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Editor Work2014 Vol. 22, No. 2
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2014, 22(2): 181-187.
Abstract
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The long-term deformation of structural soils inevitably affects soil structure. Through triaxial creep test for structural soft dredger fill, the micro-mechanics and the changes of structure strength were studied by choosing representative sample during the creep. The results show that the essence of creep is the process about mutual transformation between hardening and softening of the internal structure of soil. When the stress level is less than the structure yield stress, the hardening accounts for the main portion in the process of creep, and the change of micro-structure is gradually stabilized, the structure strength increases accordingly. The softening accounts for the main portion in the process of creep when the stress level exceeds the structure yield stress. This stage can be subdivided into two stages. They are the heavy soil structure destruction stage and the soil ultimate failure stage. The micro-structure is changed from the stable stage to the unstable stage, eventually back to the disorder stage.
The long-term deformation of structural soils inevitably affects soil structure. Through triaxial creep test for structural soft dredger fill, the micro-mechanics and the changes of structure strength were studied by choosing representative sample during the creep. The results show that the essence of creep is the process about mutual transformation between hardening and softening of the internal structure of soil. When the stress level is less than the structure yield stress, the hardening accounts for the main portion in the process of creep, and the change of micro-structure is gradually stabilized, the structure strength increases accordingly. The softening accounts for the main portion in the process of creep when the stress level exceeds the structure yield stress. This stage can be subdivided into two stages. They are the heavy soil structure destruction stage and the soil ultimate failure stage. The micro-structure is changed from the stable stage to the unstable stage, eventually back to the disorder stage.
2014, 22(2): 188-195.
This paper studies the characteristic of remolded grey expansive soil in Ningming of Guangxi province. A series of swelling tests were conducted for cubic expansive soil of different initial moisture contents and three-directional pressures. The test device is a home-madethree-directional swelling and shrinkage of expansive soil tester. The tests investigate the natural law of the effects of the initial moisture content and the three-directional pressure to the maximum water content the three-directional expansion rate. According to the test results, the vertical expansion rate is always larger than horizontal expansion rate when three-directional pressure is equal. Their ratio is 1.21～1.27. The ratio is unrelated to the initial moisture content and the three-directional pressure. The time-deformation history of the three-directional expansion rate includes three phases the rapid expansion, the slow expansion and the stabilization. The maximum water content has a linear correlation to the logarithm of the three-directional pressure. But it does not associated with the initial moisture. The three-directional expansion rate has a linear correlation to the logarithm of the three-directional pressure, when the expansive soil has the same initial moisture content and dry density characteristic.
This paper studies the characteristic of remolded grey expansive soil in Ningming of Guangxi province. A series of swelling tests were conducted for cubic expansive soil of different initial moisture contents and three-directional pressures. The test device is a home-madethree-directional swelling and shrinkage of expansive soil tester. The tests investigate the natural law of the effects of the initial moisture content and the three-directional pressure to the maximum water content the three-directional expansion rate. According to the test results, the vertical expansion rate is always larger than horizontal expansion rate when three-directional pressure is equal. Their ratio is 1.21～1.27. The ratio is unrelated to the initial moisture content and the three-directional pressure. The time-deformation history of the three-directional expansion rate includes three phases the rapid expansion, the slow expansion and the stabilization. The maximum water content has a linear correlation to the logarithm of the three-directional pressure. But it does not associated with the initial moisture. The three-directional expansion rate has a linear correlation to the logarithm of the three-directional pressure, when the expansive soil has the same initial moisture content and dry density characteristic.
2014, 22(2): 196-202.
During the shield construction, the surrounding soil would be disturbed for unloading due to shield-end structural spacing. The soil disturbance is especially for clay with strong structure. This paper is to simulate the unloading disturbance of shield soils. The drained shear creep tests are conducted. The results indicate that the deformation under the same load increases with unload increasing. The deformation is steady creep when loading stress is small. Creep rate becomes greater with unloads increasing. The deformation is attenuation creep when loading stress is large. The results are compared with Singh-Mitchell creep model. It is found that the calculated value coincides well with the test data under small loading stress. But, it has large deviation under big loading stress. Therefore we revise the parameters of Singh-Mitchell creep model. A revised Singh-Mitchell creep model considering unloading disturbance is put forward. The calculated value coincides well with the test data under big loading stress and unloading stress.
During the shield construction, the surrounding soil would be disturbed for unloading due to shield-end structural spacing. The soil disturbance is especially for clay with strong structure. This paper is to simulate the unloading disturbance of shield soils. The drained shear creep tests are conducted. The results indicate that the deformation under the same load increases with unload increasing. The deformation is steady creep when loading stress is small. Creep rate becomes greater with unloads increasing. The deformation is attenuation creep when loading stress is large. The results are compared with Singh-Mitchell creep model. It is found that the calculated value coincides well with the test data under small loading stress. But, it has large deviation under big loading stress. Therefore we revise the parameters of Singh-Mitchell creep model. A revised Singh-Mitchell creep model considering unloading disturbance is put forward. The calculated value coincides well with the test data under big loading stress and unloading stress.
2014, 22(2): 203-209.
The hydrogeochemical reaction of the high-pressure bentonite in the high-level nuclear waste repository was simulated with the software Phreeqc. A one-dimensional transport model is established in consideration of the cation exchange of K+,Ca2+,Na+,Mg2+ and mineral dissolution and precipitation reactions. The curves of the bentonite chemical components changing over time and space are obtained, which verifies that the decay in swelling capacity is mainly caused by the transformation from Na-montmorillonite into Ca-montmorillonite. The degree of decay in swelling capacity is evaluated. Decay coefficients of the GMZ and MX80 bentonite respectively reach 0.83 and 0.79 in the seawater and 0.91 and 0.90 in the underground water after 10000 years.
