2019 Vol. 27, No. 6

Others
Damage of the fractured rock mass tends to be more serious under the freezing-thawing action. It is of great practical significance to study the related mechanical properties and damage evolution law. In this paper,the rock-like material is used to simulate the influence of different length fissures and freezing-thawing action on the mechanical properties of rock. The compressive strength,elastic modulus and stress-strain curves of the rock after multi freeze-thaw action are obtained. The results show that the compressive strength and elastic modulus of the rock decrease with the crack length,but the peak strain increases. The whole deformation process of the specimens can be divided into four stages:(1) Prefabricated fissure closed stage,(2) Prefabricated fissure opening stage,(3) Trunk fissure extension stage and (4) Fracture failure stage. The effect of freezing and thawing on the formation of (1) and (3) is the most obvious. The stage (1) increases. For the stage (3),the secondary fissures of the rock accompanied by the expansion of the main fissures are obviously reduced. The testing samples undergoing freeze-thaw action is much looser than the reference samples after experiment is finished,accompanied by a large number of rock powder and mineral particles. For the different lengths of the fracture specimens,increase of the crack length makes the sample more fragmented,and the destruction mode is more and more complex. The results of this study can be expected to provide a reference for the study on the damage and fracture characteristics of fractured rock mass undergoing freeze-thaw action. Damage of the fractured rock mass tends to be more serious under the freezing-thawing action. It is of great practical significance to study the related mechanical properties and damage evolution law. In this paper,the rock-like material is used to simulate the influence of different length fissures and freezing-thawing action on the mechanical properties of rock. The compressive strength,elastic modulus and stress-strain curves of the rock after multi freeze-thaw action are obtained. The results show that the compressive strength and elastic modulus of the rock decrease with the crack length,but the peak strain increases. The whole deformation process of the specimens can be divided into four stages:(1) Prefabricated fissure closed stage,(2) Prefabricated fissure opening stage,(3) Trunk fissure extension stage and (4) Fracture failure stage. The effect of freezing and thawing on the formation of (1) and (3) is the most obvious. The stage (1) increases. For the stage (3),the secondary fissures of the rock accompanied by the expansion of the main fissures are obviously reduced. The testing samples undergoing freeze-thaw action is much looser than the reference samples after experiment is finished,accompanied by a large number of rock powder and mineral particles. For the different lengths of the fracture specimens,increase of the crack length makes the sample more fragmented,and the destruction mode is more and more complex. The results of this study can be expected to provide a reference for the study on the damage and fracture characteristics of fractured rock mass undergoing freeze-thaw action.
High level radioactive waste is the inevitable product of nuclear power development. The whole world has paid more attention to the safety disposal of the waste so as to maintain the sustainable development of nuclear power. At present,deep geological disposal has become a recognized permanent disposal method of high level radioactive waste,and surrounding rock mass quality assessment is the key to the selection of high-level waste disposal repository. Alxa is a pre-selected area for high-level radioactive waste disposal in China. Based on BQ-system,the rock mass quality of Bayannuorigong borehole NRG01 in Alxa region was assessed. BQ-system is a comprehensive rock mass quality assessment method,which take the rock mass hardness and integrity into consideration. The borehole data of NRG01 is rich. The evalution parameters of BQ-system were obtained by different methods and techniques such as core logging,wave velocity logging,hydrofracturing in situ stress measurement,rock ultrasonic wave velocity measurement and uniaxial compression test. The BQ value was calculated using those parameters. Then,according to the effects of ground water,weak structural surface and initial crustal stress,the BQ value was modified. The modified[BQ] value was used to classify the quality of rockmass into five categories. Result shows that the rock mass quality of borehole NRG01 is good,about 90%rock belong to Ⅰ and Ⅱ category,the rock mas range of 410~500 m can be regarded as the target rock for the construction of the repository. The qualitive conclusion of BQ-system was compared with that by RQD index. RQD index is simple and straightforward which is the most commonly used indicator for rock mass quality assessment. Comparison result showed that two methods have good coherence. However,BQ-system take more factors into consideration,therefore it is more comprehensive and refined. Evaluation results can provide reference for siting the repository of high-radioactive waste disposal and the the selection of the target rock. High level radioactive waste is the inevitable product of nuclear power development. The whole world has paid more attention to the safety disposal of the waste so as to maintain the sustainable development of nuclear power. At present,deep geological disposal has become a recognized permanent disposal method of high level radioactive waste,and surrounding rock mass quality assessment is the key to the selection of high-level waste disposal repository. Alxa is a pre-selected area for high-level radioactive waste disposal in China. Based on BQ-system,the rock mass quality of Bayannuorigong borehole NRG01 in Alxa region was assessed. BQ-system is a comprehensive rock mass quality assessment method,which take the rock mass hardness and integrity into consideration. The borehole data of NRG01 is rich. The evalution parameters of BQ-system were obtained by different methods and techniques such as core logging,wave velocity logging,hydrofracturing in situ stress measurement,rock ultrasonic wave velocity measurement and uniaxial compression test. The BQ value was calculated using those parameters. Then,according to the effects of ground water,weak structural surface and initial crustal stress,the BQ value was modified. The modified[BQ] value was used to classify the quality of rockmass into five categories. Result shows that the rock mass quality of borehole NRG01 is good,about 90%rock belong to Ⅰ and Ⅱ category,the rock mas range of 410~500 m can be regarded as the target rock for the construction of the repository. The qualitive conclusion of BQ-system was compared with that by RQD index. RQD index is simple and straightforward which is the most commonly used indicator for rock mass quality assessment. Comparison result showed that two methods have good coherence. However,BQ-system take more factors into consideration,therefore it is more comprehensive and refined. Evaluation results can provide reference for siting the repository of high-radioactive waste disposal and the the selection of the target rock.
