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Editor Work2014 Vol. 22, No. 6
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2014, 22(6): 1023-1027.
Abstract
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A significantsize effect is observed in tensile strength of solid particles such as ice, rock, ceramics and concrete. The tensile strength is not independent of the fragment size, but decreases with increasing size. Recent developments in fractal theory suggest that fractals may provide a more realistic representation of solid particles. In this paper, a fractal model for crushing of rock particle is constructed using the Steacy and Sammis model. The size effect of crushing strength is then derived. The size effect of the crushing strength is expressed by fdD-3. It is shown by the published data that the fractal dimension of the rock particle distribution is nearly 2.5-2.6. The size effect of crushing strength can be expressed by the fractal model for particle crushing.
A significantsize effect is observed in tensile strength of solid particles such as ice, rock, ceramics and concrete. The tensile strength is not independent of the fragment size, but decreases with increasing size. Recent developments in fractal theory suggest that fractals may provide a more realistic representation of solid particles. In this paper, a fractal model for crushing of rock particle is constructed using the Steacy and Sammis model. The size effect of crushing strength is then derived. The size effect of the crushing strength is expressed by fdD-3. It is shown by the published data that the fractal dimension of the rock particle distribution is nearly 2.5-2.6. The size effect of crushing strength can be expressed by the fractal model for particle crushing.
2014, 22(6): 1028-1033.
Upward seepage, a special kind of seepage phenomenon, can be generated in the loess(unsaturated soil) on the rise of underground water(phreatic water) level. In order to explore the upward seepage law in the loess, the upward permeameter on unsaturated soil is developed. This experimental instrument consists of water replenishing device, seepage device, connecting pipe which connects the two devices and test bed. It can simulate the interaction between soil and water under different water pressure(constant head pressure) on the rise of water table. The tester can directly observe the process of water upward seepage in the loess, the shape and the change of seepage front and can obtain the relationship between seepage frontal displacement and time(seepage velocity),the relationship between seepage pressure and seepage velocity. Revealing the upward seepage law to serve the study of loess disasters(landslide, collapse, land subsidence and the like) is of great significance. On the basis of the experimental instrument, two sets of in-situ unsaturated Lishi loess are selected to do simulation. The constant pressure heads of the two sets of soil samples are 1cm, 5cm and 10cm. The experimental results show that the instrument can effectively simulate the interaction between soil and water under constant head pressure on the rise of water table, intuitively reproduce the water seepage in the soil and obtain the required upward seepage characteristic parameters. Also, the permeameter renders certain practical value and application prospect.
Upward seepage, a special kind of seepage phenomenon, can be generated in the loess(unsaturated soil) on the rise of underground water(phreatic water) level. In order to explore the upward seepage law in the loess, the upward permeameter on unsaturated soil is developed. This experimental instrument consists of water replenishing device, seepage device, connecting pipe which connects the two devices and test bed. It can simulate the interaction between soil and water under different water pressure(constant head pressure) on the rise of water table. The tester can directly observe the process of water upward seepage in the loess, the shape and the change of seepage front and can obtain the relationship between seepage frontal displacement and time(seepage velocity),the relationship between seepage pressure and seepage velocity. Revealing the upward seepage law to serve the study of loess disasters(landslide, collapse, land subsidence and the like) is of great significance. On the basis of the experimental instrument, two sets of in-situ unsaturated Lishi loess are selected to do simulation. The constant pressure heads of the two sets of soil samples are 1cm, 5cm and 10cm. The experimental results show that the instrument can effectively simulate the interaction between soil and water under constant head pressure on the rise of water table, intuitively reproduce the water seepage in the soil and obtain the required upward seepage characteristic parameters. Also, the permeameter renders certain practical value and application prospect.
2014, 22(6): 1034-1038.
The present paper proposes an evaluation of corrosion rock strength parameters approach to analyze the corrosion calcareous rock strength parameters. The parameters are obtained through laboratory and in situ tests and cannot apply to the engineering directly. The proposed approach utilizes a numerical model in conjunction with the distribution of corrosion. It is based on site investigation to analyze the strength parameters of the corrosion rock. The relationships between strength parameters and corrosion are determined. In the meantime, laboratory triaxial tests are carried out. The results show that the relationship built on the numerical model is correct.
The present paper proposes an evaluation of corrosion rock strength parameters approach to analyze the corrosion calcareous rock strength parameters. The parameters are obtained through laboratory and in situ tests and cannot apply to the engineering directly. The proposed approach utilizes a numerical model in conjunction with the distribution of corrosion. It is based on site investigation to analyze the strength parameters of the corrosion rock. The relationships between strength parameters and corrosion are determined. In the meantime, laboratory triaxial tests are carried out. The results show that the relationship built on the numerical model is correct.
2014, 22(6): 1039-1045.
This paper determines the consolidation characteristics and the influence of water content and load ratio on the coefficient of secondary consolidation of hydraulic fill ultra soft soil in Tianjin. A series of step-loading consolidation tests are performed on both ultra soft soil and remolded specimens using a modified oedometer with low applied stress and the ordinary oedometer. The results show that the coefficient of consolidation of the remolded specimens increases with the increasing consolidation pressure. But the ultra soft soil has aSshape of Cv-lgp curves. ThisSshape involves two parts divided by the consolidation yield stress(16kPa).The one prior to the yield stress is responsible for concave increase while the other after the yield stress is responsible for linear increase with the decreasing incrementary ratio. Unlike to the normal sedimentary remolded soils, the coefficient of secondary consolidation of hydraulic fill ultra soft soil shows a peak value as the consolidation pressure is applied. Load ratio had significant influence on the coefficient of secondary consolidation of hydraulic fill ultra soft soil. The smaller incremental load can reduce the coefficient of secondary consolidation. The coefficients of secondary consolidation of the ultra soft soil and normal sedimentary remolded soils are increased with increasing moisture content.
This paper determines the consolidation characteristics and the influence of water content and load ratio on the coefficient of secondary consolidation of hydraulic fill ultra soft soil in Tianjin. A series of step-loading consolidation tests are performed on both ultra soft soil and remolded specimens using a modified oedometer with low applied stress and the ordinary oedometer. The results show that the coefficient of consolidation of the remolded specimens increases with the increasing consolidation pressure. But the ultra soft soil has aSshape of Cv-lgp curves. ThisSshape involves two parts divided by the consolidation yield stress(16kPa).The one prior to the yield stress is responsible for concave increase while the other after the yield stress is responsible for linear increase with the decreasing incrementary ratio. Unlike to the normal sedimentary remolded soils, the coefficient of secondary consolidation of hydraulic fill ultra soft soil shows a peak value as the consolidation pressure is applied. Load ratio had significant influence on the coefficient of secondary consolidation of hydraulic fill ultra soft soil. The smaller incremental load can reduce the coefficient of secondary consolidation. The coefficients of secondary consolidation of the ultra soft soil and normal sedimentary remolded soils are increased with increasing moisture content.
2014, 22(6): 1046-1051.
This paper adopts cracking experiments and micro experiment observations of compacted clay specimens under the influence of different wetting-drying cycles. It investigates the effects of wetting-drying cycles on clay cracking and pore structure. Moreover it compares the experimental results of Mercury Intrusion Porosimetry(MIP) and Scanning Electron Microscopy(SEM)tests with those of the macro cracking experiments. The experimental results show that the wetting-drying cycles have a great influence on compacted clay cracking. The Cracking Intensity Factor(CIF),representing the degree of compacted clay cracking, increases as moisture contents decrease, and is obviously larger than that before the wetting-drying cycles. As the number of wetting-drying cycles increases, the total volume of the pores, as the median pore diameter, the mean pore diameter, the mean porosity and the intra-aggregate pores increase. But the intra-particle pores, the inter-particle pores and the inter-aggregate pores reduce obviously. The wetting-drying cycles make the large aggregates of the clay gradually transform into small particles and increase the convexity of the soil particles. Besides, it is observed from the analysis of SEM binary image that the porosity increases with the wetting-drying cycles growing. It is plausible to employ Mercury Intrusion Porosimetry(MIP) and Scanning Electron Microscopy(SEM)tests to analyze and explain the clay cracking. The micro pore characteristics derived from the tests are in line with the macro clay cracking law.
This paper adopts cracking experiments and micro experiment observations of compacted clay specimens under the influence of different wetting-drying cycles. It investigates the effects of wetting-drying cycles on clay cracking and pore structure. Moreover it compares the experimental results of Mercury Intrusion Porosimetry(MIP) and Scanning Electron Microscopy(SEM)tests with those of the macro cracking experiments. The experimental results show that the wetting-drying cycles have a great influence on compacted clay cracking. The Cracking Intensity Factor(CIF),representing the degree of compacted clay cracking, increases as moisture contents decrease, and is obviously larger than that before the wetting-drying cycles. As the number of wetting-drying cycles increases, the total volume of the pores, as the median pore diameter, the mean pore diameter, the mean porosity and the intra-aggregate pores increase. But the intra-particle pores, the inter-particle pores and the inter-aggregate pores reduce obviously. The wetting-drying cycles make the large aggregates of the clay gradually transform into small particles and increase the convexity of the soil particles. Besides, it is observed from the analysis of SEM binary image that the porosity increases with the wetting-drying cycles growing. It is plausible to employ Mercury Intrusion Porosimetry(MIP) and Scanning Electron Microscopy(SEM)tests to analyze and explain the clay cracking. The micro pore characteristics derived from the tests are in line with the macro clay cracking law.
2014, 22(6): 1052-1057.
Normal sedimentary soil generally has the characteristics of original structures. Up to now, the most soil constitutive models are developed and built up based on the non-structure soils. If they are directly used to describe stress-strain relations of structure soils, a great difference can be produced between the measured value and the calculated value. This paper is based on the modified Cambridge model. The stress-strain relationship is established considering the influence of original structure property of the structural soft dredger fill. Compared with the modified Cambridge model, the new model only increases the number of parameters. They can be obtained through the conventional triaxial test. The types of parameters are unchanged. The triaxial compression test are conducted of the structural dredger fill which are treated by vacuum preloading method in Tianjin Binhai new area. Compared with the test value and the simulation value, the new model can consider the effect of original structural impact.
