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Editor Work2017 Vol. 25, No. 4
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2017, 25(4): 903-911.
Abstract
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This paper aims to examine composite curing method based on polymeric soil consolidator and fiber material to reinforce the sand. Especially the test uses different concentrations of polyurethane curing agent and different content polypropylene fiber. All of the composite soil samples are subjected to the direct shear test and the unconfined compression test in this experiment. The results and the mechanism are discussed. The following are found. When the composite reinforcing agent in curing agent concentration is certain, unconfined compressive strength and cohesion of sands increase first and then decrease as the fiber content increases. They reach their peak values at the fiber contents of 0.3% and 0.2%.When the fiber content of composite reinforcement agent is certain, the unconfined compressive strength and cohesion restriction of sands increase as the curing agent concentration increases, but the angle of internal friction has little change. Finally, composite reinforcing agent is a combination of physical and chemical reinforcement methods. It can quickly and effectively improve the strength of sand, and also provide a reference for the further research and application of composite reinforcement materials.
This paper aims to examine composite curing method based on polymeric soil consolidator and fiber material to reinforce the sand. Especially the test uses different concentrations of polyurethane curing agent and different content polypropylene fiber. All of the composite soil samples are subjected to the direct shear test and the unconfined compression test in this experiment. The results and the mechanism are discussed. The following are found. When the composite reinforcing agent in curing agent concentration is certain, unconfined compressive strength and cohesion of sands increase first and then decrease as the fiber content increases. They reach their peak values at the fiber contents of 0.3% and 0.2%.When the fiber content of composite reinforcement agent is certain, the unconfined compressive strength and cohesion restriction of sands increase as the curing agent concentration increases, but the angle of internal friction has little change. Finally, composite reinforcing agent is a combination of physical and chemical reinforcement methods. It can quickly and effectively improve the strength of sand, and also provide a reference for the further research and application of composite reinforcement materials.
2017, 25(4): 912-919.
This paper studies the effects and mechanical properties of soil reinforced with coconut fiber and double polyethylene polymer. The examined factors include the content of coconut fiber, the length of coconut fiber, and the content of double polyethylene material. They can influence stabilized soil mechanical properties and permeability. We use the orthogonal experiment method to conduct unconfined compressive strength tests and permeability tests by adding coconut fiber and double polyethylene polymer. Test results show that:the unconfined compressive strength improves and the permeability decreases after coconut fiber and double polyethylene material are added into the soil. Compared with the obvious impact of coconut fiber length on the unconfined compressive strength, coconut fiber content and double polyethylene material content have significant impact. Though coconut fiber length has no significant impact on the permeability coefficient, the influence of coconut fiber content and double polyethylene material content is clear. When fiber contents come to 0.9% and double polyethylene material contents reach 0.375%, the soil sample is of the largest unconfined compressive strength. When fiber contents arrive 0.9%, and double polyethylene material content 0.325%, the minimum permeability coefficient is observed.
This paper studies the effects and mechanical properties of soil reinforced with coconut fiber and double polyethylene polymer. The examined factors include the content of coconut fiber, the length of coconut fiber, and the content of double polyethylene material. They can influence stabilized soil mechanical properties and permeability. We use the orthogonal experiment method to conduct unconfined compressive strength tests and permeability tests by adding coconut fiber and double polyethylene polymer. Test results show that:the unconfined compressive strength improves and the permeability decreases after coconut fiber and double polyethylene material are added into the soil. Compared with the obvious impact of coconut fiber length on the unconfined compressive strength, coconut fiber content and double polyethylene material content have significant impact. Though coconut fiber length has no significant impact on the permeability coefficient, the influence of coconut fiber content and double polyethylene material content is clear. When fiber contents come to 0.9% and double polyethylene material contents reach 0.375%, the soil sample is of the largest unconfined compressive strength. When fiber contents arrive 0.9%, and double polyethylene material content 0.325%, the minimum permeability coefficient is observed.
2017, 25(4): 920-925.
The stability of deep foundation pit is an important engineering problem, in which effective supporting structure is the basis of foundation pit engineering. The discrete element method is employed in this paper, and a modeling and numerical simulation method of foundation pit and supporting structure is proposed. A close-packed discrete element model is used to build the model of initial layers, and the clump model of discrete element is used to build pipe piles with smooth surfaces. A deep foundation pit is taken as an example. The geometrical model can be built using the three-dimensional discrete element software MatDEM3D.The mechanical parameters of elements are determined according to the mechanical properties of soil. In numerical simulations, the soil layers are compacted using a pre-balancing operation, after which the deformation of soil and piles are simulated during the excavation process of foundation pit. The numerical simulation results are compared with the measured monitoring data to evaluate the effectiveness of foundation pit support structures. The discrete element numerical simulation method of foundation pit has potential application prospect in the stability prediction of foundation pit excavation process and the evaluation of the effectiveness of supporting structures.
The stability of deep foundation pit is an important engineering problem, in which effective supporting structure is the basis of foundation pit engineering. The discrete element method is employed in this paper, and a modeling and numerical simulation method of foundation pit and supporting structure is proposed. A close-packed discrete element model is used to build the model of initial layers, and the clump model of discrete element is used to build pipe piles with smooth surfaces. A deep foundation pit is taken as an example. The geometrical model can be built using the three-dimensional discrete element software MatDEM3D.The mechanical parameters of elements are determined according to the mechanical properties of soil. In numerical simulations, the soil layers are compacted using a pre-balancing operation, after which the deformation of soil and piles are simulated during the excavation process of foundation pit. The numerical simulation results are compared with the measured monitoring data to evaluate the effectiveness of foundation pit support structures. The discrete element numerical simulation method of foundation pit has potential application prospect in the stability prediction of foundation pit excavation process and the evaluation of the effectiveness of supporting structures.
2017, 25(4): 926-934.
Deformation and failure of overlying rock strata during coal mining poses a threat to the safety of mining roadway, can cause land subsidence, and can affect the safety of the buildings on the ground surface and the geological environments. Therefore, it is of great significance to carry out real-time deformation monitoring of overlying strata during coal mining. In this paper, the deformation and failure mechanism of overlying strata in coal seam is investigated through laboratory model test. The distributed fiber optic sensing technique is used. The fiber optic cables are vertically buried in the model to form a fiber optic monitoring system for measuring distributed deformation information. The fiber optic test results are consistent with the results of conventional photogrammetry system. They reveal the deformation mechanism and evolution process of the overlying rock mass during coal mining. It is found that using empirical formula, the height of water flowing fractured zone is calculated to be about 30.6cm, which fits well with the fiber optic estimated results of 30cm. The test results show that the application of distributed fiber optic sensing technology to the model test on mining-induced damage of overlying strata is feasible and accurate, which provides a new method for relevant research in the future.
Deformation and failure of overlying rock strata during coal mining poses a threat to the safety of mining roadway, can cause land subsidence, and can affect the safety of the buildings on the ground surface and the geological environments. Therefore, it is of great significance to carry out real-time deformation monitoring of overlying strata during coal mining. In this paper, the deformation and failure mechanism of overlying strata in coal seam is investigated through laboratory model test. The distributed fiber optic sensing technique is used. The fiber optic cables are vertically buried in the model to form a fiber optic monitoring system for measuring distributed deformation information. The fiber optic test results are consistent with the results of conventional photogrammetry system. They reveal the deformation mechanism and evolution process of the overlying rock mass during coal mining. It is found that using empirical formula, the height of water flowing fractured zone is calculated to be about 30.6cm, which fits well with the fiber optic estimated results of 30cm. The test results show that the application of distributed fiber optic sensing technology to the model test on mining-induced damage of overlying strata is feasible and accurate, which provides a new method for relevant research in the future.
