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Editor Work2009 Vol. 17, No. 3
Previous Issue
2009, 17(3): 289-295.
Abstract
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The safety of dams becomes one of the major issues concerned greatly by the general public and professional communities in the Wenchuan Earthquake. This paper proposes some polices and suggestions for how to response to the possible and potential great risks brought by strong earthquakes in dam construction. This issue should be considered from two aspects: one is the development level of earthquake sciences and the other is the extreme significance of dam safety. On one hand, the study of seismic geological environment should be paid significant attention from the strategic level in the watershed planning and professional planning of hydropower. The conventional concept that the cascade dams must be jointed together must be used for generating electricity should also be abandoned. The planning of hydropower stations on the rivers where strong earthquakes may occur nearby should be absolutely forbidden. On the other hand, some sensitive regions, especially the regions with complex geological background and low magnitude earthquake in history, shoud be paid more attention from the tactical level. In the engineering geological investigation, a great importance should be given to the stability of the rock masses and mountains under intensive ground motion at or nearby the dam sites in earthquake zone. It has been recognized that it is more difficult for us to understand the stability of the rock masses and mountains and to stabilize them than to the seismic design of dams. However, their hazards to dams may be more serious than the seismic damage of dams themselves.
The safety of dams becomes one of the major issues concerned greatly by the general public and professional communities in the Wenchuan Earthquake. This paper proposes some polices and suggestions for how to response to the possible and potential great risks brought by strong earthquakes in dam construction. This issue should be considered from two aspects: one is the development level of earthquake sciences and the other is the extreme significance of dam safety. On one hand, the study of seismic geological environment should be paid significant attention from the strategic level in the watershed planning and professional planning of hydropower. The conventional concept that the cascade dams must be jointed together must be used for generating electricity should also be abandoned. The planning of hydropower stations on the rivers where strong earthquakes may occur nearby should be absolutely forbidden. On the other hand, some sensitive regions, especially the regions with complex geological background and low magnitude earthquake in history, shoud be paid more attention from the tactical level. In the engineering geological investigation, a great importance should be given to the stability of the rock masses and mountains under intensive ground motion at or nearby the dam sites in earthquake zone. It has been recognized that it is more difficult for us to understand the stability of the rock masses and mountains and to stabilize them than to the seismic design of dams. However, their hazards to dams may be more serious than the seismic damage of dams themselves.
The safety of dams becomes one of the major issues concerned greatly by the general public and professional communities in the Wenchuan Earthquake. This paper proposes some polices and suggestions for how to response to the possible and potential great risks brought by strong earthquakes in dam construction. This issue should be considered from two aspects: one is the development level of earthquake sciences and the other is the extreme significance of dam safety. On one hand, the study of seismic geological environment should be paid significant attention from the strategic level in the watershed planning and professional planning of hydropower. The conventional concept that the cascade dams must be jointed together must be used for generating electricity should also be abandoned. The planning of hydropower stations on the rivers where strong earthquakes may occur nearby should be absolutely forbidden. On the other hand, some sensitive regions, especially the regions with complex geological background and low magnitude earthquake in history, shoud be paid more attention from the tactical level. In the engineering geological investigation, a great importance should be given to the stability of the rock masses and mountains under intensive ground motion at or nearby the dam sites in earthquake zone. It has been recognized that it is more difficult for us to understand the stability of the rock masses and mountains and to stabilize them than to the seismic design of dams. However, their hazards to dams may be more serious than the seismic damage of dams themselves.
The safety of dams becomes one of the major issues concerned greatly by the general public and professional communities in the Wenchuan Earthquake. This paper proposes some polices and suggestions for how to response to the possible and potential great risks brought by strong earthquakes in dam construction. This issue should be considered from two aspects: one is the development level of earthquake sciences and the other is the extreme significance of dam safety. On one hand, the study of seismic geological environment should be paid significant attention from the strategic level in the watershed planning and professional planning of hydropower. The conventional concept that the cascade dams must be jointed together must be used for generating electricity should also be abandoned. The planning of hydropower stations on the rivers where strong earthquakes may occur nearby should be absolutely forbidden. On the other hand, some sensitive regions, especially the regions with complex geological background and low magnitude earthquake in history, shoud be paid more attention from the tactical level. In the engineering geological investigation, a great importance should be given to the stability of the rock masses and mountains under intensive ground motion at or nearby the dam sites in earthquake zone. It has been recognized that it is more difficult for us to understand the stability of the rock masses and mountains and to stabilize them than to the seismic design of dams. However, their hazards to dams may be more serious than the seismic damage of dams themselves.