Normal sedimentary soil generally has the characteristics of original structures. Up to now, the most soil constitutive models are developed and built up based on the non-structure soils. If they are directly used to describe stress-strain relations of structure soils, a great difference can be produced between the measured value and the calculated value. This paper is based on the modified Cambridge model. The stress-strain relationship is established considering the influence of original structure property of the structural soft dredger fill. Compared with the modified Cambridge model, the new model only increases the number of parameters. They can be obtained through the conventional triaxial test. The types of parameters are unchanged. The triaxial compression test are conducted of the structural dredger fill which are treated by vacuum preloading method in Tianjin Binhai new area. Compared with the test value and the simulation value, the new model can consider the effect of original structural impact.
2014, 22(6): 1058-1065.
This paper compares the ASTM and Chinese standards about plate loading test. It summarizes their main differences in the following two aspects: plate size and steady standard of settlement. It analyzes that two aspects can bring about effect for test result, and puts forward interrelated attentive issue during project. ASTM standard is more universal and greatly flexible. The Chinese standard is detailed and rigorous. The plate load tests in Botswana power plant are carried out according to US standards and Chinese standard respectively. The test results indicate that the differences between two test results are not obvious for high strength formations(for example sand soil).The results can be used as reference for Chinese surveyors and designers in their overseas projects.
This paper compares the ASTM and Chinese standards about plate loading test. It summarizes their main differences in the following two aspects: plate size and steady standard of settlement. It analyzes that two aspects can bring about effect for test result, and puts forward interrelated attentive issue during project. ASTM standard is more universal and greatly flexible. The Chinese standard is detailed and rigorous. The plate load tests in Botswana power plant are carried out according to US standards and Chinese standard respectively. The test results indicate that the differences between two test results are not obvious for high strength formations(for example sand soil).The results can be used as reference for Chinese surveyors and designers in their overseas projects.
2014, 22(6): 1066-1070.
Saturation curve model is proposed to satisfy the characteristics of S-style settlement process. Firstly, it is improved that the suggested model owns the same properties with S-style settlement process. The properties include boundedly convergent, monotonically increasing and inflection point existing. Meanwhile, influence of parameters is analyzed. Subsequently, parameter acquisition method and settlement prediction procedure are clarified. Finally, the rationality of given model is evaluated by several examples. Results show that the saturation curve model is of good applicability, precision and stability, and can be applied to settlement prediction during the whole construction period. Comparing with the hyperbola method, exponential curve method, Hoshino method and logistic curve method, the suggested settlement prediction model is more reliable and thus possesses a momentous engineering value and spreading significance.
Saturation curve model is proposed to satisfy the characteristics of S-style settlement process. Firstly, it is improved that the suggested model owns the same properties with S-style settlement process. The properties include boundedly convergent, monotonically increasing and inflection point existing. Meanwhile, influence of parameters is analyzed. Subsequently, parameter acquisition method and settlement prediction procedure are clarified. Finally, the rationality of given model is evaluated by several examples. Results show that the saturation curve model is of good applicability, precision and stability, and can be applied to settlement prediction during the whole construction period. Comparing with the hyperbola method, exponential curve method, Hoshino method and logistic curve method, the suggested settlement prediction model is more reliable and thus possesses a momentous engineering value and spreading significance.
2014, 22(6): 1071-1076.
The classical failure criteria for prediction of rock strength can not be accurate. This study uses the diagonal intersection least squares SVM(DILSSVM)as new method for prediction of the rock strength in a wide loading such as uniaxial and triaxial loading. For each rock type, data obtained from field experiments and laboratory experiments are divided into training and test sets. DILSSVM is employed to train with the compressive stress (c) and minor principal stress (3) and to predict the value of major principal stress (1f) at failure. The training sets are used in regression analysis for m in Hoek-Brown (H-B) equation. Then, the test sets are used to examine the accuracy of target rock strength with DILSSVM after training and these of the two H-B model(with different m). Comparison of the results of the DILSSVM with the two H-B models shows that the DILSSVM always has less root mean squared error(decreased 45% ～55%) and higher coefficient of determination(enhanced 0.055～0.085,near to 1). The DILSSVM shows better flexibility in 1f at failure in each rock type and a wide loading range.
The classical failure criteria for prediction of rock strength can not be accurate. This study uses the diagonal intersection least squares SVM(DILSSVM)as new method for prediction of the rock strength in a wide loading such as uniaxial and triaxial loading. For each rock type, data obtained from field experiments and laboratory experiments are divided into training and test sets. DILSSVM is employed to train with the compressive stress (c) and minor principal stress (3) and to predict the value of major principal stress (1f) at failure. The training sets are used in regression analysis for m in Hoek-Brown (H-B) equation. Then, the test sets are used to examine the accuracy of target rock strength with DILSSVM after training and these of the two H-B model(with different m). Comparison of the results of the DILSSVM with the two H-B models shows that the DILSSVM always has less root mean squared error(decreased 45% ～55%) and higher coefficient of determination(enhanced 0.055～0.085,near to 1). The DILSSVM shows better flexibility in 1f at failure in each rock type and a wide loading range.
2014, 22(6): 1077-1085.
Intensive dynamic loading is generated when a train is running on railway due to the uneven track. Accordingly, intensive dynamic response occurs in the roadbed and foundation of railway. The excessive vibration response of roadbed and foundation is harmful for the security of running train, and also would make passengers feel uncomfortable. Furthermore, it also would bring harmful vibration to surrounding buildings, and noise pollution to people living around. Therefore, it is practically meaningful to investigate the dynamic response of roadbed and foundation of railways. This paper employs the Biot's dynamic equation as the governing equation, and takes the FEM package FSSI-CAS 2D as the numerical tool. The dynamics of a sandy foundation with ground-water under train running loading is comprehensively investigated. The consideration of the unsaturated zone in the foundation over the static ground-water line is a special point in this investigation. The numerical results indicate that the railway foundation system intensively responds to the running loading of train. Among them, the vertical dynamics with low frequency is the dominant part. It is also observed that the dynamic response of roadbed and foundation of railway both damps in horizontal and vertical direction. The negative pore pressure in unsaturated zone keeps unchanged due to the minor relative displacement of soil particles. The methods, tool and computational cases in this paper can be a research example for evaluating the safety, travelling comfort of a train running on a sandy foundation with ground-water.
Intensive dynamic loading is generated when a train is running on railway due to the uneven track. Accordingly, intensive dynamic response occurs in the roadbed and foundation of railway. The excessive vibration response of roadbed and foundation is harmful for the security of running train, and also would make passengers feel uncomfortable. Furthermore, it also would bring harmful vibration to surrounding buildings, and noise pollution to people living around. Therefore, it is practically meaningful to investigate the dynamic response of roadbed and foundation of railways. This paper employs the Biot's dynamic equation as the governing equation, and takes the FEM package FSSI-CAS 2D as the numerical tool. The dynamics of a sandy foundation with ground-water under train running loading is comprehensively investigated. The consideration of the unsaturated zone in the foundation over the static ground-water line is a special point in this investigation. The numerical results indicate that the railway foundation system intensively responds to the running loading of train. Among them, the vertical dynamics with low frequency is the dominant part. It is also observed that the dynamic response of roadbed and foundation of railway both damps in horizontal and vertical direction. The negative pore pressure in unsaturated zone keeps unchanged due to the minor relative displacement of soil particles. The methods, tool and computational cases in this paper can be a research example for evaluating the safety, travelling comfort of a train running on a sandy foundation with ground-water.
2014, 22(6): 1086-1093.
The structural fractures(mainly refers to the joints scale) in granitic rock are selected as the research object. The spatial patterns of fractures are analyzed with the geostatistic tool that aims at fracture density P21 as regionalized variable. It turns out that the spatial distribution of fractures in Beishan area is obviously anisotropic and has a significant variation axis direction. Meanwhile, the geostatistical characteristics of grouped fractures in variation spindle region indicate that the first grouped fracture is not stochastic uniform but with an obvioushole-effect characteristic. This characteristic should be considered in the 3D fracture network modeling work. And a new method for 3D fracture network modeling is proposed based on the consideration of hole-effect characteristic.
The structural fractures(mainly refers to the joints scale) in granitic rock are selected as the research object. The spatial patterns of fractures are analyzed with the geostatistic tool that aims at fracture density P21 as regionalized variable. It turns out that the spatial distribution of fractures in Beishan area is obviously anisotropic and has a significant variation axis direction. Meanwhile, the geostatistical characteristics of grouped fractures in variation spindle region indicate that the first grouped fracture is not stochastic uniform but with an obvioushole-effect characteristic. This characteristic should be considered in the 3D fracture network modeling work. And a new method for 3D fracture network modeling is proposed based on the consideration of hole-effect characteristic.
2014, 22(6): 1094-1101.
The mechanical behavior of unsaturated sands inevitably follows the principles of thermodynamics. By this method, we can study the hydraulic-mechanical behavior of soils with a general insight under a more universal law. Based on thermodynamical theory, and considering the relations among dilatancy, anisotropy and plastic dissipation of sands, a solid-liquid coupled constitutive modeling framework is established which can deeply indicate many complex behavior and properties for unsaturated sands.
The mechanical behavior of unsaturated sands inevitably follows the principles of thermodynamics. By this method, we can study the hydraulic-mechanical behavior of soils with a general insight under a more universal law. Based on thermodynamical theory, and considering the relations among dilatancy, anisotropy and plastic dissipation of sands, a solid-liquid coupled constitutive modeling framework is established which can deeply indicate many complex behavior and properties for unsaturated sands.
2014, 22(6): 1102-1108.
The sand-clay mixtures are made by mixing sand and marine clay with different dry weight proportions homogeneously. Undrained triaxial tests are conducted to study the effects of sand content variation and confining pressure on the initial shear modulus and stress-strain relationships of the mixtures. Mechanisms are analyzed. Tests results show that there is no obvious relationship between the initial shear modulus and the sand content variation when sand content is less than 50%.For sand-clay mixtures with sand content ranging from 50% to 80%,the initial shear modulus increases linearly with the growing sand content. The sand content parameter should be introduced into the initial shear modulus so that the modified Duncan-Chang model can be used to imitate the stress-strain relationships of the sand-clay mixtures with sand content less than 80%effectively. When the sand percentage is over than 80%,the characteristic of strain softening occurs. The initial shear modulus is kept steady gradually. The peak strain becomes smaller. The softening model is useful to describe the stress-strain relationships of sand-clay mixtures in this case. The confining pressure has a visible effect on the stress-strain relationship of sand-clay mixtures. As the confining pressure increases, the initial shear modulus shows a linear growing trend in double logarithmic coordinate.