2017, 25(4): 935-942.
The closure, opening and propagation of internal fissures of natural rock under compressive load can affect the mechanical properties of rock directly. Based on the classical moving point regression technique, Poisson's ratio is introduced to propose the six stage division method which is called comprehensive stiffness technique(CST).The results of uniaxial compression test under different loading paths show the following.(1) Contact strain ε0, closure strain of cracks εc, elastic strain εe, stable crack propagation εi, unstable crack propagation εd and post-peak strain εf of hard and brittle rock can be achieved by the CST.(2) Under uniaxial compression test, the closure strain of cracks at 44.2% of pre-peak strain is larger than the elastic strain of rhyolite. The pre-peak crack propagation strain and post-peak strain are all small. Actually the rhyolite is significantly brittle.(3) Loading and unloading test in elastic stage shows that the contact strain can be removed by comprehensive stiffness technique and the closure strain of cracks. The comprehensive stiffness technique is more suitable to the deformation analysis of hard and brittle rock, since it can remove the contact strain and achieve more accurate strain of different stages, especially the closure strain of cracks. These strains can be the quantitative parameters of the evaluation of crack density in rock.
The closure, opening and propagation of internal fissures of natural rock under compressive load can affect the mechanical properties of rock directly. Based on the classical moving point regression technique, Poisson's ratio is introduced to propose the six stage division method which is called comprehensive stiffness technique(CST).The results of uniaxial compression test under different loading paths show the following.(1) Contact strain ε0, closure strain of cracks εc, elastic strain εe, stable crack propagation εi, unstable crack propagation εd and post-peak strain εf of hard and brittle rock can be achieved by the CST.(2) Under uniaxial compression test, the closure strain of cracks at 44.2% of pre-peak strain is larger than the elastic strain of rhyolite. The pre-peak crack propagation strain and post-peak strain are all small. Actually the rhyolite is significantly brittle.(3) Loading and unloading test in elastic stage shows that the contact strain can be removed by comprehensive stiffness technique and the closure strain of cracks. The comprehensive stiffness technique is more suitable to the deformation analysis of hard and brittle rock, since it can remove the contact strain and achieve more accurate strain of different stages, especially the closure strain of cracks. These strains can be the quantitative parameters of the evaluation of crack density in rock.
2017, 25(4): 943-952.
This paper examines the anisotropic characteristics of schist. The indoor triaxial compression test is used to obtain the stress-strain curves and the strength and deformation data of schist specimens with three kinds of schistose angles of α=0°, α=45ånd α=90°.Then, seven groups of standard cylinder models with different schistose angles are established. The mechanical parameters of model material are selected by back analysis of the laboratory test data. FLAC3D is used to simulate and discusses the failure modes of schist with different schistose angles as well as the schistose angle effect and confining pressure effect influencing compressive strength. The results show that under the condition of triaxial compression, failure modes of schist are mainly divided into shear failure oblique cutting schistose plane and shear sliding failure along schistose plane. The corresponding control structure for deformation and damage is also different. Under the same confining pressure, the compressive strength of schist, changing with schistose inclination, shows the asymmetric "U" type. The maximum compressive strength is always located at α=90ånd the minimum distribution at α=45°or α=60°.The enhancement effect of increasing confining pressure on the strength of schist tends to weaken, where the failure mode is the mode of shear-sliding failure along schistose plane. Furthermore, factors impacting on the distribution of maximum compressive strength of anisotropic rock are analyzed by numerical simulation. It is found that uniformity degree of anisotropic rock has important effect on the distribution of the maximum compressive strength. With poor uniformity, the maximum value is located at α=90°.Otherwise, the maximum value appears at α=0°.
This paper examines the anisotropic characteristics of schist. The indoor triaxial compression test is used to obtain the stress-strain curves and the strength and deformation data of schist specimens with three kinds of schistose angles of α=0°, α=45ånd α=90°.Then, seven groups of standard cylinder models with different schistose angles are established. The mechanical parameters of model material are selected by back analysis of the laboratory test data. FLAC3D is used to simulate and discusses the failure modes of schist with different schistose angles as well as the schistose angle effect and confining pressure effect influencing compressive strength. The results show that under the condition of triaxial compression, failure modes of schist are mainly divided into shear failure oblique cutting schistose plane and shear sliding failure along schistose plane. The corresponding control structure for deformation and damage is also different. Under the same confining pressure, the compressive strength of schist, changing with schistose inclination, shows the asymmetric "U" type. The maximum compressive strength is always located at α=90ånd the minimum distribution at α=45°or α=60°.The enhancement effect of increasing confining pressure on the strength of schist tends to weaken, where the failure mode is the mode of shear-sliding failure along schistose plane. Furthermore, factors impacting on the distribution of maximum compressive strength of anisotropic rock are analyzed by numerical simulation. It is found that uniformity degree of anisotropic rock has important effect on the distribution of the maximum compressive strength. With poor uniformity, the maximum value is located at α=90°.Otherwise, the maximum value appears at α=0°.
2017, 25(4): 953-958.
The aim of this study is to assess the method for measuring the total suction of compacted soil samples of Chengdu Clay with Chilled-mirror dew-point technology, an indirect measurement method for soil suction. The total suction of compacted soil samples of Chengdu Clay is measured with a WP4-C dew point potentiometer. Soil samples are taken from the depths of a foundation pit in the eastern suburbs of Chengdu. After grinding to pass 0.075mm sieve, configured into 10 different initial moisture content, the remoulded soil is then statically compacted into a fixed volume with a custom mold of diameter 3.5cm and thickness 0.5cm. A total of 40 soil samples are prepared. The average dry density is 1.7g ·cm-3.Based on the Van Genuchten model and the Origin software, we obtain the SWCC curve of the Chengdu Clay, and the reference value of the fitting parameter. The conductivity of the soil sample is measured by the CT-3031 conductivity meter. It is calculated with the conversion formula to obtain the osmotic suction. For the matrix suction is equal to the total suction minus the osmotic suction, the relationship between the matrix suction and the water content is indirectly obtained. It is pointed out that there is a certain deviation between the design moisture content and the actual moisture content of the soil sample, because the size of the soil sample is too small to maintain a constant water content when it is transferred from the sealed bag to the chilled-mirror dew-point meter. After the end of the test, it is necessary to recalculate the moisture content of soil samples. Next, another SWCC curve is obtained using the filter paper method to test the same soil samples. The test results obtained by the two test methods are compared. It is concluded that the suction values measured by the chilled-mirror dew-point technology is lower than that measured by the filter paper method, when the soil samples are at the same water content. This conclusion is in accordance with that of S.S.Agus, which proves that the chilled-mirror dew-point technology has the characteristics of fastness, convenience and accuracy. As a fast method of measuring the suction, the chilled-mirror dew-point technology has a wide range of suction measurement, which can reduce more testing time than the filter paper method. The SWCC curves in this study show that the chilled-mirror dew-point technology is feasible in suction test of the unsaturated Chengdu Clay, and can be extended to the suction test in geotechnical engineering fields in China.