2009, 17(3): 296-300.
his paper uses radon concentration measurements on the profile of active fault to assess the position, scope and activity of faults in Chengdu Region. It can be found that Wenchuan Earthquake affected faults strongly. The radon concentrations were monitored on profiles of Beichuan Fault, Pengguan Fault and Xinjin-Pujiang Fault. The results indicate that the background radon concentration on the profile of active faults is higher than other places. The closer r to the epicenter, the higher the value of radon concentration on the profile of active faults. By data processing, the ratios of radon anomaly threshold value to background value of radon concentration are no more than three and the ratios of maximum radon concentration to background value of radon concentration are less than five. Considering the geological conditions of measurement location such as the topography and surface soil structure, the activities of active faults in Chengdu region are evaluated after the earthquake. There is no fault with high level of activity in Chengdu region. Moreover, the activity of Beichuan Fault and Xinjin-Pujiang Fault is higher than that of Pengguan Fault.
his paper uses radon concentration measurements on the profile of active fault to assess the position, scope and activity of faults in Chengdu Region. It can be found that Wenchuan Earthquake affected faults strongly. The radon concentrations were monitored on profiles of Beichuan Fault, Pengguan Fault and Xinjin-Pujiang Fault. The results indicate that the background radon concentration on the profile of active faults is higher than other places. The closer r to the epicenter, the higher the value of radon concentration on the profile of active faults. By data processing, the ratios of radon anomaly threshold value to background value of radon concentration are no more than three and the ratios of maximum radon concentration to background value of radon concentration are less than five. Considering the geological conditions of measurement location such as the topography and surface soil structure, the activities of active faults in Chengdu region are evaluated after the earthquake. There is no fault with high level of activity in Chengdu region. Moreover, the activity of Beichuan Fault and Xinjin-Pujiang Fault is higher than that of Pengguan Fault.
CHARACTERISTICS OF GEOLOGICAL HAZARDS IN BAZHOU REGION OF SICHUAN PROVINCE AFTER WENCHUAN EARTHQUAKE
2009, 17(3): 301-307.
This paper presents the results of site investigation on the influence of the 512 Wenchuan Earthquake on the geological hazards in Bazhou region of Sichuan province.The paper considers that the geological structure and landform are the fundamental factors that control the geological hazards in this region. The rainfall is the most important one among the geological hazard inducing factors. The site investigation reveals that collapses and landslides are the main types of geological hazards. The main form of collapses in this region is rock fall and the main form of landslides is eluvium landslide. Both of them distribute on low-mid mountain regions with the eroded landforms that are so-called rock desks. The analysis shows that the earthquake has greatly weakened the stability of potential collapse rock slopes.
This paper presents the results of site investigation on the influence of the 512 Wenchuan Earthquake on the geological hazards in Bazhou region of Sichuan province.The paper considers that the geological structure and landform are the fundamental factors that control the geological hazards in this region. The rainfall is the most important one among the geological hazard inducing factors. The site investigation reveals that collapses and landslides are the main types of geological hazards. The main form of collapses in this region is rock fall and the main form of landslides is eluvium landslide. Both of them distribute on low-mid mountain regions with the eroded landforms that are so-called rock desks. The analysis shows that the earthquake has greatly weakened the stability of potential collapse rock slopes.
2009, 17(3): 308-312.
he Shuangxi deposition is made of detritus and distributed abroad along the upper reach of the Dalinghe river. It has close relations with rockfalls, landslide and debris flows. At Shuangxi village, Zhongba village and Shenjiping village along Daninghe river, the mudstone and siltstone rocks of the Silurian age are soft and can be easily weathered. They are distributed at the lower and gentle slopes. The limestone of the Permian and Triassic age are distributed at the upper and steep slopes. It is hard and solid. The Shuangxi deposition spreads in the foot of the mountains.
he Shuangxi deposition is made of detritus and distributed abroad along the upper reach of the Dalinghe river. It has close relations with rockfalls, landslide and debris flows. At Shuangxi village, Zhongba village and Shenjiping village along Daninghe river, the mudstone and siltstone rocks of the Silurian age are soft and can be easily weathered. They are distributed at the lower and gentle slopes. The limestone of the Permian and Triassic age are distributed at the upper and steep slopes. It is hard and solid. The Shuangxi deposition spreads in the foot of the mountains.
2009, 17(3): 313-316.
The process of stream trenching and slope formation cause a continuous change in the stress field of the river bank slopes. The superficial rockmass is unloaded in the change of stress field. The depth of unloading should be indifferent in the same area. An investigation is carried on the stress field at a hydropower station in southwest China. The station has two dams. The up and downtream dams have a distance of 1.4km. The investigation detected that unloading depths of the rockmasses at the two dam sites have wider differences. At the upstream dam site, the unloadin depth is more than 20m, and its extreme depth can reach to 90 m. At the downstream dam site, the unloading depthis only 5~20m. Field survey and numerical simulation indicate that orientation of the rock formation is the key factor for the difference in the unloading depths at the up and downstream dams. Trends of rock formation and river bank slopes at the upstream dam are paralleled. The rockmass of steep dip angle is easy to be cracked. The weathering is invaded. The depth of the rockmass unloading is deep. At the downstram dam, the trends of the rock formation and river bank slopes are nearly are perpendicular. The strength of the rockmass is greater than the bedding planes. The structural surfaces that parallel to the river bank slopes are less. Therefore, the unloading depth of rockmass is within 20m.