This paper explores the effects of rock physical mechanical parameters on the specific chiseling work and attrition value of tunnel boring machine(TBM). It is based on the Zhong Tianshan tunnel of the second line of Nan Jiang railway with TBM. A series of in-situ and laboratory experiments are carried out on the tunnel surrounding rock. The basic mechanical parameters are obtained. They include the longitudinal wave velocity,the uniaxial compressive strength,the uniaxial tensile strength,the static modulus of elasticity,and the cohesive force. Then correlation analysis between the basic mechanical parameters and those of the specific chiseling work and attrition value is carried out using the software SPSS22. The results show that the single factor correlation is weak. On the premise of taking the specific chiseling work and the attrition value as dependent variables respectively and mechanical parameters as the independent variable,we carried out multi-factor regression analysis and polynomial fitting of the data by stepwise method. The results show that the dependent variable is highly correlated with the uniaxial compressive strength and the rock mass integrity coefficient. During the validation of the fitting model,under the condition of uniaxial compressive strength greater than 100 MPa and KV greater than 0.5,the use of fitting model has a higher accuracy. This paper explores the effects of rock physical mechanical parameters on the specific chiseling work and attrition value of tunnel boring machine(TBM). It is based on the Zhong Tianshan tunnel of the second line of Nan Jiang railway with TBM. A series of in-situ and laboratory experiments are carried out on the tunnel surrounding rock. The basic mechanical parameters are obtained. They include the longitudinal wave velocity,the uniaxial compressive strength,the uniaxial tensile strength,the static modulus of elasticity,and the cohesive force. Then correlation analysis between the basic mechanical parameters and those of the specific chiseling work and attrition value is carried out using the software SPSS22. The results show that the single factor correlation is weak. On the premise of taking the specific chiseling work and the attrition value as dependent variables respectively and mechanical parameters as the independent variable,we carried out multi-factor regression analysis and polynomial fitting of the data by stepwise method. The results show that the dependent variable is highly correlated with the uniaxial compressive strength and the rock mass integrity coefficient. During the validation of the fitting model,under the condition of uniaxial compressive strength greater than 100 MPa and KV greater than 0.5,the use of fitting model has a higher accuracy.
This paper aims at the uncoordinated deformation phenomenon of composite rock mass in metal mine contact zone. It carries out the uniaxial compression test of physical similar samples. It studies the influence of the difference of mechanical properties of different media on the mechanical properties and failure modes of composite samples in combination with the theoretical analysis. The test results show that the uniaxial compressive strength(UCS) and elastic modulus of the composite samples are smaller than the larger values of UCS and elastic modulus of the two media. The reduction amplitude increases with the increase of the difference degree of the mechanical properties of the medium(λ). Meanwhile,with increase of the degree of difference(λ),the composite samples gradually change from single incline plane shear failure to complex lateral tensile failure. Theoretical analysis shows that the uncoordinated deformation at the contact surface is caused by the difference of Poisson ratio(Δv) in different media. The mechanical properties of composite samples are weaken by the formed lateral constraint stress. The correlation between the degree of uncoordinated deformation and Δv is quantified by introducing the uncoordinated deformation coefficient α. The expression of elastic modulus and axial stress-strain constitutive relation of composite samples determined by the mechanical parameters of two kinds of media was constructed. The results can provide a theoretical basis for further analysis of the uncoordinated deformation and failure of the contact zone composite rock mass. This paper aims at the uncoordinated deformation phenomenon of composite rock mass in metal mine contact zone. It carries out the uniaxial compression test of physical similar samples. It studies the influence of the difference of mechanical properties of different media on the mechanical properties and failure modes of composite samples in combination with the theoretical analysis. The test results show that the uniaxial compressive strength(UCS) and elastic modulus of the composite samples are smaller than the larger values of UCS and elastic modulus of the two media. The reduction amplitude increases with the increase of the difference degree of the mechanical properties of the medium(λ). Meanwhile,with increase of the degree of difference(λ),the composite samples gradually change from single incline plane shear failure to complex lateral tensile failure. Theoretical analysis shows that the uncoordinated deformation at the contact surface is caused by the difference of Poisson ratio(Δv) in different media. The mechanical properties of composite samples are weaken by the formed lateral constraint stress. The correlation between the degree of uncoordinated deformation and Δv is quantified by introducing the uncoordinated deformation coefficient α. The expression of elastic modulus and axial stress-strain constitutive relation of composite samples determined by the mechanical parameters of two kinds of media was constructed. The results can provide a theoretical basis for further analysis of the uncoordinated deformation and failure of the contact zone composite rock mass.