The aim of this study is to assess the method for measuring the total suction of compacted soil samples of Chengdu Clay with Chilled-mirror dew-point technology, an indirect measurement method for soil suction. The total suction of compacted soil samples of Chengdu Clay is measured with a WP4-C dew point potentiometer. Soil samples are taken from the depths of a foundation pit in the eastern suburbs of Chengdu. After grinding to pass 0.075mm sieve, configured into 10 different initial moisture content, the remoulded soil is then statically compacted into a fixed volume with a custom mold of diameter 3.5cm and thickness 0.5cm. A total of 40 soil samples are prepared. The average dry density is 1.7g ·cm-3.Based on the Van Genuchten model and the Origin software, we obtain the SWCC curve of the Chengdu Clay, and the reference value of the fitting parameter. The conductivity of the soil sample is measured by the CT-3031 conductivity meter. It is calculated with the conversion formula to obtain the osmotic suction. For the matrix suction is equal to the total suction minus the osmotic suction, the relationship between the matrix suction and the water content is indirectly obtained. It is pointed out that there is a certain deviation between the design moisture content and the actual moisture content of the soil sample, because the size of the soil sample is too small to maintain a constant water content when it is transferred from the sealed bag to the chilled-mirror dew-point meter. After the end of the test, it is necessary to recalculate the moisture content of soil samples. Next, another SWCC curve is obtained using the filter paper method to test the same soil samples. The test results obtained by the two test methods are compared. It is concluded that the suction values measured by the chilled-mirror dew-point technology is lower than that measured by the filter paper method, when the soil samples are at the same water content. This conclusion is in accordance with that of S.S.Agus, which proves that the chilled-mirror dew-point technology has the characteristics of fastness, convenience and accuracy. As a fast method of measuring the suction, the chilled-mirror dew-point technology has a wide range of suction measurement, which can reduce more testing time than the filter paper method. The SWCC curves in this study show that the chilled-mirror dew-point technology is feasible in suction test of the unsaturated Chengdu Clay, and can be extended to the suction test in geotechnical engineering fields in China.
2017, 25(4): 959-967.
Water cycle and balance of carrying soil is an important issue in the research of biotechnical slope protection. This paper takes the carrying soil with matrix as the research object to carry out evaporation test. The moisture content is measured at different depths of the slope. Moisture content changing with time under the natural sunlight is observed. This paper uses the micro-lysimeter to test the evaporation capacity at different thickness, slope, temperature and ratio of matrix of carrying soil. The result is used to analyze influence factors of evaporation capacity. The results show that the time of carrying soil with water holding agent and peat being saturated is significantly shorter compared with no water holding agent and peat, which indicates that they increase the water imbibition of carrying soil. However, the addition of water holding agent and peat soil also reduces the weight of soil. Eleven days cumulative evaporation of samples with 0.2%water holding agent is 21.2mm higher than that of samples with 0%water holding agent. It indicates that 0.2%water holding agent and 12%peat can effectively reduce the rate of evaporation and water desorption. Moisture content presents periodic change over time. In addition, the moisture content is different at the different depths of samples. Among the influence factors, the temperature is the direct influence factor to the evaporation of carrying soil. The gradient and thickness affect evaporation through influencing the water content. At the same time, they also control the energy supply of evaporation process. But the big slope gradient and thickness are not conducive to the slope stability of carrying soil. It is recommended that the slope gradient of carrying-soil spray seeding be less than 1︰0.75 and the thickness be controlled between 10cm and 20cm. So it can greatly increase the available water holding capacity of vegetation. The above research can provide the basis for the biotechnical slope protection.
Water cycle and balance of carrying soil is an important issue in the research of biotechnical slope protection. This paper takes the carrying soil with matrix as the research object to carry out evaporation test. The moisture content is measured at different depths of the slope. Moisture content changing with time under the natural sunlight is observed. This paper uses the micro-lysimeter to test the evaporation capacity at different thickness, slope, temperature and ratio of matrix of carrying soil. The result is used to analyze influence factors of evaporation capacity. The results show that the time of carrying soil with water holding agent and peat being saturated is significantly shorter compared with no water holding agent and peat, which indicates that they increase the water imbibition of carrying soil. However, the addition of water holding agent and peat soil also reduces the weight of soil. Eleven days cumulative evaporation of samples with 0.2%water holding agent is 21.2mm higher than that of samples with 0%water holding agent. It indicates that 0.2%water holding agent and 12%peat can effectively reduce the rate of evaporation and water desorption. Moisture content presents periodic change over time. In addition, the moisture content is different at the different depths of samples. Among the influence factors, the temperature is the direct influence factor to the evaporation of carrying soil. The gradient and thickness affect evaporation through influencing the water content. At the same time, they also control the energy supply of evaporation process. But the big slope gradient and thickness are not conducive to the slope stability of carrying soil. It is recommended that the slope gradient of carrying-soil spray seeding be less than 1︰0.75 and the thickness be controlled between 10cm and 20cm. So it can greatly increase the available water holding capacity of vegetation. The above research can provide the basis for the biotechnical slope protection.
2017, 25(4): 968-974.
The extraction of microstructure of sandy soil in the compression process can benefit to understand the micro-mechanism of the compression deformation and failure. In order to fix, extract and quantify the microstructure of sandy soil during compression, this paper designs an extraction technology of microstructure of sand soil in the compression process. It is mainly composed of two parts, an apparatus for blue epoxy injection and an improved sand collecting box. In consolidation tests of sandy soil, a step motor is used to drive blue epoxy into the compacted sandy soil sample, via the preset hose and the bottom side of permeable stone. Thin sections can be made when the epoxy is consolidated. The microstructure images can be captured by optical microscope. Using the technology, the microstructure of sandy soil is consolidated and captured during compressive process. This paper introduces the extraction technology. Three kinds of quartz sands with different particle sizes and sorting are compressed and consolidated in laboratory. When the microscopic images are obtained, the PCAS software is used to quantify the microstructures.
The extraction of microstructure of sandy soil in the compression process can benefit to understand the micro-mechanism of the compression deformation and failure. In order to fix, extract and quantify the microstructure of sandy soil during compression, this paper designs an extraction technology of microstructure of sand soil in the compression process. It is mainly composed of two parts, an apparatus for blue epoxy injection and an improved sand collecting box. In consolidation tests of sandy soil, a step motor is used to drive blue epoxy into the compacted sandy soil sample, via the preset hose and the bottom side of permeable stone. Thin sections can be made when the epoxy is consolidated. The microstructure images can be captured by optical microscope. Using the technology, the microstructure of sandy soil is consolidated and captured during compressive process. This paper introduces the extraction technology. Three kinds of quartz sands with different particle sizes and sorting are compressed and consolidated in laboratory. When the microscopic images are obtained, the PCAS software is used to quantify the microstructures.
2017, 25(4): 975-984.
This paper addresses the long-term settlement of embankment induced by the traffic loading and soil structure of natural soft clay. The artificial structured soils with different bonding strength are prepared. A series of compression test and dynamic triaxial tests are carried out to investigate the effects of cycle number, dynamic stress ratio and structured strength on the accumulative deformation behavior. The results indicate that accumulative deformation increases with the increase of cycle number and dynamic stress ratio, and decreases with the increase of structured strength. Three curve categories can be distinguished to describe relationships between accumulative plastic strain and cycle number. They are destructive, stable and critical types. Considering the impact of soil structure, a structured parameter called stress sensitivity Sσ is introduced into existing accumulated deformation prediction model. Then destructive and stable empirical formulas are established. They can better predict various accumulative strain curves of structured soft soils with different deformation conditions. The variation of model parameters with the stress level and structure strength is also analyzed.
This paper addresses the long-term settlement of embankment induced by the traffic loading and soil structure of natural soft clay. The artificial structured soils with different bonding strength are prepared. A series of compression test and dynamic triaxial tests are carried out to investigate the effects of cycle number, dynamic stress ratio and structured strength on the accumulative deformation behavior. The results indicate that accumulative deformation increases with the increase of cycle number and dynamic stress ratio, and decreases with the increase of structured strength. Three curve categories can be distinguished to describe relationships between accumulative plastic strain and cycle number. They are destructive, stable and critical types. Considering the impact of soil structure, a structured parameter called stress sensitivity Sσ is introduced into existing accumulated deformation prediction model. Then destructive and stable empirical formulas are established. They can better predict various accumulative strain curves of structured soft soils with different deformation conditions. The variation of model parameters with the stress level and structure strength is also analyzed.