The process of stream trenching and slope formation cause a continuous change in the stress field of the river bank slopes. The superficial rockmass is unloaded in the change of stress field. The depth of unloading should be indifferent in the same area. An investigation is carried on the stress field at a hydropower station in southwest China. The station has two dams. The up and downtream dams have a distance of 1.4km. The investigation detected that unloading depths of the rockmasses at the two dam sites have wider differences. At the upstream dam site, the unloadin depth is more than 20m, and its extreme depth can reach to 90 m. At the downstream dam site, the unloading depthis only 5~20m. Field survey and numerical simulation indicate that orientation of the rock formation is the key factor for the difference in the unloading depths at the up and downstream dams. Trends of rock formation and river bank slopes at the upstream dam are paralleled. The rockmass of steep dip angle is easy to be cracked. The weathering is invaded. The depth of the rockmass unloading is deep. At the downstram dam, the trends of the rock formation and river bank slopes are nearly are perpendicular. The strength of the rockmass is greater than the bedding planes. The structural surfaces that parallel to the river bank slopes are less. Therefore, the unloading depth of rockmass is within 20m.
2009, 17(3): 317-321.
The stability of rock slope with cataclastic texture is controlled by joints that are crossed each other, and affected by terrain, rainfall and other factors. This paper presents a case study on the stability of a granitic rock slope with broken and cataclastic structures. The geological condition and the rockmass structure properties were investigated in detail. This study further took into account the data that are revealed during construction and monitoring of the slope. It thoroughly analyzed the slope deformation mechanism during the excavating. On the basis of the slope stability results, it suggested the stabilization measures. The results show that the slip surface in top of the slope was formed by unloading cracks. The other slip surfaces were developed under the effects of two groups of structural planes. In particular, the multi-point extensometers buried in the slope recorded the slope deformation characteristics during the 5.12 Wenchuan Earthquake and afterward railfalls. Then after the supporting, the slope deformation was obviously under the control.
The stability of rock slope with cataclastic texture is controlled by joints that are crossed each other, and affected by terrain, rainfall and other factors. This paper presents a case study on the stability of a granitic rock slope with broken and cataclastic structures. The geological condition and the rockmass structure properties were investigated in detail. This study further took into account the data that are revealed during construction and monitoring of the slope. It thoroughly analyzed the slope deformation mechanism during the excavating. On the basis of the slope stability results, it suggested the stabilization measures. The results show that the slip surface in top of the slope was formed by unloading cracks. The other slip surfaces were developed under the effects of two groups of structural planes. In particular, the multi-point extensometers buried in the slope recorded the slope deformation characteristics during the 5.12 Wenchuan Earthquake and afterward railfalls. Then after the supporting, the slope deformation was obviously under the control.
2009, 17(3): 329-334.
he 500kV Direct Transmission Line is across the entire Qinghai-Tibet plateau. So its environment has a tight link with frozen soils. Because of freezing soil specialty of frost-heaving and thaw-settlement, the transmission line would meet the great challenge in survey, design, construction and operation in post-construction stage. Therefore, in order to learn more about permafrost engineering problems of transmission line, the physical and mechanical tests are conducted. This paper analyzes the influence factors on the tower stability. The test results show that freezing and thawing behavior can increase the sensitivity as the water content increases for the same soil samples. If the water content keeps the same, the freezing and thawing behavior increases the sensitivity as the particle size decreases for different soil samples. Also, the results show that the geological environment, harmful features of frozen ground, different geomorphic units, thermal stability characteristics of permafrost, and the convenient construction are the factors influencing the tower foundation stability.
he 500kV Direct Transmission Line is across the entire Qinghai-Tibet plateau. So its environment has a tight link with frozen soils. Because of freezing soil specialty of frost-heaving and thaw-settlement, the transmission line would meet the great challenge in survey, design, construction and operation in post-construction stage. Therefore, in order to learn more about permafrost engineering problems of transmission line, the physical and mechanical tests are conducted. This paper analyzes the influence factors on the tower stability. The test results show that freezing and thawing behavior can increase the sensitivity as the water content increases for the same soil samples. If the water content keeps the same, the freezing and thawing behavior increases the sensitivity as the particle size decreases for different soil samples. Also, the results show that the geological environment, harmful features of frozen ground, different geomorphic units, thermal stability characteristics of permafrost, and the convenient construction are the factors influencing the tower foundation stability.
2009, 17(3): 332-338.
This paper uses the attribute reduction algorithm of rough sets and the classify function of support vector machines to establish a model of rock slope stability evaluation. At first, the rough set theory is used to acquire the knowledge of classification, which includes decision table construction, attribute discretization, attribute importance ranking, attribution reduction and rule abstract. Then, the key components are extracted as the input of support vector machine. The method can reduce the dimensions of the data and the complexity, and raises the efficiency of training and the accuracy of prediction. The effect extent to the slope stability of these factors can be obtained. The analyzed results show that this method can predict stability and destroy style of slope.
This paper uses the attribute reduction algorithm of rough sets and the classify function of support vector machines to establish a model of rock slope stability evaluation. At first, the rough set theory is used to acquire the knowledge of classification, which includes decision table construction, attribute discretization, attribute importance ranking, attribution reduction and rule abstract. Then, the key components are extracted as the input of support vector machine. The method can reduce the dimensions of the data and the complexity, and raises the efficiency of training and the accuracy of prediction. The effect extent to the slope stability of these factors can be obtained. The analyzed results show that this method can predict stability and destroy style of slope.
