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Editor Work2016 Vol. 24, No. 1
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2016, 24(1): 1-9.
Abstract
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Artificial excavation is one of the main inducing factors of the landslide formation in loess area. It causes unloading rebound and stress redistribution within the scope of slopes. The process of slope stress rebalancing is followed by slope deformation, which even causes damage. The landslide happened at Baota Zaoyuan town in Yan'an city is a typical induced loess slope excavation. This paper chooses the Yangya landslide as the geological prototype. It uses the type of TLJ-500geotechnical centrifuge for the condition of excavation slope foot test to simulate the deformation and failure process. It studies the characteristics of the displacement of slope deformation before and after the excavation of the slope foot, slope soil pressure response and mechanism of slope deformation and destruction through analysis of the model monitoring data at monitoring points. Results show that partial collapse happens after the slope toe excavation near the international airport face. The slope displacement, shear stress concentration belt and tensile fracture increase progressively from the front part to the inner part of the slope. After excavation, the slope internal zone can produce obvious stress relaxation. The closer to the excavation face the more obvious effect of unloading. Excavation influences a majority of the front and middle parts of the main slope. So there is less or even no effect at the back slope, which means that slope deformation failure mechanism is the typical-steps-back type.
Artificial excavation is one of the main inducing factors of the landslide formation in loess area. It causes unloading rebound and stress redistribution within the scope of slopes. The process of slope stress rebalancing is followed by slope deformation, which even causes damage. The landslide happened at Baota Zaoyuan town in Yan'an city is a typical induced loess slope excavation. This paper chooses the Yangya landslide as the geological prototype. It uses the type of TLJ-500geotechnical centrifuge for the condition of excavation slope foot test to simulate the deformation and failure process. It studies the characteristics of the displacement of slope deformation before and after the excavation of the slope foot, slope soil pressure response and mechanism of slope deformation and destruction through analysis of the model monitoring data at monitoring points. Results show that partial collapse happens after the slope toe excavation near the international airport face. The slope displacement, shear stress concentration belt and tensile fracture increase progressively from the front part to the inner part of the slope. After excavation, the slope internal zone can produce obvious stress relaxation. The closer to the excavation face the more obvious effect of unloading. Excavation influences a majority of the front and middle parts of the main slope. So there is less or even no effect at the back slope, which means that slope deformation failure mechanism is the typical-steps-back type.
2016, 24(1): 10-18.
Parameter inversion is an effective way to obtain more reliable strength parameters of slope. In the article, after discriminating the position of the critical slip surface, the explicit formulas for inversion of strength parameters are deduced by the established relation between strength parameters and one to one relationship among strength parameters, and the critical slip surface. The classical Swedish slice method is used for calculating the factor of safety. Then, the inversion results are used to study the stability of slope reinforced by anchorage cable. Through analyzing actual case, the feasibility and practicability of the current method are verified. Some conclusion are obtained as follows:(1)Pre-stress cable has an effective reinforcement on slope. Its role on slope stability is more effective when the position of pre-stress cable on slope surface is more near to the lower sliding point of the slip surface; (2)The calculated factor of safety is larger as the pre-stress of cable is larger. Increase of horizontal inclination of anchorage cable has small effect on the calculated factor of safety.
Parameter inversion is an effective way to obtain more reliable strength parameters of slope. In the article, after discriminating the position of the critical slip surface, the explicit formulas for inversion of strength parameters are deduced by the established relation between strength parameters and one to one relationship among strength parameters, and the critical slip surface. The classical Swedish slice method is used for calculating the factor of safety. Then, the inversion results are used to study the stability of slope reinforced by anchorage cable. Through analyzing actual case, the feasibility and practicability of the current method are verified. Some conclusion are obtained as follows:(1)Pre-stress cable has an effective reinforcement on slope. Its role on slope stability is more effective when the position of pre-stress cable on slope surface is more near to the lower sliding point of the slip surface; (2)The calculated factor of safety is larger as the pre-stress of cable is larger. Increase of horizontal inclination of anchorage cable has small effect on the calculated factor of safety.
2016, 24(1): 19-28.