2017, 25(4): 985-992.
The deep overburden dam foundation of strong and weak layers is always met in Southwest and Northwest China. Weak aquifer in deep overburden dam foundation has a great influence on seepage. The influence law needs to be explored in depth. Weak aquifer is set at different positions underneath dam foundation in this test. The depth of vertical cuttoff wall is variable. The result of this test shows that when weak aquifer at the middle of dam foundation, cuttoff wall can form semi-closed combined seepage prevention system, which can effectively decrease seepage discharge of dam foundation and exit gradient. When the semi-closed combined seepage prevention system is adopted in Shangjiang dam, seepage discharge and exit gradient meet allowable requirements. If weak aquife can be utilized, the depth of cuttoff wall can be greatly reduced. This study also finds that when the position of cuttoff wall is deeper, the seepage control of semi-closed combined seepage prevention system can effectively reduce seepage discharge and exit gradient. The results can provide some theoretical reference and suggestions for similar projects, so as to reduce the project cost.
The deep overburden dam foundation of strong and weak layers is always met in Southwest and Northwest China. Weak aquifer in deep overburden dam foundation has a great influence on seepage. The influence law needs to be explored in depth. Weak aquifer is set at different positions underneath dam foundation in this test. The depth of vertical cuttoff wall is variable. The result of this test shows that when weak aquifer at the middle of dam foundation, cuttoff wall can form semi-closed combined seepage prevention system, which can effectively decrease seepage discharge of dam foundation and exit gradient. When the semi-closed combined seepage prevention system is adopted in Shangjiang dam, seepage discharge and exit gradient meet allowable requirements. If weak aquife can be utilized, the depth of cuttoff wall can be greatly reduced. This study also finds that when the position of cuttoff wall is deeper, the seepage control of semi-closed combined seepage prevention system can effectively reduce seepage discharge and exit gradient. The results can provide some theoretical reference and suggestions for similar projects, so as to reduce the project cost.
2017, 25(4): 993-1000.
The deep unloading fissure is a non-tectogenetic geological phenomenon in the high mountain and canyon areas. This special phenomenon has an important influence on the engineering construction. This paper surveys the characteristics of both conventional and deep unloading fissures in an adit at a hydroelectric power station. The fissures are simulated by rock discontinuity network simulation. Then a statistical code is implemented into Autolisp based on definition of RQD, and used to calculate the rock quality indices. The results of these analyses are used to detect the rock RQD value and its discrete standard under the different thresholds. Through the differences of RQD values, the type of unloading fissures can be identified. Furthermore, non-homogeneous characteristic of cracked rock mass is performed according to the dispersion of RQD values discrete standard.
The deep unloading fissure is a non-tectogenetic geological phenomenon in the high mountain and canyon areas. This special phenomenon has an important influence on the engineering construction. This paper surveys the characteristics of both conventional and deep unloading fissures in an adit at a hydroelectric power station. The fissures are simulated by rock discontinuity network simulation. Then a statistical code is implemented into Autolisp based on definition of RQD, and used to calculate the rock quality indices. The results of these analyses are used to detect the rock RQD value and its discrete standard under the different thresholds. Through the differences of RQD values, the type of unloading fissures can be identified. Furthermore, non-homogeneous characteristic of cracked rock mass is performed according to the dispersion of RQD values discrete standard.
2017, 25(4): 1001-1009.
In the 1970s, a large volume of chrome-containing wastewater was discharged into ground in Shanghai. Hexavalent chromium has the characteristics of high toxicity, high solubility and strong mobility. It can easily contaminate groundwater system. Efficient and economic remediation methods are of great significance. This paper systematically summarizes the remediation status of hexavalent chromium. They include reduction and stabilization remediation, permeable reactive barrier, electrokinetic remediation and biological remediation. It is appropriate to take electrokinetic reactive barriers with strengthening reagent in low-permeability soil when deeper than 4m below ground surface.
In the 1970s, a large volume of chrome-containing wastewater was discharged into ground in Shanghai. Hexavalent chromium has the characteristics of high toxicity, high solubility and strong mobility. It can easily contaminate groundwater system. Efficient and economic remediation methods are of great significance. This paper systematically summarizes the remediation status of hexavalent chromium. They include reduction and stabilization remediation, permeable reactive barrier, electrokinetic remediation and biological remediation. It is appropriate to take electrokinetic reactive barriers with strengthening reagent in low-permeability soil when deeper than 4m below ground surface.
2017, 25(4): 1010-1016.
Discontinuities play a key role in the strength and stability of rock mass. During site selection of a project, granite is considered to be the ground or wall rock because of its high strength and integrality. Drillholes are the direct data of the target depth and reveal the rock mass during investigation. In the paper, Dayawan granite at Shenzhen is used as an example can to examine about the distribution of discontinuities in granite. Tectonic and secondary discontinuities are examined along drillhole depth. First, the discontinuities along drillhole and in the ground surface are contrasted. The occurrence distribution is similar because the same tectonic effect at the same site area. Secondly, the distance between two adjacent discontinuities along drillholes are analyzed (for direct effect RQD of drill cores).The discontinuity spacing and its frequency have evident power function relationship which is relevant to the RQD value.
Discontinuities play a key role in the strength and stability of rock mass. During site selection of a project, granite is considered to be the ground or wall rock because of its high strength and integrality. Drillholes are the direct data of the target depth and reveal the rock mass during investigation. In the paper, Dayawan granite at Shenzhen is used as an example can to examine about the distribution of discontinuities in granite. Tectonic and secondary discontinuities are examined along drillhole depth. First, the discontinuities along drillhole and in the ground surface are contrasted. The occurrence distribution is similar because the same tectonic effect at the same site area. Secondly, the distance between two adjacent discontinuities along drillholes are analyzed (for direct effect RQD of drill cores).The discontinuity spacing and its frequency have evident power function relationship which is relevant to the RQD value.
2017, 25(4): 1017-1026.
The influence of drying-wetting cycle to the shear characteristic of saturated laterite is studied in this paper. Undrained triaxial tests of Yunnan laterite at drying-wetting cycle are performed using type TSZ-2 full automatic triaxial test apparatus. It considers drying-wetting cycle number and drying-wetting cycle amplitude. The results show that as the drying-wetting cycle number and the drying-wetting cycle amplitude increase, the strain-softening phenomenon of saturated laterite generally enhances, the initial slope of stress-strain curve and pore water pressure peak increase, the peak shear strength and its corresponding axial strain, cohesion, internal friction angle decrease under unconsolidated undrained condition. The influence of drying-wetting cycle number is more obvious than that of its amplitude. Interaction between laterite and water is the essence of the change of shear characteristic of saturated laterite at drying-wetting cycle. They include the escape of water, the adsorption of laterite particles, hardening and shrinkage of laterite under the condition of dehydration and the wedging, lubricating, softening of water, expansion of laterite in the process of moistening. The deepening and intensifying of above actions at drying-wetting cycle can seriously damage the microstructure of laterite, ultimately change its shear characteristic.