The hydrogeochemical reaction of the high-pressure bentonite in the high-level nuclear waste repository was simulated with the software Phreeqc. A one-dimensional transport model is established in consideration of the cation exchange of K+,Ca2+,Na+,Mg2+ and mineral dissolution and precipitation reactions. The curves of the bentonite chemical components changing over time and space are obtained, which verifies that the decay in swelling capacity is mainly caused by the transformation from Na-montmorillonite into Ca-montmorillonite. The degree of decay in swelling capacity is evaluated. Decay coefficients of the GMZ and MX80 bentonite respectively reach 0.83 and 0.79 in the seawater and 0.91 and 0.90 in the underground water after 10000 years.
2014, 22(2): 210-217.
This paper is to find out the strain state, variation and development of cracking in unsaturated expansive soil during dry-wet cycle. A model box with 150cm long, 10cm wide and 60cm high is designed. A high spatial resolution distributed optical fiber strain measuring technique(PPP - BOTDA) is used to monitor the strain status of the sensing fibers embedded in unsaturated soil at 4 different depths during the dry-wet cycle. At the same depth, the sensing fibers include 4 different kinds and are laid along the longitudinal direction of the model. The experiments show that strain of the sensing fiber is under the influence of soil cracking. Spatially, the strain status is not uniform and characterizing with alternate distribution of tension and compression. Temporally, with the decreasing of soil water content, the stain state of the sensing fibers across cracking zone changes from compression to tension and the stain value has correlation with the total crack opening. With the increasing of the embedded depth, strain distributions of the sensing fibers are more uniform as the influence of the surface cracks to the deep fibers is relatively small. During the wetting process, the strain state of the sensing fibers across the cracks changes from tension to compression with the closing of cracks, whereas the fiber strain near the cracks goes tensile. The results indicate that PPP-BOTDA based distributed optical fiber sensing technology can monitor the strain state of expansive soil during dry-wet cycle and locate the cracks of the soil accurately. The PPP-BOTDA can be a new technical means for soil deformation monitoring and disaster assessment.
This paper is to find out the strain state, variation and development of cracking in unsaturated expansive soil during dry-wet cycle. A model box with 150cm long, 10cm wide and 60cm high is designed. A high spatial resolution distributed optical fiber strain measuring technique(PPP - BOTDA) is used to monitor the strain status of the sensing fibers embedded in unsaturated soil at 4 different depths during the dry-wet cycle. At the same depth, the sensing fibers include 4 different kinds and are laid along the longitudinal direction of the model. The experiments show that strain of the sensing fiber is under the influence of soil cracking. Spatially, the strain status is not uniform and characterizing with alternate distribution of tension and compression. Temporally, with the decreasing of soil water content, the stain state of the sensing fibers across cracking zone changes from compression to tension and the stain value has correlation with the total crack opening. With the increasing of the embedded depth, strain distributions of the sensing fibers are more uniform as the influence of the surface cracks to the deep fibers is relatively small. During the wetting process, the strain state of the sensing fibers across the cracks changes from tension to compression with the closing of cracks, whereas the fiber strain near the cracks goes tensile. The results indicate that PPP-BOTDA based distributed optical fiber sensing technology can monitor the strain state of expansive soil during dry-wet cycle and locate the cracks of the soil accurately. The PPP-BOTDA can be a new technical means for soil deformation monitoring and disaster assessment.
2014, 22(2): 218-225.
This paper decides the discipline of soft soil subgrade lateral deformation after the approach of plastic drainage plate in the southwest area. Based on the project of expressway from Suining to Ziyang in Sichuan Province, we sort out the typical observation data of monitoring sections deformation. We analyze the variation law of lateral deformation from the angle of time and depth. Meanwhile we propose the forecasting model according to the characteristic of deformation. The results indicate that the following.(1)During the process of filling, the lateral deformation near the ground surface alters violently. (2)The lateral deformation distributes three variation laws: during the filling stage, the relationship between the lateral deformation and time is ym=SD. The height from the critical filling to the design process, the relationship is ym=0.15SD. In the consolidation stage, it is ym=0.3SD. The maximum lateral deformation is distributed as S-shape with time. The maximum deformation position does not change. (3)We propose and predicte the y(z)=ae-z(bsinz+ccosz)、y(t)=a/(1+e(b-ctr)) curve according to the variation law of lateral horizontal deformation from the angle of depth and time. The result indicates that the predicted life matches the real data.
This paper decides the discipline of soft soil subgrade lateral deformation after the approach of plastic drainage plate in the southwest area. Based on the project of expressway from Suining to Ziyang in Sichuan Province, we sort out the typical observation data of monitoring sections deformation. We analyze the variation law of lateral deformation from the angle of time and depth. Meanwhile we propose the forecasting model according to the characteristic of deformation. The results indicate that the following.(1)During the process of filling, the lateral deformation near the ground surface alters violently. (2)The lateral deformation distributes three variation laws: during the filling stage, the relationship between the lateral deformation and time is ym=SD. The height from the critical filling to the design process, the relationship is ym=0.15SD. In the consolidation stage, it is ym=0.3SD. The maximum lateral deformation is distributed as S-shape with time. The maximum deformation position does not change. (3)We propose and predicte the y(z)=ae-z(bsinz+ccosz)、y(t)=a/(1+e(b-ctr)) curve according to the variation law of lateral horizontal deformation from the angle of depth and time. The result indicates that the predicted life matches the real data.
2014, 22(2): 226-232.
