. This paper takes the Longpan slope as a case study and uses the discrete element method to simulate the deformation evolution process of the slope rock mass. Based on the viewpoint of time-dependent deformation, the strength reduction method is introduced to evaluate the factor of safety of the anti-dip rock slope. The numerical modeling result verifies that the geological mechanism is actually a deep-seated gravitational bending deformation. In accordance with the expansion way of the shear yielding zones, the progressive shear failure mechanism of the large-scale anti-dip rock masses with effects of interbedded strata and soft foundation is proposed in the paper. This mechanism is believed to have significance in the slope failure prevention.
2009, 17(4): 483-488.
The Gelongbu landslide located at the reservoir region of Jishixia hydropower station dam in upper reach Yellow River. Its volume was of 50.4106 m3. It had 4 regions. The result of landslide investigation indicates that the formation mechanism of Gelongbu landslide is sliding-fracturing. The landslide debris flew down with a high speed on the right side of Yellow River and hit a hill. . Part of its debris flew across the river and deposited on the left side. Its debris had blocked the river for several hundred years and formed a landslide dam like. The thickness of sediment in the landslide dam lake was 30 m based on the measurement of this investigation. Height of the landslide dam was about 100 m and water depth of the lake was about 70 m based on the preliminary analysis of this investigation. The epoch of landslide is Q4. The debris were still left on left and right sides of Yellow River. The Yellow river path was changed at this location. It was possibly due to a sudden collapse of the landslide dam.
The Gelongbu landslide located at the reservoir region of Jishixia hydropower station dam in upper reach Yellow River. Its volume was of 50.4106 m3. It had 4 regions. The result of landslide investigation indicates that the formation mechanism of Gelongbu landslide is sliding-fracturing. The landslide debris flew down with a high speed on the right side of Yellow River and hit a hill. . Part of its debris flew across the river and deposited on the left side. Its debris had blocked the river for several hundred years and formed a landslide dam like. The thickness of sediment in the landslide dam lake was 30 m based on the measurement of this investigation. Height of the landslide dam was about 100 m and water depth of the lake was about 70 m based on the preliminary analysis of this investigation. The epoch of landslide is Q4. The debris were still left on left and right sides of Yellow River. The Yellow river path was changed at this location. It was possibly due to a sudden collapse of the landslide dam.
2009, 17(4): 489-495.
Stability of slopes comprising colluvium is very important to the hydropower station construction in the southeast of China especially. The key tasks are to find the answers for the questions: the reasons of accumulation formation, mechanical parameter values and slope stability under different conditions. This paper analyzes the typical engineering geology condition of the dam site zone of a hydropower station at Gushui. The lower zone is slate and the upper is colluvium. The paper examines the history of the engineering geology condition at this region. It further examines the formation of the colluvium at the upper zone and obtains the topping deformation of slate at the lower zone. Due to schlep effect, the colluvium was formed. The rock-soil materials on the top of slope move down in schlep effect of outwash. The colluvium has a clear layering structure. The slate experiences a continuous increase in under the effect of tectonic movement, incised valley and weathering unloading and also the weight of upper colluvium. Breaking of the slate is happened and lead to topping deformation. Based on the analysis of physical and mechanical characteristics of the colluvium, and combined with the survey of engineering geology condition, the mechanism of failure and deformation of the colluvium slope is obtained. Its contains the wholly slide failure along the weakly layer and the locally arc slide failure.
Stability of slopes comprising colluvium is very important to the hydropower station construction in the southeast of China especially. The key tasks are to find the answers for the questions: the reasons of accumulation formation, mechanical parameter values and slope stability under different conditions. This paper analyzes the typical engineering geology condition of the dam site zone of a hydropower station at Gushui. The lower zone is slate and the upper is colluvium. The paper examines the history of the engineering geology condition at this region. It further examines the formation of the colluvium at the upper zone and obtains the topping deformation of slate at the lower zone. Due to schlep effect, the colluvium was formed. The rock-soil materials on the top of slope move down in schlep effect of outwash. The colluvium has a clear layering structure. The slate experiences a continuous increase in under the effect of tectonic movement, incised valley and weathering unloading and also the weight of upper colluvium. Breaking of the slate is happened and lead to topping deformation. Based on the analysis of physical and mechanical characteristics of the colluvium, and combined with the survey of engineering geology condition, the mechanism of failure and deformation of the colluvium slope is obtained. Its contains the wholly slide failure along the weakly layer and the locally arc slide failure.