2009, 17(3): 335-342.
A proposed reservoir dam stands in a V-shaped valley. The ground is composed with the semi-longitudinal brick red sandstone and foliated or lenticular mudstone, silty sand mudstone intermediate layer. It has no evident fault structure. It has an old landslide. The rain is plenty. Based on investigation, the old landside has landslide debris accumulation, slipped surface and the bottom disturbed zone. The development of vertical and horizontal structure planes of the landslide area and bedding plane constitute a wedge-shaped slot. The cause of the landslide formation can be due to the fact that the slippage-tension failure took place at the wedge-shaped slot under heavy rain. The limit equilibrium method is used to calculate the stability factors. The stability factors are 1.45 in the natural state, 1.39 in the seismic state and 1.27 in the heavy rain state, respectively. Therefore, the landslide is stable in the natural state. The role of earthquake impact in the stability is not significant. But the stability of the landslide will be lower under the heavy rain. Finally, the stress-strain field and deformation failure features of the ancient landslide at this stage are reproduced through finite element simulation.
A proposed reservoir dam stands in a V-shaped valley. The ground is composed with the semi-longitudinal brick red sandstone and foliated or lenticular mudstone, silty sand mudstone intermediate layer. It has no evident fault structure. It has an old landslide. The rain is plenty. Based on investigation, the old landside has landslide debris accumulation, slipped surface and the bottom disturbed zone. The development of vertical and horizontal structure planes of the landslide area and bedding plane constitute a wedge-shaped slot. The cause of the landslide formation can be due to the fact that the slippage-tension failure took place at the wedge-shaped slot under heavy rain. The limit equilibrium method is used to calculate the stability factors. The stability factors are 1.45 in the natural state, 1.39 in the seismic state and 1.27 in the heavy rain state, respectively. Therefore, the landslide is stable in the natural state. The role of earthquake impact in the stability is not significant. But the stability of the landslide will be lower under the heavy rain. Finally, the stress-strain field and deformation failure features of the ancient landslide at this stage are reproduced through finite element simulation.
2009, 17(3): 343-348.
he rainfall threshold is the key to the warning of rainfall-induced landslides. Because of the available data in the study area is limited, the threshold value is hard to ascertained, which have influence over the effect of landslide warning. The probability analysis of predictive result is proposed on condition of scant prerequisite as a result. This article analyzes the relevance of precipitation and threshold value of landslides occurrence and accesses rainfall-induced landslides probability by calculating frequencies of landslide occurrence and rainfall-induced landslides. The method of probability analysis is brought forth in the warning of rainfall-induced landslides, which is based on the developed landslide warning system. The credibility of the method is shown by applying it to the modeling of Muchuan county. The application of probability analysis method was capable of effectually improving landslide warning system.
he rainfall threshold is the key to the warning of rainfall-induced landslides. Because of the available data in the study area is limited, the threshold value is hard to ascertained, which have influence over the effect of landslide warning. The probability analysis of predictive result is proposed on condition of scant prerequisite as a result. This article analyzes the relevance of precipitation and threshold value of landslides occurrence and accesses rainfall-induced landslides probability by calculating frequencies of landslide occurrence and rainfall-induced landslides. The method of probability analysis is brought forth in the warning of rainfall-induced landslides, which is based on the developed landslide warning system. The credibility of the method is shown by applying it to the modeling of Muchuan county. The application of probability analysis method was capable of effectually improving landslide warning system.
2009, 17(3): 349-356.
This paper examines the soil characteristic and liquefaction degree of hard shell seams at the subaqueous delta of the Yellow River. Four typical areas were chosen for measuring, testing and studying. The hard shell seam strength was measured by in-situ Proctor penetrometer. Undisturbed soil sample of 1 m long was excavated for laboratory soil property test. Sledge hammers were dropped down freely to hit the load board to simulate the wave force acted on the hard shell seam. The excess pore pressure and strength variation were observed. The liquefaction depth of the hard shell seams at four study areas under different wave storms were calculated by theory. From the studies, some conclusions were gotten: (1) the hard shell seams are in overconsolidated state, and overconsolidation ratio decreases with depth. The strength of the hard shell seams at Dawangbei and Diaokou are twice of those at Xintan and Guangli ports. The strength variation coefficient near the estuary is bigger than those far from estuary. (2) According to the pore pressure variation with vibration times, the pore pressure variation can be divided into four stages, initial stage, growth stage, stabilization stage and attenuation stage. During vibration, the surface soil liquefied, however the deeper soil did not liquefy. (3) The liquefaction depth of the hard shell seam at Da Wang Bei is 7 to 11 cm under 6th to 10th storms, and they reach 32 to 42cm at Xin Tan and Guang Li ports. The liquefaction depth of the hard shell seam with high strength was small, however the seam with low strength liquefied deeper, thus the difference of liquefaction depth caused the non-uniformity of seabed.