The resistance of wet-dry cycles is an important durability index of solidified soil. It is important to explore the effect of environmental features, namely wet-dry cycles, on the performance and durability of loess solidification. In this paper, the solidified agent of SH is used in the loess solidification. By simulating the climate change of wet-dry cycles characteristics indoor, the effects of wet-dry cycles on compressive strength and shear strength of the solidified loess are analyzed. The test results show that: the strength of samples after wet-dry cycles is declined or weakened in overall. With the increase of number of cycles, the compressive strength values for samples exponential decline, but they are higher than the loess. SH content increases, the compressive strength losses reduce. The weight losses are very smaller, and the integrities are good. The parameters of shear strength decrease with SH content. The effects of wet-dry cycles on cohesion are obvious. During the beginning of three wet-dry cycles, the cohesions of the loess solidification by different contents of SH are decreased; after fourth cycles, the cohesions have a little increase, and then show a little decrease. With the increase of wet-dry cycles, they proceed to a relatively steady state. The internal friction angles of the solidified loess express a decreasing tendency, and maintain stability. Because of the change of water quality during the condensation-evaporation process, the weight and volumetric changes of specimens are flexuous. By analyzing the relationship between the stress and strain of the loess solidification by 10%SH content, it is concluded that the solidified loess has hardening characteristic. The loess solidification by more than 10%SH content is durable against 15 cycles for its higher and more steadying strength. Subsequent to that, it is good in water stability, and solidified agent of SH applied in loess of anti-wet-dry cycle has a prominent role. SH has a broad prospect in application.
The resistance of wet-dry cycles is an important durability index of solidified soil. It is important to explore the effect of environmental features, namely wet-dry cycles, on the performance and durability of loess solidification. In this paper, the solidified agent of SH is used in the loess solidification. By simulating the climate change of wet-dry cycles characteristics indoor, the effects of wet-dry cycles on compressive strength and shear strength of the solidified loess are analyzed. The test results show that: the strength of samples after wet-dry cycles is declined or weakened in overall. With the increase of number of cycles, the compressive strength values for samples exponential decline, but they are higher than the loess. SH content increases, the compressive strength losses reduce. The weight losses are very smaller, and the integrities are good. The parameters of shear strength decrease with SH content. The effects of wet-dry cycles on cohesion are obvious. During the beginning of three wet-dry cycles, the cohesions of the loess solidification by different contents of SH are decreased; after fourth cycles, the cohesions have a little increase, and then show a little decrease. With the increase of wet-dry cycles, they proceed to a relatively steady state. The internal friction angles of the solidified loess express a decreasing tendency, and maintain stability. Because of the change of water quality during the condensation-evaporation process, the weight and volumetric changes of specimens are flexuous. By analyzing the relationship between the stress and strain of the loess solidification by 10%SH content, it is concluded that the solidified loess has hardening characteristic. The loess solidification by more than 10%SH content is durable against 15 cycles for its higher and more steadying strength. Subsequent to that, it is good in water stability, and solidified agent of SH applied in loess of anti-wet-dry cycle has a prominent role. SH has a broad prospect in application.
2014, 22(2): 233-237.
This paper deals with the two damage forms: rock mass crushing and plastic changes in underground engineering. It is based on Mohr-Coulomb criterion. The radii of crushed circle under the action of shock wave is obtained. It applies Von Mises yielding criterion to calculate the rock plastic zone under stress wave. It uses the KUBELA 420 explosive as an example. For sandstone in Chongqing under blasting load, the radii of crushed circle is not more than 1.7 times of charging radius and plastic zone radius does not exceed 25.06 times of charging radius. The prediction is close to the numerical simulation results.
This paper deals with the two damage forms: rock mass crushing and plastic changes in underground engineering. It is based on Mohr-Coulomb criterion. The radii of crushed circle under the action of shock wave is obtained. It applies Von Mises yielding criterion to calculate the rock plastic zone under stress wave. It uses the KUBELA 420 explosive as an example. For sandstone in Chongqing under blasting load, the radii of crushed circle is not more than 1.7 times of charging radius and plastic zone radius does not exceed 25.06 times of charging radius. The prediction is close to the numerical simulation results.
2014, 22(2): 238-243.
This paper is to realize the disintegration characteristics of argillaceous shale in acid and alkali environment separately. It carries out the static disintegration test and slake disintegration test of argillaceous shale. The influence rule between pH value and disintegration of argillaceous shale are obtained. It shows that the pH value plays an important role in the disintegration of argillaceous shale. The smaller the pH value, the stronger the disintegration. As the grain diameter increases, the slake disintegration index of argillaceous shale can increase. Moreover, the smaller the pH value, the less the slake disintegration index. The acid environment plays a more important role than the alkaline environment.
This paper is to realize the disintegration characteristics of argillaceous shale in acid and alkali environment separately. It carries out the static disintegration test and slake disintegration test of argillaceous shale. The influence rule between pH value and disintegration of argillaceous shale are obtained. It shows that the pH value plays an important role in the disintegration of argillaceous shale. The smaller the pH value, the stronger the disintegration. As the grain diameter increases, the slake disintegration index of argillaceous shale can increase. Moreover, the smaller the pH value, the less the slake disintegration index. The acid environment plays a more important role than the alkaline environment.
2014, 22(2): 244-249.
This paper uses the Raman Optical Time Domain Reflectometer(ROTDR) and Fiber Bragg Gratting(FBG)to monitor the hydration heat of large base-slab concreting for ship lock. The base-slab is 14.8m wide, 29.2m long and 3m thick. The monitoring shows the following results. The peak temperature in core of the concrete block thick can reach 54.5℃at the 5th day after the concreting. The surface temperature can reach the peak temperature 46.7℃ at the 6th day. According to the monitoring results, a comprehensive analysis of concrete hydration heat release process is carried out to verify the feasibility of ROTDR and FBG to be used in monitoring the hydration temperature field changes during mass concreting. These results can provide reliable data for appraisal of safety and stability of the ship lock.
