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Editor Work2009 Vol. 17, No. 2
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2009, 17(2): 145-152.
Abstract
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The Wenchuan earthquake of May 12th, 2008 on the tectonic margin between the Longmenshan orogenic belt and Sichuan basin had a magnitude of 8.0 Ms, on the Yingxiu-Beichuan fault. A 350-km-long surface rupture zone exhibits right-lateral and left-step features. It is related to the west-dip Wenchuan-Maowen-Qingchuan fault, Yingxiu-Beichuan fault and the Jiangyou-Dujiangyan fault which show dextral strike-slip and thrust. The brittle seismogenic faults in the upper crust，which controlled surface rupture zones and landslides, were produced by slowly ductile flow of lower crust with the stress and strain accumulation at the ductile-brittle shear zone of the middle crust. Seismic source locates at the connection spot between the ductile-brittle shear zone in middle crust and brittle active faults in upper crust.
This paper examines the Wenchuan Earthquake in association with the basic characters of intra-plate earthquake. It is believed that it is necessary to develop the theory of regional stability for engineering by continental dynamic theory. The evaluating system must be established together by plate theory, geological mechanics and continental dynamic theory. Some opinions about active faults and earthquake prediction are discussed. It is stressed that earthquake prediction only by active fault is insufficient or improper. The causative structure in lower crust, ductile-brittle transition zone in middle crust and brittle seismogenic faults in upper crust must be considered as a whole in the study. At last, an evaluation index system of regional crustal stability for engineering projects is put forward and the key index for safety island is pointed out.
The Wenchuan earthquake of May 12th, 2008 on the tectonic margin between the Longmenshan orogenic belt and Sichuan basin had a magnitude of 8.0 Ms, on the Yingxiu-Beichuan fault. A 350-km-long surface rupture zone exhibits right-lateral and left-step features. It is related to the west-dip Wenchuan-Maowen-Qingchuan fault, Yingxiu-Beichuan fault and the Jiangyou-Dujiangyan fault which show dextral strike-slip and thrust. The brittle seismogenic faults in the upper crust，which controlled surface rupture zones and landslides, were produced by slowly ductile flow of lower crust with the stress and strain accumulation at the ductile-brittle shear zone of the middle crust. Seismic source locates at the connection spot between the ductile-brittle shear zone in middle crust and brittle active faults in upper crust.
This paper examines the Wenchuan Earthquake in association with the basic characters of intra-plate earthquake. It is believed that it is necessary to develop the theory of regional stability for engineering by continental dynamic theory. The evaluating system must be established together by plate theory, geological mechanics and continental dynamic theory. Some opinions about active faults and earthquake prediction are discussed. It is stressed that earthquake prediction only by active fault is insufficient or improper. The causative structure in lower crust, ductile-brittle transition zone in middle crust and brittle seismogenic faults in upper crust must be considered as a whole in the study. At last, an evaluation index system of regional crustal stability for engineering projects is put forward and the key index for safety island is pointed out.
2009, 17(2): 153-166.
The extremely rapid and long run-out landslides triggered by the Wenchuan Earthquake were occurred along the Yingxiu-Gaochuan-Beichuan-Nanba-Qingchuan of the main seismic fault. The estimated maximum sliding velocity is greater than 70ms-1 under the over 1.5g earthquake acceleration, compared with conventional rainfall or liquefaction induced landslides. The run-out distance of landslide-debris is several or several ten times of the rockmass length from crown to exit due to the air layer lubrication in where lots of landslide dams occurred. The maximum run-out distance is 3200m. The three cases are studied from the Niuquangou rockslide-debris flow at the south west segment of the main seismic fault(Yingxiu, Wenchuan), the Chengxi rockslide at the middle segment of the main seismic fault (Beichuan) and the Donghekou rockslide-debris flow at the north east segment of the main seismic fault.The three cases illustrates following common characteristics: (1)parent rockmass is broken under long geologic processing and weathered; (2) Rockmass was separately expanded and thrown under long-period strong ground vibration in which the vertical motion was predominant along the main seismic fault; (3)sliding mass was crashed at the exiting zone and transferred to fragment material; (4) The secondary landslide was triggered underneath the exiting zone due to the powerful crashing and shaving processes that provides more mass to debris body and cushion shape；(5) The a long run-out distance fragment flow is occurred under air layer lubrication. The air layer was pressed and turbulently flowed in the narrow-shaped valley, or laminarly flowed in the extensive flatland.
The extremely rapid and long run-out landslides triggered by the Wenchuan Earthquake were occurred along the Yingxiu-Gaochuan-Beichuan-Nanba-Qingchuan of the main seismic fault. The estimated maximum sliding velocity is greater than 70ms-1 under the over 1.5g earthquake acceleration, compared with conventional rainfall or liquefaction induced landslides. The run-out distance of landslide-debris is several or several ten times of the rockmass length from crown to exit due to the air layer lubrication in where lots of landslide dams occurred. The maximum run-out distance is 3200m. The three cases are studied from the Niuquangou rockslide-debris flow at the south west segment of the main seismic fault(Yingxiu, Wenchuan), the Chengxi rockslide at the middle segment of the main seismic fault (Beichuan) and the Donghekou rockslide-debris flow at the north east segment of the main seismic fault.The three cases illustrates following common characteristics: (1)parent rockmass is broken under long geologic processing and weathered; (2) Rockmass was separately expanded and thrown under long-period strong ground vibration in which the vertical motion was predominant along the main seismic fault; (3)sliding mass was crashed at the exiting zone and transferred to fragment material; (4) The secondary landslide was triggered underneath the exiting zone due to the powerful crashing and shaving processes that provides more mass to debris body and cushion shape；(5) The a long run-out distance fragment flow is occurred under air layer lubrication. The air layer was pressed and turbulently flowed in the narrow-shaped valley, or laminarly flowed in the extensive flatland.