2009, 17(4): 496-502.
The Cigu landslide is located near a reservoir region. Its stability would be largely influenced after water is stored in the reservoir because the water level will be at 1/3 of the landslide slope height. Geological conditions of the landslide are complex and the progressive mechanism is toppling or slip. This paper examines the slide zone clay shear strength with different moisture contents. The test results show that the cohesion has a good correlation with the moisture content but the friction does not have a good correlation. The landslide stability before and after the storage of reservoir water is analyzed with limit equilibrium method combined with FEA under conditions of natural heavy-rain and earthquake. The numerical analysis shows that the landslide would be stable after water storage under native and rainstorm conditions, but unstable under earthquake. The factor of safety is less than 1, which indicates the landslide instable.
The Cigu landslide is located near a reservoir region. Its stability would be largely influenced after water is stored in the reservoir because the water level will be at 1/3 of the landslide slope height. Geological conditions of the landslide are complex and the progressive mechanism is toppling or slip. This paper examines the slide zone clay shear strength with different moisture contents. The test results show that the cohesion has a good correlation with the moisture content but the friction does not have a good correlation. The landslide stability before and after the storage of reservoir water is analyzed with limit equilibrium method combined with FEA under conditions of natural heavy-rain and earthquake. The numerical analysis shows that the landslide would be stable after water storage under native and rainstorm conditions, but unstable under earthquake. The factor of safety is less than 1, which indicates the landslide instable.
2009, 17(4): 503-507.
Classification of rock mass permeability structure types is the important content for geological exploration of water resources and hydropower engineering and evaluation of permeability. Based on the seepage controlling effects of rock mass structures, key factors that control permeability characteristics of rock mass are analyzed. They are lithology, faulted structure, weathering and unloading and karst effect. Principle of dividing rock mass permeability structure types are put forward. The anisotropic characteristics of rock mass is considered. According to the macroscopic permeability characteristics of rock mass, the permeability structures are classified into five types. They are discrete mass permeability structure, layered permeability structure, zonal permeability structure, netlike permeability structure and duct-like permeability structure. The classification method is applied to actual engineering cases. The classified results of permeability structure types of rock mass at the Xiaolangdi Project and the Three Gorges Project dam sites are present. The results show that reasonable identification of permeability structure types of rock mass is of the most significance for seepage control and drainage design of water resources and hydropower engineering.
Classification of rock mass permeability structure types is the important content for geological exploration of water resources and hydropower engineering and evaluation of permeability. Based on the seepage controlling effects of rock mass structures, key factors that control permeability characteristics of rock mass are analyzed. They are lithology, faulted structure, weathering and unloading and karst effect. Principle of dividing rock mass permeability structure types are put forward. The anisotropic characteristics of rock mass is considered. According to the macroscopic permeability characteristics of rock mass, the permeability structures are classified into five types. They are discrete mass permeability structure, layered permeability structure, zonal permeability structure, netlike permeability structure and duct-like permeability structure. The classification method is applied to actual engineering cases. The classified results of permeability structure types of rock mass at the Xiaolangdi Project and the Three Gorges Project dam sites are present. The results show that reasonable identification of permeability structure types of rock mass is of the most significance for seepage control and drainage design of water resources and hydropower engineering.
2009, 17(4): 508-515.
Qinghai-Tibet 500kV DC power transmission line traverse the permafrost in Qinghai-Tibet Plateau, special engineering problems of permafrost will have the important impacts on the engineering design, construction and safe running. Because of structural trait of point and linear engineering, this means stability of tower footing have relation to the stability of all the line, but the tower footing is adjustable in degree. So the distributing character of permafrost and ground ice have more significance for the route selection and position selection than other linear engineering. In the base of distribution of permafrost along the transmission line, the article primarily study and analyze the rules of distribution and development of frozen soil and thick ground ice under the condition of tiny landform and physiognomy, and combining the engineering characteristics of transmission line, the principles of the route selection and position selection are studied and confirmed.
Qinghai-Tibet 500kV DC power transmission line traverse the permafrost in Qinghai-Tibet Plateau, special engineering problems of permafrost will have the important impacts on the engineering design, construction and safe running. Because of structural trait of point and linear engineering, this means stability of tower footing have relation to the stability of all the line, but the tower footing is adjustable in degree. So the distributing character of permafrost and ground ice have more significance for the route selection and position selection than other linear engineering. In the base of distribution of permafrost along the transmission line, the article primarily study and analyze the rules of distribution and development of frozen soil and thick ground ice under the condition of tiny landform and physiognomy, and combining the engineering characteristics of transmission line, the principles of the route selection and position selection are studied and confirmed.