The sand-clay mixtures are made by mixing sand and marine clay with different dry weight proportions homogeneously. Undrained triaxial tests are conducted to study the effects of sand content variation and confining pressure on the initial shear modulus and stress-strain relationships of the mixtures. Mechanisms are analyzed. Tests results show that there is no obvious relationship between the initial shear modulus and the sand content variation when sand content is less than 50%.For sand-clay mixtures with sand content ranging from 50% to 80%,the initial shear modulus increases linearly with the growing sand content. The sand content parameter should be introduced into the initial shear modulus so that the modified Duncan-Chang model can be used to imitate the stress-strain relationships of the sand-clay mixtures with sand content less than 80%effectively. When the sand percentage is over than 80%,the characteristic of strain softening occurs. The initial shear modulus is kept steady gradually. The peak strain becomes smaller. The softening model is useful to describe the stress-strain relationships of sand-clay mixtures in this case. The confining pressure has a visible effect on the stress-strain relationship of sand-clay mixtures. As the confining pressure increases, the initial shear modulus shows a linear growing trend in double logarithmic coordinate.
2014, 22(6): 1109-1114.
The stability of expansive soil can be improved after its treatment with ionic stabilizer(ISS). Laboratory tests of direct shear, water ratio limit and free expansive rate are conducted, before and after the soil is meliorated, to analyze the ISS improvement effect on the expansive soils with different initial moisture contents. Results show that the expansibility of the soil has been eliminated. The shear strength is improved dramatically when the initial moisture content is at the range of 11% to 30%. However, little effects are revealed outside the boundaries. The ionic stabilizer is neither adsorbed by capillary suction when the soil is dried nor stuck to soil surface due to the penetration of the solution in saturated state can react with all the clay particles. Findings of the experiment are of great significance in determining the initial moisture content when site improvements on expansive soil with ISS.
The stability of expansive soil can be improved after its treatment with ionic stabilizer(ISS). Laboratory tests of direct shear, water ratio limit and free expansive rate are conducted, before and after the soil is meliorated, to analyze the ISS improvement effect on the expansive soils with different initial moisture contents. Results show that the expansibility of the soil has been eliminated. The shear strength is improved dramatically when the initial moisture content is at the range of 11% to 30%. However, little effects are revealed outside the boundaries. The ionic stabilizer is neither adsorbed by capillary suction when the soil is dried nor stuck to soil surface due to the penetration of the solution in saturated state can react with all the clay particles. Findings of the experiment are of great significance in determining the initial moisture content when site improvements on expansive soil with ISS.
2014, 22(6): 1115-1122.
A finite element method is established for calculating the seepage flow in loess with consideration of its joints' influence. The basic seepage flow equation in unsaturated media is worked out with the view of conservation of mass. It is about the velocity and the saturation's expression. Appling the Darcy law, the variable can be changed from velocity to hydraulic head in the equation. The parameter in the basic flow equation of loess joints is determined according to the characteristic of loess vertical joints. Using the quadrilateral isoparametric element, the finite element form of the equation is given with the Galerkin weighted residual method. Under local Dirichlet boundary condition, the loess 2-D seepage problem is numerically studied considering the influence of loess joint. The results show that joint has a huge influence on the migration of wetting front.
A finite element method is established for calculating the seepage flow in loess with consideration of its joints' influence. The basic seepage flow equation in unsaturated media is worked out with the view of conservation of mass. It is about the velocity and the saturation's expression. Appling the Darcy law, the variable can be changed from velocity to hydraulic head in the equation. The parameter in the basic flow equation of loess joints is determined according to the characteristic of loess vertical joints. Using the quadrilateral isoparametric element, the finite element form of the equation is given with the Galerkin weighted residual method. Under local Dirichlet boundary condition, the loess 2-D seepage problem is numerically studied considering the influence of loess joint. The results show that joint has a huge influence on the migration of wetting front.
2014, 22(6): 1123-1127.
Groundwater pumping is an important factor for surface settlement. Based on the Konzeny-Carman seepage model of elastic porous medium, a modified model with changeable permeability coefficient using soil strain is established through consideration of soil internal changes of physical and mechanical properties in the process of the strata deformation due to water pumping. A concept of permeability influential coefficient is then introduced. Using the multi-physical field coupling finite element software COMSOL,a three-dimensional model is built to analyze the variation law among soil settlement and permeability coefficient and influential coefficient. The model is based on the completely coupled method of Darcy seepage and elastic porous medium, and compares the measured settlement data with calculated values. The results show that the calculated values using the modified changeable permeability coefficient model agree fairly well with the actual measured values. This model can better reflect the process of sedimentation causing by pumping.
Groundwater pumping is an important factor for surface settlement. Based on the Konzeny-Carman seepage model of elastic porous medium, a modified model with changeable permeability coefficient using soil strain is established through consideration of soil internal changes of physical and mechanical properties in the process of the strata deformation due to water pumping. A concept of permeability influential coefficient is then introduced. Using the multi-physical field coupling finite element software COMSOL,a three-dimensional model is built to analyze the variation law among soil settlement and permeability coefficient and influential coefficient. The model is based on the completely coupled method of Darcy seepage and elastic porous medium, and compares the measured settlement data with calculated values. The results show that the calculated values using the modified changeable permeability coefficient model agree fairly well with the actual measured values. This model can better reflect the process of sedimentation causing by pumping.
2014, 22(6): 1128-1134.
When subjected to earthquake motions, the deep soft soil easily undergoes large deform due to its low shear modulus. The equivalent linear method is traditionally used to perform site response. For deep soft deposit site, the high frequency composites and peak acceleration values of the site response are underestimated if the equivalent linear method is used. It is dangerous for the structure if the site response is used to perform anti-seismic design. The frequency-dependent equivalent linear method is proposed in this paper. It considers the moving average and Parzen spectrum window theory. Results of the two methods are compared with the observed earthquake motions. This comparison shows that the method proposed in this paper is more effective than the traditional method in simulating wave propagation in the deep soft site. Finally, the two methods are used to perform the site reponse for one engineering site located at Binhai New District. The results are analyzed.
When subjected to earthquake motions, the deep soft soil easily undergoes large deform due to its low shear modulus. The equivalent linear method is traditionally used to perform site response. For deep soft deposit site, the high frequency composites and peak acceleration values of the site response are underestimated if the equivalent linear method is used. It is dangerous for the structure if the site response is used to perform anti-seismic design. The frequency-dependent equivalent linear method is proposed in this paper. It considers the moving average and Parzen spectrum window theory. Results of the two methods are compared with the observed earthquake motions. This comparison shows that the method proposed in this paper is more effective than the traditional method in simulating wave propagation in the deep soft site. Finally, the two methods are used to perform the site reponse for one engineering site located at Binhai New District. The results are analyzed.
2014, 22(6): 1135-1146.
In recent years, due to the change of natural environment and the influence of human engineering activities, the occurrence probability of geological disasters such as soil erosion and landslides have been increasing. These geological disasters bring some damages to people's living and productive activities. Methods of soil fixation and slope protection by vegetation can prevent and control the geological disasters. The soil fixation and slope protection by vegetation can be mainly reflected in two aspects: hydrological effect by the stems and leaves of plants and the mechanical effect by the root of plants. Hydrological effect includes rainfall interception effect and rainfall reallocation effect by plant stems and leaves, effect of reduction in raindrop splash erosion by foliage, and plant residues and surface runoff retardation effect by plant above-ground residues. The mechanical effect includes reinforcement effect by fibril roots, anchorage effect by taproots, and traction effect by horizontal roots. The paper highlights the research status of hydrological effect and mechanical effect. For hydrological effect, content such as rainfall interception effect and rainfall reallocation effect by plant stems and leaves, effect of reduction in raindrop splash erosion by foliage and so on are the key contents. For mechanical effect, the theoretical models for the additional cohesion force due to the presence of roots, the interaction between plant roots and the surrounding soil matrix and the numerical simulation methods for the mechanical effect of the slope protection by vegetation are emphasized. In addition, the development tendency of soil fixation and slope protection by vegetation has been predicted. For hydrological effect, a further investigation on the influence of water migration among atmosphere-soil-plant on slope stability is desirable. For the theoretical models of root-soil composite system, a further exploration on the working conditions for which the Wu-Waldron-Model and Fiber-Bundle-Model can be suitable, is necessary. For the numerical simulation methods, effort is needed to explore a model that meet the real condition. With the establishment of numerical model, the parameters such as the root architecture features, root length and so on, as well as these parameters influencing on the calculation results should be taken into account systematically. For the engineering practice, a further study on the application of slope protection by vegetation should be performed to explore the application and maintenance of slope protection by vegetation in different geological and climatic conditions to ensure that slope protection by vegetation can play an eminent role in engineering practice as well as embodying the combination of hydrological effect, mechanical effect and landscape effect.