2009, 17(2): 167-174.
This paper presents the field geological investigation, engineering geological exploration and other related studies on the collapsed and slided debris mass induced by the Xiaonanhai Earthquake in Chongqing city. Basic characteristics and formation mechanism of the debris mass are elaborated. It is held that the forming process of the mass consists of four steps: namely weathering and denudation, shocking and projecting, collapse-slide accumulating and dammed lake formation. Collapses rather than landslides appeared in process of rock mass fracturing and rock blocks in accumulation body are quite and even more fragmental. Research shows that the mass is a result of comprehensive actions including seismotectonic moving and stress field, rock mass structure, topography and geomorphology, and seismic wave. First of all, the left lateral tensile-slip fracture in Xiaonanhai fault block was induced by X-shaped seismotectonic combination. It consists of the NE trending right lateral Qianjiang reverse-slip fracture and the NNW trending left lateral Yangtoushan reverse-slip fault. The NWW trending axially tectonic compression resulted in the M61/4 earthquake. Secondly, the rock mass near both Dakuayan and Xiaokuayan with three groups of tectonic joints forming X-shape collapsed respectively towards their free faces, at about 145~155 direction. Thirdly, the limestone rubbles discovered in the collapse-slide mass prove that mountain body before moving contains limestone belong Qixia and Maokou formations during the Permian period. This discovery provides the evidence for restoring mountain body before its collapse-slide. Finally, the diameter of rock blocks in accumulation body decreases from northwest to southeast along 150 direction. I It proves indirectly that the direction of rock mass ejecting is along 150o direction. What's more, the collapse-slide masses from mountain body near Dakuayan and Xiaokuayan form their accumulation bodies, respectively. Therefore their overlapping part is small.
This paper presents the field geological investigation, engineering geological exploration and other related studies on the collapsed and slided debris mass induced by the Xiaonanhai Earthquake in Chongqing city. Basic characteristics and formation mechanism of the debris mass are elaborated. It is held that the forming process of the mass consists of four steps: namely weathering and denudation, shocking and projecting, collapse-slide accumulating and dammed lake formation. Collapses rather than landslides appeared in process of rock mass fracturing and rock blocks in accumulation body are quite and even more fragmental. Research shows that the mass is a result of comprehensive actions including seismotectonic moving and stress field, rock mass structure, topography and geomorphology, and seismic wave. First of all, the left lateral tensile-slip fracture in Xiaonanhai fault block was induced by X-shaped seismotectonic combination. It consists of the NE trending right lateral Qianjiang reverse-slip fracture and the NNW trending left lateral Yangtoushan reverse-slip fault. The NWW trending axially tectonic compression resulted in the M61/4 earthquake. Secondly, the rock mass near both Dakuayan and Xiaokuayan with three groups of tectonic joints forming X-shape collapsed respectively towards their free faces, at about 145~155 direction. Thirdly, the limestone rubbles discovered in the collapse-slide mass prove that mountain body before moving contains limestone belong Qixia and Maokou formations during the Permian period. This discovery provides the evidence for restoring mountain body before its collapse-slide. Finally, the diameter of rock blocks in accumulation body decreases from northwest to southeast along 150 direction. I It proves indirectly that the direction of rock mass ejecting is along 150o direction. What's more, the collapse-slide masses from mountain body near Dakuayan and Xiaokuayan form their accumulation bodies, respectively. Therefore their overlapping part is small.
2009, 17(2): 175-179.
The profession of engineering geology provides knowledge and methods to cognize the regulation and course of the interaction between engineering and geology. Its task is to guarantee the safety of engineering activity of human beings. Its essential theories include (a) geology of origination and evolution, (b) domination of geological structure, and (c) interaction between engineering and geology. These three theories have the similar thinking process that the origination determines the structure, the structure dominates the behaviors. Engineering geological process is actually a process of interaction between engineering and geology. At present, engineering projects have become larger and larger and deeper and deeper and their encountered geological conditions have become more and more complicated. Consequentlyengineering geological problems present new features and its objects have become remarkably large, deep, dynamic and high temperature. Coupled actions among fluid, stress, temperature and chemistry have challenged the exist theories that were developed for relatively simple ground conditions. Research on engineering geological process should be further extended. Further combination among geology, geophysics, mechanics and engineering sciences is believed the most effective approach. Paying equal attention to theory, technology and practice is the basic mode for the further development of engineering geology profession.
The profession of engineering geology provides knowledge and methods to cognize the regulation and course of the interaction between engineering and geology. Its task is to guarantee the safety of engineering activity of human beings. Its essential theories include (a) geology of origination and evolution, (b) domination of geological structure, and (c) interaction between engineering and geology. These three theories have the similar thinking process that the origination determines the structure, the structure dominates the behaviors. Engineering geological process is actually a process of interaction between engineering and geology. At present, engineering projects have become larger and larger and deeper and deeper and their encountered geological conditions have become more and more complicated. Consequentlyengineering geological problems present new features and its objects have become remarkably large, deep, dynamic and high temperature. Coupled actions among fluid, stress, temperature and chemistry have challenged the exist theories that were developed for relatively simple ground conditions. Research on engineering geological process should be further extended. Further combination among geology, geophysics, mechanics and engineering sciences is believed the most effective approach. Paying equal attention to theory, technology and practice is the basic mode for the further development of engineering geology profession.