This paper examines the soil characteristic and liquefaction degree of hard shell seams at the subaqueous delta of the Yellow River. Four typical areas were chosen for measuring, testing and studying. The hard shell seam strength was measured by in-situ Proctor penetrometer. Undisturbed soil sample of 1 m long was excavated for laboratory soil property test. Sledge hammers were dropped down freely to hit the load board to simulate the wave force acted on the hard shell seam. The excess pore pressure and strength variation were observed. The liquefaction depth of the hard shell seams at four study areas under different wave storms were calculated by theory. From the studies, some conclusions were gotten: (1) the hard shell seams are in overconsolidated state, and overconsolidation ratio decreases with depth. The strength of the hard shell seams at Dawangbei and Diaokou are twice of those at Xintan and Guangli ports. The strength variation coefficient near the estuary is bigger than those far from estuary. (2) According to the pore pressure variation with vibration times, the pore pressure variation can be divided into four stages, initial stage, growth stage, stabilization stage and attenuation stage. During vibration, the surface soil liquefied, however the deeper soil did not liquefy. (3) The liquefaction depth of the hard shell seam at Da Wang Bei is 7 to 11 cm under 6th to 10th storms, and they reach 32 to 42cm at Xin Tan and Guang Li ports. The liquefaction depth of the hard shell seam with high strength was small, however the seam with low strength liquefied deeper, thus the difference of liquefaction depth caused the non-uniformity of seabed.
2009, 17(3): 357-362.
At first, this paper compares the Burgers creep model with the Bingham-Kelvin creep model. Based on the comparison, the Bingham-Kelvin creep model is employed to study the creep damage characteristics of structural plane in rock mass. Under the condition that the shear stress applied on the plane is less than its shear strength (i.e., 0s), this paper derivates the expression of shear modulus with the Bingham-Kelvin model, and defines a damage variable taking the shear modulus as variable. Based on the shear tests on mudstone, this paper further calculates the shear modulus and damage value of the structural plane under the same normal compressive stress. The results show that: (1) When 0s, the shear modulus and damage value of the structural plane vary little as the time goes, and the damage value of the structural plane is little at the first two phases, and (2) when 0s, the damage value alters suddenly some time later. The initial shear modulus increases with the increasing in the shear stress, and under higher shear stress, they reduce more quickly with time and decrease more while creep reaches to the stable phase. The creep deformation of structural plane increases with the increasing in shear stress and time, [JP3]and the damage increases more under higher shear stress when creep attains to the stable phase. [JP]
〖WT5HZ〗Key words〓〖WT〗Rock mechanics， Creep damage, Shear modulus, Structural plane, Bingham-Kelvin creep model, Mudstone
〖HT〗
At first, this paper compares the Burgers creep model with the Bingham-Kelvin creep model. Based on the comparison, the Bingham-Kelvin creep model is employed to study the creep damage characteristics of structural plane in rock mass. Under the condition that the shear stress applied on the plane is less than its shear strength (i.e., 0s), this paper derivates the expression of shear modulus with the Bingham-Kelvin model, and defines a damage variable taking the shear modulus as variable. Based on the shear tests on mudstone, this paper further calculates the shear modulus and damage value of the structural plane under the same normal compressive stress. The results show that: (1) When 0s, the shear modulus and damage value of the structural plane vary little as the time goes, and the damage value of the structural plane is little at the first two phases, and (2) when 0s, the damage value alters suddenly some time later. The initial shear modulus increases with the increasing in the shear stress, and under higher shear stress, they reduce more quickly with time and decrease more while creep reaches to the stable phase. The creep deformation of structural plane increases with the increasing in shear stress and time, [JP3]and the damage increases more under higher shear stress when creep attains to the stable phase. [JP]
〖WT5HZ〗Key words〓〖WT〗Rock mechanics， Creep damage, Shear modulus, Structural plane, Bingham-Kelvin creep model, Mudstone
〖HT〗
2009, 17(3): 363-366.
Basalt rocks at different geological conditions have a different structures. At first, if the rock is under in-situ confining pressure, the structure of the rock face has close mosaic, the rock has good integrity. The structural integrity of the rock face for rock structure evaluation does not have good correlation with the minimum distance of structural planes. The integrity of the evaluation index should be used. Secondly, if the rock is a state of stress relaxation. The rock integrity is poor. the structural integrity of the surface has a very good correlation with the minimum distance of structural planes. The minimum distance should be used as the evaluation index. This paper further uses the rock foundation of a hydropower station in southwest China as a case study. The rocks are under different environments. The rock structure is evaluated and the the rock integrity index is selected for the deep rocks.
Basalt rocks at different geological conditions have a different structures. At first, if the rock is under in-situ confining pressure, the structure of the rock face has close mosaic, the rock has good integrity. The structural integrity of the rock face for rock structure evaluation does not have good correlation with the minimum distance of structural planes. The integrity of the evaluation index should be used. Secondly, if the rock is a state of stress relaxation. The rock integrity is poor. the structural integrity of the surface has a very good correlation with the minimum distance of structural planes. The minimum distance should be used as the evaluation index. This paper further uses the rock foundation of a hydropower station in southwest China as a case study. The rocks are under different environments. The rock structure is evaluated and the the rock integrity index is selected for the deep rocks.
2009, 17(3): 367-370.