The influence of drying-wetting cycle to the shear characteristic of saturated laterite is studied in this paper. Undrained triaxial tests of Yunnan laterite at drying-wetting cycle are performed using type TSZ-2 full automatic triaxial test apparatus. It considers drying-wetting cycle number and drying-wetting cycle amplitude. The results show that as the drying-wetting cycle number and the drying-wetting cycle amplitude increase, the strain-softening phenomenon of saturated laterite generally enhances, the initial slope of stress-strain curve and pore water pressure peak increase, the peak shear strength and its corresponding axial strain, cohesion, internal friction angle decrease under unconsolidated undrained condition. The influence of drying-wetting cycle number is more obvious than that of its amplitude. Interaction between laterite and water is the essence of the change of shear characteristic of saturated laterite at drying-wetting cycle. They include the escape of water, the adsorption of laterite particles, hardening and shrinkage of laterite under the condition of dehydration and the wedging, lubricating, softening of water, expansion of laterite in the process of moistening. The deepening and intensifying of above actions at drying-wetting cycle can seriously damage the microstructure of laterite, ultimately change its shear characteristic.
IMPACT OF STONE CONTENT TO SHEAR PROPERTIES OF SOIL-ROCK MIXTURE USING PARTICLE FLOW CODE SIMULATION
2017, 25(4): 1035-1045.
DEM numerical models based on PFC2D contact bond model are performed to probe the impact of stone content variation to shear properties of soil-rock mixture(S-RM).The micro parameters of unbound granular materials are calibrated with lab large-scale direct shear tests. Then the shear properties of S-RM of different stone content under different normal stress are studied. The result shows that for S-RM under the same normal stress, the high stone content would result in the high peak shear stress, the high shear strain at peak shear stress, the high post-softening strength, the stronger dilatation behavior, the more shear "leap" behavior. The friction angle of the S-RM increases and the cohesion decreases with the increase of the stone content. The cohesion keeps almost constant after stone content exceeds 50%. For S-RM with the same stone content, the high normal stress would have the high peak shear stress and the stronger strain-softening behavior. The shearing process of S-RM mainly overcomes the friction energy and strain energy are overcome whilst the change of the kinetic energy is almost zero.
DEM numerical models based on PFC2D contact bond model are performed to probe the impact of stone content variation to shear properties of soil-rock mixture(S-RM).The micro parameters of unbound granular materials are calibrated with lab large-scale direct shear tests. Then the shear properties of S-RM of different stone content under different normal stress are studied. The result shows that for S-RM under the same normal stress, the high stone content would result in the high peak shear stress, the high shear strain at peak shear stress, the high post-softening strength, the stronger dilatation behavior, the more shear "leap" behavior. The friction angle of the S-RM increases and the cohesion decreases with the increase of the stone content. The cohesion keeps almost constant after stone content exceeds 50%. For S-RM with the same stone content, the high normal stress would have the high peak shear stress and the stronger strain-softening behavior. The shearing process of S-RM mainly overcomes the friction energy and strain energy are overcome whilst the change of the kinetic energy is almost zero.
2017, 25(4): 1046-1056.
After Wenchuan Earthquake in China, debris flows as a kind of geohazard occur frequently in Wenjia Gully. The debris flows have already cost millions of property and casualty losses to the local community. For the purpose of preventing debris flows, geological engineering treatments have been implemented in multiple locations of Wenjia Gully. The adopted preventive measures include water and sediment separation upstream, reinforce bottom of channel reinforcement and slope protection midstream, damming against and silting downstream. To evaluate the effectiveness of these treatments, this paper presents a data-driven method to conduct this research by collecting data during five seasons of heavy rainfalls. Survival analysis, Bootstrap method and Extreme Learning Machine(ELM) are selected to build data-driven models. By implementing survival analysis models, the survival probabilities of locations without treatment decrease to 0%.The survival probability of the locations with treatment stay at 55.6%after the five rainfall seasons. Meanwhile, the maximum hourly rainfall in the post-treatment period is 2.571 times as the one in pre-treatment period. Total rainfall volume of post-treatment period is 1.232 times as the one in pre-treatment period. Total time period of rainfall of post-treatment is 5.435 times as the one of pre-treatment. Comparing the survival probabilities, the effect of treatments are significant in the prevention of debris flows. After resampling by bootstrap method, the predictive results from Extreme Learning Machine indicate that, without geological treatment, the probability of having debris flow under 10 times of heavy rainfall is 100%.It is much higher than the observed 30% between the year of 2011 and 2015. The predicted debris flows magnitudes are also significantly higher than the observed ones with treatment. Hence, geological engineering treatment is crucial in reducing and preventing geohazards.
After Wenchuan Earthquake in China, debris flows as a kind of geohazard occur frequently in Wenjia Gully. The debris flows have already cost millions of property and casualty losses to the local community. For the purpose of preventing debris flows, geological engineering treatments have been implemented in multiple locations of Wenjia Gully. The adopted preventive measures include water and sediment separation upstream, reinforce bottom of channel reinforcement and slope protection midstream, damming against and silting downstream. To evaluate the effectiveness of these treatments, this paper presents a data-driven method to conduct this research by collecting data during five seasons of heavy rainfalls. Survival analysis, Bootstrap method and Extreme Learning Machine(ELM) are selected to build data-driven models. By implementing survival analysis models, the survival probabilities of locations without treatment decrease to 0%.The survival probability of the locations with treatment stay at 55.6%after the five rainfall seasons. Meanwhile, the maximum hourly rainfall in the post-treatment period is 2.571 times as the one in pre-treatment period. Total rainfall volume of post-treatment period is 1.232 times as the one in pre-treatment period. Total time period of rainfall of post-treatment is 5.435 times as the one of pre-treatment. Comparing the survival probabilities, the effect of treatments are significant in the prevention of debris flows. After resampling by bootstrap method, the predictive results from Extreme Learning Machine indicate that, without geological treatment, the probability of having debris flow under 10 times of heavy rainfall is 100%.It is much higher than the observed 30% between the year of 2011 and 2015. The predicted debris flows magnitudes are also significantly higher than the observed ones with treatment. Hence, geological engineering treatment is crucial in reducing and preventing geohazards.
2017, 25(4): 1057-1064.
Ground penetrating radar(GPR)responses are examined with a number of synthetic models resembling main landslide factors with different physical and geometrical parameters. The factors include slip band thick, slip band with different filling mediums, type of rock and soil, different cracks. The GPR responses are simulated using an improved finite difference time domain forward modeling algorithm. It is shown that there are mathematical relationships between the characteristics of GPR responses and the respective geometrical and physical parameters of landslide. Such mathematical relationships are applied to real field data for deriving estimations of hidden subsurface landslide parameters which can be used to assess the landslide accurately. In order to show the applicability of this study, the GPR field data of Jiangjuntan landslide in Three Gorges Reservoir area is chosen to infer using the mathematical relationships. The result is shown that factors including the depth and distribution of the landslide, the development of the cracks, can be successfully identified.
Ground penetrating radar(GPR)responses are examined with a number of synthetic models resembling main landslide factors with different physical and geometrical parameters. The factors include slip band thick, slip band with different filling mediums, type of rock and soil, different cracks. The GPR responses are simulated using an improved finite difference time domain forward modeling algorithm. It is shown that there are mathematical relationships between the characteristics of GPR responses and the respective geometrical and physical parameters of landslide. Such mathematical relationships are applied to real field data for deriving estimations of hidden subsurface landslide parameters which can be used to assess the landslide accurately. In order to show the applicability of this study, the GPR field data of Jiangjuntan landslide in Three Gorges Reservoir area is chosen to infer using the mathematical relationships. The result is shown that factors including the depth and distribution of the landslide, the development of the cracks, can be successfully identified.
2017, 25(4): 1065-1072.