2009, 17(2): 180-187.
The heat island effect of major cities around the world and the associated environmental and ecological problems have become more and more serious with the global warming and the speedup of urbanization process. In the view of geological and environmental protection, this paper analyzes the causes and characteristics of urban heat island effect and its impact on the geological environment. I In particular, this paper focuses on the variation of soil engineering properties that arise from the effect and corresponding disaster effect. Furthermore, this paper presents four key scientific issues: i.e., soil temperature changes, moisture migration laws in the soil, the variation of soil engineering properties and the geological disaster effect in the urban heat island. The paper also analyzes their detailed research contents. This paper points out the great theoretical and practical significance for understanding urban heat island effect on soil engineering properties, urban geological disaster prevention and reduction, and the urban sustainable development.
The heat island effect of major cities around the world and the associated environmental and ecological problems have become more and more serious with the global warming and the speedup of urbanization process. In the view of geological and environmental protection, this paper analyzes the causes and characteristics of urban heat island effect and its impact on the geological environment. I In particular, this paper focuses on the variation of soil engineering properties that arise from the effect and corresponding disaster effect. Furthermore, this paper presents four key scientific issues: i.e., soil temperature changes, moisture migration laws in the soil, the variation of soil engineering properties and the geological disaster effect in the urban heat island. The paper also analyzes their detailed research contents. This paper points out the great theoretical and practical significance for understanding urban heat island effect on soil engineering properties, urban geological disaster prevention and reduction, and the urban sustainable development.
2009, 17(2): 188-194.
The Ranwu to Lulang section of Sichuan-Tibet highway locates in Palong River drainage area, north edge of eastern Himalayan structure junction. The tectonic activities are so strong that a large number of faults and folds are formed in the area. Under coupling of the endogenic and exogenic geological processes, there are many loose Quaternary deposits, and they are the main carrier of most geological hazards. Under the river cutting and construction of Sichuan-Tibet highway, many slopes are formed, especially moraine slopes. The particle size characteristic of moraine is different with other sediments, because of the particles distribution from clay to gravel and more coarse particles. The structure and mechanical features of the slopes are also different with other slopes because of particle size characteristics, and they are varied with the size scale. At the same time, the mechanical feature is affected by content and distribution of the different particles and age of moraine. This paper presents the surveyed results of some typical moraine slopes along the highway. A laser profiler and a total station were used in the topographical survey. It is obvious that the slopes are high and steep, but they are stable. Based on the limit equilibrium theory, themoraine high slopes are analyzed for their stabilities. And Different methods are used to analyze the stability of the slopes in natural state. At last, the stabilities of the slopes are estimated wuth the effect of earthquake.
The Ranwu to Lulang section of Sichuan-Tibet highway locates in Palong River drainage area, north edge of eastern Himalayan structure junction. The tectonic activities are so strong that a large number of faults and folds are formed in the area. Under coupling of the endogenic and exogenic geological processes, there are many loose Quaternary deposits, and they are the main carrier of most geological hazards. Under the river cutting and construction of Sichuan-Tibet highway, many slopes are formed, especially moraine slopes. The particle size characteristic of moraine is different with other sediments, because of the particles distribution from clay to gravel and more coarse particles. The structure and mechanical features of the slopes are also different with other slopes because of particle size characteristics, and they are varied with the size scale. At the same time, the mechanical feature is affected by content and distribution of the different particles and age of moraine. This paper presents the surveyed results of some typical moraine slopes along the highway. A laser profiler and a total station were used in the topographical survey. It is obvious that the slopes are high and steep, but they are stable. Based on the limit equilibrium theory, themoraine high slopes are analyzed for their stabilities. And Different methods are used to analyze the stability of the slopes in natural state. At last, the stabilities of the slopes are estimated wuth the effect of earthquake.
2009, 17(2): 195-199.
The development of economy in China has resulted in more and more infrastructural constructions such as highways in mountainous areas. As a result, more and more man-made slopes are excavated. The stabilities of rock cut slopes with gentle inclined layer structure are generally adequate under normal circumstances. However, they may generate deformation and damage under particular combination of discontinuities. This paper uses l cut highway slopes with weak discontinuities and long joints as an example to study the failure modes and supporting measures. The study is based on investigation of rock mass structure and analysis of slope deformation phenomenon over a certain scope of the studied area. The paper further adopts a three dimension discrete element method to analyze the failure modes of the cut rock slope. The numerical result is in accordance with the result of engineering geological analog. At last, the supporting measures are advanced in close combination with the characteristics of the slope failure mode.
The study results indicate that the slipping and cracking deformation can be generated in gentle inclined layered slopes when the discontinuities can form trailing edge and lateral boundary in the slope body. However, there is one special case. The rotary type slipping and cracking deformation can be generated when there is an angle between the trends of sliding surface and slope surface. It is also found that the stabilities of gentle inclined layered slopes are controlled by the key blocks located in the lower-middle part of the slope. The key block failure can cause a chain type of failures of the upper blocks. Consequently, the deformation controlling measures should focus on the region where the key blocks locate. Supporting measures of the cut rock slope established based on the failure mode analysis can guarantee the safety under both construction and operation conditions, which are shown by monitored results.