On July 22, 2013, an earthquake of MS6.6 occurred at the junction area of the Minxian and Zhangxian Counties, Gansu Province, China. The earthquake had triggered at least 2330 landslides according to the previous studies. This paper takes seismic intensity Ⅷ zone of the earthquake as the study area. Based on the earthquake induced-landslide inventory interpreted from field investigations and visual interpretation of high-resolution satellite images before and after earthquake, five influence factors of slope, aspect, drainage, lithology and fault are selected. Then the landslide susceptibility of the study area is evaluated under GIS platform by applying fuzzy logic model, information value model and Shannon's entropy integrated information value model separately. Results show: (1)Landslides are prone to occur in the central part of the study area. When closer to drainage, it is more susceptible to landslides. By counting landslides in buffer zones of drainage, it finds that majority landslides occurred in 0～50m zone. The percentage of landslides in 0～100m buffer zone is up to 50% of all. (2)The AUC values of three models are 0.8488(Information value model), 0.8502(Shannon's entropy integrated information value model), 0.7640(Fuzzy logic model). It indicates well performances of information value model and Shannon's entropy integrated information value model, and the modest performance of fuzzy logic model. (3)By comparing the areas of each susceptibility levels and landslides proportions in each susceptibility levels of three models, it finds that each level's area ration in Shannon's entropy integrated information value model tends to normal distribution, and the model also has the highest landslide rations in very high and high susceptibility levels. Shannon's entropy integrated information value model increases each unit's information value which leads to a more obvious result. It demonstrates that Shannon's entropy integrated information value model is more suitable for disaster risk evaluation and emergency risk management.
On July 22, 2013, an earthquake of MS6.6 occurred at the junction area of the Minxian and Zhangxian Counties, Gansu Province, China. The earthquake had triggered at least 2330 landslides according to the previous studies. This paper takes seismic intensity Ⅷ zone of the earthquake as the study area. Based on the earthquake induced-landslide inventory interpreted from field investigations and visual interpretation of high-resolution satellite images before and after earthquake, five influence factors of slope, aspect, drainage, lithology and fault are selected. Then the landslide susceptibility of the study area is evaluated under GIS platform by applying fuzzy logic model, information value model and Shannon's entropy integrated information value model separately. Results show: (1)Landslides are prone to occur in the central part of the study area. When closer to drainage, it is more susceptible to landslides. By counting landslides in buffer zones of drainage, it finds that majority landslides occurred in 0～50m zone. The percentage of landslides in 0～100m buffer zone is up to 50% of all. (2)The AUC values of three models are 0.8488(Information value model), 0.8502(Shannon's entropy integrated information value model), 0.7640(Fuzzy logic model). It indicates well performances of information value model and Shannon's entropy integrated information value model, and the modest performance of fuzzy logic model. (3)By comparing the areas of each susceptibility levels and landslides proportions in each susceptibility levels of three models, it finds that each level's area ration in Shannon's entropy integrated information value model tends to normal distribution, and the model also has the highest landslide rations in very high and high susceptibility levels. Shannon's entropy integrated information value model increases each unit's information value which leads to a more obvious result. It demonstrates that Shannon's entropy integrated information value model is more suitable for disaster risk evaluation and emergency risk management.
2016, 24(1): 29-34.
The Dalong formation of Permain and the Daye formation of Triassic are the main slippery strata in Qingjiang River catchment of western Hubei province. Pianshan landslide is a typical example. Its lower part is composed of thin-bed limestone of Daye formation. Its slide belt is formed with mudstone or shale of the top of Dalong formation. Depending on field investigation, sampling and mechanical tests in laboratory, following results on the mineral and chemical compositions and mechanical properties are obtained for the two formation materials. The main clay mineral in the mudstone is montmorillonite with good swelling and shrinkage character. The content of clay minerals is 40%～75%.The strength of the mudstone decreases obviously after argillization, companying with typical creep deformation. For long term strength properties, the cohesion is 23kPa and the internal friction angle is 18.1,which are achieved with rheological tests. The amount of clay minerals in the thin bed limestone is high. The main components are illite and chlorite and the bedding surfaces are very smooth. The surfaces are abraded and the clay is oriented between the layers due to the bedding slipping deformation. The strength of interlayers decreases obviously and forms the slide surface inside the landslide body when the layers are saturated. There are good mutual effect and acceleration between the landslide evolution and Qingjiang River development. The similar geological structure and water reciprocating strip should be taken seriously.
The Dalong formation of Permain and the Daye formation of Triassic are the main slippery strata in Qingjiang River catchment of western Hubei province. Pianshan landslide is a typical example. Its lower part is composed of thin-bed limestone of Daye formation. Its slide belt is formed with mudstone or shale of the top of Dalong formation. Depending on field investigation, sampling and mechanical tests in laboratory, following results on the mineral and chemical compositions and mechanical properties are obtained for the two formation materials. The main clay mineral in the mudstone is montmorillonite with good swelling and shrinkage character. The content of clay minerals is 40%～75%.The strength of the mudstone decreases obviously after argillization, companying with typical creep deformation. For long term strength properties, the cohesion is 23kPa and the internal friction angle is 18.1,which are achieved with rheological tests. The amount of clay minerals in the thin bed limestone is high. The main components are illite and chlorite and the bedding surfaces are very smooth. The surfaces are abraded and the clay is oriented between the layers due to the bedding slipping deformation. The strength of interlayers decreases obviously and forms the slide surface inside the landslide body when the layers are saturated. There are good mutual effect and acceleration between the landslide evolution and Qingjiang River development. The similar geological structure and water reciprocating strip should be taken seriously.