This paper is based on the prototype slope with weak interlayer inclusion and anchor-frame reinforcement at the MK10+250 of Zhaoyin Expressway. A 1/30 downscale model slope is designed and shaking table tests with 20 loading cases are then conducted. The influences of slope elevation and seismic wave amplitude on the PGA amplification coefficient and the PEP oscillation coefficient are focused in this paper. The PGA amplification coefficients inside and upon the slope always increase with the slope elevation. Due to the isolation effect of weak interlayer and the reinforcement effect of anchor-frame, however, the acceleration response of slope tends to be entirety and no whiplash effect is presented. The PGA amplification coefficients decease linearly(at lower elevation) or exponentially(at upper elevation) with the amplitude of input seismic wave. The PEP oscillation coefficients inside the slop increase linearly with the cover depth, while increase non-linearly with the amplitude of input seismic wave. When excited by the seismic waves with larger amplitude, the additional horizontal pressure towards outside tends to be greater than the counterpart towards inside. The failure characteristic of model slope during shaking table tests is carefully inspected and described. The cracks concentrate in the upper part of slope above the weak interlayer, especially upon the top face of slope. However, no overall instability is presented along the weak interlayer due to the reinforcement effect of anchor-frame.
This paper is based on the prototype slope with weak interlayer inclusion and anchor-frame reinforcement at the MK10+250 of Zhaoyin Expressway. A 1/30 downscale model slope is designed and shaking table tests with 20 loading cases are then conducted. The influences of slope elevation and seismic wave amplitude on the PGA amplification coefficient and the PEP oscillation coefficient are focused in this paper. The PGA amplification coefficients inside and upon the slope always increase with the slope elevation. Due to the isolation effect of weak interlayer and the reinforcement effect of anchor-frame, however, the acceleration response of slope tends to be entirety and no whiplash effect is presented. The PGA amplification coefficients decease linearly(at lower elevation) or exponentially(at upper elevation) with the amplitude of input seismic wave. The PEP oscillation coefficients inside the slop increase linearly with the cover depth, while increase non-linearly with the amplitude of input seismic wave. When excited by the seismic waves with larger amplitude, the additional horizontal pressure towards outside tends to be greater than the counterpart towards inside. The failure characteristic of model slope during shaking table tests is carefully inspected and described. The cracks concentrate in the upper part of slope above the weak interlayer, especially upon the top face of slope. However, no overall instability is presented along the weak interlayer due to the reinforcement effect of anchor-frame.
2017, 25(4): 1073-1082.
This study builds the basin model of Zengda gully using SCS method and Kinematic wave method in HEC-HMS.Then it calculates the clear water flow of basin model under 12 different types of rainfall and discusses the flow characteristics under different rainfall types. The results show that the peak flow rate is linear positive correlation with the arrival time of the peak of rainfall and the concentration degree of rainfall(the power number of rainfall model).The delay time of peak flow is twice correlation with the arrival time of the peak of rainfall and the concentration degree of rainfall. The two elements multiple equation fitting for the two groups of variables and the fitting effect is good. By comparing the calculated results of HEC-HMS with the results of the inference formula method, the differences between the two results and their advantages of each method are evaluated.
This study builds the basin model of Zengda gully using SCS method and Kinematic wave method in HEC-HMS.Then it calculates the clear water flow of basin model under 12 different types of rainfall and discusses the flow characteristics under different rainfall types. The results show that the peak flow rate is linear positive correlation with the arrival time of the peak of rainfall and the concentration degree of rainfall(the power number of rainfall model).The delay time of peak flow is twice correlation with the arrival time of the peak of rainfall and the concentration degree of rainfall. The two elements multiple equation fitting for the two groups of variables and the fitting effect is good. By comparing the calculated results of HEC-HMS with the results of the inference formula method, the differences between the two results and their advantages of each method are evaluated.
2017, 25(4): 1083-1093.
A high fill airport in southwestern China suffered a half month of heavy rainfall immediately after its earthwork has been completed. A landslide occurred at 4 hours after the sudden rainstorm. This paper uses the methods of surveillance, detection, scene investigation, in situ tests, laboratory test and numerical simulation and makes a comprehensive analysis. The slope sliding is due to the following aspects. The embankment of dynamic compaction reinforcement destroyed the original gravel drainage layer in the body of the soil surface area. The affected slope area is the ground with gravel filling of cohesive soil. The rainfall can not be discharged from the channel slot area. High groundwater pressure, seepage deformation, soak softening, and others cause the slide. The emergency measures include film covering the top surface of the filling body, network installation graded gravel filtration and drainage on slope water point, sliding slope gravel bags backfill and permanent disposal method of filling the top of cohesive backfill, slope gravel replacement and yang inclined tube drainage. They effectively control the further slump deformation and slide, achieve good results.
A high fill airport in southwestern China suffered a half month of heavy rainfall immediately after its earthwork has been completed. A landslide occurred at 4 hours after the sudden rainstorm. This paper uses the methods of surveillance, detection, scene investigation, in situ tests, laboratory test and numerical simulation and makes a comprehensive analysis. The slope sliding is due to the following aspects. The embankment of dynamic compaction reinforcement destroyed the original gravel drainage layer in the body of the soil surface area. The affected slope area is the ground with gravel filling of cohesive soil. The rainfall can not be discharged from the channel slot area. High groundwater pressure, seepage deformation, soak softening, and others cause the slide. The emergency measures include film covering the top surface of the filling body, network installation graded gravel filtration and drainage on slope water point, sliding slope gravel bags backfill and permanent disposal method of filling the top of cohesive backfill, slope gravel replacement and yang inclined tube drainage. They effectively control the further slump deformation and slide, achieve good results.
2017, 25(4): 1105-1112.
The chemical properties of clay reflect its depositional environment and the depositional environment affects the engineering properties of clay. Their correlation is an important research content of soil mechanics. The test methods for the chemical properties of soft soil pore solution are introduced, and the tests on upper Shanghai clays are carried out. The distribution of each chemical properties index is given. Combined with the sea-level change in the Shanghai region, the history of changing depositional environment is reflected by the chemical properties of shallow Shanghai clays. Especially the Quaternary transgressive and regressive impact on chemical properties of clay is examined. The correlation between the chemical properties of Shanghai clays and their physical and mechanical properties is analyzed. Two opposite influences of salt content on sensitivity and physical parameters in different depositional environments(transgression and regression) are obtained.
The chemical properties of clay reflect its depositional environment and the depositional environment affects the engineering properties of clay. Their correlation is an important research content of soil mechanics. The test methods for the chemical properties of soft soil pore solution are introduced, and the tests on upper Shanghai clays are carried out. The distribution of each chemical properties index is given. Combined with the sea-level change in the Shanghai region, the history of changing depositional environment is reflected by the chemical properties of shallow Shanghai clays. Especially the Quaternary transgressive and regressive impact on chemical properties of clay is examined. The correlation between the chemical properties of Shanghai clays and their physical and mechanical properties is analyzed. Two opposite influences of salt content on sensitivity and physical parameters in different depositional environments(transgression and regression) are obtained.
2017, 25(4): 1113-1122.
The stone-quarrying industry in China has flourished for a very long history, which is featured by large scale, long duration, and numerous remains of ancient quarrying caverns. Zhejiang Province, one of the dozens of provinces in China, is particularly important in the ancient quarrying industry, and is home to many famous ancient underground caverns which are mostly tourism attractions now. Changyudongtian ancient underground quarry cavern in Zhejiang, for instance, is now listed as the world geopark and national mine park. It is found during field investigation that the ancient quarryman has invented a special quarrying technique in Changyudongtian. It consists of such seven processes including exploring, enlarging, eluding, excavating, draining, distributing and discharging, wand is now named as 4E3D technique. The Changyudongtian ancient quarry cavern group is an assemble of 28 large cavern complexes like Shuiyun cavern complex. It is extremely large in dimension. The 4E3D technique has played an important role in the quarrying process of Changyudongtian and undoubtedly extremely effective for stone quarrying. It is verified to be invented with full consideration of the local engineering geological conditions and the development level of the quarrying tools at the time.