This paper uses the Raman Optical Time Domain Reflectometer(ROTDR) and Fiber Bragg Gratting(FBG)to monitor the hydration heat of large base-slab concreting for ship lock. The base-slab is 14.8m wide, 29.2m long and 3m thick. The monitoring shows the following results. The peak temperature in core of the concrete block thick can reach 54.5℃at the 5th day after the concreting. The surface temperature can reach the peak temperature 46.7℃ at the 6th day. According to the monitoring results, a comprehensive analysis of concrete hydration heat release process is carried out to verify the feasibility of ROTDR and FBG to be used in monitoring the hydration temperature field changes during mass concreting. These results can provide reliable data for appraisal of safety and stability of the ship lock.
2014, 22(2): 250-254.
This paper investigated the Cavern No.4 in Tang Dynasty Gold Cavern of Suichang Gold Mine. The surrounding rock of ancient passages is found to be hard metamorphic rock. Its Protodyakonov coefficient is as high as 14～19. From field research, four interesting phenomena are founded. Firstly, the joint planes in ancient passages have the feather of high density, high dip angel and small spacing. Secondly, the strike between axis in ancient passages and joint plane are basically consistent. Thirdly, the ratio of height to width in cross-section of ancient passages has the values ranging from 4 to 6,which is large. Fourthly, most of ancient passage axes are arc shape. As it is known, tensile strength and cohesion on joint planes are low. More than a thousand years ago, the ancients understood the above feather of joint planes with high dip angle and could make good use of them to excavate the passages. In order to take full advantage of the above feather, the ancients adjusted the direction of axis in ancient passages according to the strike of joint planes, and made them be consistent. Because the strikes of joint planes can change, the shape of ancient passages axis become arc. This shows that the ancients at the Tang Dynasty had mastered a considerable amount of geological knowledge, which was successfully applied in their engineering practice.
This paper investigated the Cavern No.4 in Tang Dynasty Gold Cavern of Suichang Gold Mine. The surrounding rock of ancient passages is found to be hard metamorphic rock. Its Protodyakonov coefficient is as high as 14～19. From field research, four interesting phenomena are founded. Firstly, the joint planes in ancient passages have the feather of high density, high dip angel and small spacing. Secondly, the strike between axis in ancient passages and joint plane are basically consistent. Thirdly, the ratio of height to width in cross-section of ancient passages has the values ranging from 4 to 6,which is large. Fourthly, most of ancient passage axes are arc shape. As it is known, tensile strength and cohesion on joint planes are low. More than a thousand years ago, the ancients understood the above feather of joint planes with high dip angle and could make good use of them to excavate the passages. In order to take full advantage of the above feather, the ancients adjusted the direction of axis in ancient passages according to the strike of joint planes, and made them be consistent. Because the strikes of joint planes can change, the shape of ancient passages axis become arc. This shows that the ancients at the Tang Dynasty had mastered a considerable amount of geological knowledge, which was successfully applied in their engineering practice.
2014, 22(2): 255-262.
Strong rainstorm can induce a burst of large number of small scale landslides. In typhoon areas, storm-induced landslides pose a high risk to the human lives and properties. It is therefore of great significance to study the occurrence of the landslides in typhoon areas. In this study, the critical duration of rainfall is estimated according to the reactivation period of extreme rainfall calculated using the Extreme Value Theory(EVT).Then, a threshold curve of the storm-induced landslides in typhoon areas is obtained based on a statistical approach. A typical typhoon region, the Fujian Province in the southeast China, is taken as a study area. Three typical regions with high occurrence of landslides are detected in the Fujian Province: the Nanping-Sanming region, the Quanzhou region and the Ningde region. It is found that, although the rainfall threshold of the Nanping-Sanming region is relatively higher, landslides happen more frequently and are mainly caused by continuous rainfall in three days. The Quanzhou region is susceptible to the influence of both short-term(3 days) and long-term(8 days) continuous heavy rainfall. The landslides in the Ningde Region are mainly caused by continuous rainfall in one day. This comparative study in different areas shows that the threshold of rainfall-induced landslide is affected by complex factors dominated with climate, geological environment and soil depth. The threshold of rainfall-induced landslide in typhoon areas is higher than that in non-typhoon areas, since the climate is the primary controlling factor of the threshold of rainfall-induced landslides.
Strong rainstorm can induce a burst of large number of small scale landslides. In typhoon areas, storm-induced landslides pose a high risk to the human lives and properties. It is therefore of great significance to study the occurrence of the landslides in typhoon areas. In this study, the critical duration of rainfall is estimated according to the reactivation period of extreme rainfall calculated using the Extreme Value Theory(EVT).Then, a threshold curve of the storm-induced landslides in typhoon areas is obtained based on a statistical approach. A typical typhoon region, the Fujian Province in the southeast China, is taken as a study area. Three typical regions with high occurrence of landslides are detected in the Fujian Province: the Nanping-Sanming region, the Quanzhou region and the Ningde region. It is found that, although the rainfall threshold of the Nanping-Sanming region is relatively higher, landslides happen more frequently and are mainly caused by continuous rainfall in three days. The Quanzhou region is susceptible to the influence of both short-term(3 days) and long-term(8 days) continuous heavy rainfall. The landslides in the Ningde Region are mainly caused by continuous rainfall in one day. This comparative study in different areas shows that the threshold of rainfall-induced landslide is affected by complex factors dominated with climate, geological environment and soil depth. The threshold of rainfall-induced landslide in typhoon areas is higher than that in non-typhoon areas, since the climate is the primary controlling factor of the threshold of rainfall-induced landslides.
2014, 22(2): 263-271.