This paper introduces the fuzzy mathematics theory to solve the defects of traditional methods that are insufficient consideration of complexity in extremely soft rock classification. It establishes the evaluation indexes with total uniaxial compressive strength,drill core quality RQD,spacing of discontinuities,conditions of discontinuities,water content and dry saturated hydroscopic moisture ratio of rock. It adopts the entropy method to calculate index weight so as to avoid subjectivity of evaluation index assignment. Thus,an entropy weight fuzzy based comprehensive evaluation model for rock classification is established. This model is applied to a hydropower station tunnel in Indonesia. It chooses 15 tunnel sections for evaluation. The results show that the surrounding rock are mainly class Ⅳ or Ⅴ. The results are highly consistent with tunnel support types that are determined on site. It is considered that the classification results of this model are better than the traditional RMR classification method through comparison and analysis. It shows that the fuzzy mathematics can solve the complexity and fuzziness problems of extremely soft rock influencing factors. The entropy weight method can reduce the subjectivity of human factors. The combination of the two methods can achieve objective evaluation. This approach can provide reference for the classification of extremely soft rock tunnel. This paper introduces the fuzzy mathematics theory to solve the defects of traditional methods that are insufficient consideration of complexity in extremely soft rock classification. It establishes the evaluation indexes with total uniaxial compressive strength,drill core quality RQD,spacing of discontinuities,conditions of discontinuities,water content and dry saturated hydroscopic moisture ratio of rock. It adopts the entropy method to calculate index weight so as to avoid subjectivity of evaluation index assignment. Thus,an entropy weight fuzzy based comprehensive evaluation model for rock classification is established. This model is applied to a hydropower station tunnel in Indonesia. It chooses 15 tunnel sections for evaluation. The results show that the surrounding rock are mainly class Ⅳ or Ⅴ. The results are highly consistent with tunnel support types that are determined on site. It is considered that the classification results of this model are better than the traditional RMR classification method through comparison and analysis. It shows that the fuzzy mathematics can solve the complexity and fuzziness problems of extremely soft rock influencing factors. The entropy weight method can reduce the subjectivity of human factors. The combination of the two methods can achieve objective evaluation. This approach can provide reference for the classification of extremely soft rock tunnel.
The surface roughness is one of the important factors in the mechanical properties. And,more significantly,the surface roughness has size effect characteristics. So,investigation of size effect characteristics of surface roughness is of great significance for further understanding of mechanical properties of structural surface. In view of this,firstly,we improve the Projective Covering Method by a new calculation that the random number is applied to the triangular element division. Secondly,to investigate the size effect of surface roughness of rock joints,we select six sampling windows,respectively,from the central and four corners part of structural planes(2 m×2 m). The sampling windows range from 62.5 mm×62.5 mm to 2000 mm×2000 mm. And then,we calculate fractal parameters of the different size surfaces using the improved projective covering method at the same resolution. Thirdly,we discuss the method of determining the reasonable structural surface by the parameter ΔDmaxSD. This parameter is the difference of the maximum fractal dimensions of the same size structural surfaces in different regions. The results show that:(1) The size effect of structure surface is different with different morphological surface. Generally,as the size increases,the roughness of structure surface increases and then decreases. There is positive size effect in small scale and negative size effect in large scale. (2) For a certain structural surface,when the same size surfaces are selected from different locations of the structural planes,and the size effect characteristics are also different. (3) As the size of the structure surface increases,the parameter ΔDmaxSD gradually decreases and tends to almost constant. The result of this study is a useful supplement to the comprehensive understanding of the size effect of structural surface roughness. The surface roughness is one of the important factors in the mechanical properties. And,more significantly,the surface roughness has size effect characteristics. So,investigation of size effect characteristics of surface roughness is of great significance for further understanding of mechanical properties of structural surface. In view of this,firstly,we improve the Projective Covering Method by a new calculation that the random number is applied to the triangular element division. Secondly,to investigate the size effect of surface roughness of rock joints,we select six sampling windows,respectively,from the central and four corners part of structural planes(2 m×2 m). The sampling windows range from 62.5 mm×62.5 mm to 2000 mm×2000 mm. And then,we calculate fractal parameters of the different size surfaces using the improved projective covering method at the same resolution. Thirdly,we discuss the method of determining the reasonable structural surface by the parameter ΔDmaxSD. This parameter is the difference of the maximum fractal dimensions of the same size structural surfaces in different regions. The results show that:(1) The size effect of structure surface is different with different morphological surface. Generally,as the size increases,the roughness of structure surface increases and then decreases. There is positive size effect in small scale and negative size effect in large scale. (2) For a certain structural surface,when the same size surfaces are selected from different locations of the structural planes,and the size effect characteristics are also different. (3) As the size of the structure surface increases,the parameter ΔDmaxSD gradually decreases and tends to almost constant. The result of this study is a useful supplement to the comprehensive understanding of the size effect of structural surface roughness.