The stone-quarrying industry in China has flourished for a very long history, which is featured by large scale, long duration, and numerous remains of ancient quarrying caverns. Zhejiang Province, one of the dozens of provinces in China, is particularly important in the ancient quarrying industry, and is home to many famous ancient underground caverns which are mostly tourism attractions now. Changyudongtian ancient underground quarry cavern in Zhejiang, for instance, is now listed as the world geopark and national mine park. It is found during field investigation that the ancient quarryman has invented a special quarrying technique in Changyudongtian. It consists of such seven processes including exploring, enlarging, eluding, excavating, draining, distributing and discharging, wand is now named as 4E3D technique. The Changyudongtian ancient quarry cavern group is an assemble of 28 large cavern complexes like Shuiyun cavern complex. It is extremely large in dimension. The 4E3D technique has played an important role in the quarrying process of Changyudongtian and undoubtedly extremely effective for stone quarrying. It is verified to be invented with full consideration of the local engineering geological conditions and the development level of the quarrying tools at the time.
2017, 25(4): 1123-1131.
According to the long-term mining experience, the ancient quarrymen quarry rocks to form the bell-shape caverns without any pillar. Because the north-south and southwest-northeast gradients are different, the caverns have different cross-sections. So the bottom of caverns is approximately oval. This paper explores the scientific rules of structural features of the bell-shape caverns of Huaxuan caverns and Huaju caverns in Changyu, Wenlin, Zhejiang province, and the scientific rules of structural features. It examines the characteristics of the structure parameters of bell-shape caverns for further analysis of the influence factors of the large cavern group. The topographic slope, the span-high radio and the buried depth and height ratio of cavern are analyzed with the FLAC for analyzing the structure parameter character of the bell-shape caverns. Analysis of the stress and plastic zone shows the following results. For the gentle slope surface, the span-high radio is less than 1.44 and the height ratio is less than 1.8. For the steep slope surfacedirection, the span-high radio is less than 1.28 and the height ratio is less than 1.8. About 67.7% of the 24 caverns can meet these rules. So, the reasonable structure character of the bell-shape cavern has resulted them to have been stability for one thousand years.
According to the long-term mining experience, the ancient quarrymen quarry rocks to form the bell-shape caverns without any pillar. Because the north-south and southwest-northeast gradients are different, the caverns have different cross-sections. So the bottom of caverns is approximately oval. This paper explores the scientific rules of structural features of the bell-shape caverns of Huaxuan caverns and Huaju caverns in Changyu, Wenlin, Zhejiang province, and the scientific rules of structural features. It examines the characteristics of the structure parameters of bell-shape caverns for further analysis of the influence factors of the large cavern group. The topographic slope, the span-high radio and the buried depth and height ratio of cavern are analyzed with the FLAC for analyzing the structure parameter character of the bell-shape caverns. Analysis of the stress and plastic zone shows the following results. For the gentle slope surface, the span-high radio is less than 1.44 and the height ratio is less than 1.8. For the steep slope surfacedirection, the span-high radio is less than 1.28 and the height ratio is less than 1.8. About 67.7% of the 24 caverns can meet these rules. So, the reasonable structure character of the bell-shape cavern has resulted them to have been stability for one thousand years.
2017, 25(4): 1132-1140.
This paper aims at a variety of failure phenomena of ancient city walls in different regions of China. It is based on the analysis of the failure mechanism. It uses the method of classification and induction to study the failure modes of ancient city wall. It puts forward a variety of ancient city wall failure modes. It uses the control factors that lead to the failure of the wall to classify the failure modes. It summarizes 11 typical failure modes including uneven settlement of foundation, surface bulging, wind erosion and heavy rainfall erosion. The corresponding occurring conditions and failure mechanisms are recommended for each failure modes. The protective measures are also proposed. Combined with the numerical simulation method, the failure mode of an ancient city wall in China is identified. The results show that the main failure mode of this ancient city wall is rainstorm erosion. The rainfall degree, the duration of rainfall, and the drainage channel in the wall all have a significant impact on the deformation of the wall. The rainfall leads to the bulging phenomenon in the lower part of the surface of the wall. The results can provide a scientific basis for the protection of the ancient city wall, effectively avoid the occurrence of local instability problems and provide a reference for the protection and restoration of the ancient city wall under various failure modes.
This paper aims at a variety of failure phenomena of ancient city walls in different regions of China. It is based on the analysis of the failure mechanism. It uses the method of classification and induction to study the failure modes of ancient city wall. It puts forward a variety of ancient city wall failure modes. It uses the control factors that lead to the failure of the wall to classify the failure modes. It summarizes 11 typical failure modes including uneven settlement of foundation, surface bulging, wind erosion and heavy rainfall erosion. The corresponding occurring conditions and failure mechanisms are recommended for each failure modes. The protective measures are also proposed. Combined with the numerical simulation method, the failure mode of an ancient city wall in China is identified. The results show that the main failure mode of this ancient city wall is rainstorm erosion. The rainfall degree, the duration of rainfall, and the drainage channel in the wall all have a significant impact on the deformation of the wall. The rainfall leads to the bulging phenomenon in the lower part of the surface of the wall. The results can provide a scientific basis for the protection of the ancient city wall, effectively avoid the occurrence of local instability problems and provide a reference for the protection and restoration of the ancient city wall under various failure modes.
STUDY ON SEISMIC FAULT AND SOURCE RUPTURE TECTONIC DYNAMIC MECHANISM OF JIUZHAIGOU MS 7.0 EARTHQUAKE
2017, 25(4): 1141-1150.
The seismic fault and source rupture tectonic dynamics mechanism of Jiuzhaigou MS7.0 Earthquake were studied in this paper based on the combination of geological investigation, test and source tectonic dynamic theoretical analysis. This earthquake occurred at the intersection of the northern margin of the Minshan uplift belt and the south of Wenxian-Maqin fault in the south margin of the West Qinling trough, where is under sinistral shear stress with high law stress. There are two tectonic ruptures with NW trending fissure zone along the line of "Jiuzhaigou Paradise"-epicenter-Wuhuahai and Shangsizhai Village-Zhongcha-Bimang, which is ground coseismic rupture caused by "hidden" earthquake fault, former is the structure controlling this earthquake, the later is the sub-coseismic resurrection and extension of the NW-trending fault; the displacement of source fault in this earthquake is strike-slip shear fracture dominated by deep angle fault with strike NW331ånd dip angle ∠87°, and the aftershock activity is controlled by two NW-trending faults, the shear fracture at both ends of the fault showed continuous expansion trends. The source tectonic dynamic mechanism is actually sinistral cutting "protrusion" along NW in the deep of crust. The continuous expansion of rupture at both ends of seismic fault will produce the gradual breakthrough of the crustal "protrusion".
The seismic fault and source rupture tectonic dynamics mechanism of Jiuzhaigou MS7.0 Earthquake were studied in this paper based on the combination of geological investigation, test and source tectonic dynamic theoretical analysis. This earthquake occurred at the intersection of the northern margin of the Minshan uplift belt and the south of Wenxian-Maqin fault in the south margin of the West Qinling trough, where is under sinistral shear stress with high law stress. There are two tectonic ruptures with NW trending fissure zone along the line of "Jiuzhaigou Paradise"-epicenter-Wuhuahai and Shangsizhai Village-Zhongcha-Bimang, which is ground coseismic rupture caused by "hidden" earthquake fault, former is the structure controlling this earthquake, the later is the sub-coseismic resurrection and extension of the NW-trending fault; the displacement of source fault in this earthquake is strike-slip shear fracture dominated by deep angle fault with strike NW331ånd dip angle ∠87°, and the aftershock activity is controlled by two NW-trending faults, the shear fracture at both ends of the fault showed continuous expansion trends. The source tectonic dynamic mechanism is actually sinistral cutting "protrusion" along NW in the deep of crust. The continuous expansion of rupture at both ends of seismic fault will produce the gradual breakthrough of the crustal "protrusion".