The Xiquan Street landslide encountered an especially heavy rain of 115 years return period in middle July 2007. The heavy rainfall led to an obvious deformation failure phenomenon. This paper is based on the survey work and the saturated-unsaturated seepage theory. By considered the rainfall infiltration, it uses the finite element analysis software Geo-Studio to simulate the changes of the landslide stability for different rain conditions. Then the landslide seepage field, stress field and displacement field for different rain conditions are further studied through the numerical simulation method. The results show the following result. (1)The seepage field and displacement field of the landslide have good similarity under the action of rainfall. Namely the groundwater velocity vector and displacement vector have consistent variations. (2)Displacements of the front edge and back edge of the landslide have positive correlation with the rainfall density and rainfall duration. The displacement of front edge is bigger than that of the back edge. (3)Under the continuous function of rainstorm and heavy rainstorm, the X-Y direction max shear stress is centralized at the front of the landslide and the scarp place. The landslide has a sliding tendency at local area. Under the sustaining action of torrential rain, the maximum shear stress in the X-Y direction distributes relatively uniform near the sliding zone. The landslide has an integral sliding tendency. (4)Under the heavy rainfall, the landslide deformation damage law is mainly as follows: first bulging deformation is at front edge, then the tensile deformation appears at the back edge, which is consistent with the actual deformation.
The Xiquan Street landslide encountered an especially heavy rain of 115 years return period in middle July 2007. The heavy rainfall led to an obvious deformation failure phenomenon. This paper is based on the survey work and the saturated-unsaturated seepage theory. By considered the rainfall infiltration, it uses the finite element analysis software Geo-Studio to simulate the changes of the landslide stability for different rain conditions. Then the landslide seepage field, stress field and displacement field for different rain conditions are further studied through the numerical simulation method. The results show the following result. (1)The seepage field and displacement field of the landslide have good similarity under the action of rainfall. Namely the groundwater velocity vector and displacement vector have consistent variations. (2)Displacements of the front edge and back edge of the landslide have positive correlation with the rainfall density and rainfall duration. The displacement of front edge is bigger than that of the back edge. (3)Under the continuous function of rainstorm and heavy rainstorm, the X-Y direction max shear stress is centralized at the front of the landslide and the scarp place. The landslide has a sliding tendency at local area. Under the sustaining action of torrential rain, the maximum shear stress in the X-Y direction distributes relatively uniform near the sliding zone. The landslide has an integral sliding tendency. (4)Under the heavy rainfall, the landslide deformation damage law is mainly as follows: first bulging deformation is at front edge, then the tensile deformation appears at the back edge, which is consistent with the actual deformation.
2014, 22(2): 272-279.
Lushan earthquake not only caused heavy property loss and personal injuries, but also induced many geological hazards such as avalanches and landslides. This paper is based on the analysis of geological environment condition of the earthquake-stricken area. It deeply analyzes the distribution law, types and characteristics and development tendency of the geological hazards. The earthquake induced 1337geological hazards which mainly include moderate - small scale avalanches, landslides and unstable slopes. The hazards are mainly developed in sandstone and mudstone of the Cretaceous and Triassic system, carbonatite of the Permian system, conglomerate of the Tertiary system and weathered crust and debris of the Quaternary system. They are densely distributed on steep slopes of both sides of the Longmen southern fault (Zhonglin-Shuangshi fault) and Baoxing, Linguan and Lushan river and on the inside slopes of some roads. The earthquake not only induced many geo-hazards, but also caused many potential and hidden geo-hazards. So, the geo-hazards in the disaster area will appear with an increasing trend in the future. This study can provide a reference for disaster prevention and mitigation in the post-earthquake reconstruction.
Lushan earthquake not only caused heavy property loss and personal injuries, but also induced many geological hazards such as avalanches and landslides. This paper is based on the analysis of geological environment condition of the earthquake-stricken area. It deeply analyzes the distribution law, types and characteristics and development tendency of the geological hazards. The earthquake induced 1337geological hazards which mainly include moderate - small scale avalanches, landslides and unstable slopes. The hazards are mainly developed in sandstone and mudstone of the Cretaceous and Triassic system, carbonatite of the Permian system, conglomerate of the Tertiary system and weathered crust and debris of the Quaternary system. They are densely distributed on steep slopes of both sides of the Longmen southern fault (Zhonglin-Shuangshi fault) and Baoxing, Linguan and Lushan river and on the inside slopes of some roads. The earthquake not only induced many geo-hazards, but also caused many potential and hidden geo-hazards. So, the geo-hazards in the disaster area will appear with an increasing trend in the future. This study can provide a reference for disaster prevention and mitigation in the post-earthquake reconstruction.
2014, 22(2): 280-291.
The MS5.7 earthquake occurred at 11:19 on September 7, 2012 in Yiliang county, Yunnan province, China. Later, a MS5.6 earthquake occurred again at 12:16. Many geological hazards were induced by the two earthquakes. They include collapses, landslides, mudslides and other secondary geological hazards. Field investigations show the following major characteristics of the secondary geological hazards of the Yiliang earthquakes. The number of secondary geological hazards was increased significantly after the earthquakes. The distribution of geological hazards that induced directly by the earthquake is controlled obviously by distance to the epicenter. The geological hazards densities at the Ⅷ and Ⅶ intensity areas respectively are 11 and 4.5 times of that at the Ⅵ intensity area. The distribution of geological hazards clearly shows the effect of hanging and foot walls of the geological fault. The seismic geological hazards density of the fault hanging wall is 2.6～3.9 times as that of the foot wall. The distribution of new secondary geological hazards is obviously controlled by the properties of rock types after earthquake. The effect is obviously that the superposition of rainfall and the geological hazards chain of secondary geological hazards after earthquakes. The main characteristics are small magnitude with large disaster and more hazards with small scale in Yiliang earthquakes.