2016, 24(1): 35-43.
In this article we expand applications of Two Section Method from two-dimension to three-dimension. We use the Microsoft Visual Studio where meantime ArcGIS Engine component is embedded. The software program is designed to compute the width and volume of reservoir bank slope failure. By inputting some parameters including stable slope angle, lithological boundary and flood level line, it automatically runs. Hence, the prediction of bank slope failure can be completed via simple man-machine interaction, which improves the efficiency of prediction. At the meantime, the bank slope shape can be comprised between,before and after bank failure through three-dimension visualization, which can provide more reliable support of data and decision for bank protecting project. In the process of software program, there are three ways of achieving the parameters according to the need of program. They are: (1)Using the field survey and geotechnical test results, the parameters such as bank slope angle stabilized above and underwater, can be obtained,(2)From the geological map and high-resolution Images, lithological boundary, flood level line and low level line can be achieved, and (3)From high-resolution DEM,the terrain profile line can be drawn that acts as the terminal condition of the program.
In this article we expand applications of Two Section Method from two-dimension to three-dimension. We use the Microsoft Visual Studio where meantime ArcGIS Engine component is embedded. The software program is designed to compute the width and volume of reservoir bank slope failure. By inputting some parameters including stable slope angle, lithological boundary and flood level line, it automatically runs. Hence, the prediction of bank slope failure can be completed via simple man-machine interaction, which improves the efficiency of prediction. At the meantime, the bank slope shape can be comprised between,before and after bank failure through three-dimension visualization, which can provide more reliable support of data and decision for bank protecting project. In the process of software program, there are three ways of achieving the parameters according to the need of program. They are: (1)Using the field survey and geotechnical test results, the parameters such as bank slope angle stabilized above and underwater, can be obtained,(2)From the geological map and high-resolution Images, lithological boundary, flood level line and low level line can be achieved, and (3)From high-resolution DEM,the terrain profile line can be drawn that acts as the terminal condition of the program.
2016, 24(1): 44-55.
The Outang landslide is a giant ancient consequent bedding rockslide of about 9.0107m3 in volume and 1.78km2 in area. It is a huge threat to the safety of lives and property of more than 3900 people. It involves the entire town relocation, which can be one of the serious landslide disasters in this area. On the basis of field investigation and engineering-geological exploration, the special geologic environment and characters of Outang landslide are examined in detail. The deformation characteristics of the landslide are studied in-depth with field monitoring data. On this basis the deformation and failure mechanism of Outang landslide are analyzed from the two following aspects. They are the geologic origin and the environment origin. The deformation trend of the landslide is also predicted using the stability calculation result. The result shows that:(1)The Outang landslide is a multi-phase consequent bedding rockslide with three landslide phases. It has the characteristics of apparent dip slide in 3D spatial form. (2)The particular geological factors include the landform, stratum lithology, geological structure and are the internal factors of landslide formation. (3)The cyclical fluctuation of the reservoir water and the concentrated rainfall are the external environment factors inducing the landslide deformation. Analysis shows that the landslide deformation is significantly related to the water level reduction and the concentrated rainfall. Because the reducing speed of reservoir water level is much faster than that of the underground water, it forms seepage force in the landslide body apparently, and promotes the landslide deformation. The concentrated rainfall increases the self-weight and reduces the strength of slope mass, which makes a lot of water enrichment in easy sliding soft layer, softens sliding zone and hastens the landslide creep deformation. (4)The third phase landslide mass and the western side strong deformation zone have the possibility of unstable statement under extreme conditions. So it is inferred that the major failure mode of the landslide is a local buckling failure. In view of this, it is suggested to strengthen monitoring and to take corresponding engineering measures.
The Outang landslide is a giant ancient consequent bedding rockslide of about 9.0107m3 in volume and 1.78km2 in area. It is a huge threat to the safety of lives and property of more than 3900 people. It involves the entire town relocation, which can be one of the serious landslide disasters in this area. On the basis of field investigation and engineering-geological exploration, the special geologic environment and characters of Outang landslide are examined in detail. The deformation characteristics of the landslide are studied in-depth with field monitoring data. On this basis the deformation and failure mechanism of Outang landslide are analyzed from the two following aspects. They are the geologic origin and the environment origin. The deformation trend of the landslide is also predicted using the stability calculation result. The result shows that:(1)The Outang landslide is a multi-phase consequent bedding rockslide with three landslide phases. It has the characteristics of apparent dip slide in 3D spatial form. (2)The particular geological factors include the landform, stratum lithology, geological structure and are the internal factors of landslide formation. (3)The cyclical fluctuation of the reservoir water and the concentrated rainfall are the external environment factors inducing the landslide deformation. Analysis shows that the landslide deformation is significantly related to the water level reduction and the concentrated rainfall. Because the reducing speed of reservoir water level is much faster than that of the underground water, it forms seepage force in the landslide body apparently, and promotes the landslide deformation. The concentrated rainfall increases the self-weight and reduces the strength of slope mass, which makes a lot of water enrichment in easy sliding soft layer, softens sliding zone and hastens the landslide creep deformation. (4)The third phase landslide mass and the western side strong deformation zone have the possibility of unstable statement under extreme conditions. So it is inferred that the major failure mode of the landslide is a local buckling failure. In view of this, it is suggested to strengthen monitoring and to take corresponding engineering measures.