The development of economy in China has resulted in more and more infrastructural constructions such as highways in mountainous areas. As a result, more and more man-made slopes are excavated. The stabilities of rock cut slopes with gentle inclined layer structure are generally adequate under normal circumstances. However, they may generate deformation and damage under particular combination of discontinuities. This paper uses l cut highway slopes with weak discontinuities and long joints as an example to study the failure modes and supporting measures. The study is based on investigation of rock mass structure and analysis of slope deformation phenomenon over a certain scope of the studied area. The paper further adopts a three dimension discrete element method to analyze the failure modes of the cut rock slope. The numerical result is in accordance with the result of engineering geological analog. At last, the supporting measures are advanced in close combination with the characteristics of the slope failure mode.
The study results indicate that the slipping and cracking deformation can be generated in gentle inclined layered slopes when the discontinuities can form trailing edge and lateral boundary in the slope body. However, there is one special case. The rotary type slipping and cracking deformation can be generated when there is an angle between the trends of sliding surface and slope surface. It is also found that the stabilities of gentle inclined layered slopes are controlled by the key blocks located in the lower-middle part of the slope. The key block failure can cause a chain type of failures of the upper blocks. Consequently, the deformation controlling measures should focus on the region where the key blocks locate. Supporting measures of the cut rock slope established based on the failure mode analysis can guarantee the safety under both construction and operation conditions, which are shown by monitored results.
2009, 17(2): 200-205.
Slope collapse is the primary problem of geological projects in slopes with interbeddings of soft and hard rocks in red bedrock area. This paper examines a highway slope in southwest area of China. The collapse mechanism of formation and the characteristics of structure are studied using field investigation. The slope characteristics of failure and deformation after collapse are studied with the nonlinear finite element method of two dimensions. The slope stability is also evaluated with quantitative method. The result shows that owing to the discrepant weathering, the lower soft rock mass has some notch that can cause the collapse and the cracks in the upper hard rock mass. The cracks link up gradually. If it is not stabilized in time, the upper hard rock mass can collapse when the cracks in the hard rock mass link up to 60% in thickness. Based on the comprehensive analysis of the present slope stability and the potential pattern of failure and deformation, the scheme is settled. It includes cleaning slope surface, cutting parts of the slope, hanging the net of reinforcing bar and sprayed concrete, reinforced concrete support column, and drainage system. The focal treatment measure is to control the development of the cracks in the upper rock mass above the notchand to make waterproof and drain establishment.
Slope collapse is the primary problem of geological projects in slopes with interbeddings of soft and hard rocks in red bedrock area. This paper examines a highway slope in southwest area of China. The collapse mechanism of formation and the characteristics of structure are studied using field investigation. The slope characteristics of failure and deformation after collapse are studied with the nonlinear finite element method of two dimensions. The slope stability is also evaluated with quantitative method. The result shows that owing to the discrepant weathering, the lower soft rock mass has some notch that can cause the collapse and the cracks in the upper hard rock mass. The cracks link up gradually. If it is not stabilized in time, the upper hard rock mass can collapse when the cracks in the hard rock mass link up to 60% in thickness. Based on the comprehensive analysis of the present slope stability and the potential pattern of failure and deformation, the scheme is settled. It includes cleaning slope surface, cutting parts of the slope, hanging the net of reinforcing bar and sprayed concrete, reinforced concrete support column, and drainage system. The focal treatment measure is to control the development of the cracks in the upper rock mass above the notchand to make waterproof and drain establishment.
2009, 17(2): 212-219.
This paper investigates the characteristics of surface geological hazards and their impacts on the Three Gorges Water Diversion Project in the section of the Qinling-Daba mountain region. It gives a brief analysis of the regional and linear engineering geological conditions. It focuses on the analysis of characteristics of the distribution of geological hazards and their impacts on the water diversion project. At present, the following are found: (1) there are many types of shallow surface geological hazards with cluster and belt distribution characteristics and different volumes in Qinling-Daba mountain region; (2) the main diagnostic factors of Qinling-Daba mountain geological hazards are tectonic landscape, high and steep slopes, slope structure and landslide-prone combination of stratigraphy. The main triggering factors are concentration of the heavy rainfall, linear projects (mainly roads) slope-cutting and erosion; (3) the main impacts of surface geological hazards on the water division project are the safety of water facilities and related road construction, the reservoir and aqueduct sites, on which attention should be paid.
This paper investigates the characteristics of surface geological hazards and their impacts on the Three Gorges Water Diversion Project in the section of the Qinling-Daba mountain region. It gives a brief analysis of the regional and linear engineering geological conditions. It focuses on the analysis of characteristics of the distribution of geological hazards and their impacts on the water diversion project. At present, the following are found: (1) there are many types of shallow surface geological hazards with cluster and belt distribution characteristics and different volumes in Qinling-Daba mountain region; (2) the main diagnostic factors of Qinling-Daba mountain geological hazards are tectonic landscape, high and steep slopes, slope structure and landslide-prone combination of stratigraphy. The main triggering factors are concentration of the heavy rainfall, linear projects (mainly roads) slope-cutting and erosion; (3) the main impacts of surface geological hazards on the water division project are the safety of water facilities and related road construction, the reservoir and aqueduct sites, on which attention should be paid.