The weathered soil in red beds has the characteristics of disintegration when it encounters water. Its water stability is poor. It is easy to break down in the hot and rainy climate in Southern China. Therefore,its disintegration characteristics and its control mechanism have become one of the hot issues in practical engineering. In view of the deficiencies of the current researches on the disintegration characteristics of weathered soil in red beds,we design and develop a set of disintegration test equipment. We carry out the disintegration test of typical weathered soil in red beds in Southern China under different water contents and compactness conditions. We also analyze the disintegration mechanism of weathered soil in red beds from the perspective of composition and structure. Then,based on this,we carry out soil modification test by incorporating high performance ester materials. We explore a solution by modification control to improve the anti-disintegration of weathered soil in red beds. The results show that the lower initial water content of the soil and smaller compactness lead to stronger disintegration of the weathered soil in red beds,faster disintegration rate and more significant damage. The factors controlling the disintegration are mainly the mineral composition,chemical composition,pore fracture and cement characteristics of the soil. High-performance ester materials can enhance the cementation and agglomeration between soil particles,thereby improving the water stability of the soil and controlling the disintegration characteristics of the weathered soil in red beds. Our research has certain reference significance for revealing the water disintegration characteristics and disintegration mechanism of weathered soil in red beds and improving its anti-disintegration from the perspective of soil modification. The weathered soil in red beds has the characteristics of disintegration when it encounters water. Its water stability is poor. It is easy to break down in the hot and rainy climate in Southern China. Therefore,its disintegration characteristics and its control mechanism have become one of the hot issues in practical engineering. In view of the deficiencies of the current researches on the disintegration characteristics of weathered soil in red beds,we design and develop a set of disintegration test equipment. We carry out the disintegration test of typical weathered soil in red beds in Southern China under different water contents and compactness conditions. We also analyze the disintegration mechanism of weathered soil in red beds from the perspective of composition and structure. Then,based on this,we carry out soil modification test by incorporating high performance ester materials. We explore a solution by modification control to improve the anti-disintegration of weathered soil in red beds. The results show that the lower initial water content of the soil and smaller compactness lead to stronger disintegration of the weathered soil in red beds,faster disintegration rate and more significant damage. The factors controlling the disintegration are mainly the mineral composition,chemical composition,pore fracture and cement characteristics of the soil. High-performance ester materials can enhance the cementation and agglomeration between soil particles,thereby improving the water stability of the soil and controlling the disintegration characteristics of the weathered soil in red beds. Our research has certain reference significance for revealing the water disintegration characteristics and disintegration mechanism of weathered soil in red beds and improving its anti-disintegration from the perspective of soil modification.
Creep test was conducted on Shanghai soft clays under both drained and undrained conditions by means of triaxial creep apparatus. The creep properties of Shanghai soft clays can be influenced by factors including confining pressures,loading and unloading stress ratios,which is analyzed accordingly. Experimental results show that the confining pressures,loading and unloading stress levels can affect the creep deformation of the soft clays. The creep behavior of the soft clays is closely related to the drainage conditions and the consolidation can help to cease the creep phenomenon. The creep and resilience deformations of the soft soils are larger under the undrained condition,compared with those under the drained condition. The history of build-up of pore water pressures is similar to the development of axial strains with time under the undrained condition. Consolidation deformation and creep deformation exist simultaneously in the drained tests,however,the volume of water discharge doesn't drop right after unloading. Creep test was conducted on Shanghai soft clays under both drained and undrained conditions by means of triaxial creep apparatus. The creep properties of Shanghai soft clays can be influenced by factors including confining pressures,loading and unloading stress ratios,which is analyzed accordingly. Experimental results show that the confining pressures,loading and unloading stress levels can affect the creep deformation of the soft clays. The creep behavior of the soft clays is closely related to the drainage conditions and the consolidation can help to cease the creep phenomenon. The creep and resilience deformations of the soft soils are larger under the undrained condition,compared with those under the drained condition. The history of build-up of pore water pressures is similar to the development of axial strains with time under the undrained condition. Consolidation deformation and creep deformation exist simultaneously in the drained tests,however,the volume of water discharge doesn't drop right after unloading.
We use a home-developed loading and measuring system to study failure processes of clay specimens with holes under displacement-controlled loading and in plane strain condition. We use gasbags to apply the internal and lateral pressures for the displacement-controlled loading. We further use the digital image correlation method to obtain the strain fields. We arrange the monitored lines to investigate distributions and evolution of the maximum shear strains and principal strain axis rotational angles inside shear bands and outside. We find the following results. With an increase of the vertical strain, clay specimens undergo uniform deformations and subsequent localized deformation, as found from spatiotemporal distributions of the maximum shear strains. For monitored points outside shear bands, the maximum shear strains have an increasing tendency when they are far away from the hole, which is due to unloading, i.e., the decrease of the elastic strain resulting from damages inside shear bands. For monitored points in the vicinity of the hole surface, changes of the maximum shear strains are complex, which is related to competition between the decrease of the elastic part and the increase of the plastic part. For the monitored point at the shear band tip, in comparison with monitored points in its forward and backward directions, the horizontal linear strain rapidly increases, the value of the vertical linear strain rapidly decreases, and the value of the shear strain rapidly increases, leading to a rapid increase of the value(about 30 degrees) of the principal strain axis rotational angle. At the same vertical strain, the vertical stress of the clay specimen with a hole increases as internal and lateral pressures increase. We use a home-developed loading and measuring system to study failure processes of clay specimens with holes under displacement-controlled loading and in plane strain condition. We use gasbags to apply the internal and lateral pressures for the displacement-controlled loading. We further use the digital image correlation method to obtain the strain fields. We arrange the monitored lines to investigate distributions and evolution of the maximum shear strains and principal strain axis rotational angles inside shear bands and outside. We find the following results. With an increase of the vertical strain, clay specimens undergo uniform deformations and subsequent localized deformation, as found from spatiotemporal distributions of the maximum shear strains. For monitored points outside shear bands, the maximum shear strains have an increasing tendency when they are far away from the hole, which is due to unloading, i.e., the decrease of the elastic strain resulting from damages inside shear bands. For monitored points in the vicinity of the hole surface, changes of the maximum shear strains are complex, which is related to competition between the decrease of the elastic part and the increase of the plastic part. For the monitored point at the shear band tip, in comparison with monitored points in its forward and backward directions, the horizontal linear strain rapidly increases, the value of the vertical linear strain rapidly decreases, and the value of the shear strain rapidly increases, leading to a rapid increase of the value(about 30 degrees) of the principal strain axis rotational angle. At the same vertical strain, the vertical stress of the clay specimen with a hole increases as internal and lateral pressures increase.