In recent years, due to the change of natural environment and the influence of human engineering activities, the occurrence probability of geological disasters such as soil erosion and landslides have been increasing. These geological disasters bring some damages to people's living and productive activities. Methods of soil fixation and slope protection by vegetation can prevent and control the geological disasters. The soil fixation and slope protection by vegetation can be mainly reflected in two aspects: hydrological effect by the stems and leaves of plants and the mechanical effect by the root of plants. Hydrological effect includes rainfall interception effect and rainfall reallocation effect by plant stems and leaves, effect of reduction in raindrop splash erosion by foliage, and plant residues and surface runoff retardation effect by plant above-ground residues. The mechanical effect includes reinforcement effect by fibril roots, anchorage effect by taproots, and traction effect by horizontal roots. The paper highlights the research status of hydrological effect and mechanical effect. For hydrological effect, content such as rainfall interception effect and rainfall reallocation effect by plant stems and leaves, effect of reduction in raindrop splash erosion by foliage and so on are the key contents. For mechanical effect, the theoretical models for the additional cohesion force due to the presence of roots, the interaction between plant roots and the surrounding soil matrix and the numerical simulation methods for the mechanical effect of the slope protection by vegetation are emphasized. In addition, the development tendency of soil fixation and slope protection by vegetation has been predicted. For hydrological effect, a further investigation on the influence of water migration among atmosphere-soil-plant on slope stability is desirable. For the theoretical models of root-soil composite system, a further exploration on the working conditions for which the Wu-Waldron-Model and Fiber-Bundle-Model can be suitable, is necessary. For the numerical simulation methods, effort is needed to explore a model that meet the real condition. With the establishment of numerical model, the parameters such as the root architecture features, root length and so on, as well as these parameters influencing on the calculation results should be taken into account systematically. For the engineering practice, a further study on the application of slope protection by vegetation should be performed to explore the application and maintenance of slope protection by vegetation in different geological and climatic conditions to ensure that slope protection by vegetation can play an eminent role in engineering practice as well as embodying the combination of hydrological effect, mechanical effect and landscape effect.
2014, 22(6): 1147-1153.
Engineering geological problems are characterized by many influence factors including both qualitative and quantitative indicators. Therefore, quantitative evaluation of engineering geological problems is extremely difficult. The quantification theory guides to quantify the quantified and qualitative data, and to build the formula for prediction and evaluation. The quantification theory provides the convenience for the analysis of engineering geological problems. This paper summarizes the application of quantification theory to engineering geological analysis including recognition, prediction, coupling analysis and correlation analysis. Recognition refers to select significant geological features in numerous factors of the geological model, makes the evaluation of its importance. The prediction means to establish a model for similar samples calculated to evaluate its possible outcomes by using the data of existing factors and results of the evaluation. The discrimination of geological factors and correlation analysis of its consequent are the analysis of positive and negative correlation of the factors by inter-model affecting. According to the problems encountered in the practical application of quantification theory, the limitations of the theory is analyzed, which are otherness between the regions,posteriori comparisons of assessment and the scientificity of indicator selection. Two approaches to solve the problems are put forward: i)the model should be created based on geological survey for the site that match the model, ii) depending on the model created by a large number of different types of samples, such as lithology, combination of structural plane, discontinuities types, etc. When applying the geological model, specific computational model should be considered to evaluate the geological problems. At last, the suitability, the evaluation methodology and development trends of quantification theory are analyzed.
Engineering geological problems are characterized by many influence factors including both qualitative and quantitative indicators. Therefore, quantitative evaluation of engineering geological problems is extremely difficult. The quantification theory guides to quantify the quantified and qualitative data, and to build the formula for prediction and evaluation. The quantification theory provides the convenience for the analysis of engineering geological problems. This paper summarizes the application of quantification theory to engineering geological analysis including recognition, prediction, coupling analysis and correlation analysis. Recognition refers to select significant geological features in numerous factors of the geological model, makes the evaluation of its importance. The prediction means to establish a model for similar samples calculated to evaluate its possible outcomes by using the data of existing factors and results of the evaluation. The discrimination of geological factors and correlation analysis of its consequent are the analysis of positive and negative correlation of the factors by inter-model affecting. According to the problems encountered in the practical application of quantification theory, the limitations of the theory is analyzed, which are otherness between the regions,posteriori comparisons of assessment and the scientificity of indicator selection. Two approaches to solve the problems are put forward: i)the model should be created based on geological survey for the site that match the model, ii) depending on the model created by a large number of different types of samples, such as lithology, combination of structural plane, discontinuities types, etc. When applying the geological model, specific computational model should be considered to evaluate the geological problems. At last, the suitability, the evaluation methodology and development trends of quantification theory are analyzed.
2014, 22(6): 1154-1158.
The rock physics is a research focus in deep oil and gas engineering. Due to weathering and structure, there is a big difference between geophysical properties of rock mass and rock in the shallow rocks within a certain range. Starting from Archie formula, this paper introduces the petrophysical research. It is based on the rock mass structure and engineering geophysical research. It draws on the concept of rock physical properties. It introduces the concept of the physical properties of rock mass structure and research methods. It conducted a preliminary exploration that the physical properties of rock mass structure in various geophysical parameters can be used to help an accurate description of the rock mass structure. The physical properties of rock mass structure is a new research direction.
The rock physics is a research focus in deep oil and gas engineering. Due to weathering and structure, there is a big difference between geophysical properties of rock mass and rock in the shallow rocks within a certain range. Starting from Archie formula, this paper introduces the petrophysical research. It is based on the rock mass structure and engineering geophysical research. It draws on the concept of rock physical properties. It introduces the concept of the physical properties of rock mass structure and research methods. It conducted a preliminary exploration that the physical properties of rock mass structure in various geophysical parameters can be used to help an accurate description of the rock mass structure. The physical properties of rock mass structure is a new research direction.
2014, 22(6): 1159-1167.
Recent research demonstrates that sliding is the most common instability mechanism type of large-scale catastrophic landslides. Usually sliding associates with stress concentration and brittle failure in locked patch(stress concentration and key load-bearing region). It's the strength and deformation of the locked patch determine the overall stability of the slope which are defined as locked patch landslides by author. Cases of 36 large-scale catastrophic landslides are analyzed in this paper. The types and formation conditions of the locked patch landslides are classified, generalized and summarized. Moreover, a pre-decision method is proposed. The research has the premise of disaster prevention and mitigation for locked patch landslides, and has good scientific significance and guiding value in disaster prevention and mitigation.
Recent research demonstrates that sliding is the most common instability mechanism type of large-scale catastrophic landslides. Usually sliding associates with stress concentration and brittle failure in locked patch(stress concentration and key load-bearing region). It's the strength and deformation of the locked patch determine the overall stability of the slope which are defined as locked patch landslides by author. Cases of 36 large-scale catastrophic landslides are analyzed in this paper. The types and formation conditions of the locked patch landslides are classified, generalized and summarized. Moreover, a pre-decision method is proposed. The research has the premise of disaster prevention and mitigation for locked patch landslides, and has good scientific significance and guiding value in disaster prevention and mitigation.
2014, 22(6): 1168-1175.
The underground mining can usually cause the surface crack and even geological disasters such as collapse and landslide. Stability of mining slope has been the practical concern. This paper takes the Meidongpo slope of underground mining as an example. It is in Duyun city of Guizhou province. The paper formulates a stability calculation equation of mining slope on combined wedge block principle. The formulation is based on slope failure mechanism analysis. The calculation of slope safety factor is carried out under the natural, water-saturated and fissure water filling situation. The comprehensive value of strength parameters is based on experiment, and analogy experience method, and mining empty rate. These results show that the Meidongpo mining slope is usually in a stable state, but its stability becomes worse in long-time rainfall or rainstorm condition, and even unstable. The safety factor of Meidongpo slope decreases as the internal friction angle decreases and the height of fissure water filling increases. Once the back block extrudes front block, there can be a threshold that the safety factor decreases sharply. It formulates a formula of depth of fracture water with rainfall from the relationship between depth of fracture water and rainfall infiltration of crack. It finds that the slope can fail when the rainfall exceeds more than 192mm in a very short time.
The underground mining can usually cause the surface crack and even geological disasters such as collapse and landslide. Stability of mining slope has been the practical concern. This paper takes the Meidongpo slope of underground mining as an example. It is in Duyun city of Guizhou province. The paper formulates a stability calculation equation of mining slope on combined wedge block principle. The formulation is based on slope failure mechanism analysis. The calculation of slope safety factor is carried out under the natural, water-saturated and fissure water filling situation. The comprehensive value of strength parameters is based on experiment, and analogy experience method, and mining empty rate. These results show that the Meidongpo mining slope is usually in a stable state, but its stability becomes worse in long-time rainfall or rainstorm condition, and even unstable. The safety factor of Meidongpo slope decreases as the internal friction angle decreases and the height of fissure water filling increases. Once the back block extrudes front block, there can be a threshold that the safety factor decreases sharply. It formulates a formula of depth of fracture water with rainfall from the relationship between depth of fracture water and rainfall infiltration of crack. It finds that the slope can fail when the rainfall exceeds more than 192mm in a very short time.
2014, 22(6): 1176-1186.
This paper uses GIS technology as the operating platform and adopts the certainty factor method to carry out a more detailed susceptibility analysis of the 2013 Lushan earthquake-triggered landslides. The analysis combines the basic situation of the earthquake zone and is based on the existing relevant factor data including topographic factors(elevation, slope angle, slope aspect, curvature),geological factors(lithology, distance from the deep active faults) and seismic factors(PGA,distance from the epicenter).Firstly, the eight seismic landslide impact factors are graded according to the characteristics of the study area with GIS technology as the platform. A different grading impact factor raster layer is built to complete the parameter statistics of seismic landslide distribution. The most sensitive grading interval is extracted for sensitivity analysis to measure the susceptibility sensitive degree of seismic landslide by different factors grading interval, which is from the value of certainty factor of eight seismic landslide impact factors. The sensitivity analysis of seismic landslide factor shows that the other six factors are very sensitive for landslide-prone and they are the main factors of terrain, geology and earthquake respectively except for curvature and the epicenter factor. The results that the curvature and the epicenter factor are not very sensitive for landslide-prone are further analyzed and discussed. The effect of the internal other factors is also analyzed. The SW aspect is likely to limit the sensitivity of curvature acting on seismic landslide-prone. The limiting is more obvious for lithology than the epicenter factor. Such limiting may not be applicable for the rock strata in Ordovician and Silurian. The results have a certain approach theoretical significance and a certain reference value for earthquake disaster reduction.