2009, 17(2): 220-227.
A landslide with volume of 130104m3 occurred at Fuling Fifth Middle School in Chongqing on Jan 3，2008. It is a bedding monoclinic rock landslide. This paper presents the investigation on the characteristics and causes of the landslide. The paper summarizes the findings. At firstly，the inclined terrace and cracked rock mass were the structural factors causing the landslide. Secondly, because they were softened in water and acted by tectonic stress in geologic history, the argillaceous sandstone and mudstone were prone to argillation and forming weak seams. The weak seams comprised montmorillonite and illite. The weak seams were the controlling factor causing the landslide. Thirdly, water weakened the strength of the weak seam. Finally, digging slope toe was one of the inducing factors to the landslide. With creeping of the landslide, the factors acted each other and led to the occurrence of the landslide.
A landslide with volume of 130104m3 occurred at Fuling Fifth Middle School in Chongqing on Jan 3，2008. It is a bedding monoclinic rock landslide. This paper presents the investigation on the characteristics and causes of the landslide. The paper summarizes the findings. At firstly，the inclined terrace and cracked rock mass were the structural factors causing the landslide. Secondly, because they were softened in water and acted by tectonic stress in geologic history, the argillaceous sandstone and mudstone were prone to argillation and forming weak seams. The weak seams comprised montmorillonite and illite. The weak seams were the controlling factor causing the landslide. Thirdly, water weakened the strength of the weak seam. Finally, digging slope toe was one of the inducing factors to the landslide. With creeping of the landslide, the factors acted each other and led to the occurrence of the landslide.
2009, 17(2): 228-232.
This investigates and analyzes the geological environment conditions of Ganzixi bank in Three Gorges reservoir area. It points out the typical of bank is an earthy one. According to some principles, the typical collapses of the bank can be classified into (1) washing and abrasion type and (2) slope type. At the same time, the paper also discusses the methods of getting forecasting parameters, calculates the stability of the land in the different cases. The results show that three engineering geological cross-sections are less stable in the case 6, but stable in other cases. The scope of bank collapse prediction is in line with the actual data.
This investigates and analyzes the geological environment conditions of Ganzixi bank in Three Gorges reservoir area. It points out the typical of bank is an earthy one. According to some principles, the typical collapses of the bank can be classified into (1) washing and abrasion type and (2) slope type. At the same time, the paper also discusses the methods of getting forecasting parameters, calculates the stability of the land in the different cases. The results show that three engineering geological cross-sections are less stable in the case 6, but stable in other cases. The scope of bank collapse prediction is in line with the actual data.
2009, 17(2): 233-239.
The Qianjiangping landslide is at the left bank of Qinggan river, a tributary of Changjiang River around the Three Gorges Reservoir. It is 44 km away from and above the Three Gorges Dam. At the time of 00:20 on July 13, 2003, a landslide in bedrock occurred at the village called Qianjiangping in Zigui county around the Three Gorges Reservoir. This disaster caused, 15 fatalities, 9 missing, and destroyed four township enterprises. Then the event also aroused wide attention of the public at large. Through the geological investigation in detail after the landslide, this paper gives details on the geological features, precursors as well as the processes of the landslide. According to its substances and structures, the landslide is divided into four zones. They are a) block stone zone, b) base rock fractured zone, c) earth bearing block stone zone and d) boulders and gravels zone from the backscarp to the debris frontier. Furthermore, the paper analyzes physical and mechanical characteristics of slipping zone, and studies the mechanism of the landslide. It concludes that the slope had structures, geomorphology as well as litholgoy prone to landslide. Finally the landslide was induced under the combination of precipitation, irrigation and the impoundment of the Three Gorges Reservoir
The Qianjiangping landslide is at the left bank of Qinggan river, a tributary of Changjiang River around the Three Gorges Reservoir. It is 44 km away from and above the Three Gorges Dam. At the time of 00:20 on July 13, 2003, a landslide in bedrock occurred at the village called Qianjiangping in Zigui county around the Three Gorges Reservoir. This disaster caused, 15 fatalities, 9 missing, and destroyed four township enterprises. Then the event also aroused wide attention of the public at large. Through the geological investigation in detail after the landslide, this paper gives details on the geological features, precursors as well as the processes of the landslide. According to its substances and structures, the landslide is divided into four zones. They are a) block stone zone, b) base rock fractured zone, c) earth bearing block stone zone and d) boulders and gravels zone from the backscarp to the debris frontier. Furthermore, the paper analyzes physical and mechanical characteristics of slipping zone, and studies the mechanism of the landslide. It concludes that the slope had structures, geomorphology as well as litholgoy prone to landslide. Finally the landslide was induced under the combination of precipitation, irrigation and the impoundment of the Three Gorges Reservoir
2009, 17(2): 240-243.
The joint space or frequency are more suitable for the definition of volumetric joint count Jv in the Code of Engineering Rock Mass Classification. The suitability of Jv for rock mass with one, two or three sets of persistent joints is discussed. A correction factor K1 of Jv is calculated with the formula: K1=|sin(n1,n2[DD(-1][HT5SS]^[HT][][DD)])||cos(n1n2,n3[DD(-1][HT5SS]^[HT][][DD)])| . The influence of intersection angles between different joint sets on Jv is discussed. Then the definition of Jv for rock mass containing intermittent joints is deduced on the basis of joint persistence ratio with a new formula of Jv=K1[DD(][]i[DD)]Sini(i3). The degree of joints in rock mass could be expressed more objectively with the proposed formula.