Based on laboratory sand falling device and particle flow software PFC2D, we study the effects of particle size and friction coefficient on the pressure characteristics of sand accumulation structure. In the laboratory test, we select dry sand, wet sand, wet sand+loess to analyze the effects of particle size and inter-particle friction coefficient on the bottom pressure of the sand heap. We use the built-in command of PFC software(ball generate) to generate particles with three different particle sizes and used its ball property command to assign six different friction coefficients to the particles. In addition, we analyze its influence on the internal structure of sand heap from the perspective of force chain. The results show that particle size and inter-particle friction coefficient have significant influence on the bottom pressure of this structure. Under the condition of the same friction coefficient, the larger the particle size, the more sparse the distribution of the contact force chain, and the smaller the bottom pressure. Under the condition of the same particle size, the bottom pressure of sand heap decreases first and then tends to be stable with the increase of friction coefficient. That is, the influence of friction coefficient on the bottom pressure of sand heap has an upper limit. Based on laboratory sand falling device and particle flow software PFC2D, we study the effects of particle size and friction coefficient on the pressure characteristics of sand accumulation structure. In the laboratory test, we select dry sand, wet sand, wet sand+loess to analyze the effects of particle size and inter-particle friction coefficient on the bottom pressure of the sand heap. We use the built-in command of PFC software(ball generate) to generate particles with three different particle sizes and used its ball property command to assign six different friction coefficients to the particles. In addition, we analyze its influence on the internal structure of sand heap from the perspective of force chain. The results show that particle size and inter-particle friction coefficient have significant influence on the bottom pressure of this structure. Under the condition of the same friction coefficient, the larger the particle size, the more sparse the distribution of the contact force chain, and the smaller the bottom pressure. Under the condition of the same particle size, the bottom pressure of sand heap decreases first and then tends to be stable with the increase of friction coefficient. That is, the influence of friction coefficient on the bottom pressure of sand heap has an upper limit.
High-locality landslide is one of the most catastrophic hazards because of its insidious feature. Analyzing the grain size distribution form the basis of landslide failure process inversion, which is significate for prediction of rock avalanche hazards. In this paper, we propose a novel framework to handle this issue. It contains two main parts:field investigation and PCAS software. First, the high precision images of landslide deposit is obtained using UAV. Then, damage situation of local houses is analyzed in detail. Last, we quantify the grain size of the rock avalanche deposit using image data with PCAS software, and analyze the relationship between the grain size distribution and the damage situation of local houses. A case study is conducted on Pusacun rock avalanches of August 28, 2017. It turns out the following results. (1) The PCAS software can results in reliable image identifications. (2) The proportion of small particle size increases in pace with the runout distance. (3) The proportion of large particle shows bimodal distribution, but the peak value decreases along the sliding deration. (4) The similarity of lateral distribution enhances as the runout distance increases. (5) The houses have the ability for "trapping the coarse particles and discharging the fine particles". The results demonstrate the framework proposed has superior performance in related researches. High-locality landslide is one of the most catastrophic hazards because of its insidious feature. Analyzing the grain size distribution form the basis of landslide failure process inversion, which is significate for prediction of rock avalanche hazards. In this paper, we propose a novel framework to handle this issue. It contains two main parts:field investigation and PCAS software. First, the high precision images of landslide deposit is obtained using UAV. Then, damage situation of local houses is analyzed in detail. Last, we quantify the grain size of the rock avalanche deposit using image data with PCAS software, and analyze the relationship between the grain size distribution and the damage situation of local houses. A case study is conducted on Pusacun rock avalanches of August 28, 2017. It turns out the following results. (1) The PCAS software can results in reliable image identifications. (2) The proportion of small particle size increases in pace with the runout distance. (3) The proportion of large particle shows bimodal distribution, but the peak value decreases along the sliding deration. (4) The similarity of lateral distribution enhances as the runout distance increases. (5) The houses have the ability for "trapping the coarse particles and discharging the fine particles". The results demonstrate the framework proposed has superior performance in related researches.
Based on the existing studies of the MgO-carbonated soft soils, model tests of mucky soils are conducted through the carbonation stabilization technology. The mucky soil taken from Chang-Yi highway(from Yixing to Changzhou) is used for the reactive MgO-mass carbonation and stabilization experiments. Some parameters including temperature, moisture content and pH are measured to analyze the degree of carbonization. Laboratory micro penetration test(MPT) and compression tests are conducted to evaluate the bearing capacity and compressibility of carbonated mucky soil. The results indicate that(1) the mucky soil can achieve the better treatment effect after MgO carbonation when its initial moisture content is 35%, its state is hard plastic state transformed from its soft plastic state, and its bearing capacity reaches 300 kPa. (2) When the initial water content of mucky soil is 46%, the migration distance of carbon dioxide is restricted, resulting in that its carbonization degree and bearing capacity improvement are limited and the soil state is still the plastic state except that the limited areas near the surface and vents can be effectively improved. (3) Carbonation can obviously reduce compression of mucky soil even only through simple compaction measures. Comparing with other treatment methods of mucky soil, it is considered that the air permeability of mucky soil can be increased by some auxiliary measures, e.g., adding water reducer or fine sand under the conditions of low construction requirements and inconvenient drainage, the better treatment effect may be obtained by magnesium oxide carbonation method. Based on the existing studies of the MgO-carbonated soft soils, model tests of mucky soils are conducted through the carbonation stabilization technology. The mucky soil taken from Chang-Yi highway(from Yixing to Changzhou) is used for the reactive MgO-mass carbonation and stabilization experiments. Some parameters including temperature, moisture content and pH are measured to analyze the degree of carbonization. Laboratory micro penetration test(MPT) and compression tests are conducted to evaluate the bearing capacity and compressibility of carbonated mucky soil. The results indicate that(1) the mucky soil can achieve the better treatment effect after MgO carbonation when its initial moisture content is 35%, its state is hard plastic state transformed from its soft plastic state, and its bearing capacity reaches 300 kPa. (2) When the initial water content of mucky soil is 46%, the migration distance of carbon dioxide is restricted, resulting in that its carbonization degree and bearing capacity improvement are limited and the soil state is still the plastic state except that the limited areas near the surface and vents can be effectively improved. (3) Carbonation can obviously reduce compression of mucky soil even only through simple compaction measures. Comparing with other treatment methods of mucky soil, it is considered that the air permeability of mucky soil can be increased by some auxiliary measures, e.g., adding water reducer or fine sand under the conditions of low construction requirements and inconvenient drainage, the better treatment effect may be obtained by magnesium oxide carbonation method.