This paper uses GIS technology as the operating platform and adopts the certainty factor method to carry out a more detailed susceptibility analysis of the 2013 Lushan earthquake-triggered landslides. The analysis combines the basic situation of the earthquake zone and is based on the existing relevant factor data including topographic factors(elevation, slope angle, slope aspect, curvature),geological factors(lithology, distance from the deep active faults) and seismic factors(PGA,distance from the epicenter).Firstly, the eight seismic landslide impact factors are graded according to the characteristics of the study area with GIS technology as the platform. A different grading impact factor raster layer is built to complete the parameter statistics of seismic landslide distribution. The most sensitive grading interval is extracted for sensitivity analysis to measure the susceptibility sensitive degree of seismic landslide by different factors grading interval, which is from the value of certainty factor of eight seismic landslide impact factors. The sensitivity analysis of seismic landslide factor shows that the other six factors are very sensitive for landslide-prone and they are the main factors of terrain, geology and earthquake respectively except for curvature and the epicenter factor. The results that the curvature and the epicenter factor are not very sensitive for landslide-prone are further analyzed and discussed. The effect of the internal other factors is also analyzed. The SW aspect is likely to limit the sensitivity of curvature acting on seismic landslide-prone. The limiting is more obvious for lithology than the epicenter factor. Such limiting may not be applicable for the rock strata in Ordovician and Silurian. The results have a certain approach theoretical significance and a certain reference value for earthquake disaster reduction.
2014, 22(6): 1187-1193.
This paper is based on the extraction and analysis of Majiagou landslide's surface, boundary and drilling information in the Three Gorges Reservoir Area. It uses GIS spatial interpolation and grid computing, combining with the mechanical formula. It then calculates and zones the stability of Majiagou No.1 landslide. First, it gets the preliminary form of the slip surface shape, which is based on proceed spatial interpolation with the known two slip plane drilling information. Then it speculates the sliding surface information of the rest four drilling with the comparison of the slip surface and the remaining four drilling stratum information. Finally, it gets the whole slip form, based on proceed spatial interpolation with all drilling information. After comparison, it analyzes the spatial interpolation methods of determining slip plane space form. It puts forward that based on a small amount accurate information of slip surface, the result can be more in line with the actual situation when using the radial basis function interpolation. It assumes that the groundwater level in the landslide body and the reservoir water level are the same. It uses the formula of infinite slope safety factor in the ArcGIS raster calculator to obtain the safety coefficient zoning map of Majiagou No.1 landslide without considering the interaction between grid columns. The calculation result shows that the unstable area of Majiagou No.1 landslide mainly concentrates in the leading edge of the sliding body, while the relatively stable areas are distributed in the front, middle and rear middle parts. And as the water level rises, the slope safety factor has a certain degree of decline. Especially the landslide leading edge can be a part of the reservoir water immersion. So the key protection governance position can be divided for Majiagou landslide, which can provide valuable reference for the prevention and treatment scheme of Majiagou landslide.
This paper is based on the extraction and analysis of Majiagou landslide's surface, boundary and drilling information in the Three Gorges Reservoir Area. It uses GIS spatial interpolation and grid computing, combining with the mechanical formula. It then calculates and zones the stability of Majiagou No.1 landslide. First, it gets the preliminary form of the slip surface shape, which is based on proceed spatial interpolation with the known two slip plane drilling information. Then it speculates the sliding surface information of the rest four drilling with the comparison of the slip surface and the remaining four drilling stratum information. Finally, it gets the whole slip form, based on proceed spatial interpolation with all drilling information. After comparison, it analyzes the spatial interpolation methods of determining slip plane space form. It puts forward that based on a small amount accurate information of slip surface, the result can be more in line with the actual situation when using the radial basis function interpolation. It assumes that the groundwater level in the landslide body and the reservoir water level are the same. It uses the formula of infinite slope safety factor in the ArcGIS raster calculator to obtain the safety coefficient zoning map of Majiagou No.1 landslide without considering the interaction between grid columns. The calculation result shows that the unstable area of Majiagou No.1 landslide mainly concentrates in the leading edge of the sliding body, while the relatively stable areas are distributed in the front, middle and rear middle parts. And as the water level rises, the slope safety factor has a certain degree of decline. Especially the landslide leading edge can be a part of the reservoir water immersion. So the key protection governance position can be divided for Majiagou landslide, which can provide valuable reference for the prevention and treatment scheme of Majiagou landslide.
2014, 22(6): 1194-1203.
At 10:30 AM on July 10, 2013, a large-scale landslide occurred at Wulipo Sanxi Village, Zhongxing Town of Dujiangyan City in Sichuan province. The rock mass of about 264104m3 rushed down and destroyed 11 village houses that are 500m beneath the landslide rock mass in 2minutes, killed 44 people and buried 117 people, as well as damaged many rural houses. This paper interprets the environment conditions and the deformation characteristics at pre-landsliding and the characteristics at post-landsliding, using 3-stage remote sensing images. Meanwhile, the lithology, attitude of rocks and cracks of the landslide are surveyed utilizing UAV images, geomorphological mapping and field investigation. Based on these results, this paper analyzes the formation mechanism and failure mode of Wulipo landslide. Results show that under effective combination of good freeing conditions and structural surface, Wulipo landslide is triggered by heavy precipitation. By the effect of continuous heavy precipitation, the sliding rock mass is separated from the bed rock, slides towards freeing direction along the sliding surface under the pressure of dynamic water. After crossing the 36-meter high scarp at the front edge, the movement mode of the landslide becomes landslip-collapse movement. The landslide mass is accelerated instantly and breaks into pieces, and forms high speed debris flow. In this process, the floods transfer the landslide-debris flow further into mud-rock flow and cause the chain disaster of landslide-debris flow-mud rock flow. The movement and damage mode of the landslide are typical and deserve further research.
At 10:30 AM on July 10, 2013, a large-scale landslide occurred at Wulipo Sanxi Village, Zhongxing Town of Dujiangyan City in Sichuan province. The rock mass of about 264104m3 rushed down and destroyed 11 village houses that are 500m beneath the landslide rock mass in 2minutes, killed 44 people and buried 117 people, as well as damaged many rural houses. This paper interprets the environment conditions and the deformation characteristics at pre-landsliding and the characteristics at post-landsliding, using 3-stage remote sensing images. Meanwhile, the lithology, attitude of rocks and cracks of the landslide are surveyed utilizing UAV images, geomorphological mapping and field investigation. Based on these results, this paper analyzes the formation mechanism and failure mode of Wulipo landslide. Results show that under effective combination of good freeing conditions and structural surface, Wulipo landslide is triggered by heavy precipitation. By the effect of continuous heavy precipitation, the sliding rock mass is separated from the bed rock, slides towards freeing direction along the sliding surface under the pressure of dynamic water. After crossing the 36-meter high scarp at the front edge, the movement mode of the landslide becomes landslip-collapse movement. The landslide mass is accelerated instantly and breaks into pieces, and forms high speed debris flow. In this process, the floods transfer the landslide-debris flow further into mud-rock flow and cause the chain disaster of landslide-debris flow-mud rock flow. The movement and damage mode of the landslide are typical and deserve further research.
2014, 22(6): 1204-1210.
Debris landslide is one of the most common types of landslides in reservoir region. Slope gradient is an important internal cause of the development of landslides. The relation between slope gradient and probability of occurrence of debris landslide in reservoir region has important significance to debris landslide risk assessment in reservoir region. This paper takes 139 debris landslides in the Three Gorges Reservoir region and Danjiangkou Reservoir region as example. Firstly, it divides the slope gradient into 7 intervals. Each adjoining 5is an interval. Based on above, the influence that slope gradient contributes to landslide growth is quantitatively analyzed by contribution rate method. The results show that, the slope gradients of 15～25 have the maximum contribution rate. The slope gradients of 10～15and 25～30have the intermediate contribution rate. The slope gradients greater than 30and less than 10have the minimal contribution rate. The results can provide potential gist to risk evaluation for debris landslide in reservoir region.
Debris landslide is one of the most common types of landslides in reservoir region. Slope gradient is an important internal cause of the development of landslides. The relation between slope gradient and probability of occurrence of debris landslide in reservoir region has important significance to debris landslide risk assessment in reservoir region. This paper takes 139 debris landslides in the Three Gorges Reservoir region and Danjiangkou Reservoir region as example. Firstly, it divides the slope gradient into 7 intervals. Each adjoining 5is an interval. Based on above, the influence that slope gradient contributes to landslide growth is quantitatively analyzed by contribution rate method. The results show that, the slope gradients of 15～25 have the maximum contribution rate. The slope gradients of 10～15and 25～30have the intermediate contribution rate. The slope gradients greater than 30and less than 10have the minimal contribution rate. The results can provide potential gist to risk evaluation for debris landslide in reservoir region.
2014, 22(6): 1211-1220.
Many numerical analyses are carried out using the software Flac3D to investigate the amplification effect of topography and geomorphology on seismic waves. Research findings indicate that both the peak acceleration of natural seismic wave and harmonic wave can be amplified linearly in the vertical direction and along the surface of the slope when the single-sided slope is low. When the single-sided slope is high and the slope angle is small, the acceleration contour lines of the two waveforms can be parallel to the slope surface approximately. At the same time, the effect of extremum under the top of the single-sided slope is unobvious, and becomes more obvious with the slope angle increasing and there are some rhythmical local minimum strips which are parallel to the slope surface and have the tend to become one strip with the slope angle increasing for natural seismic waves. There are some rhythmical local minimum strips which are parallel to the slope surface for harmonic wave no matter the slope angle is low or high and the effect of extremum under the top of the single-sided slope is not as obvious as natural seismic waves and can disappear with the slope angle increasing. When the slope angle is high, there are some extremal circles in the peak acceleration profiles along the slope surface. The amplification effect on peak acceleration is more intense for thinner ridge of the two-sided slope. The amplification coefficient of crest of two-sided slope tends to be a stable value with the width of the two-sided slope increasing. The amplification effect of two-sided slope on peak acceleration is more intense than the single-sided slope. The amplification effect of multimodal slope on peak acceleration is more intense than that of bimodal slope and the amplification effect of bimodal slope on peak acceleration is more intense than that of unimodal slope. The amplification effect on peak acceleration is more obvious on the upper half of the V-shaped valley than that of U-shaped valley. However, the dynamic response on the middle bottom of U-shaped valley is stronger than that of U-shaped valley. The local irregularities on the surface of a slope can only have effect on the local distribution of peak acceleration near the surface of the slope. The key factors to the distribution of peak acceleration are slope height, slope angle and geometry of the slope top.