The joint space or frequency are more suitable for the definition of volumetric joint count Jv in the Code of Engineering Rock Mass Classification. The suitability of Jv for rock mass with one, two or three sets of persistent joints is discussed. A correction factor K1 of Jv is calculated with the formula: K1=|sin(n1,n2[DD(-1][HT5SS]^[HT][][DD)])||cos(n1n2,n3[DD(-1][HT5SS]^[HT][][DD)])| . The influence of intersection angles between different joint sets on Jv is discussed. Then the definition of Jv for rock mass containing intermittent joints is deduced on the basis of joint persistence ratio with a new formula of Jv=K1[DD(][]i[DD)]Sini(i3). The degree of joints in rock mass could be expressed more objectively with the proposed formula.
2009, 17(2): 244-248.
After air entrance, an unsaturated area is formed in saturated soil. So, in fact, air permeation in saturated soil aquifer is an unsaturated permeation problem. Based on the constitutive equation, which is deduced from porous media theory with consideration of the compressibility of air, the characteristics of air permeation in saturated soil aquifer in Shanghai area is studied through laboratory tests. Results show that the air permeation in saturated clayey soil has a threshold of pressure about 100~200 kPa, which nearly equals to the air-entry value of the corresponding soil. The air permeation velocity and pressure gradient curve in the soil show clearly in step-phase. The main reason for this phenomenon may be due to that in saturated porous soil, all the channels are full of water. At the initial stage of air entrance, only a small mount of absorbed water can move under low air pressure. And with the air pressure increases, the air permeation channel expands, more air can be transmitted. The study of air permeation in saturated soft soil is helpful for air pneumatic underground engineering construction activities in saturated soft soils.
After air entrance, an unsaturated area is formed in saturated soil. So, in fact, air permeation in saturated soil aquifer is an unsaturated permeation problem. Based on the constitutive equation, which is deduced from porous media theory with consideration of the compressibility of air, the characteristics of air permeation in saturated soil aquifer in Shanghai area is studied through laboratory tests. Results show that the air permeation in saturated clayey soil has a threshold of pressure about 100~200 kPa, which nearly equals to the air-entry value of the corresponding soil. The air permeation velocity and pressure gradient curve in the soil show clearly in step-phase. The main reason for this phenomenon may be due to that in saturated porous soil, all the channels are full of water. At the initial stage of air entrance, only a small mount of absorbed water can move under low air pressure. And with the air pressure increases, the air permeation channel expands, more air can be transmitted. The study of air permeation in saturated soft soil is helpful for air pneumatic underground engineering construction activities in saturated soft soils.
2009, 17(2): 249-252.
Karst rocky desertification in the southwest of China has seriously influenced local people's life. Essentially, soil erosion is the key causing rocky desertification. The red clay, which widely distribute in karst region, is more easily to be eroded under the rainfall, because it's shear strength is changeable with water content. This paper presents a comparative analysis of direct shear test for undisturbed and remolded soil samples (modeling the reclaimed soil). The analysis preliminarily reveals the laws of the shear strength of red clay changing with water content. It is found that whenits water content 35%, the the cohesion and internal friction angle of the red clay decrease with the increasing of water content. The shear strength of undisturbed soil is significantly larger than that of the remolded soil under the same water suction. As water content increases, the shear strength of the remolded soil samples attenuates more drastically than that of the undisturbed soil. It shows that the reclaimed red clay is more easily to be eroded under the rainfall.
Karst rocky desertification in the southwest of China has seriously influenced local people's life. Essentially, soil erosion is the key causing rocky desertification. The red clay, which widely distribute in karst region, is more easily to be eroded under the rainfall, because it's shear strength is changeable with water content. This paper presents a comparative analysis of direct shear test for undisturbed and remolded soil samples (modeling the reclaimed soil). The analysis preliminarily reveals the laws of the shear strength of red clay changing with water content. It is found that whenits water content 35%, the the cohesion and internal friction angle of the red clay decrease with the increasing of water content. The shear strength of undisturbed soil is significantly larger than that of the remolded soil under the same water suction. As water content increases, the shear strength of the remolded soil samples attenuates more drastically than that of the undisturbed soil. It shows that the reclaimed red clay is more easily to be eroded under the rainfall.
2009, 17(2): 253-257.
The relationship between slope stability and influencing factors is complex and nonlinear. Support vector machine (SVM) is used to build the nonlinear relationship. The parameters of SVM are optimized with a continuous ant colony algorithm (CACA). Thus the ACAC-SVM is proposed for forecasting slope stability. Slope of right-bank spandrel groove at Jinping is forward slope. A majority of the slope surface is bare and comprised of bedrock. the natural slope is comprised of marbleand stability now. The CACA-SVM is used to analysis the stability of the slope of right-bank spandrel groove at Jinping. The results are in good agreement with the actual data, which indicates that the CACA-SVM can be well applied to the analysis of slope stability
The relationship between slope stability and influencing factors is complex and nonlinear. Support vector machine (SVM) is used to build the nonlinear relationship. The parameters of SVM are optimized with a continuous ant colony algorithm (CACA). Thus the ACAC-SVM is proposed for forecasting slope stability. Slope of right-bank spandrel groove at Jinping is forward slope. A majority of the slope surface is bare and comprised of bedrock. the natural slope is comprised of marbleand stability now. The CACA-SVM is used to analysis the stability of the slope of right-bank spandrel groove at Jinping. The results are in good agreement with the actual data, which indicates that the CACA-SVM can be well applied to the analysis of slope stability
2009, 17(2): 258-262.