2009, 17(4): 516-521.
This paper is based on detailed field survey results about road slopes with thick soft-hard inter-beddings. It is found that the rock slopes with different bedding orientations and different excavation orientations would have different failure modes. According to many field examples, the paper summarized several failure modes with different bedding orientations. The modes of rock slope failures with gentle bedding dip angles have three types : sliding-falling、toppling and falling. The modes with middle bedding dip angles have two types : sliding and falling. The modes with high dip angle have two types: sliding-falling and falling. On the basis of force analyzing and deforming character analyzing, the paper gives engineering measures respectively. This shows that the slope deformation failure and geo-force mode is closely related with slope rockmass structures. Through studying the rockmass failure modes with different dip angles, it can evaluate slope stability systemically. On practicing, it can forecast potential geo-hazards according to different dip angle in cutting slope construction. Consequently, people can adopt suitable measures according to different failure modes.
This paper is based on detailed field survey results about road slopes with thick soft-hard inter-beddings. It is found that the rock slopes with different bedding orientations and different excavation orientations would have different failure modes. According to many field examples, the paper summarized several failure modes with different bedding orientations. The modes of rock slope failures with gentle bedding dip angles have three types : sliding-falling、toppling and falling. The modes with middle bedding dip angles have two types : sliding and falling. The modes with high dip angle have two types: sliding-falling and falling. On the basis of force analyzing and deforming character analyzing, the paper gives engineering measures respectively. This shows that the slope deformation failure and geo-force mode is closely related with slope rockmass structures. Through studying the rockmass failure modes with different dip angles, it can evaluate slope stability systemically. On practicing, it can forecast potential geo-hazards according to different dip angle in cutting slope construction. Consequently, people can adopt suitable measures according to different failure modes.
2009, 17(4): 522-527.
Based on research of the stability of roadbeds in permafrost regions, an evaluation system for stability of roadbeds is constructed in this paper. Twelve factors influencing the stability of roadbeds are selected as the evaluation indices. Five aspects are considered in the evaluation system. They are permafrost type, temperature, thickness, geological conditions and project management. The safety reliability and relationships of each factor are considered. The fuzzy synthetic model is built by adopting AHP and fuzzy mathematics theory. And the fuzzy synthetic evaluation method is advanced based on the safety reliability. At last, the case of Qinghai-Tibet highway in Qingshuihe section is calculated and analyzed with the proposed method. The results are consistent with the field observations.
Based on research of the stability of roadbeds in permafrost regions, an evaluation system for stability of roadbeds is constructed in this paper. Twelve factors influencing the stability of roadbeds are selected as the evaluation indices. Five aspects are considered in the evaluation system. They are permafrost type, temperature, thickness, geological conditions and project management. The safety reliability and relationships of each factor are considered. The fuzzy synthetic model is built by adopting AHP and fuzzy mathematics theory. And the fuzzy synthetic evaluation method is advanced based on the safety reliability. At last, the case of Qinghai-Tibet highway in Qingshuihe section is calculated and analyzed with the proposed method. The results are consistent with the field observations.
2009, 17(4): 528-532.
Brazilian disc test is an indirect experiment, proposed by International Society for Rock Mechanics, to determine the tensile strength of rock materials. The theoretical foundation is the distribution of stress field in the disc under the concentration loads applied. In this study, the analytic stress solution in the form of Cartesian Coordinates of any point in the disc is given with a new method. It is completely different with the complex function method according to the Airy stress function and the superposition principle of linear elasticity. Comparing the analytic stress solution obtained here and the typical solution given by Н. И. Мусхелишьили, it is found that they are consistent with each other completely. Accordingly, it is proved that the procedure and the method adopted here are both reasonable and appropriate.
Brazilian disc test is an indirect experiment, proposed by International Society for Rock Mechanics, to determine the tensile strength of rock materials. The theoretical foundation is the distribution of stress field in the disc under the concentration loads applied. In this study, the analytic stress solution in the form of Cartesian Coordinates of any point in the disc is given with a new method. It is completely different with the complex function method according to the Airy stress function and the superposition principle of linear elasticity. Comparing the analytic stress solution obtained here and the typical solution given by Н. И. Мусхелишьили, it is found that they are consistent with each other completely. Accordingly, it is proved that the procedure and the method adopted here are both reasonable and appropriate.