Many numerical analyses are carried out using the software Flac3D to investigate the amplification effect of topography and geomorphology on seismic waves. Research findings indicate that both the peak acceleration of natural seismic wave and harmonic wave can be amplified linearly in the vertical direction and along the surface of the slope when the single-sided slope is low. When the single-sided slope is high and the slope angle is small, the acceleration contour lines of the two waveforms can be parallel to the slope surface approximately. At the same time, the effect of extremum under the top of the single-sided slope is unobvious, and becomes more obvious with the slope angle increasing and there are some rhythmical local minimum strips which are parallel to the slope surface and have the tend to become one strip with the slope angle increasing for natural seismic waves. There are some rhythmical local minimum strips which are parallel to the slope surface for harmonic wave no matter the slope angle is low or high and the effect of extremum under the top of the single-sided slope is not as obvious as natural seismic waves and can disappear with the slope angle increasing. When the slope angle is high, there are some extremal circles in the peak acceleration profiles along the slope surface. The amplification effect on peak acceleration is more intense for thinner ridge of the two-sided slope. The amplification coefficient of crest of two-sided slope tends to be a stable value with the width of the two-sided slope increasing. The amplification effect of two-sided slope on peak acceleration is more intense than the single-sided slope. The amplification effect of multimodal slope on peak acceleration is more intense than that of bimodal slope and the amplification effect of bimodal slope on peak acceleration is more intense than that of unimodal slope. The amplification effect on peak acceleration is more obvious on the upper half of the V-shaped valley than that of U-shaped valley. However, the dynamic response on the middle bottom of U-shaped valley is stronger than that of U-shaped valley. The local irregularities on the surface of a slope can only have effect on the local distribution of peak acceleration near the surface of the slope. The key factors to the distribution of peak acceleration are slope height, slope angle and geometry of the slope top.
2014, 22(6): 1221-1226.
The random distribution characteristic of discontinuities is always rarely considered when analysing the stability of jointed rock slope. Joint network simulation can simulate the random distribution of discontinuities. So this method is applied to analysing the stability of jointed rock slopes. Firstly, the joint network simulation method is used to establish the joint network model of the slope. Then the result is combined with shear strength reduction method to calculate the safety factor of the slope. Subsequently, many joint network simulations and their relative safety factors are used to analyse the reliability of the slope. The result of a real project shows the following. (1)The stability of the rock slope is mainly controlled by the quantity and combination relationship of discontinuities. The more is the discontinuities' quantity and persistence, the lower is the slope's safety factor. (2)The average safety factor of the slope is 3.06 and its probability of failure is 5%,which indicate the good reliability of the slope. This result is in accordance with the real condition of the slope. The analysis method in this paper mainly considers the random distribution of discontinuities, and it presents a new way to analyse the stability of jointed rock slope.
The random distribution characteristic of discontinuities is always rarely considered when analysing the stability of jointed rock slope. Joint network simulation can simulate the random distribution of discontinuities. So this method is applied to analysing the stability of jointed rock slopes. Firstly, the joint network simulation method is used to establish the joint network model of the slope. Then the result is combined with shear strength reduction method to calculate the safety factor of the slope. Subsequently, many joint network simulations and their relative safety factors are used to analyse the reliability of the slope. The result of a real project shows the following. (1)The stability of the rock slope is mainly controlled by the quantity and combination relationship of discontinuities. The more is the discontinuities' quantity and persistence, the lower is the slope's safety factor. (2)The average safety factor of the slope is 3.06 and its probability of failure is 5%,which indicate the good reliability of the slope. This result is in accordance with the real condition of the slope. The analysis method in this paper mainly considers the random distribution of discontinuities, and it presents a new way to analyse the stability of jointed rock slope.
2014, 22(6): 1227-1233.
A Bayesian theory based model is developed for the assessment of regional terrain stability. This model combines the statistical model with the infinite slope stability model. The uncertainty of parameters in the assessment of regional terrain stability is eliminated because the parameters can be adjusted according to the real historical events. The adjustment of parameters are based on the assumption that the failed slope is stable before it rains and unstable after it rains. First, the initial distribution of parameters is set up. Then, the final distribution of parameters is calculated through MCMC(Markov Chain Monte Carlo) methods. This model is applied to the landslide events in a watershed, in Caiyuan Village, Fujian Province, China. The parameters of the model are adjusted using the proposed approach in this study case, where the adjusted dimensionless cohesion C of the area is 0.028,the adjusted effective friction angle is 16.7, and the adjusted ratio of hydraulic conductivity to rainfall is 529.026m. The unstable areas take up to 76.0% of the whole area. This model, which automatically adjusts parameters according to historical landslide events, would be a useful tool for landslide hazard assessment.
A Bayesian theory based model is developed for the assessment of regional terrain stability. This model combines the statistical model with the infinite slope stability model. The uncertainty of parameters in the assessment of regional terrain stability is eliminated because the parameters can be adjusted according to the real historical events. The adjustment of parameters are based on the assumption that the failed slope is stable before it rains and unstable after it rains. First, the initial distribution of parameters is set up. Then, the final distribution of parameters is calculated through MCMC(Markov Chain Monte Carlo) methods. This model is applied to the landslide events in a watershed, in Caiyuan Village, Fujian Province, China. The parameters of the model are adjusted using the proposed approach in this study case, where the adjusted dimensionless cohesion C of the area is 0.028,the adjusted effective friction angle is 16.7, and the adjusted ratio of hydraulic conductivity to rainfall is 529.026m. The unstable areas take up to 76.0% of the whole area. This model, which automatically adjusts parameters according to historical landslide events, would be a useful tool for landslide hazard assessment.
2014, 22(6): 1234-1240.
The load of strong motion in Longmen Shan area leads to severely damage of a large number of existing retaining structures. How to do assessment for the damaged retaining walls in the earthquake zone is a problem to be solved urgently. This paper summarizes five types of retaining walls' failure modes through the earthquake damage analysis in the research area. They include sliding failure, settlement failure, toppling failure, material failure, and overtopping failure. Then the influence factors of seismic safety evaluation are qualitatively analyzed and classified on the basis of comprehensive principle, important principle and scientific principle. Combining with the failure modes of retaining wall, we put forward the sensitive factor and some general factors. We take the range of 60 percent damage as a sensitive factor. The general factors are divided into two levels and 10 indexes including the sliding distance, the settlement depth, the inclination angle, the number of cracks, the ratio of crack length and the retaining wall length, the ratio of crack depth and the retaining wall thickness, the crack width, the dislocation distance, the range of retaining wall collapsed, the coverage of rock and soil on the retaining wall. Finally, the seismic safety evaluation system of retaining walls is built with grey correlation analysis and fuzzy mathematic theory. We can take prevention instead of post processing, and to serve the post-earthquake recovery and reconstruction.
The load of strong motion in Longmen Shan area leads to severely damage of a large number of existing retaining structures. How to do assessment for the damaged retaining walls in the earthquake zone is a problem to be solved urgently. This paper summarizes five types of retaining walls' failure modes through the earthquake damage analysis in the research area. They include sliding failure, settlement failure, toppling failure, material failure, and overtopping failure. Then the influence factors of seismic safety evaluation are qualitatively analyzed and classified on the basis of comprehensive principle, important principle and scientific principle. Combining with the failure modes of retaining wall, we put forward the sensitive factor and some general factors. We take the range of 60 percent damage as a sensitive factor. The general factors are divided into two levels and 10 indexes including the sliding distance, the settlement depth, the inclination angle, the number of cracks, the ratio of crack length and the retaining wall length, the ratio of crack depth and the retaining wall thickness, the crack width, the dislocation distance, the range of retaining wall collapsed, the coverage of rock and soil on the retaining wall. Finally, the seismic safety evaluation system of retaining walls is built with grey correlation analysis and fuzzy mathematic theory. We can take prevention instead of post processing, and to serve the post-earthquake recovery and reconstruction.
2014, 22(6): 1241-1249.
Southern and East southern China have wide distribution of weathered granitic residual soils. Some have depths of more than 100m. Large numbers of railways and roads have induced many man-made slopes in weathered granitic soils in these areas. It is very important to better understand the engineering specialties of the slopes and then provide effective targeting reinforcement methods for the safe construction and normal operation of the railways and roads. This paper is based on the investigation of 44 weathered granitic soil slopes along four express ways in Guangdong and Guangxi provinces. This kind of slopes is classified as dyke separator slope, netlike structure slope, out-dip structure slope, and isolated boulder slope according to the specialty of the special medium, slope body structures, and the effects of discontinues in the slope body. And then the corresponding stability calculation methods and the influencing factors of slope stability are put forward. Three engineering specialties are brought out from the investigation and research. The temporary stability of dyke separator slope, netlike structure slope is good. Unloading during excavation can strongly affect the stability and other characters of the weathered granitic soil slope because of the existing of discontinues in slope bodies. Weathered granitic soil slope, especially the superficial layer, can be easily scoured. The cause of these specialties are brought forward and discussed. According to each style of the weathered granitic soil slopes, the reinforcement methods and some suggestions are advanced considering the specialties of this kind of slopes. According to the better temporary stability, steep excavation with strong reinforcement is suggested in this paper. Step-by-step excavation with local supporting, anti-erosion measures, foot protection and crest coping, and water drainage are emphasized.
Southern and East southern China have wide distribution of weathered granitic residual soils. Some have depths of more than 100m. Large numbers of railways and roads have induced many man-made slopes in weathered granitic soils in these areas. It is very important to better understand the engineering specialties of the slopes and then provide effective targeting reinforcement methods for the safe construction and normal operation of the railways and roads. This paper is based on the investigation of 44 weathered granitic soil slopes along four express ways in Guangdong and Guangxi provinces. This kind of slopes is classified as dyke separator slope, netlike structure slope, out-dip structure slope, and isolated boulder slope according to the specialty of the special medium, slope body structures, and the effects of discontinues in the slope body. And then the corresponding stability calculation methods and the influencing factors of slope stability are put forward. Three engineering specialties are brought out from the investigation and research. The temporary stability of dyke separator slope, netlike structure slope is good. Unloading during excavation can strongly affect the stability and other characters of the weathered granitic soil slope because of the existing of discontinues in slope bodies. Weathered granitic soil slope, especially the superficial layer, can be easily scoured. The cause of these specialties are brought forward and discussed. According to each style of the weathered granitic soil slopes, the reinforcement methods and some suggestions are advanced considering the specialties of this kind of slopes. According to the better temporary stability, steep excavation with strong reinforcement is suggested in this paper. Step-by-step excavation with local supporting, anti-erosion measures, foot protection and crest coping, and water drainage are emphasized.