The MS5.7 earthquake occurred at 11:19 on September 7, 2012 in Yiliang county, Yunnan province, China. Later, a MS5.6 earthquake occurred again at 12:16. Many geological hazards were induced by the two earthquakes. They include collapses, landslides, mudslides and other secondary geological hazards. Field investigations show the following major characteristics of the secondary geological hazards of the Yiliang earthquakes. The number of secondary geological hazards was increased significantly after the earthquakes. The distribution of geological hazards that induced directly by the earthquake is controlled obviously by distance to the epicenter. The geological hazards densities at the Ⅷ and Ⅶ intensity areas respectively are 11 and 4.5 times of that at the Ⅵ intensity area. The distribution of geological hazards clearly shows the effect of hanging and foot walls of the geological fault. The seismic geological hazards density of the fault hanging wall is 2.6～3.9 times as that of the foot wall. The distribution of new secondary geological hazards is obviously controlled by the properties of rock types after earthquake. The effect is obviously that the superposition of rainfall and the geological hazards chain of secondary geological hazards after earthquakes. The main characteristics are small magnitude with large disaster and more hazards with small scale in Yiliang earthquakes.
2014, 22(2): 292-299.
Massive landslides can be induced by earthquake because of the strong earthquake activity and fragile geological environment in Luhuo segment of the Xianshuihe fault zone. 179 landslides in 1973 and 62 landslides before 1973 are obtained through data collection and geological investigation. This paper is based on the 62 landslides before 1973 and 179 landslides in 1973. It makes a statistical analysis of the characteristic parameters of Luhuo earthquake-triggered landslides in 1973 and before. Seven characteristic parameters of the seismic landslides are analyzed. They are seismic intensity, epicentral distance, slip direction, formation lithology, slope angle, height, distribution in NW part and SE part. This study supports the following views. (1)The most landslides have a small scale; (2)Seismic intensity zones are between Ⅸ and Ⅹ; (3)Epicentral distance between 0km to 5km and 10km to 15km are high-incidence zones; (4)Angle of slip direction and fault is between 35and 75; (5)Landslides in SE part of the fault is more than those in NW part. The NE foot of NW part has larger area; (6)Formation lithology that have the most landslides is T2-3r; (7)Heights are between 30m to 60m. Major are distributed in the lower slope; (8)Slope angles are between 30to 45.The larger landslides always have lower angles.
Massive landslides can be induced by earthquake because of the strong earthquake activity and fragile geological environment in Luhuo segment of the Xianshuihe fault zone. 179 landslides in 1973 and 62 landslides before 1973 are obtained through data collection and geological investigation. This paper is based on the 62 landslides before 1973 and 179 landslides in 1973. It makes a statistical analysis of the characteristic parameters of Luhuo earthquake-triggered landslides in 1973 and before. Seven characteristic parameters of the seismic landslides are analyzed. They are seismic intensity, epicentral distance, slip direction, formation lithology, slope angle, height, distribution in NW part and SE part. This study supports the following views. (1)The most landslides have a small scale; (2)Seismic intensity zones are between Ⅸ and Ⅹ; (3)Epicentral distance between 0km to 5km and 10km to 15km are high-incidence zones; (4)Angle of slip direction and fault is between 35and 75; (5)Landslides in SE part of the fault is more than those in NW part. The NE foot of NW part has larger area; (6)Formation lithology that have the most landslides is T2-3r; (7)Heights are between 30m to 60m. Major are distributed in the lower slope; (8)Slope angles are between 30to 45.The larger landslides always have lower angles.
2014, 22(2): 300-308.
The devastation and casualties caused by the 1556 Huaxian great earthquake are the severest in the history of mankind. According to records, more than eight hundred and thirty thousands of peoples were killed by the great earthquake. Although the earthquake occurred more than 450 years ago, some geological relics caused by the earthquake are still very clear in some counties such as Weinan, Huaxian, Huayin and Tongguan, which are located in the eastern Guanzhong Basin, Shaanxi Province, China. In the study, four typical geo-heritages including seismogenic faults, seismic-cracks, earthquake rock avalanches and earthquake landslides are investigated by means of field work. The results show that these geo-heritages are the results of strong ground motion associated with tectonic stress field, types of rock and soil, geomorphology and hydrogeololgy. The geological relics caused by the Huaxian earthquake have great values in scientific research, scientific popularization and tourism. Therefore, the protection and use of the sites should be paid more attention.
The devastation and casualties caused by the 1556 Huaxian great earthquake are the severest in the history of mankind. According to records, more than eight hundred and thirty thousands of peoples were killed by the great earthquake. Although the earthquake occurred more than 450 years ago, some geological relics caused by the earthquake are still very clear in some counties such as Weinan, Huaxian, Huayin and Tongguan, which are located in the eastern Guanzhong Basin, Shaanxi Province, China. In the study, four typical geo-heritages including seismogenic faults, seismic-cracks, earthquake rock avalanches and earthquake landslides are investigated by means of field work. The results show that these geo-heritages are the results of strong ground motion associated with tectonic stress field, types of rock and soil, geomorphology and hydrogeololgy. The geological relics caused by the Huaxian earthquake have great values in scientific research, scientific popularization and tourism. Therefore, the protection and use of the sites should be paid more attention.
2014, 22(2): 309-318.
At 10:00 on July 10, 2013, a high topographic position landslide was triggered by the extremely rainfall at the Sanxi village in Dujiangyan city of Sichuan province. The landslide debris flow run-out distance is 1260m and the volume of landslide debris flow is more than 1.5 million m3. The debris destroyed the Sanxi village and caused serious fatalities. This paper is based on the field investigation and laboratory study. It summarizes the basic characteristics of Sanxi village landslide. The forming mechanism and their sliding speeds are also analyzed. Some conclusions are as follows. 1)The landslide has the high topographic-position characteristic. The sandstones from the trailing edge of Sanxi village slipped to the NE direction, then severely hit the slope, and scraped the loose materials on the high topographic slope position, and finally formed the landslide-debris flow disaster. 2)According to its movement and accumulation characteristics, the landslide can be divided into the top sliding area, the middle collision and scraping area, and the lower debris flow deposits area. 3)The direct factor of the landslide triggers is the continuously extreme rainfall weather process. The three days of rainfall in the Dujangyan city are equivalent to 44.1% of the annual average rainfall. 4)Sanxi village landslide is triggered by Wenchuan earthquake, special structural of rocks and soils, terrain conditions and the extreme rainfall events. It is controlled by the coupling effect mechanism of endogenic and exogenic geological processes. 5)The finding of this research is useful to reduce and mitigate the disaster of high topographic-position and fast speed landslide debris flow. It proposes to strengthen the research, monitoring and early warning for high topographic-position landslide due to the increase of extremely heavy rainfall events in recent years.