2009, 17(4): 533-537.
Physical creep experiment needs long time-consuming, costs greatly, and operates more difficult. The development of experiment is more difficult. This paper establishes a numerical model using the rock soil analysis software FLAC3D, carries out simulation test for the indoor creep experiment. The numerical test adopts the test state, load design and time setting as same as those actual physical test. It can obtain the same creep curve of actual physical test. The simulated results can be used to analyze creep distortion. Moreover, the method has been extended to the test state of tri-axial compress creep test. It provides a new road for creep test research.
Physical creep experiment needs long time-consuming, costs greatly, and operates more difficult. The development of experiment is more difficult. This paper establishes a numerical model using the rock soil analysis software FLAC3D, carries out simulation test for the indoor creep experiment. The numerical test adopts the test state, load design and time setting as same as those actual physical test. It can obtain the same creep curve of actual physical test. The simulated results can be used to analyze creep distortion. Moreover, the method has been extended to the test state of tri-axial compress creep test. It provides a new road for creep test research.
2009, 17(4): 538-544.
According to the monitored data of Saleshan landslide, three nonlinear prediction models (i.e., exponential model, Verhulst model and grey GM(1,1) model) for the landslide deformation is developed in this paper. The models are based on the studying of combined model with optimum weight and Gauss-Newton method. Then the combined model with optimum weight of the landslide is built. The parameters in each individual model and the combined model are optimized using Gauss-Newton method. By analyzing and comparing, the paper can conclude that the prediction accuracy of the combined model are higher than that of an individual model. The precision for each model after optimizing parameters using Gauss-Newton method is obviously higher than that of the models before using the optimizing parameters. The combined model with the optimizing parameters in all models has the highest precision. So, it is an effective and feasible method for improving landslide prediction to use the combined model with optimum weight and Gauss-Newton method.
According to the monitored data of Saleshan landslide, three nonlinear prediction models (i.e., exponential model, Verhulst model and grey GM(1,1) model) for the landslide deformation is developed in this paper. The models are based on the studying of combined model with optimum weight and Gauss-Newton method. Then the combined model with optimum weight of the landslide is built. The parameters in each individual model and the combined model are optimized using Gauss-Newton method. By analyzing and comparing, the paper can conclude that the prediction accuracy of the combined model are higher than that of an individual model. The precision for each model after optimizing parameters using Gauss-Newton method is obviously higher than that of the models before using the optimizing parameters. The combined model with the optimizing parameters in all models has the highest precision. So, it is an effective and feasible method for improving landslide prediction to use the combined model with optimum weight and Gauss-Newton method.
2009, 17(4): 545-549.
This paper presents the mechanical performance of herbage fiber materials before and after anticorrosion and the strength characteristics of wheat straw reinforced inshore saline soil. It discusses the microstructure characteristics and the anti-corrosive method of the wheat straw. The wheat straw is tested and compared the increasing rate of weight, the water absorption, the tensile force and elongation of the wheat straws before and after anticorrosion treatment. The test results show that the soaking wheat straw into SH agent can not only protect it from corrosiveness, but also improve its mechanical properties. The results of unconfined compressive strength test of different lengths and adding ratios of wheat straw, and conditions after soaking agent show that the unconfined compressive strength of reinforced soil with 10mm long wheat straw is higher than that of the 20mm long wheat straw. The suitable adding ratio is about 0.3%~0.4% in weight. The mixture with wheat straw in wet condition after soaking SH agent is better than that in dry condition. The strength of reinforced saline soil in inshore with wheat straw is higher than the original saline soil. Preliminary results show that wheat straw is suitable for using as the reinforcement.
This paper presents the mechanical performance of herbage fiber materials before and after anticorrosion and the strength characteristics of wheat straw reinforced inshore saline soil. It discusses the microstructure characteristics and the anti-corrosive method of the wheat straw. The wheat straw is tested and compared the increasing rate of weight, the water absorption, the tensile force and elongation of the wheat straws before and after anticorrosion treatment. The test results show that the soaking wheat straw into SH agent can not only protect it from corrosiveness, but also improve its mechanical properties. The results of unconfined compressive strength test of different lengths and adding ratios of wheat straw, and conditions after soaking agent show that the unconfined compressive strength of reinforced soil with 10mm long wheat straw is higher than that of the 20mm long wheat straw. The suitable adding ratio is about 0.3%~0.4% in weight. The mixture with wheat straw in wet condition after soaking SH agent is better than that in dry condition. The strength of reinforced saline soil in inshore with wheat straw is higher than the original saline soil. Preliminary results show that wheat straw is suitable for using as the reinforcement.