This paper is based on the results of in-situ and laboratory direct tests of basalt rock mass with columnar joints. Allometric curves are fitted with the test data and empirical formulas are obtained about the shear strength of the basalt rock mass with columnar joints. The analysis shows that the values of the cohesion c and the internal frictional coefficient f vary approximately with the size of test samples as power functions. The representative elementary volumes of the c and f are analyzed. The cohesive force is more sensitive to the size of samples.
This paper is based on the results of in-situ and laboratory direct tests of basalt rock mass with columnar joints. Allometric curves are fitted with the test data and empirical formulas are obtained about the shear strength of the basalt rock mass with columnar joints. The analysis shows that the values of the cohesion c and the internal frictional coefficient f vary approximately with the size of test samples as power functions. The representative elementary volumes of the c and f are analyzed. The cohesive force is more sensitive to the size of samples.
2009, 17(3): 371-376.
This paper uses the results of standard soil triaxial tests to examine the structural and impaction factor of Xiashu soil in Nanjing. The results show that the Xiashu soil evidently has structures. . Before the yield strain, the structural strength of the soil quickly is developed. After the yield strain, the soil structure is broken. When every structural unit is re-arranged to form a stable structure, the original soil structure is totally destroyed. The impaction factors are confining pressure and moisture content. The result shows that the structure strength does not vary with the change of the confining pressure. A power function is found for the relationship between the structure strength and the moisture content. At last, the paper discusses the possibility of using structure strength to replace the matrix suction strength.
This paper uses the results of standard soil triaxial tests to examine the structural and impaction factor of Xiashu soil in Nanjing. The results show that the Xiashu soil evidently has structures. . Before the yield strain, the structural strength of the soil quickly is developed. After the yield strain, the soil structure is broken. When every structural unit is re-arranged to form a stable structure, the original soil structure is totally destroyed. The impaction factors are confining pressure and moisture content. The result shows that the structure strength does not vary with the change of the confining pressure. A power function is found for the relationship between the structure strength and the moisture content. At last, the paper discusses the possibility of using structure strength to replace the matrix suction strength.
2009, 17(3): 377-382.
Currently, a lot of tests have been done to study the change of thermal properties of silt soils with a factor. However, in the studies on the effect of a factor, other influencing parameters have not been kept unchanged. In order to build the precise relationship between thermal properties and the influencing factors of silt soils, more strict experiments are required. In addition, few tests on silt's thermal properties have been reported yet. In the present studies, a series of laboratory tests have been carried out to examine the relation between thermal conductivity and moisture content of the silt soils. In these tests, the effects of moisture content were examined individually, while the other factors (such as dry density and void ratio) are kept constant. It is indicated that the thermal conductivity increases with the increase in moisture content, and follows the logarithmic law which is consistent with sand. Subsequently, comparisons between present studies and other results reported in the previous studies were conducted. Finally, the heat transfer mechanism of the silt soil is studied to explain the present results.
Currently, a lot of tests have been done to study the change of thermal properties of silt soils with a factor. However, in the studies on the effect of a factor, other influencing parameters have not been kept unchanged. In order to build the precise relationship between thermal properties and the influencing factors of silt soils, more strict experiments are required. In addition, few tests on silt's thermal properties have been reported yet. In the present studies, a series of laboratory tests have been carried out to examine the relation between thermal conductivity and moisture content of the silt soils. In these tests, the effects of moisture content were examined individually, while the other factors (such as dry density and void ratio) are kept constant. It is indicated that the thermal conductivity increases with the increase in moisture content, and follows the logarithmic law which is consistent with sand. Subsequently, comparisons between present studies and other results reported in the previous studies were conducted. Finally, the heat transfer mechanism of the silt soil is studied to explain the present results.
2009, 17(3): 383-388.
Block theory is an effective method on stability analysis of fractured rigid rock mass. There are a lot of discontinuous planes developed in rock mass of Jinping II hydropower station conveyor tunnel. So the stability of conveyor tunnel is related with the presence of unstable blocks on excavation planes. This paper deals with the stability of the conveyor tunnel with Block theory based stereo-analytical method on the basis of detailed investigation of rock mass data. It makes judgments on the movable blocks such as sliding types that are induced by all rock discontinuous planes on each excavation plane of the conveyor tunnel. A conclusion is obtained that the sliding type of blocks is mainly single sliding. A relatively few sliding types of double-sided sliding and vertical block falling are also found. Also, the obvious statistical distribution result on the movable blocks in the conveyor tunnel indicates that there are some more instability blocks in the left wall, the left and right arches than the right wall.
Block theory is an effective method on stability analysis of fractured rigid rock mass. There are a lot of discontinuous planes developed in rock mass of Jinping II hydropower station conveyor tunnel. So the stability of conveyor tunnel is related with the presence of unstable blocks on excavation planes. This paper deals with the stability of the conveyor tunnel with Block theory based stereo-analytical method on the basis of detailed investigation of rock mass data. It makes judgments on the movable blocks such as sliding types that are induced by all rock discontinuous planes on each excavation plane of the conveyor tunnel. A conclusion is obtained that the sliding type of blocks is mainly single sliding. A relatively few sliding types of double-sided sliding and vertical block falling are also found. Also, the obvious statistical distribution result on the movable blocks in the conveyor tunnel indicates that there are some more instability blocks in the left wall, the left and right arches than the right wall.