In engineering applications, red clay is prone to shrinkage, deformation and even cracking with the change of ambient temperature and humidity, which leads to many engineering problems. It is undoubted that only by mastering the shrinkage and cracking properties of red clay can effective preventive measures be taken in time. For this reason, this paper takes the typical red clay in Inner Mongolia as the research object. On the basis of the compaction characteristics, the shrinkage characteristics of red clay under different compaction times are analyzed subsequently. The development pattern of fracture morphology of the compacted red clays is further explained by means of image processing technology. The results show that the maximum dry density of red clay increases linearly with the increase of compaction times, while the optimum moisture content decreases linearly with the increase of compaction times. At the same time, the water loss rate varies exponentially with drying time. In the early stage of drying, the water evaporation of the sample changes linearly. With the continuation of drying time, the water evaporation decreases gradually, and the water loss rate curve tends to be stable. Furthermore, with the increase of compaction times, the radial, axial and volume shrinkage changes exponentially with drying time. The shrinkage geometric factor of the red clay is less than 3, which indicates that axial shrinkage is larger than that of radial shrinkage. The shrinkage of the red clay is anisotropic. Increase in the sample compaction times can destroy the clay particles. The average crack width, total crack length and crack percentage of the red clay are increased as well. Simultaneously, the maximum adsorptive capacity of the clay to bound water is weakened. The water holding capacity is reduced, the water loss rate, shrinkage rate and crack percentage increase correspondingly. Therefore, it is inefficient and uneconomical to increase the number of compaction times in engineering application to improve the shrinkage and crack resistance of red clay. In engineering applications, red clay is prone to shrinkage, deformation and even cracking with the change of ambient temperature and humidity, which leads to many engineering problems. It is undoubted that only by mastering the shrinkage and cracking properties of red clay can effective preventive measures be taken in time. For this reason, this paper takes the typical red clay in Inner Mongolia as the research object. On the basis of the compaction characteristics, the shrinkage characteristics of red clay under different compaction times are analyzed subsequently. The development pattern of fracture morphology of the compacted red clays is further explained by means of image processing technology. The results show that the maximum dry density of red clay increases linearly with the increase of compaction times, while the optimum moisture content decreases linearly with the increase of compaction times. At the same time, the water loss rate varies exponentially with drying time. In the early stage of drying, the water evaporation of the sample changes linearly. With the continuation of drying time, the water evaporation decreases gradually, and the water loss rate curve tends to be stable. Furthermore, with the increase of compaction times, the radial, axial and volume shrinkage changes exponentially with drying time. The shrinkage geometric factor of the red clay is less than 3, which indicates that axial shrinkage is larger than that of radial shrinkage. The shrinkage of the red clay is anisotropic. Increase in the sample compaction times can destroy the clay particles. The average crack width, total crack length and crack percentage of the red clay are increased as well. Simultaneously, the maximum adsorptive capacity of the clay to bound water is weakened. The water holding capacity is reduced, the water loss rate, shrinkage rate and crack percentage increase correspondingly. Therefore, it is inefficient and uneconomical to increase the number of compaction times in engineering application to improve the shrinkage and crack resistance of red clay.