Some qualitative factors influencing the stability of rock debris slopes are difficult to be quantified using limit equilibrium and numerical analysis methods. Quantification theory can take full consideration about the influence of qualitative factors and can be used to quantify them. Based on the quantification theory, the stability assessment model of rock debris slopes are presented. According to the material composes of rock debris slopes and the contact condition of inner particles, the structural classification of rock debris slopes are presented. Based on the main factors analysis, four evaluation indexes are proposed to establish the stability assessment model. The four indexes are (a) the saturated uniaxial compressive rock strength (divided into four levels), (b) the structure of rock debris (divided into three levels), (c) the slope of ground surface (divided into three levels), and (d) the conditions of groundwater (divided into two levels). The application of the model to Yunnan Shuifu-Maliuwan highway acquired a sort of predicted values. They have a good agreement with the measured values. The model can be used for the stability assessment of similar projects.
Some qualitative factors influencing the stability of rock debris slopes are difficult to be quantified using limit equilibrium and numerical analysis methods. Quantification theory can take full consideration about the influence of qualitative factors and can be used to quantify them. Based on the quantification theory, the stability assessment model of rock debris slopes are presented. According to the material composes of rock debris slopes and the contact condition of inner particles, the structural classification of rock debris slopes are presented. Based on the main factors analysis, four evaluation indexes are proposed to establish the stability assessment model. The four indexes are (a) the saturated uniaxial compressive rock strength (divided into four levels), (b) the structure of rock debris (divided into three levels), (c) the slope of ground surface (divided into three levels), and (d) the conditions of groundwater (divided into two levels). The application of the model to Yunnan Shuifu-Maliuwan highway acquired a sort of predicted values. They have a good agreement with the measured values. The model can be used for the stability assessment of similar projects.
2009, 17(2): 263-267.
The Jiaoling tunnel in construction encountered two types of rocks along its transverse section. Half of the tunnel section is hard-rock while the other half is soft rock. The hard rock is intact and has a 40 MPa compressive strength. The soft rock is weathered and fractured and has a compressive strength 5MPa. Collapse at the side of soft rock took place during the construction. Mechanical characteristics for the hard and soft rocks and the collapse reasons were analyzed at the portal of the left tunnel line. . Then counterpart collapse treatments were employed. For example, surface with grouting reinforcement and tube-grouting frame were explained. Strength of the treated soft rock was almost equal to that of hard rock. Bearing loop was made up of treated soft rock and hard rock. At last the treated zone was monitored. It was judged from monitoring data that the zone was stable quickly. So, this treatment method is reasonable and effective. The bearing loop theory can be used to the half-hard and half-soft rock transverse-section tunnel. New idea in the paper is the suspension theory applicable to bolting and grouting-tube treatment of soft rock tunnel. This theory can improve the effectiveness of bolt reinforcing soft rock tunnel. This conclusion in the paper is useful for design and construction of tunnel in half-hard and half-soft rock.
The Jiaoling tunnel in construction encountered two types of rocks along its transverse section. Half of the tunnel section is hard-rock while the other half is soft rock. The hard rock is intact and has a 40 MPa compressive strength. The soft rock is weathered and fractured and has a compressive strength 5MPa. Collapse at the side of soft rock took place during the construction. Mechanical characteristics for the hard and soft rocks and the collapse reasons were analyzed at the portal of the left tunnel line. . Then counterpart collapse treatments were employed. For example, surface with grouting reinforcement and tube-grouting frame were explained. Strength of the treated soft rock was almost equal to that of hard rock. Bearing loop was made up of treated soft rock and hard rock. At last the treated zone was monitored. It was judged from monitoring data that the zone was stable quickly. So, this treatment method is reasonable and effective. The bearing loop theory can be used to the half-hard and half-soft rock transverse-section tunnel. New idea in the paper is the suspension theory applicable to bolting and grouting-tube treatment of soft rock tunnel. This theory can improve the effectiveness of bolt reinforcing soft rock tunnel. This conclusion in the paper is useful for design and construction of tunnel in half-hard and half-soft rock.
2009, 17(2): 268-273.
One Thick fill embankment was composed of broken rocks in Henan province. It was taken as an engineering example in this paper. A construction technology of dynamic compaction with energy of 1000 kNm and loose layer of 1.5m depth was put forward. In-situ tests were done at some segments. The loose layers turn dense after having been compacted and the horizontal efficient compaction range was 4m and was displayed from the ground radar wave shape. Rayleigh waves change little in the depth and the averaged value is 310ms-1. The segments have middle density judged with the heavy dynamic penetration tests results. The solid volume ratios tested with water replacement method were all above 83%. So, an important conclusion was obtained that the segments after having been dynamically compacted can have better compaction effect. The FEM software of ABAQUS was adopted. The dynamic compaction was simulated by taking the pounder as a rigid body and assigning the pounder with a vertical initial velocity. The efficient compaction range can be judged by the settlement of 20mm according to the conclusion from ground radar. Finally, dynamic compaction on the embankment with a buried culvert was simulated, which reveals that the depth of embankment upper culvert must be larger than 8 m for safe dynamic compaction.