2016, 24(1): 56-63.
Loose Quaternary deposits are widely distributed in Suzhou, where extracting groundwater has caused a large-scale land subsidence. The land subsidence influences the development of economy. Optical fibers are laid in a 200m borehole drilled in Shengze, Suzhou. Based on the BOTDR and FBG technologies, the Quaternary sediments deformation and land subsidence are long-term monitored. It is showed that Quaternary sediments can be divided into different aquifers(Af) and aquitards(Ad).The main compaction occurs at two thick aquitards which adjacent to the second confined aquifer. In addition, the shorter the distance between the aquitard and the pumping aquifer is,the greater the degree of compression of the aquitard is .The soil layer reaches the maximum compression in summer while a small rebound occurs in winter, showing the conformance with the pore water pressure of the pumping aquifer. We define the compression degree as the ratio of the accumulative compression and the thickness of this layer(i.e.,the unit compression).At this stage the subsidence trend can be judged by compression degree. For the aquitards, there is a tendency shows that Ad2 Ad3 Ad4 Ad1. For the aquifers, the Af2 is the main compaction layer while Af1 and Af3 remain almost constant. DFOS technique provides a very advanced monitoring method for the study of land subsidence mechanism and the evaluation of soil compression deformation potential.
Loose Quaternary deposits are widely distributed in Suzhou, where extracting groundwater has caused a large-scale land subsidence. The land subsidence influences the development of economy. Optical fibers are laid in a 200m borehole drilled in Shengze, Suzhou. Based on the BOTDR and FBG technologies, the Quaternary sediments deformation and land subsidence are long-term monitored. It is showed that Quaternary sediments can be divided into different aquifers(Af) and aquitards(Ad).The main compaction occurs at two thick aquitards which adjacent to the second confined aquifer. In addition, the shorter the distance between the aquitard and the pumping aquifer is,the greater the degree of compression of the aquitard is .The soil layer reaches the maximum compression in summer while a small rebound occurs in winter, showing the conformance with the pore water pressure of the pumping aquifer. We define the compression degree as the ratio of the accumulative compression and the thickness of this layer(i.e.,the unit compression).At this stage the subsidence trend can be judged by compression degree. For the aquitards, there is a tendency shows that Ad2 Ad3 Ad4 Ad1. For the aquifers, the Af2 is the main compaction layer while Af1 and Af3 remain almost constant. DFOS technique provides a very advanced monitoring method for the study of land subsidence mechanism and the evaluation of soil compression deformation potential.
2016, 24(1): 64-72.
LLliang area is located in West Shanxi loess plateau where geological environment is rather fragile, geo-hazards occur continually and the loess landslides and collapses cause enormous casualties and heavy economic losses. This paper is based on field investigations and combined with in-situ and laboratory tests. It studies the types and characteristics of landslides and collapses in this area. According to the formation lithology, geological structure and the position of sliding plane, loess landslides in LLliang area are divided into two basic types: Q3 homogeneous loess landslide and Q3-Q2-N2 landslide occurred in the composite structure of layers. Then the failure modes of loess collapses are classified as toppling, subsiding and stripping collapse. In the space, the loess landslides and collapses in LLliang area are distributed in four counties(Liuling, Lishi, Zhongyang and Shilou) and developed in belts along the highways and railways. In time, loess landslides and collapses have an obvious annual variation law and occur in flood period(from June to October),especially in the main flood season(from July to August).Finally, the mechanism of the Q3-Q2-N2 landslide in the composite structure is discussed, which shows that manual excavation and rainfall infiltration are the two main induced factors.