2017, 25(4): 1151-1164.
A magnitude 7.0 earthquake struck Jiuzhaigou on August 8th, 2017 in Sichuan province, which is another strong earthquake happened in Sichuan province after the 2008 great Wenchuan earthquake and the 2013 Lushan earthquake. In order to provide scientific evidence for on-the-spot rescue work and geologic hazard prevention after the earthquake, the author arrived quickly on the field and finished geologic hazard interpretation and review work in the earth-stricken areas based on high resolution remote sensing images before and after the earthquake. As a result, 1833 earthquake-induced geohazards have been obtained in the study area of 840km2, which are mainly medium-scale and small-scale shallow landslides and collapses. In terms of the results of the interpretation, the spatial distribution patterns and control factors in the cosesmic geohazards (distance from the fault, PGA, elevation, slope, aspect etc.) are analyzed, the research shows that the geohazards triggered by earthquake have the features of zonal distribution mainly distributed along north-west and east-south, especially along the roads and valleys. The width of strong development zone along the field inferred seismogenic fault is about 2km, showing a distinct faulting effect, but the spatial correlation betweem geohazards and Tazang fault is weak. Based on the above-described analysis, logistic regression model is taken quick comments and divisions of geologic hazard susceptibility are made. After statists and testing, the accuracy of this model has reached 0.851, a comparatively high precise data.
A magnitude 7.0 earthquake struck Jiuzhaigou on August 8th, 2017 in Sichuan province, which is another strong earthquake happened in Sichuan province after the 2008 great Wenchuan earthquake and the 2013 Lushan earthquake. In order to provide scientific evidence for on-the-spot rescue work and geologic hazard prevention after the earthquake, the author arrived quickly on the field and finished geologic hazard interpretation and review work in the earth-stricken areas based on high resolution remote sensing images before and after the earthquake. As a result, 1833 earthquake-induced geohazards have been obtained in the study area of 840km2, which are mainly medium-scale and small-scale shallow landslides and collapses. In terms of the results of the interpretation, the spatial distribution patterns and control factors in the cosesmic geohazards (distance from the fault, PGA, elevation, slope, aspect etc.) are analyzed, the research shows that the geohazards triggered by earthquake have the features of zonal distribution mainly distributed along north-west and east-south, especially along the roads and valleys. The width of strong development zone along the field inferred seismogenic fault is about 2km, showing a distinct faulting effect, but the spatial correlation betweem geohazards and Tazang fault is weak. Based on the above-described analysis, logistic regression model is taken quick comments and divisions of geologic hazard susceptibility are made. After statists and testing, the accuracy of this model has reached 0.851, a comparatively high precise data.
2017, 25(4): 1027-1034.
The fiber optic sensing technique has been widely applied to geohazard monitoring and deformation measurement of geomaterials. This paper aims to understand the coupling mechanism between strain sensing optic fibers and the surrounding soil masses for interpreting the monitoring results. It examines the influence of fiber embedment length on the mechanical property of fiber-soil interface. There are insufficient investigations on the strain distribution and transfer mechanism along the sensing optic fiber during pullout process. Using the newly designed pullout devices, this paper evaluates the influence of four different embedment lengths of sensing optic fiber on the fiber-soil interfacial property. A mathematical model is used to fit the pullout curves. The results show that the effective pullout displacement and the maximum pullout force increase linearly with the increase of fiber embedment length. But the fiber-soil interfacial shear strength decreases with the increase of the embedment length. Furthermore, the Brillouin optical fiber time domain analysis(BOTDA)technology is used to measure the strain distribution along the sensing optical fiber during its gradual decoupling process from the soil mass. The distribution of fiber-soil interfacial shear stress is also calculated, which shows that the interface failure is highly progressive. These findings can provide reference for understanding the interaction mechanism between strain sensing fiber and surrounding soil, and promote the application of fiber optic sensing technique to geoengineering monitoring.
The fiber optic sensing technique has been widely applied to geohazard monitoring and deformation measurement of geomaterials. This paper aims to understand the coupling mechanism between strain sensing optic fibers and the surrounding soil masses for interpreting the monitoring results. It examines the influence of fiber embedment length on the mechanical property of fiber-soil interface. There are insufficient investigations on the strain distribution and transfer mechanism along the sensing optic fiber during pullout process. Using the newly designed pullout devices, this paper evaluates the influence of four different embedment lengths of sensing optic fiber on the fiber-soil interfacial property. A mathematical model is used to fit the pullout curves. The results show that the effective pullout displacement and the maximum pullout force increase linearly with the increase of fiber embedment length. But the fiber-soil interfacial shear strength decreases with the increase of the embedment length. Furthermore, the Brillouin optical fiber time domain analysis(BOTDA)technology is used to measure the strain distribution along the sensing optical fiber during its gradual decoupling process from the soil mass. The distribution of fiber-soil interfacial shear stress is also calculated, which shows that the interface failure is highly progressive. These findings can provide reference for understanding the interaction mechanism between strain sensing fiber and surrounding soil, and promote the application of fiber optic sensing technique to geoengineering monitoring.
2017, 25(4): 1094-1104.
In recent years, the constructions of airport, highway and railway transportation network and urbanization in the loess hilly areas have been carried out more and more frequent. They have formed a large quantities of high loess embankment slope. Although the annual rainfall of these areas is semiarid, rainfall is the main factor for the failure of loess slopes. This paper analyses the in-situ seepage experiment and the transient unsaturated seepage under the conditions considering the fractures and the mechanical properties of saturated loess. It examines the failure mechanism of high fill retaining loess slope. The results show the following. (1) The maximum infiltration depth of the test pit center is 1.30m after 3 days in the in situ seepage experiment. The maximum depth of the wetting front is 0.20m below the maximum infiltration depth. (2) When the confining pressure is less than 300kPa, the axial strain of the saturated soil increases to about 20%, and reaches the steady state. Under the condition that static driving shearing stress is larger than the steady shear strength, the local flowslide failure of the high fill slope can occur. (3) In general, the formation mechanism of deformation and failure of the retaining high embankment slopes is as follows:push creeping-retaining structural failure-progressive slip shear-traction collapse.
In recent years, the constructions of airport, highway and railway transportation network and urbanization in the loess hilly areas have been carried out more and more frequent. They have formed a large quantities of high loess embankment slope. Although the annual rainfall of these areas is semiarid, rainfall is the main factor for the failure of loess slopes. This paper analyses the in-situ seepage experiment and the transient unsaturated seepage under the conditions considering the fractures and the mechanical properties of saturated loess. It examines the failure mechanism of high fill retaining loess slope. The results show the following. (1) The maximum infiltration depth of the test pit center is 1.30m after 3 days in the in situ seepage experiment. The maximum depth of the wetting front is 0.20m below the maximum infiltration depth. (2) When the confining pressure is less than 300kPa, the axial strain of the saturated soil increases to about 20%, and reaches the steady state. Under the condition that static driving shearing stress is larger than the steady shear strength, the local flowslide failure of the high fill slope can occur. (3) In general, the formation mechanism of deformation and failure of the retaining high embankment slopes is as follows:push creeping-retaining structural failure-progressive slip shear-traction collapse.
2017, 25(4): 901-902.
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