2014, 22(6): 1250-1256.
This paper aims at finding out the functional relationship between landslide and impact factors, using statistics analysis under logistic regression model and certainty factor. It tries to draw the block map of the hazard zonation according to the level of risk of landslide occurrence in Guizhou Province using GIS technology. First, a calculation of the certainty factor of landslide occurrence is done according to the area of occurred disasters in impact factor subset and the area of impact factor subset. Secondly, the possibility of landslide occurrence is defined as dependent variable. The certainty factor of occurring disaster in subset is defined as independent variable. Then, an analysis is done to find out the functional relationship between them under logistic regression model. Thirdly, a calculation of the probability of landslide occurrence p is initiated. It tries to divide the research area into 10 risk level sub-areas according to the p result with the aim to draw block map of the hazard zonation of landslide. Finally, an evaluation on the hazard zonation of landslide is carried out. The result shows that the hazard zonation method, based on logistic regression model and certainty factor for landslide, is effective.
This paper aims at finding out the functional relationship between landslide and impact factors, using statistics analysis under logistic regression model and certainty factor. It tries to draw the block map of the hazard zonation according to the level of risk of landslide occurrence in Guizhou Province using GIS technology. First, a calculation of the certainty factor of landslide occurrence is done according to the area of occurred disasters in impact factor subset and the area of impact factor subset. Secondly, the possibility of landslide occurrence is defined as dependent variable. The certainty factor of occurring disaster in subset is defined as independent variable. Then, an analysis is done to find out the functional relationship between them under logistic regression model. Thirdly, a calculation of the probability of landslide occurrence p is initiated. It tries to divide the research area into 10 risk level sub-areas according to the p result with the aim to draw block map of the hazard zonation of landslide. Finally, an evaluation on the hazard zonation of landslide is carried out. The result shows that the hazard zonation method, based on logistic regression model and certainty factor for landslide, is effective.
2014, 22(6): 1257-1262.
This paper presents FLAC/PFC2D hybrid numerical models for a typical toppling rock slope with intermittent bedding planes and orthogonal secondary rock joints inside. The seismically induced failure processes of the slope are simulated and analysed. The simulation results reveal that the rock bedding plane generally fails in shear during the dynamic failure process. Very few tensile failure of the bedding plane can occur on the top of the slope. But the tensile failure always appears after the collapse of the whole slope. Therefore the tensile strength of the beddings cannot serve to affect the actual dynamic stability of the slope in a whole. Secondary rock joints on the top of slope can only fail in tension, resulting rock layer toppling. The joints on the bottom of the slope can fail both in tension and shear, inducing shearing displacement along the penetrating joint surfaces. Moreover, the joint failure at the top of slope always occurs before the joint failure at the bottom, which is completely opposite to the classic failure sequence of toppling rock slope on static condition. This difference may be due to the dynamic amplification effect on the crest of slope and the difference on position and depth for failing secondary rock joints on the top and on the bottom.
This paper presents FLAC/PFC2D hybrid numerical models for a typical toppling rock slope with intermittent bedding planes and orthogonal secondary rock joints inside. The seismically induced failure processes of the slope are simulated and analysed. The simulation results reveal that the rock bedding plane generally fails in shear during the dynamic failure process. Very few tensile failure of the bedding plane can occur on the top of the slope. But the tensile failure always appears after the collapse of the whole slope. Therefore the tensile strength of the beddings cannot serve to affect the actual dynamic stability of the slope in a whole. Secondary rock joints on the top of slope can only fail in tension, resulting rock layer toppling. The joints on the bottom of the slope can fail both in tension and shear, inducing shearing displacement along the penetrating joint surfaces. Moreover, the joint failure at the top of slope always occurs before the joint failure at the bottom, which is completely opposite to the classic failure sequence of toppling rock slope on static condition. This difference may be due to the dynamic amplification effect on the crest of slope and the difference on position and depth for failing secondary rock joints on the top and on the bottom.
2014, 22(6): 1263-1270.
As an important means to realize the distributed monitoring technology, optical fiber sensing technology has been rapidly developed in recent years. This technology has a great potential of applications in the field of geological and geotechnical engineering monitoring. In this paper, a distributed monitoring model of soil slope stability is designed, which is based on the following two kinds of sensing technology: Brillouin Optical Time Domain Analysis(BOTDA) and Fiber Bragg Grating(FBG).Through the model test, the strain distribution and failure process of the slope by water level are studied. According to the monitoring data of FBG and BOTDA,the stability of soil slope is evaluated. The feasibility of BOTDA and FBG distributed optical fiber sensing techniques is verified for slope deformation monitoring. The research results have an important significance for application of the distributed fiber sensing technology and analysis of soil slope stability in multiple fields.
As an important means to realize the distributed monitoring technology, optical fiber sensing technology has been rapidly developed in recent years. This technology has a great potential of applications in the field of geological and geotechnical engineering monitoring. In this paper, a distributed monitoring model of soil slope stability is designed, which is based on the following two kinds of sensing technology: Brillouin Optical Time Domain Analysis(BOTDA) and Fiber Bragg Grating(FBG).Through the model test, the strain distribution and failure process of the slope by water level are studied. According to the monitoring data of FBG and BOTDA,the stability of soil slope is evaluated. The feasibility of BOTDA and FBG distributed optical fiber sensing techniques is verified for slope deformation monitoring. The research results have an important significance for application of the distributed fiber sensing technology and analysis of soil slope stability in multiple fields.
2014, 22(6): 1271-1278.
This paper deals with the occurrence frequency of debris flow hazard in the areas lack of the accurate rainfall data. It uses numerical simulation and establishes an estimation model of debris flow's occurrence frequency. It is based on the reductionism theory. The model determines the volume of source materials, volume of flood flow and the sediment concentration by volume by employing the source material module and hydrograph module. Then, the interval period of debris flow is confirmed by finding out the most realistic simulation scenario in FLO-2D numerical simulation module. The paper takes Majingzi gully and Xiongjia gully debris flows for instance. They occurred in Shimian county, southwestern China, on 4th July 2013. Their interval periods are all 100 years. It is concluded that this model is able to calculate quantitatively the occurrence frequency of debris flow, and has significant theoretical and practical meaning on early warming and disaster mitigation for catastrophic debris flow.
This paper deals with the occurrence frequency of debris flow hazard in the areas lack of the accurate rainfall data. It uses numerical simulation and establishes an estimation model of debris flow's occurrence frequency. It is based on the reductionism theory. The model determines the volume of source materials, volume of flood flow and the sediment concentration by volume by employing the source material module and hydrograph module. Then, the interval period of debris flow is confirmed by finding out the most realistic simulation scenario in FLO-2D numerical simulation module. The paper takes Majingzi gully and Xiongjia gully debris flows for instance. They occurred in Shimian county, southwestern China, on 4th July 2013. Their interval periods are all 100 years. It is concluded that this model is able to calculate quantitatively the occurrence frequency of debris flow, and has significant theoretical and practical meaning on early warming and disaster mitigation for catastrophic debris flow.
2014, 22(6): 1279-1286.
Long-term weathering of rock will cause the rock surface recession, which will cause irreparable damage to stone cultural relics. Those precious stone cultural relics are being protected for a long time. But the result is not optimistic. In theory, in order to protect them well, it is important to study the relationship between the rock surface recession and the relative weathering rate with the different lithology in the same environment. The paper is intended to study the surface recession of different lithology rock blocks and their weathering rate. The rock blocks are part of the Tongxian gate of Quzhou ancient walls of national key cultural relics protection sites. An especially designed movable instrument is used. By analyzing the measured data, the weathering rates of different rocks are attained so as to provide an actual basis for the stone cultural relics and the development of relevant protective measures. The measurement results are from tufa, sandstone, conglomerate, pebbly sandstone and siltstone. Their weathering rates with respect to limestone are 0.005～0.059, 0.032～0.097, 0.004～0.058, 0.021～0.033 and 0.015mm a-1,respectively. The results also show that under the same weathering environment, different weathering rates of rock block order from large to small is VsandstoneVtufaVpebblysandstoneVconglomerateVsiltstoneVlimestone,which means that the rock weathering resistance from strong to weak is:VlimestoneVsiltstoneVconglomerateVpebblysandstoneVtufaVsandstone.This study can provide an important data basis for the long-term protection of stone relics and formulate relevant protective measures.
Long-term weathering of rock will cause the rock surface recession, which will cause irreparable damage to stone cultural relics. Those precious stone cultural relics are being protected for a long time. But the result is not optimistic. In theory, in order to protect them well, it is important to study the relationship between the rock surface recession and the relative weathering rate with the different lithology in the same environment. The paper is intended to study the surface recession of different lithology rock blocks and their weathering rate. The rock blocks are part of the Tongxian gate of Quzhou ancient walls of national key cultural relics protection sites. An especially designed movable instrument is used. By analyzing the measured data, the weathering rates of different rocks are attained so as to provide an actual basis for the stone cultural relics and the development of relevant protective measures. The measurement results are from tufa, sandstone, conglomerate, pebbly sandstone and siltstone. Their weathering rates with respect to limestone are 0.005～0.059, 0.032～0.097, 0.004～0.058, 0.021～0.033 and 0.015mm a-1,respectively. The results also show that under the same weathering environment, different weathering rates of rock block order from large to small is VsandstoneVtufaVpebblysandstoneVconglomerateVsiltstoneVlimestone,which means that the rock weathering resistance from strong to weak is:VlimestoneVsiltstoneVconglomerateVpebblysandstoneVtufaVsandstone.This study can provide an important data basis for the long-term protection of stone relics and formulate relevant protective measures.