2009, 17(4): 550-556.
This paper investigates the characteristics of the deformation and shear strength of laterite clay. Three kinds of laterite clays in Jingxi, Guangxi Province are studied with laboratory tests including compression tests and triaixal shear tests. The samples are undisturbed or remolded specimens. They are either saturated or unsaturated. The studies show that at a greater consolidation pressure, the void ratio of samples after compression is still very great; and the failure surface under triaixal shear condition takes on a complicated shape (i.e., not a plane surface). Although an obvious failure surface (i.e., showing a brittle failure characteristics) takes place, the stress-strain curve takes on a hardening characteristics, which reflects the viscosity of laterite clay.
This paper investigates the characteristics of the deformation and shear strength of laterite clay. Three kinds of laterite clays in Jingxi, Guangxi Province are studied with laboratory tests including compression tests and triaixal shear tests. The samples are undisturbed or remolded specimens. They are either saturated or unsaturated. The studies show that at a greater consolidation pressure, the void ratio of samples after compression is still very great; and the failure surface under triaixal shear condition takes on a complicated shape (i.e., not a plane surface). Although an obvious failure surface (i.e., showing a brittle failure characteristics) takes place, the stress-strain curve takes on a hardening characteristics, which reflects the viscosity of laterite clay.
2009, 17(4): 557-562.
This paper is about the Zhengzhou-Xi'an high-speed railway, in particular, the Tongguan section about their potential seismic subsidence. A large number of undisturbed loess samples were collected at Tongguan section. By inputting artificial synthetic seismic wave to the dynamic triaxial testing of the samples, the seismic subsidence experiments were carried out. Based the laboratory tests, the paper obtains the following results. Firstly, the seismic subsidence of loess foundation was estimated and the foundation dynamic numerical model was established. Secondly, It further examined the permanent deformation of the sub-grade loess at the levels of 10% and 2% exceedance probability in 50 years under the earthquake effect and the sub-grade loess after soil treatment. The results showed that, the settlement occurred mainly in Q3 loess. The foundation treatment measures such as dynamic compaction, down-hole dynamic consolidation can effectively reduce the settlement of the loess foundation. However, larger settlement can still be generated under strong earthquakes if the soil treatment depth is not deep enough. The results presented in the paper can provide a basis for the foundation seismic treatment.
This paper is about the Zhengzhou-Xi'an high-speed railway, in particular, the Tongguan section about their potential seismic subsidence. A large number of undisturbed loess samples were collected at Tongguan section. By inputting artificial synthetic seismic wave to the dynamic triaxial testing of the samples, the seismic subsidence experiments were carried out. Based the laboratory tests, the paper obtains the following results. Firstly, the seismic subsidence of loess foundation was estimated and the foundation dynamic numerical model was established. Secondly, It further examined the permanent deformation of the sub-grade loess at the levels of 10% and 2% exceedance probability in 50 years under the earthquake effect and the sub-grade loess after soil treatment. The results showed that, the settlement occurred mainly in Q3 loess. The foundation treatment measures such as dynamic compaction, down-hole dynamic consolidation can effectively reduce the settlement of the loess foundation. However, larger settlement can still be generated under strong earthquakes if the soil treatment depth is not deep enough. The results presented in the paper can provide a basis for the foundation seismic treatment.
2009, 17(4): 563-568.
The Multipurpose hydropower project in Baise of Guangxi province includes a huge reservoir and a high dam and many rock caverns for underground powerhouse. They are built on the thin diabase dike with complex geological condition. The ground consists of poor integrity of the rock mass, deeply weathered rock in low-intensity of the upper and lower contact alteration zone. The foundation of stilling basin is uneven because weathered interface is buried deeply causing by a major fault developed in the diabase dike along the riverbed. So many geological problems were encountered. In the construction process, the different preventive measures were carried out to stablize the foundations of the buildings with different geological problems. Deep consolidation grouting was carried out to treat the upper and lower contact alteration zone. Deep cut and concrete backfill, strengthen consolidation grouting measures were carried out to treat the fault. Thickening the bottom layer, consolidation grouting and anchor processing were carried out to treat the foundation of the stilling basin. Tension bolt and cable reinforcement were carried out at the plastically deforming area of thin rock wall and the shallow buried section of the underground powerhouse. The project has been operating normally after the treatments. The observed data of the deformation of the dam foundation and the caverns, stress and osmotic pressure are within the design scope.