At 10:00 on July 10, 2013, a high topographic position landslide was triggered by the extremely rainfall at the Sanxi village in Dujiangyan city of Sichuan province. The landslide debris flow run-out distance is 1260m and the volume of landslide debris flow is more than 1.5 million m3. The debris destroyed the Sanxi village and caused serious fatalities. This paper is based on the field investigation and laboratory study. It summarizes the basic characteristics of Sanxi village landslide. The forming mechanism and their sliding speeds are also analyzed. Some conclusions are as follows. 1)The landslide has the high topographic-position characteristic. The sandstones from the trailing edge of Sanxi village slipped to the NE direction, then severely hit the slope, and scraped the loose materials on the high topographic slope position, and finally formed the landslide-debris flow disaster. 2)According to its movement and accumulation characteristics, the landslide can be divided into the top sliding area, the middle collision and scraping area, and the lower debris flow deposits area. 3)The direct factor of the landslide triggers is the continuously extreme rainfall weather process. The three days of rainfall in the Dujangyan city are equivalent to 44.1% of the annual average rainfall. 4)Sanxi village landslide is triggered by Wenchuan earthquake, special structural of rocks and soils, terrain conditions and the extreme rainfall events. It is controlled by the coupling effect mechanism of endogenic and exogenic geological processes. 5)The finding of this research is useful to reduce and mitigate the disaster of high topographic-position and fast speed landslide debris flow. It proposes to strengthen the research, monitoring and early warning for high topographic-position landslide due to the increase of extremely heavy rainfall events in recent years.
2014, 22(2): 319-325.
Rock and coal in coal bearing formation belong to layered sedimentary rocks. Their large-scale subsidence may occur because of coal mining. Thus, it is one of research highlights to develop an analytical tool suitable for these layered rocks. This paper presents a new Boundary Element Method (BEM) for analysis of the surface subsidence due to coal mining. The BEM uses the fundamental solution of layered materials,4～8 noded elements to discretize the boundaries, and effective numerical methods to calculate the singular integrals. An example with exact solutions is used to verify the numerical method. Finally, the numerical method is used to analyze in situ surface subsidence due to coal mining. The result shows that the proposed BEM can analyze the surface subsidence due to coal mining with high efficiency and good accuracy.
Rock and coal in coal bearing formation belong to layered sedimentary rocks. Their large-scale subsidence may occur because of coal mining. Thus, it is one of research highlights to develop an analytical tool suitable for these layered rocks. This paper presents a new Boundary Element Method (BEM) for analysis of the surface subsidence due to coal mining. The BEM uses the fundamental solution of layered materials,4～8 noded elements to discretize the boundaries, and effective numerical methods to calculate the singular integrals. An example with exact solutions is used to verify the numerical method. Finally, the numerical method is used to analyze in situ surface subsidence due to coal mining. The result shows that the proposed BEM can analyze the surface subsidence due to coal mining with high efficiency and good accuracy.
2014, 22(2): 326-333.
Under the combined influences of the human activities and climatic warming, the thawing hazards are widely distributed in the permafrost regions along the Qinghai-Tibet Engineering Corridor. Research of development status of the thawing hazards and their impact on permafrost thermal regime within the corridor are significant to the engineering construction and environment protection in the future. Based on the field investigations, we summarize the types and development status of the thawing hazards within the corridor. We also monitor the ground temperature of three typical thawing hazards and analyzed their thermal influence on permafrost. The research results show that the typical thawing hazards developed in the corridor mainly include thaw slump and landslide, thermokarst pond, thawing settlement. They are widely distributed in the high ice content permafrost regions along the Qinghai-Tibet Highway and Railway. According to the field ground temperature monitoring, thawing hazards have significantly influenced the thermal regime of permafrost in development area and nearby area. The influence scope is differed among the three thawing hazards. Thaw slump and thaw subsidence usually influence the shallow permafrost. But the influence of thermokarst lake is more significant, which usually results in the formation of talik under the lake bottom. In addition, the modeled results show that the thawing hazards always release heat to its nearby permafrost. The amount of heat released by thermokarst lake is usually more than that released by thawing ditch. The thawing ditch is usually more than the thaw slump. If the thawing hazards are close to the roadbed, the lateral thermal erosion would lead to the temperature increases in frozen soil subgrade and induce the embankment disease. Therefore, full consideration of all kinds of thawing hazards must be given for road construction in permafrost regions. If the condition allows, the road should bypass or away from these hazards.