2014, 22(6): 1287-1293.
The oil and gas structures at Longquan Mountains have the full combination including generation, reservoir and cap rock. The Jurassic and Cretaceous are non-coal strata. There are seven structural heights and jointed fracture zones which are favorable to gather shallow gas. The sandstone of Shaximiao formation is the primary reservoir of the shallow gas. It is so easy to generate engineering accidents when tunneling across the layer. The tunneling would be harmed by enriched shallow gas. There are three lines including the east extension of Cheng-Luo highway, the Cheng-An-Yu expressway and the Cheng-Yu railway. The analyses of gas concentrations that come from twenty drillings of eight tunnels show that the eight tunnels have gas presence. The highest gas concentration is 8.654% and the lowest gas concentration is 0.081%,which reveal that the eight tunnels have been affected by the gas. The present study has found that the main influencing factors of the tunnels are structure location and rock properties. Tunneling would be harmed when it is near the high point of oil and gas structures or passes the fractured formations with high concentration gas.
The oil and gas structures at Longquan Mountains have the full combination including generation, reservoir and cap rock. The Jurassic and Cretaceous are non-coal strata. There are seven structural heights and jointed fracture zones which are favorable to gather shallow gas. The sandstone of Shaximiao formation is the primary reservoir of the shallow gas. It is so easy to generate engineering accidents when tunneling across the layer. The tunneling would be harmed by enriched shallow gas. There are three lines including the east extension of Cheng-Luo highway, the Cheng-An-Yu expressway and the Cheng-Yu railway. The analyses of gas concentrations that come from twenty drillings of eight tunnels show that the eight tunnels have gas presence. The highest gas concentration is 8.654% and the lowest gas concentration is 0.081%,which reveal that the eight tunnels have been affected by the gas. The present study has found that the main influencing factors of the tunnels are structure location and rock properties. Tunneling would be harmed when it is near the high point of oil and gas structures or passes the fractured formations with high concentration gas.
2014, 22(6): 1294-1300.
The earlier settlement of railway roadbed caused by train-induced vibration loading has great effects on the train driving safety if loose sand layers are included in the railway foundation. Accordingly, the GDS triaxial hollow cylindrical multi-function apparatus is used to model the real stress path of the train-induced vibration loading. The tested fine sand is distributed in Nanjing area, near to Yangtze rive. Its dynamic deformation properties are studied by taking into consideration of the drain condition and the confining pressure and the load amplitude. As results, the confining pressure has a greater effect on the vertical accumulated deformation of the test samples. The amplitude of vibration loading has a greater effect on the vertical accumulated deformation if the confining pressure is smaller. Also, the drain condition has a greater effect on the earlier settlement of roadbed than on the later settlement. At the same time, the new formulas and its parameters are developed and can be used to predict the vertical accumulated deformation of Nanjing fine sand with flake-shape structure. They are given based on the test results. These research conclusions can be used to predict the long-term settlement of railway roadbed with the newly deposited fine sand included in roadbed.
The earlier settlement of railway roadbed caused by train-induced vibration loading has great effects on the train driving safety if loose sand layers are included in the railway foundation. Accordingly, the GDS triaxial hollow cylindrical multi-function apparatus is used to model the real stress path of the train-induced vibration loading. The tested fine sand is distributed in Nanjing area, near to Yangtze rive. Its dynamic deformation properties are studied by taking into consideration of the drain condition and the confining pressure and the load amplitude. As results, the confining pressure has a greater effect on the vertical accumulated deformation of the test samples. The amplitude of vibration loading has a greater effect on the vertical accumulated deformation if the confining pressure is smaller. Also, the drain condition has a greater effect on the earlier settlement of roadbed than on the later settlement. At the same time, the new formulas and its parameters are developed and can be used to predict the vertical accumulated deformation of Nanjing fine sand with flake-shape structure. They are given based on the test results. These research conclusions can be used to predict the long-term settlement of railway roadbed with the newly deposited fine sand included in roadbed.
2014, 22(6): 1301-1308.
This paper is about the geological investigation results at a proposed large hydropower station site. The sheet joints with gentle and medium dips are developed in the superficial slope and manifested as disjunctive distribution of joint concentration areas and joint sparse areas. They control the rock mass structure and stability of high slope. This finding is based on massive field investigation. The paper summarizes and analyzes the basic geological characteristics and distribution characteristics of the sheet joints at the dam site, and explains the joints formation mechanism and development model. The results of the study show that:(1)Sheet joints paralleled to bank slope belong to tension joints-system due to down-cutting of valley and displacement of stress.(2)The formation of bank slope is a result of repeated down-cutting of valley. After down-cutting, the angle of slope becomes steeper. That's mean dip angle of sheet joints formed in the late is steeper than that in the early stage. When the valley generates down-cutting and lateral erosion, the convex bank slope is beneficial to save earlier gentle joints. This is the reason that both gentle dip joints and moderate dip joints are available in the upper-middle part of the convex bank. (3)The canyon is formed by intermittent rapid down-cutting. During relative stable stage, sheet joints are developed in bank slope. During rapid down-cutting stage, vertical unloading mainly develops in the valley bottom. Thus in the bank slope, the disjunctive distribution of joint concentration areas and joint sparse areas are observed, which corresponds to relative stable stage and rapid down-cutting stage, respectively.
This paper is about the geological investigation results at a proposed large hydropower station site. The sheet joints with gentle and medium dips are developed in the superficial slope and manifested as disjunctive distribution of joint concentration areas and joint sparse areas. They control the rock mass structure and stability of high slope. This finding is based on massive field investigation. The paper summarizes and analyzes the basic geological characteristics and distribution characteristics of the sheet joints at the dam site, and explains the joints formation mechanism and development model. The results of the study show that:(1)Sheet joints paralleled to bank slope belong to tension joints-system due to down-cutting of valley and displacement of stress.(2)The formation of bank slope is a result of repeated down-cutting of valley. After down-cutting, the angle of slope becomes steeper. That's mean dip angle of sheet joints formed in the late is steeper than that in the early stage. When the valley generates down-cutting and lateral erosion, the convex bank slope is beneficial to save earlier gentle joints. This is the reason that both gentle dip joints and moderate dip joints are available in the upper-middle part of the convex bank. (3)The canyon is formed by intermittent rapid down-cutting. During relative stable stage, sheet joints are developed in bank slope. During rapid down-cutting stage, vertical unloading mainly develops in the valley bottom. Thus in the bank slope, the disjunctive distribution of joint concentration areas and joint sparse areas are observed, which corresponds to relative stable stage and rapid down-cutting stage, respectively.
2014, 22(6): 1309-1315.
During the process of mineral exploitation, extensive unreasonable slag discharge and mine debris flow induced by high intensity rainfall can cause tremendous risks to the normal production and personnel safety. Meanwhile, massive slag heaps are distributed along the gully. The slag heap at lower elevation can be impacted by the debris flow caused by the failure of slag heap at higher elevation. Its failure probability can greatly increase. The disaster chain effect, shown with the spatial successive influence, is an important formation character of mine debris flow. The Luanshi gully is taken as study area. It is at Xiaoqinling, China. The study is based on the detailed investigation of slag heaps. The height, slope angle and volume of slag heaps, continuing heaping or not, original terrain slope and rainfall confluence cumulant are selected as indexes to evaluate the stability of slag heaps. The travel distances of mine debris flow are estimated using an empirical-statistical model(UBCDFLOW)considering width of path, slope angle and the type of flow behavior. Subsequently, the chain effect of the mine debris flow and the relative position between the slag heaps at higher and lower elevation are considered. The slag heap hazard assessment under disaster chain effect is obtained. It is concluded that the failure probabilities of slag heaps influenced by debris flow are increased distinctly. The results can provide useful advices for risk assessment and treatment design of slag heaps in Xiaoqinling Luanshi gully.
During the process of mineral exploitation, extensive unreasonable slag discharge and mine debris flow induced by high intensity rainfall can cause tremendous risks to the normal production and personnel safety. Meanwhile, massive slag heaps are distributed along the gully. The slag heap at lower elevation can be impacted by the debris flow caused by the failure of slag heap at higher elevation. Its failure probability can greatly increase. The disaster chain effect, shown with the spatial successive influence, is an important formation character of mine debris flow. The Luanshi gully is taken as study area. It is at Xiaoqinling, China. The study is based on the detailed investigation of slag heaps. The height, slope angle and volume of slag heaps, continuing heaping or not, original terrain slope and rainfall confluence cumulant are selected as indexes to evaluate the stability of slag heaps. The travel distances of mine debris flow are estimated using an empirical-statistical model(UBCDFLOW)considering width of path, slope angle and the type of flow behavior. Subsequently, the chain effect of the mine debris flow and the relative position between the slag heaps at higher and lower elevation are considered. The slag heap hazard assessment under disaster chain effect is obtained. It is concluded that the failure probabilities of slag heaps influenced by debris flow are increased distinctly. The results can provide useful advices for risk assessment and treatment design of slag heaps in Xiaoqinling Luanshi gully.
2014, 22(6): 1316-1325.
The NSFC proposals and grants of engineering geology in 2014 are analyzed. The number of proposals falls. The number of the general program proposals has fallen substantially in recent two years. The peer-reviewed experts accurately grasp the scale of peer-review about the proposals especially the proposals for the NSFC Young Scientists Fund. The age distribution of the applicants tends to be reasonable. There are reasonable differences of funded ratios between different age groups. The young scientists do not actively participate in the grants of National Science Fund for Distinguished Young and Excellent Young Scientists Fund. The applicant of the Key Program tended to be older. The project principals of the Key Program tend to be older severely.
The NSFC proposals and grants of engineering geology in 2014 are analyzed. The number of proposals falls. The number of the general program proposals has fallen substantially in recent two years. The peer-reviewed experts accurately grasp the scale of peer-review about the proposals especially the proposals for the NSFC Young Scientists Fund. The age distribution of the applicants tends to be reasonable. There are reasonable differences of funded ratios between different age groups. The young scientists do not actively participate in the grants of National Science Fund for Distinguished Young and Excellent Young Scientists Fund. The applicant of the Key Program tended to be older. The project principals of the Key Program tend to be older severely.
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