To further investigate the effect of elastic visco-plasticity and variable permeability of saturated clay on one-dimensional consolidation process, we introduced the unified hardened(UH) constitutive model considering time effect to describe the elastic visco-plasticity of saturated clay, and used Taylor's empirical relation to describe the relationship between its permeability coefficient and void ratio. Then we modified Terzaghi's one-dimensional consolidation theory, and employed the finite difference solution format. By comparing the numerical solutions with the results of one-dimensional rheological consolidation test, we verified the effectiveness of the proposed method and the applicability of the UH model. Base on this, we investigated the effects of parameters of UH model, the ratio of compression index to permeability index and the load intensity on the consolidation process. Numerical results indicate that the viscosity of saturated clay makes the pore pressure rise in the early stage of consolidation, slows down the overall dissipation of pore pressure in the middle and late stage of consolidation, and increases the settlement of soil layer. This phenomenon is more obvious with the increase of the initial overconsolidation parameters. In addition, with the decrease of the ratio of compression index to permeability index, the consolidation process of soil layer will be accelerated, but the final settlement will not be affected by the ratio. In the later stage of consolidation, the pore pressure dissipation in the soil layer with less load is slower if the compression index is not greater than the permeability index. However, the effect of the load intensity on the pore pressure dissipation is relatively small if the compression index is larger than the permeability index. To further investigate the effect of elastic visco-plasticity and variable permeability of saturated clay on one-dimensional consolidation process, we introduced the unified hardened(UH) constitutive model considering time effect to describe the elastic visco-plasticity of saturated clay, and used Taylor's empirical relation to describe the relationship between its permeability coefficient and void ratio. Then we modified Terzaghi's one-dimensional consolidation theory, and employed the finite difference solution format. By comparing the numerical solutions with the results of one-dimensional rheological consolidation test, we verified the effectiveness of the proposed method and the applicability of the UH model. Base on this, we investigated the effects of parameters of UH model, the ratio of compression index to permeability index and the load intensity on the consolidation process. Numerical results indicate that the viscosity of saturated clay makes the pore pressure rise in the early stage of consolidation, slows down the overall dissipation of pore pressure in the middle and late stage of consolidation, and increases the settlement of soil layer. This phenomenon is more obvious with the increase of the initial overconsolidation parameters. In addition, with the decrease of the ratio of compression index to permeability index, the consolidation process of soil layer will be accelerated, but the final settlement will not be affected by the ratio. In the later stage of consolidation, the pore pressure dissipation in the soil layer with less load is slower if the compression index is not greater than the permeability index. However, the effect of the load intensity on the pore pressure dissipation is relatively small if the compression index is larger than the permeability index.
A new geotextile technique is proposed to solve the slip problem of drainage channel in irrigation area of Ningxia Yellow River diversion. This new form of masonry protection is first attempted in the Ningxia region. This paper examines the effect of this kind of masonry. In this paper, the extended simplified Bishop formula under the condition of geotextile masonry protection is derived. The MATLAB calculation program is compiled according to this formula. According to the program, the four working conditions of farmland drainage channel are calculated. The four conditions are homogeneous soil slope, geotextile protection slope, homogeneous soil slope when considering quicksand layer and geotextile protecting slope when considering quicksand layer. The results of program calculation and the position of slip plane searched by program are compared with the results of geotechnical engineering software GeoStudio2007 and the actual prototype monitoring results. Finally, we come to the following conclusions. (1) The result of self-programmed program is in good agreement with that of GeoStudio2007 in the same mode, which shows that the result of self-programmed program is reliable. (2) The stability of homogeneous soil slope can be improved by about 33%in the form of geotechnical bag, but the effect is not obvious when there is quicksand layer in the bottom of the trench. It is suggested that the combination of geotextile and anti-slide pile should be adopted. (3) Field monitoring data show that the internal displacement of geotextile masonry slope increases with the increase of depth, which is basically consistent with the trend of slip plane position searched by the self-compiled program. (4) The internal displacement and annual displacement of geotextile masonry slope are smaller than those of traditional grass soil willow pile slope and the stability of the slope is high. A new geotextile technique is proposed to solve the slip problem of drainage channel in irrigation area of Ningxia Yellow River diversion. This new form of masonry protection is first attempted in the Ningxia region. This paper examines the effect of this kind of masonry. In this paper, the extended simplified Bishop formula under the condition of geotextile masonry protection is derived. The MATLAB calculation program is compiled according to this formula. According to the program, the four working conditions of farmland drainage channel are calculated. The four conditions are homogeneous soil slope, geotextile protection slope, homogeneous soil slope when considering quicksand layer and geotextile protecting slope when considering quicksand layer. The results of program calculation and the position of slip plane searched by program are compared with the results of geotechnical engineering software GeoStudio2007 and the actual prototype monitoring results. Finally, we come to the following conclusions. (1) The result of self-programmed program is in good agreement with that of GeoStudio2007 in the same mode, which shows that the result of self-programmed program is reliable. (2) The stability of homogeneous soil slope can be improved by about 33%in the form of geotechnical bag, but the effect is not obvious when there is quicksand layer in the bottom of the trench. It is suggested that the combination of geotextile and anti-slide pile should be adopted. (3) Field monitoring data show that the internal displacement of geotextile masonry slope increases with the increase of depth, which is basically consistent with the trend of slip plane position searched by the self-compiled program. (4) The internal displacement and annual displacement of geotextile masonry slope are smaller than those of traditional grass soil willow pile slope and the stability of the slope is high.