LLliang area is located in West Shanxi loess plateau where geological environment is rather fragile, geo-hazards occur continually and the loess landslides and collapses cause enormous casualties and heavy economic losses. This paper is based on field investigations and combined with in-situ and laboratory tests. It studies the types and characteristics of landslides and collapses in this area. According to the formation lithology, geological structure and the position of sliding plane, loess landslides in LLliang area are divided into two basic types: Q3 homogeneous loess landslide and Q3-Q2-N2 landslide occurred in the composite structure of layers. Then the failure modes of loess collapses are classified as toppling, subsiding and stripping collapse. In the space, the loess landslides and collapses in LLliang area are distributed in four counties(Liuling, Lishi, Zhongyang and Shilou) and developed in belts along the highways and railways. In time, loess landslides and collapses have an obvious annual variation law and occur in flood period(from June to October),especially in the main flood season(from July to August).Finally, the mechanism of the Q3-Q2-N2 landslide in the composite structure is discussed, which shows that manual excavation and rainfall infiltration are the two main induced factors.
2016, 24(1): 73-77.
After the 2008 Wenchuan Earthquake, debris flow disasters were strong. So far, many rainfall processes had happened. How can we accurate analyze the accumulation evolution of debris flow. We should make sure the volume of sources. In order to solve the question, 5 debris flow gullies were chosen along Minjiang River as a research area near Yingxiu. First, using field survey, we got the volume and area of 167 sources. Then analysising the relationship between the volume and area, we got the volume model. Last, we verified the model by 48 sources. Through the remote sensing interpretation, combining with volume model, this paper expounds debris flowsource activity in the studied area.
After the 2008 Wenchuan Earthquake, debris flow disasters were strong. So far, many rainfall processes had happened. How can we accurate analyze the accumulation evolution of debris flow. We should make sure the volume of sources. In order to solve the question, 5 debris flow gullies were chosen along Minjiang River as a research area near Yingxiu. First, using field survey, we got the volume and area of 167 sources. Then analysising the relationship between the volume and area, we got the volume model. Last, we verified the model by 48 sources. Through the remote sensing interpretation, combining with volume model, this paper expounds debris flowsource activity in the studied area.
2016, 24(1): 78-86.
In coal mining with backfill, backfill material dominates the benefit, efficiency and effect. In order to get the characteristics varying pattern of cemented and high concentration backfill material with wind-blown sand as aggregate, fly ash is selected as variables to test and analyze the characteristics varying pattern of backfill material with the mix proportion of fly ash. The results show that, as the mix proportion of fly ash increases in a proper range in backfill material, the compressive strength increases, the bleeding rate decreases in general, the layered degree declines by linear pattern, the coagulation time grows up by exponential pattern, and the slump is growing consecutively. But, with the higher mix proportion of fly ash, the compressive strength and slump will drop comparatively. When the mix proportion of fly ash is in proper range, the fly ash optimizes the particle size gradient of backfill material, and makes water and cement distribution uniform in backfill material. As a result, the strength characteristic and rheological performance can be improved. However, some characteristics will degenerate with higher mix proportion of fly ash.
In coal mining with backfill, backfill material dominates the benefit, efficiency and effect. In order to get the characteristics varying pattern of cemented and high concentration backfill material with wind-blown sand as aggregate, fly ash is selected as variables to test and analyze the characteristics varying pattern of backfill material with the mix proportion of fly ash. The results show that, as the mix proportion of fly ash increases in a proper range in backfill material, the compressive strength increases, the bleeding rate decreases in general, the layered degree declines by linear pattern, the coagulation time grows up by exponential pattern, and the slump is growing consecutively. But, with the higher mix proportion of fly ash, the compressive strength and slump will drop comparatively. When the mix proportion of fly ash is in proper range, the fly ash optimizes the particle size gradient of backfill material, and makes water and cement distribution uniform in backfill material. As a result, the strength characteristic and rheological performance can be improved. However, some characteristics will degenerate with higher mix proportion of fly ash.
2016, 24(1): 87-95.
Rock mass deformation modulus is the important parameter in the study of rock mass deformation characteristics. It is also of great importance to the stability analysis and optimal design of engineering rock mass. A method for predicting the rock mass deformation modulus is presented in this paper. It uses the BP neural network based on factor analysis. It is applied to the case of a hydropower station in Tibet. On the basis of laboratory tests and in-situ tests, a database of 48 data sets including density, water absorption, vertical-pace, uniaxial compressive strength, rock mass deformation modulus and poisson's ratio factors is established. Three public factors are obtained using the factor analysis method to analyze the six factors. The three public factors act as the input parameters and are used to make BP neural network predictions. Some important conclusions are drawn: The factor analysis can eliminate the defect that the excessive inputting data slows down the processing speed in BP neural network. The prediction accuracy can be improved using this method. This research idea is not only an useful attempt to predict rock mass deformation modulus, but also a great reference value to solve similar geotechnical engineering problems.