The Multipurpose hydropower project in Baise of Guangxi province includes a huge reservoir and a high dam and many rock caverns for underground powerhouse. They are built on the thin diabase dike with complex geological condition. The ground consists of poor integrity of the rock mass, deeply weathered rock in low-intensity of the upper and lower contact alteration zone. The foundation of stilling basin is uneven because weathered interface is buried deeply causing by a major fault developed in the diabase dike along the riverbed. So many geological problems were encountered. In the construction process, the different preventive measures were carried out to stablize the foundations of the buildings with different geological problems. Deep consolidation grouting was carried out to treat the upper and lower contact alteration zone. Deep cut and concrete backfill, strengthen consolidation grouting measures were carried out to treat the fault. Thickening the bottom layer, consolidation grouting and anchor processing were carried out to treat the foundation of the stilling basin. Tension bolt and cable reinforcement were carried out at the plastically deforming area of thin rock wall and the shallow buried section of the underground powerhouse. The project has been operating normally after the treatments. The observed data of the deformation of the dam foundation and the caverns, stress and osmotic pressure are within the design scope.
2009, 17(4): 569-573.
Shear strength of discontinuities is an important parameter for landslide engineering. The back analysis is a low cost and effective method to determine shear strength of instability slope. This paper focuses on how to determine the shear strength of instability slope at Xibaipo Memorial Site using back analysis and laboratory test respectively. The instability slope has a single bedding slip. The results show that the shear strength of discontinuities of back analysis is similar to that of laboratory test. The back analysis can be used to evaluate the stability of bilateral slopes.
Shear strength of discontinuities is an important parameter for landslide engineering. The back analysis is a low cost and effective method to determine shear strength of instability slope. This paper focuses on how to determine the shear strength of instability slope at Xibaipo Memorial Site using back analysis and laboratory test respectively. The instability slope has a single bedding slip. The results show that the shear strength of discontinuities of back analysis is similar to that of laboratory test. The back analysis can be used to evaluate the stability of bilateral slopes.
2009, 17(4): 574-579.
An experimental apparatus for large dynamical consolidation with drain is developed. It can be used to carry out the laboratory model test to consolidate the dredger fill. The apparatus includes soil container, lifting appliance, hammer rans, measuring and data acquisition units. The main characteristics of the equipment are: (1) It can realize both half-model and complete-model tests and can simulate multi-points rammer besides one-point rammer. (2) It can realize real-time observation of the vertical fractures in soil and the movements of measuring points. It also can take real-time measuring and data acquisition of pore press, displacement and active stress. (3)It can simulate the field construction quite well through automatic lifting and ramming. (4) Different consolidation methods such as tests with different ramming parameters, different thickness of consolidated soil, different drainage system etc can be modeled with the apparatus. The model test results can provide the best design parameters, i.e. the best parameters used in the field dynamic consolidation with drains to consolidate soft clay soil; (5)The equipment is very convenient to dismantle and combine. It can be used to simulate many situations such as slope, roadbed, retaining wall and landslide. Two model tests with different drainage systems have been carried out using the apparatus. The apparatus kept a good working state during the long test period of 6 months.
An experimental apparatus for large dynamical consolidation with drain is developed. It can be used to carry out the laboratory model test to consolidate the dredger fill. The apparatus includes soil container, lifting appliance, hammer rans, measuring and data acquisition units. The main characteristics of the equipment are: (1) It can realize both half-model and complete-model tests and can simulate multi-points rammer besides one-point rammer. (2) It can realize real-time observation of the vertical fractures in soil and the movements of measuring points. It also can take real-time measuring and data acquisition of pore press, displacement and active stress. (3)It can simulate the field construction quite well through automatic lifting and ramming. (4) Different consolidation methods such as tests with different ramming parameters, different thickness of consolidated soil, different drainage system etc can be modeled with the apparatus. The model test results can provide the best design parameters, i.e. the best parameters used in the field dynamic consolidation with drains to consolidate soft clay soil; (5)The equipment is very convenient to dismantle and combine. It can be used to simulate many situations such as slope, roadbed, retaining wall and landslide. Two model tests with different drainage systems have been carried out using the apparatus. The apparatus kept a good working state during the long test period of 6 months.
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