2009, 17(3): 389-393.
Xian city has been experiencing serious land subsidence and ground fissure activities for a long time. SAR interferometry (InSAR) has been applied to monitor the spatio-temperal characteristics of land subsidence and ground fissure in this area since 1992, where adaptive interferogram filtering and phase unwrapping algorithms with gross elimination are considered in each interferometric pair. The InSAR results are calibrated with leveling and GPS results in the similar monitoring time, respectively. One centimeter precision is achieved. In conclusion, the main subsidence regions are the eastern and southern suburbs. The second subsidence stage was the maximum stage with nearly 21cm subsidence in 1996. The subsidence rate has decreased to 8 cm while the subsidence cone has shifted to southwestern suburb. It is also detected that the non-linear deformation is in active ground fissure areas and the subsidence rate in the south is larger than the north. This research results can give a great data support for further inversion and hazard mitigation.
Xian city has been experiencing serious land subsidence and ground fissure activities for a long time. SAR interferometry (InSAR) has been applied to monitor the spatio-temperal characteristics of land subsidence and ground fissure in this area since 1992, where adaptive interferogram filtering and phase unwrapping algorithms with gross elimination are considered in each interferometric pair. The InSAR results are calibrated with leveling and GPS results in the similar monitoring time, respectively. One centimeter precision is achieved. In conclusion, the main subsidence regions are the eastern and southern suburbs. The second subsidence stage was the maximum stage with nearly 21cm subsidence in 1996. The subsidence rate has decreased to 8 cm while the subsidence cone has shifted to southwestern suburb. It is also detected that the non-linear deformation is in active ground fissure areas and the subsidence rate in the south is larger than the north. This research results can give a great data support for further inversion and hazard mitigation.
2009, 17(3): 394-400.
In this paper, the Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) is used to analyze the mechanism and stability of the filled embankment on slope with goafs. Three cases are considered. They are (1) goafs with un-treatment (2) goafs with grouting (3) the embankment with grouting plus reinforcing to the slope. The numerical results show that the self-loading of high backfill embankment and traffic live loading can destroy the mechanical equilibrium of the original goafs. The jointing area between the filled and slope surfaces appears shear strain increment concentration, whereas the stress of goafs reaches to a new equilibrium after grouting. The shear strain increment moves down after reinforcing. As a result, the embankment stability increase obviously.
In this paper, the Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) is used to analyze the mechanism and stability of the filled embankment on slope with goafs. Three cases are considered. They are (1) goafs with un-treatment (2) goafs with grouting (3) the embankment with grouting plus reinforcing to the slope. The numerical results show that the self-loading of high backfill embankment and traffic live loading can destroy the mechanical equilibrium of the original goafs. The jointing area between the filled and slope surfaces appears shear strain increment concentration, whereas the stress of goafs reaches to a new equilibrium after grouting. The shear strain increment moves down after reinforcing. As a result, the embankment stability increase obviously.
2009, 17(3): 401-407.
The red beds soft rock of the age from Cretaceous to Eogene is widespread in Xiang-Liou Basin. It is a kind of soft rock with the features of weak diagenetic process and susceptible to weathering and can easily be disingtegrated. The practical working conditions of rock-socket pile in the soft rock is different from those in the《Technical Code for Building Pile Foundations》(JGJ94-94). The vertical static load test is adopted to investigate 4 large-diameter rock-socket pile in the rock. The variation of axis force in each pile is measured by sliding micrometer and strain gauges. Hence, the bearing capacity behavior, load transfer mechanism, the lateral friction and end bearing are researched in this paper. According to the test results, the load transfer performance of rock-socket pile is similar to that of end-bearing friction pile, the Q-s curves are slowly varying. The pile length, covering and soil around pile are all important to the load transfer mechanism and action of lateral friction. For the natural structure of the red soft rock, the critical displacements of piles are 2~6 mm and the tested result is much higher than those recommended by the Specifications, which indicates that the shaft resistance is strengthened. As the result, the bearing capacity of rock-socket pile in the soft rock is very good, while the lateral friction and end bearing cannot display simultaneously. The study results show that the design standards should be controlled by the strength and the deformation of pile foundation, and the parameter used in design should accord with the load transfer law of pile.
The red beds soft rock of the age from Cretaceous to Eogene is widespread in Xiang-Liou Basin. It is a kind of soft rock with the features of weak diagenetic process and susceptible to weathering and can easily be disingtegrated. The practical working conditions of rock-socket pile in the soft rock is different from those in the《Technical Code for Building Pile Foundations》(JGJ94-94). The vertical static load test is adopted to investigate 4 large-diameter rock-socket pile in the rock. The variation of axis force in each pile is measured by sliding micrometer and strain gauges. Hence, the bearing capacity behavior, load transfer mechanism, the lateral friction and end bearing are researched in this paper. According to the test results, the load transfer performance of rock-socket pile is similar to that of end-bearing friction pile, the Q-s curves are slowly varying. The pile length, covering and soil around pile are all important to the load transfer mechanism and action of lateral friction. For the natural structure of the red soft rock, the critical displacements of piles are 2~6 mm and the tested result is much higher than those recommended by the Specifications, which indicates that the shaft resistance is strengthened. As the result, the bearing capacity of rock-socket pile in the soft rock is very good, while the lateral friction and end bearing cannot display simultaneously. The study results show that the design standards should be controlled by the strength and the deformation of pile foundation, and the parameter used in design should accord with the load transfer law of pile.