Rock mass deformation modulus is the important parameter in the study of rock mass deformation characteristics. It is also of great importance to the stability analysis and optimal design of engineering rock mass. A method for predicting the rock mass deformation modulus is presented in this paper. It uses the BP neural network based on factor analysis. It is applied to the case of a hydropower station in Tibet. On the basis of laboratory tests and in-situ tests, a database of 48 data sets including density, water absorption, vertical-pace, uniaxial compressive strength, rock mass deformation modulus and poisson's ratio factors is established. Three public factors are obtained using the factor analysis method to analyze the six factors. The three public factors act as the input parameters and are used to make BP neural network predictions. Some important conclusions are drawn: The factor analysis can eliminate the defect that the excessive inputting data slows down the processing speed in BP neural network. The prediction accuracy can be improved using this method. This research idea is not only an useful attempt to predict rock mass deformation modulus, but also a great reference value to solve similar geotechnical engineering problems.
2016, 24(1): 96-101.
The incorporation of fly ash into cement-soil can improve its performance in a certain extent. The deformation characteristic is an important index of actual engineering applications. Therefore, researching the effects of fly ash and ages on deformation characteristics of cemente-soil has a great reference value to actual engineering applications. The unconfined compressive strength test of 0 and 8%fly ash cement-soil is done. The experiments show that the growth of the curing age and the addition of fly ash are beneficial to the growth of cement-soil deformation modulus. Especially, the addition of fly ash is beneficial to the growth of the late deformation modulus. By further analyzing the unconfined compressive strength and the average deformation modulus of 0 and 8% fly ash cement-soil specimen, it is found that there is a basically linear relationship between them. Then the conversion formula is derived between them by fitting. Finally, considering the characteristics of stress-strain curve model and regression analysis on the test data, the expression of stress-strain of cement-soil on ascent stage is deduced under the definite condition. The results provide the reference for actual engineering designs.
The incorporation of fly ash into cement-soil can improve its performance in a certain extent. The deformation characteristic is an important index of actual engineering applications. Therefore, researching the effects of fly ash and ages on deformation characteristics of cemente-soil has a great reference value to actual engineering applications. The unconfined compressive strength test of 0 and 8%fly ash cement-soil is done. The experiments show that the growth of the curing age and the addition of fly ash are beneficial to the growth of cement-soil deformation modulus. Especially, the addition of fly ash is beneficial to the growth of the late deformation modulus. By further analyzing the unconfined compressive strength and the average deformation modulus of 0 and 8% fly ash cement-soil specimen, it is found that there is a basically linear relationship between them. Then the conversion formula is derived between them by fitting. Finally, considering the characteristics of stress-strain curve model and regression analysis on the test data, the expression of stress-strain of cement-soil on ascent stage is deduced under the definite condition. The results provide the reference for actual engineering designs.
2016, 24(1): 102-108.
The behavior of undisturbed loess in the case of moistening or demoistening is investigated using double-line uniaxial compression test in this paper. The collapsible deformation rules of collapsible loess are examined and analyzed, during the growth process of humidity and pressure. And the microstructure of the samples are tested using SEM technique. Furthermore the microstructure of samples is analyzed with quantitative method and fractal theory. The results are shown the followings:(1)Rigid node failure of trellis pores can cause the loess collapsibility.(2)Water content of loess has a marked effect on its collapsible deformation. When pressure is some value, its exceeding collapsible probability can increase as moisture content increases. Similarly, the test data show that for loess with constant water content, its exceeding collapsible probability can increase gradually as pressure increases.(3)The average number of pore of sample obviously increases and the pore area decreases after the sample is collapsed. The collapse is a process that small pore increases, fractal dimension decreases, and complexity of the pore increases. The concept of the exceeding collapsible coefficient is put forward. An analysis is made on some issues about study of hydrocompaction from the view point of unsaturated soil mechanics. Finally a case study is given. It reflects the properties of collapsible deformation under different factors.
The behavior of undisturbed loess in the case of moistening or demoistening is investigated using double-line uniaxial compression test in this paper. The collapsible deformation rules of collapsible loess are examined and analyzed, during the growth process of humidity and pressure. And the microstructure of the samples are tested using SEM technique. Furthermore the microstructure of samples is analyzed with quantitative method and fractal theory. The results are shown the followings:(1)Rigid node failure of trellis pores can cause the loess collapsibility.(2)Water content of loess has a marked effect on its collapsible deformation. When pressure is some value, its exceeding collapsible probability can increase as moisture content increases. Similarly, the test data show that for loess with constant water content, its exceeding collapsible probability can increase gradually as pressure increases.(3)The average number of pore of sample obviously increases and the pore area decreases after the sample is collapsed. The collapse is a process that small pore increases, fractal dimension decreases, and complexity of the pore increases. The concept of the exceeding collapsible coefficient is put forward. An analysis is made on some issues about study of hydrocompaction from the view point of unsaturated soil mechanics. Finally a case study is given. It reflects the properties of collapsible deformation under different factors.