Under the combined influences of the human activities and climatic warming, the thawing hazards are widely distributed in the permafrost regions along the Qinghai-Tibet Engineering Corridor. Research of development status of the thawing hazards and their impact on permafrost thermal regime within the corridor are significant to the engineering construction and environment protection in the future. Based on the field investigations, we summarize the types and development status of the thawing hazards within the corridor. We also monitor the ground temperature of three typical thawing hazards and analyzed their thermal influence on permafrost. The research results show that the typical thawing hazards developed in the corridor mainly include thaw slump and landslide, thermokarst pond, thawing settlement. They are widely distributed in the high ice content permafrost regions along the Qinghai-Tibet Highway and Railway. According to the field ground temperature monitoring, thawing hazards have significantly influenced the thermal regime of permafrost in development area and nearby area. The influence scope is differed among the three thawing hazards. Thaw slump and thaw subsidence usually influence the shallow permafrost. But the influence of thermokarst lake is more significant, which usually results in the formation of talik under the lake bottom. In addition, the modeled results show that the thawing hazards always release heat to its nearby permafrost. The amount of heat released by thermokarst lake is usually more than that released by thawing ditch. The thawing ditch is usually more than the thaw slump. If the thawing hazards are close to the roadbed, the lateral thermal erosion would lead to the temperature increases in frozen soil subgrade and induce the embankment disease. Therefore, full consideration of all kinds of thawing hazards must be given for road construction in permafrost regions. If the condition allows, the road should bypass or away from these hazards.
2014, 22(2): 334-340.
Using the features of data management and analysis of GIS,this paper carries out the evaluation of shallow underground space resource in Dongying City. First of all, a systematic research is made on the engineering geological characteristics. The demand and situation of the exploitation of underground space resources are researched. On these bases, the influencing factors are analyzed for the underground space resource in Dongying City. An evaluation index system is made. Every index is calculated. By combining GIS with established mathematical model, a comprehensive evaluation of underground space resource in Dongying City is done. As a result, the survey region can be preliminarily divided into three levels and one independent zone, respectively. They make up 79.2%、 8.8%、 8.5%、 3.5% of the overall area.
Using the features of data management and analysis of GIS,this paper carries out the evaluation of shallow underground space resource in Dongying City. First of all, a systematic research is made on the engineering geological characteristics. The demand and situation of the exploitation of underground space resources are researched. On these bases, the influencing factors are analyzed for the underground space resource in Dongying City. An evaluation index system is made. Every index is calculated. By combining GIS with established mathematical model, a comprehensive evaluation of underground space resource in Dongying City is done. As a result, the survey region can be preliminarily divided into three levels and one independent zone, respectively. They make up 79.2%、 8.8%、 8.5%、 3.5% of the overall area.
2014, 22(2): 341-347.
This paper studies the relationship among the matric suction, dry density, water content, saturation and volumetric water content of Baode laterite. The water content of 36groups of experimental specimens under different water contents and dry densities are measured with filter paper method in laboratory. The associated matric suctions are computed. The soil-water characteristics curves(SWCC)for unsaturated Baode laterite under different dry densities are obtained. The results show that the relationships among the matric suction, dry density, saturation and volumetric water content are of different characteristics at different water contents. The matric suction is not sensitive to changes of dry density, saturation and volumetric water content for low water content laterite. But it is contrary for high water content laterite. Relationships among matric suction, water content, saturation and volumetric water content are nonlinear. Matrix suction decreases sharply with the increase of water content, saturation and volumetric water content with the same dry density.
This paper studies the relationship among the matric suction, dry density, water content, saturation and volumetric water content of Baode laterite. The water content of 36groups of experimental specimens under different water contents and dry densities are measured with filter paper method in laboratory. The associated matric suctions are computed. The soil-water characteristics curves(SWCC)for unsaturated Baode laterite under different dry densities are obtained. The results show that the relationships among the matric suction, dry density, saturation and volumetric water content are of different characteristics at different water contents. The matric suction is not sensitive to changes of dry density, saturation and volumetric water content for low water content laterite. But it is contrary for high water content laterite. Relationships among matric suction, water content, saturation and volumetric water content are nonlinear. Matrix suction decreases sharply with the increase of water content, saturation and volumetric water content with the same dry density.
2014, 22(2): 348-354.
Correlation distance is a very important parameter for random field theory in modelling soil profiles, and also a key point for the application of random field theory to reliability analysis in geotechnical engineering. Based on the collections of tip resistance indexes from field Cone Penetration Tests(CPT) of a project located in the centre of Jiangsu province, correlation distances of silty clays are statistically calculated by adopting different sample intervals. The influence of sample intervals on the results is also analysed. Hence, a procedure for selecting sample interval is recommended based on scale-matching principle in actual practice. In addition, many in-situ CPT data are obtained from the geotechnical investigation of an expressway in the centre of Jiangsu province. The vertical and horizontal correlation distances of lacustrine sedimentary soils are statistically analyzed by means of mean-crossings, moving average and correlation function. The conclusions of this paper provide not only a new prescription for determining sample interval in statistically estimating correlation distance, but also the characteristic values of correlation distances of regional soils in central Jiangsu. What is more, it can be very helpful to lay a solid foundation for establishing the random field model of regional soil properties and provide essential reference for reliability and statistics in geotechnical engineering in the central region of Jiangsu province.
Correlation distance is a very important parameter for random field theory in modelling soil profiles, and also a key point for the application of random field theory to reliability analysis in geotechnical engineering. Based on the collections of tip resistance indexes from field Cone Penetration Tests(CPT) of a project located in the centre of Jiangsu province, correlation distances of silty clays are statistically calculated by adopting different sample intervals. The influence of sample intervals on the results is also analysed. Hence, a procedure for selecting sample interval is recommended based on scale-matching principle in actual practice. In addition, many in-situ CPT data are obtained from the geotechnical investigation of an expressway in the centre of Jiangsu province. The vertical and horizontal correlation distances of lacustrine sedimentary soils are statistically analyzed by means of mean-crossings, moving average and correlation function. The conclusions of this paper provide not only a new prescription for determining sample interval in statistically estimating correlation distance, but also the characteristic values of correlation distances of regional soils in central Jiangsu. What is more, it can be very helpful to lay a solid foundation for establishing the random field model of regional soil properties and provide essential reference for reliability and statistics in geotechnical engineering in the central region of Jiangsu province.
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