One Thick fill embankment was composed of broken rocks in Henan province. It was taken as an engineering example in this paper. A construction technology of dynamic compaction with energy of 1000 kNm and loose layer of 1.5m depth was put forward. In-situ tests were done at some segments. The loose layers turn dense after having been compacted and the horizontal efficient compaction range was 4m and was displayed from the ground radar wave shape. Rayleigh waves change little in the depth and the averaged value is 310ms-1. The segments have middle density judged with the heavy dynamic penetration tests results. The solid volume ratios tested with water replacement method were all above 83%. So, an important conclusion was obtained that the segments after having been dynamically compacted can have better compaction effect. The FEM software of ABAQUS was adopted. The dynamic compaction was simulated by taking the pounder as a rigid body and assigning the pounder with a vertical initial velocity. The efficient compaction range can be judged by the settlement of 20mm according to the conclusion from ground radar. Finally, dynamic compaction on the embankment with a buried culvert was simulated, which reveals that the depth of embankment upper culvert must be larger than 8 m for safe dynamic compaction.
2009, 17(2): 274-279.
Firstly, the mechanical model is based on static equilibrium of the soil arch between two piles in pile-slab wall and soil resistance on its two end sections near two piles. The calculation method is developed. Then the shape function of soil arch is derived. Slide plane is ascertained after analysis of the shape function. The calculation formula of earth pressure on slab between two adjacent anti-slide piles is formulated. The formula has several factors acting on the earth pressure. The factors are analyzed. For the same test, the new earth pressure formula is compared with the Rankine method. It is shown that the distance between two adjacent piles is the main factor. Earth pressure increases as the distance increase. At the end, the calculation formula is illustrated with a practical project.
Firstly, the mechanical model is based on static equilibrium of the soil arch between two piles in pile-slab wall and soil resistance on its two end sections near two piles. The calculation method is developed. Then the shape function of soil arch is derived. Slide plane is ascertained after analysis of the shape function. The calculation formula of earth pressure on slab between two adjacent anti-slide piles is formulated. The formula has several factors acting on the earth pressure. The factors are analyzed. For the same test, the new earth pressure formula is compared with the Rankine method. It is shown that the distance between two adjacent piles is the main factor. Earth pressure increases as the distance increase. At the end, the calculation formula is illustrated with a practical project.
2009, 17(2): 280-283.
Post-grouting technique injects cement slurry into pile toe along its embedded steel pipe. It can reduce detritus of pile toe and mudcake and is used widely. It is necessary to understand fully the bearing capacity of post-grouted pile. Traditional design method of pile foundation is usually adopted and does not accord with the practical situation. Based on the results of static loading tests of two piles (one is post-grouted and the other not), the bearing properties of the two piles are analyzed comparatively. The load transfer mechanism, such as the axial load and the skin friction distribution law, is studied with the stress gages. It is found that the bearing capacity of the post-grouted pile is about 2.5 times larger than that of the ordinary one. The post-grouting technique can improve the toe resistance and skin friction. It can improve the characteristics of the interface between pile and soil, and increase the bearing capacity and decreases the settlement of pile effectively.
Post-grouting technique injects cement slurry into pile toe along its embedded steel pipe. It can reduce detritus of pile toe and mudcake and is used widely. It is necessary to understand fully the bearing capacity of post-grouted pile. Traditional design method of pile foundation is usually adopted and does not accord with the practical situation. Based on the results of static loading tests of two piles (one is post-grouted and the other not), the bearing properties of the two piles are analyzed comparatively. The load transfer mechanism, such as the axial load and the skin friction distribution law, is studied with the stress gages. It is found that the bearing capacity of the post-grouted pile is about 2.5 times larger than that of the ordinary one. The post-grouting technique can improve the toe resistance and skin friction. It can improve the characteristics of the interface between pile and soil, and increase the bearing capacity and decreases the settlement of pile effectively.
2009, 17(2): 284-288.
On the basis of the finite difference software -FLAC3D, this paper compiles program using its FISH language to simulate the effects of shield tunneling on bearing capacity of a single pile. Considering the soil pressure in the soil chamber, grouting in the shield tail, and grouting with two phases of clotted and not clotted states. The bearing capacity of a single pile is analyzed during shield tunneling. Influential factors to the single pile by shield tunneling consist of skin-friction resistance and tip resistance of a pile. The influence on the pile bearing capacity is also analyzed as changing of propellant force of the face of excavation. It shows that negative skin-friction of pile would occur at the bottom of the pile, which could decrease the bearing capacity of the pile. The bearing capacity of a pile changes with varying the soil pressure in the soil chamber.
On the basis of the finite difference software -FLAC3D, this paper compiles program using its FISH language to simulate the effects of shield tunneling on bearing capacity of a single pile. Considering the soil pressure in the soil chamber, grouting in the shield tail, and grouting with two phases of clotted and not clotted states. The bearing capacity of a single pile is analyzed during shield tunneling. Influential factors to the single pile by shield tunneling consist of skin-friction resistance and tip resistance of a pile. The influence on the pile bearing capacity is also analyzed as changing of propellant force of the face of excavation. It shows that negative skin-friction of pile would occur at the bottom of the pile, which could decrease the bearing capacity of the pile. The bearing capacity of a pile changes with varying the soil pressure in the soil chamber.
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