2016, 24(1): 109-115.
In order to study the effect of clay content on the shear strength of expansive soil, this paper conducts quick shear, saturated quick shear, saturated consolidated quick shear and repeated direct shear tests with electric strain controlled direct shear apparatus, residual shear test, and direct shear/residual shear test apparatus on the undisturbed expansive soils at Ci County Hebei of South-to-North Water Diversion. The soils have different clay contents. Studies show that: in the direct shear test, the shear strength of the expansive soil significantly reduces after the soil is saturated, and increases after it is consolidated. The effect of saturation on the strength of the expansive soil of larger clay content is more significant. The cure effect of consolidation on the strength of weak expansive soil of lesser clay content is more significant. As the clay content increases, the cohesion gradually decreases, and internal friction angle first decreases and then increases. The critical value is about 32%.In the repeated direct shear test, the shear strength after peak intensity increases as the clay content increases. The change trend is relatively flat. The residual strength f decreases exponentially as the clay content increases. While the internal friction angle r of the residual strength has a logarithmic relation with clay content. The cohesion cr has an irregular relation with the clay content.
In order to study the effect of clay content on the shear strength of expansive soil, this paper conducts quick shear, saturated quick shear, saturated consolidated quick shear and repeated direct shear tests with electric strain controlled direct shear apparatus, residual shear test, and direct shear/residual shear test apparatus on the undisturbed expansive soils at Ci County Hebei of South-to-North Water Diversion. The soils have different clay contents. Studies show that: in the direct shear test, the shear strength of the expansive soil significantly reduces after the soil is saturated, and increases after it is consolidated. The effect of saturation on the strength of the expansive soil of larger clay content is more significant. The cure effect of consolidation on the strength of weak expansive soil of lesser clay content is more significant. As the clay content increases, the cohesion gradually decreases, and internal friction angle first decreases and then increases. The critical value is about 32%.In the repeated direct shear test, the shear strength after peak intensity increases as the clay content increases. The change trend is relatively flat. The residual strength f decreases exponentially as the clay content increases. While the internal friction angle r of the residual strength has a logarithmic relation with clay content. The cohesion cr has an irregular relation with the clay content.
2016, 24(1): 116-129.
The IAEG XII Congress was held on September 15-19, 2014 at Torino, Italy. It was also a vital event for celebrating the 50th Anniversary of the IAEG foundation. An important message of this congress is that engineering geology plays an increasing important role in our changing world, especially in characterizing human responses to the dynamic changes of geo-environment. This paper summarizes the research status and frontiers for eight main topics of IAEG XII congress:(1)Climate Change and Engineering Geology; (2)Landslide Processes; (3)River basins, Reservoir Sedimentation and Water Resources; (4)Marine and Coastal Processes; (5)Urban Geology, Sustainable Planning and Landscape Exploitation; (6)Applied Geology for Major Engineering Projects; (7)Education, Professional Ethics and Public Recognition of Engineering Geology and (8)Preservation of Cultural Heritage.
The IAEG XII Congress was held on September 15-19, 2014 at Torino, Italy. It was also a vital event for celebrating the 50th Anniversary of the IAEG foundation. An important message of this congress is that engineering geology plays an increasing important role in our changing world, especially in characterizing human responses to the dynamic changes of geo-environment. This paper summarizes the research status and frontiers for eight main topics of IAEG XII congress:(1)Climate Change and Engineering Geology; (2)Landslide Processes; (3)River basins, Reservoir Sedimentation and Water Resources; (4)Marine and Coastal Processes; (5)Urban Geology, Sustainable Planning and Landscape Exploitation; (6)Applied Geology for Major Engineering Projects; (7)Education, Professional Ethics and Public Recognition of Engineering Geology and (8)Preservation of Cultural Heritage.
2016, 24(1): 130-135.
The environment and conditions for both natural and artificial soilsat different places are similar. Therefore physical and mechanical properties of soil samples are relevant. The relevance can be analyzed with random field theory. To estimate spatial characteristics of physical and mechanical properties of soil in Tianjin Port, tests such as boring in situ and standard cone penetration are employed to acquire enough test data that are essential to the employment of random field theory. Because it can continuously obtain enough data, the standard cone penetration test is the main method to get test data. The data is used to inspect the stationary and ergodicity of this area. Results show that the random field model put up by Vanmarcke can be employed in this research. In this paper, the innovation points include that the method establishing random field model in Tianjin Port is discussed and the characteristic parameters of typical layers in this area are estimated with the improved non-correlation method. The result can lay a solid foundation for reliability analysis in geotechnical engineering in Tianjin Port. This method of estimating characteristic parameters of random field can be used for other areas.