2009, 17(3): 408-414.
This paper examines the engineering properties of red clay at the Wuhan-Guangzhou section of Wuhan-Guangzhou passenger dedicated railway line. The red clay in this area has high values in liquid and plastic limits,saturation, and porosity. It has good mechanical properties with low compactibility. The soil pre-consolidation pressure is far greater than its vertical overburden pressure. The soil is overconsolidated with high porosity. Besides, it was suggested that the red clay presents the peculiar engineering characteristics thatthe upper layers are rigid and the lower layers are weak. The overconsolidation ratio and pre-consolidation pressure reduce as the depth increases. The results provide important guidance and reference to the design and construction of passenger railway line.
This paper examines the engineering properties of red clay at the Wuhan-Guangzhou section of Wuhan-Guangzhou passenger dedicated railway line. The red clay in this area has high values in liquid and plastic limits,saturation, and porosity. It has good mechanical properties with low compactibility. The soil pre-consolidation pressure is far greater than its vertical overburden pressure. The soil is overconsolidated with high porosity. Besides, it was suggested that the red clay presents the peculiar engineering characteristics thatthe upper layers are rigid and the lower layers are weak. The overconsolidation ratio and pre-consolidation pressure reduce as the depth increases. The results provide important guidance and reference to the design and construction of passenger railway line.
2009, 17(3): 421-425.
The properties of expansive soil have many changes after it is mixed with lime. This paper is based on the testing data of the lime mixed expansive soil from the expressway of Yichang-Jingmen. The changes in the engineering properties of expansive soil mixed with lime are obtained. It decreases the free swelling ratio, swelling capacity, shrinkage ratio and plastic index. It increases the shear strength and CBR. The research result can provide accurate testing data for improving the engineering properties of expansive soil in order to satisfying the requirements of the expressway engineering design.
The properties of expansive soil have many changes after it is mixed with lime. This paper is based on the testing data of the lime mixed expansive soil from the expressway of Yichang-Jingmen. The changes in the engineering properties of expansive soil mixed with lime are obtained. It decreases the free swelling ratio, swelling capacity, shrinkage ratio and plastic index. It increases the shear strength and CBR. The research result can provide accurate testing data for improving the engineering properties of expansive soil in order to satisfying the requirements of the expressway engineering design.
2009, 17(3): 426-433.
The marine soft soil in Tianjin coastal region has high water content, low strength, high compressibility and low pH. It can't meet the needs of engineering construction and has to be improved. One of the soil improvement methods is to mix feasible alkalic additive sodium hydroxide or sodium carbonate into the whisking cement soil. This method can improve the strength of pile cement soil and the bearing capacity of composite foundation, and save a great deal cement. In this paper, the marine soft soil is mixed with 10% cement added with 0.5% NaOH and 0.5% Na2CO3 separately, which form two types of new cement-soils. Comparing with the undisturbed soil and the 20% cement-soil results in that the alkalescence additive can contribute to generate a large number of needle-like, rod-like or fibriform hydrate calcium silicate crystals. The hydrate calcium silicate crystals can inhibit the generation of calcic alum crystal which would bring expansive action. At the mean time, it can separate out hydrate calcium. The hydrate calcium silicate crystals and hydrate calcium constitute the filling and inclusions together among soil particles and on the surface of soil particles, which cut down the interstices of cement soil obviously. Therefore, the soil mass can be reinforced and the intensity can be improved. Test results show that the soil-cement strength increases more than 20%. The composite foundation bearing capacity is not less than 120kPa.
The marine soft soil in Tianjin coastal region has high water content, low strength, high compressibility and low pH. It can't meet the needs of engineering construction and has to be improved. One of the soil improvement methods is to mix feasible alkalic additive sodium hydroxide or sodium carbonate into the whisking cement soil. This method can improve the strength of pile cement soil and the bearing capacity of composite foundation, and save a great deal cement. In this paper, the marine soft soil is mixed with 10% cement added with 0.5% NaOH and 0.5% Na2CO3 separately, which form two types of new cement-soils. Comparing with the undisturbed soil and the 20% cement-soil results in that the alkalescence additive can contribute to generate a large number of needle-like, rod-like or fibriform hydrate calcium silicate crystals. The hydrate calcium silicate crystals can inhibit the generation of calcic alum crystal which would bring expansive action. At the mean time, it can separate out hydrate calcium. The hydrate calcium silicate crystals and hydrate calcium constitute the filling and inclusions together among soil particles and on the surface of soil particles, which cut down the interstices of cement soil obviously. Therefore, the soil mass can be reinforced and the intensity can be improved. Test results show that the soil-cement strength increases more than 20%. The composite foundation bearing capacity is not less than 120kPa.
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