The environment and conditions for both natural and artificial soilsat different places are similar. Therefore physical and mechanical properties of soil samples are relevant. The relevance can be analyzed with random field theory. To estimate spatial characteristics of physical and mechanical properties of soil in Tianjin Port, tests such as boring in situ and standard cone penetration are employed to acquire enough test data that are essential to the employment of random field theory. Because it can continuously obtain enough data, the standard cone penetration test is the main method to get test data. The data is used to inspect the stationary and ergodicity of this area. Results show that the random field model put up by Vanmarcke can be employed in this research. In this paper, the innovation points include that the method establishing random field model in Tianjin Port is discussed and the characteristic parameters of typical layers in this area are estimated with the improved non-correlation method. The result can lay a solid foundation for reliability analysis in geotechnical engineering in Tianjin Port. This method of estimating characteristic parameters of random field can be used for other areas.
2016, 24(1): 136-141.
The initial in-situ stress field has significant influence on the stability of surrounding rock of underground carven. Nevertheless, the in-situ stress field result obtained by a single method is usually not of high reliability because of the complexity of geological conditions. This paper takes the Huangdao underground water-sealed cavern as example and analyzes its regional tectonic background and near-field faults. The in-situ stress field is tested by hydraulic fracturing method. The maximum principal stress is obtained. Its directions are is mainly oriented NWW.Its advantage direction is N73W. The stress field of study area is analyzed by geological structure analysis method. The impact of regional tectonic history on present tectonic stress field of study area is discussed. It is found that the maximum principal stress direction is NW～NNW.The maximum principal stress directions obtained by construction analysis and hydraulic fracturing method are roughly NW.But there is a certain bias. The main reason is probably due to the fact that the geological structure of research area is complicated and affected by the boundary conditions of tectonic deformation. Thus, the derived local stress field is deflected. The results suggest that the comprehensive evaluation of regional geological structure analysis and in-situ stress test should be used for stress field analysis. The result has a certain reference value for the comprehensive determination of stress field.
The initial in-situ stress field has significant influence on the stability of surrounding rock of underground carven. Nevertheless, the in-situ stress field result obtained by a single method is usually not of high reliability because of the complexity of geological conditions. This paper takes the Huangdao underground water-sealed cavern as example and analyzes its regional tectonic background and near-field faults. The in-situ stress field is tested by hydraulic fracturing method. The maximum principal stress is obtained. Its directions are is mainly oriented NWW.Its advantage direction is N73W. The stress field of study area is analyzed by geological structure analysis method. The impact of regional tectonic history on present tectonic stress field of study area is discussed. It is found that the maximum principal stress direction is NW～NNW.The maximum principal stress directions obtained by construction analysis and hydraulic fracturing method are roughly NW.But there is a certain bias. The main reason is probably due to the fact that the geological structure of research area is complicated and affected by the boundary conditions of tectonic deformation. Thus, the derived local stress field is deflected. The results suggest that the comprehensive evaluation of regional geological structure analysis and in-situ stress test should be used for stress field analysis. The result has a certain reference value for the comprehensive determination of stress field.
2016, 24(1): 142-149.
This paper is based on the particularity in exploration of deep salt caves. The theoretical foundation, detection principle and interpretation methods of earth electric field lithology detection(CYT) and Controlled source audio magnetic telluric(CSAMT) are discussed using the Yexian salt field gas storage project in Pingdignshan. The geometry, space distribution and feedback physical information of salt caves are studied as well. Firstly, the spatial range of target body is confirme-droughly with CSAMT method. Then the spatial form is determined in detail with CYT method on the basis of CSAMT results in favorable area. Exploration results show that the spatial form of salt cave is complex. The irregular holes appear on the geological section with depth of-1000～-1400m. But the single cavern is small and the radius is about 8～60m. The research results can be used to guide the site selection and construction of underground salt cavern gas storage, and provide some reference for deep salt caves detection and interpretation of lithology electric fields.
This paper is based on the particularity in exploration of deep salt caves. The theoretical foundation, detection principle and interpretation methods of earth electric field lithology detection(CYT) and Controlled source audio magnetic telluric(CSAMT) are discussed using the Yexian salt field gas storage project in Pingdignshan. The geometry, space distribution and feedback physical information of salt caves are studied as well. Firstly, the spatial range of target body is confirme-droughly with CSAMT method. Then the spatial form is determined in detail with CYT method on the basis of CSAMT results in favorable area. Exploration results show that the spatial form of salt cave is complex. The irregular holes appear on the geological section with depth of-1000～-1400m. But the single cavern is small and the radius is about 8～60m. The research results can be used to guide the site selection and construction of underground salt cavern gas storage, and provide some reference for deep salt caves detection and interpretation of lithology electric fields.
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