The world geopark Fangshan scenic spot in Daxi town, Wenling city, Zhejiang province is located on the volcanic strata of Jiuliping formation, Moshishan group, early cretaceous. The formation of volcanic platform landscape in Fangshan is related to the hard rhyolite which is not easy to be weathered. According to field investigation, the rock mass in Fangshan scenic area has layered structure, and the engineering geological conditions are evaluated as good. However, there are many rockfalls in the high and steep reverse slope near the tour road, and mud and stone falling in the water zone may occur when the typhoon comes. Therefore, a serious geological hazard may be formed in some places where tourists appear. For example, in the typhoon season of 2013, Liangyi pavilion in Fangshan scenic area was damaged by mud and stones washed down from the top of the above-mentioned high and steep slope. In addition, a large number of falling rocks scattered on the ground in Liangyi Pavilion scenic spot was found. Tourism safety is seriously threatened by geological hazards in Liangyi Pavilion scenic spot. In terms of the prevention and control of geological disasters in Liangyi Pavilion, the engineering geological method of mountain tourism planning based on the combination of engineering geology and tourism was put forward to adjust the route of scenic spots, so as to ensure the safety of tourism and maintain the original state of Fangshan scenic area. The world geopark Fangshan scenic spot in Daxi town, Wenling city, Zhejiang province is located on the volcanic strata of Jiuliping formation, Moshishan group, early cretaceous. The formation of volcanic platform landscape in Fangshan is related to the hard rhyolite which is not easy to be weathered. According to field investigation, the rock mass in Fangshan scenic area has layered structure, and the engineering geological conditions are evaluated as good. However, there are many rockfalls in the high and steep reverse slope near the tour road, and mud and stone falling in the water zone may occur when the typhoon comes. Therefore, a serious geological hazard may be formed in some places where tourists appear. For example, in the typhoon season of 2013, Liangyi pavilion in Fangshan scenic area was damaged by mud and stones washed down from the top of the above-mentioned high and steep slope. In addition, a large number of falling rocks scattered on the ground in Liangyi Pavilion scenic spot was found. Tourism safety is seriously threatened by geological hazards in Liangyi Pavilion scenic spot. In terms of the prevention and control of geological disasters in Liangyi Pavilion, the engineering geological method of mountain tourism planning based on the combination of engineering geology and tourism was put forward to adjust the route of scenic spots, so as to ensure the safety of tourism and maintain the original state of Fangshan scenic area.
Land subsidence is one of the major geological disasters in Fuzhou, south China. The land subsidence in Fuzhou was discovered by ground monitoring in the mid-20th century. This paper uses the persistent scatterer interferometry(IPTA) to process the time series TerraSAR-X data from 2008 to 2014, and obtains the time series deformation in Fuzhou during this period, the history of urban land subsidence, the status of construction and the abnormal distribution of land subsidence in the study area. Then the spatiotemporal evolution of land subsidence is analyzed under the influence of these complex factors in Fuzhou City. The results suggest that the land subsidence is about 15mm·a-1 in Fuzhou. There are many obvious rapid subsidence areas. The rapid subsidence area on the ground presents a new feature of space transfer. The subsidence center is transferred from the geothermal hot spring area to the engineering-intensive construction area comparing to the monitoring data from 1960s to 1990s. The large settlement area is dominated by rapid linear settlement. The variation of land subsidence characteristics is affected by the superposition of various complex factors, resulting in expansion of land subsidence space and increased subsidence rate. The research results can provide certain scientific basis and reference for land subsidence risk assessment and land subsidence prevention and control in Fuzhou or other coastal cities. Land subsidence is one of the major geological disasters in Fuzhou, south China. The land subsidence in Fuzhou was discovered by ground monitoring in the mid-20th century. This paper uses the persistent scatterer interferometry(IPTA) to process the time series TerraSAR-X data from 2008 to 2014, and obtains the time series deformation in Fuzhou during this period, the history of urban land subsidence, the status of construction and the abnormal distribution of land subsidence in the study area. Then the spatiotemporal evolution of land subsidence is analyzed under the influence of these complex factors in Fuzhou City. The results suggest that the land subsidence is about 15mm·a-1 in Fuzhou. There are many obvious rapid subsidence areas. The rapid subsidence area on the ground presents a new feature of space transfer. The subsidence center is transferred from the geothermal hot spring area to the engineering-intensive construction area comparing to the monitoring data from 1960s to 1990s. The large settlement area is dominated by rapid linear settlement. The variation of land subsidence characteristics is affected by the superposition of various complex factors, resulting in expansion of land subsidence space and increased subsidence rate. The research results can provide certain scientific basis and reference for land subsidence risk assessment and land subsidence prevention and control in Fuzhou or other coastal cities.
Numerical simulation is an important tool in the investigation of high-speed long-runout landslides. Taking the Xinmocun landslide in Maoxian as an example, this paper proposes a 3-dimensional discrete element modeling and numerical simulation method of large-scale landslide. On the basis of the micro-macro conversion formulas and numerical tests of discrete element method, it is able to get a discrete element deposition model that has similar mechanical properties as the sandstone of the landslide. Combined with the digital elevation model data and strata information, a 3-dimensional discrete element shell model is built, which follows the actual strata condition and rock mechanical properties. The initiation, high-speed sliding and accumulation process of Xinmocun landslide is simulated. The simulation results and the actual landslide accumulation are very similar in pattern and distribution, and the characteristics of velocity variation and time scale of simulated landslide coincide with the theoretical values and the measured seismic signal, which validate the reliability of the numerical simulation results and the effectiveness of the method. Source code of the numerical simulation is shared online(http://matdem.com), with which a three-dimensional model can be built quickly. This paper provides an alternative approach for the study of mechanism of high-speed long-runout landslide and the evaluation of corresponding disaster effects. Numerical simulation is an important tool in the investigation of high-speed long-runout landslides. Taking the Xinmocun landslide in Maoxian as an example, this paper proposes a 3-dimensional discrete element modeling and numerical simulation method of large-scale landslide. On the basis of the micro-macro conversion formulas and numerical tests of discrete element method, it is able to get a discrete element deposition model that has similar mechanical properties as the sandstone of the landslide. Combined with the digital elevation model data and strata information, a 3-dimensional discrete element shell model is built, which follows the actual strata condition and rock mechanical properties. The initiation, high-speed sliding and accumulation process of Xinmocun landslide is simulated. The simulation results and the actual landslide accumulation are very similar in pattern and distribution, and the characteristics of velocity variation and time scale of simulated landslide coincide with the theoretical values and the measured seismic signal, which validate the reliability of the numerical simulation results and the effectiveness of the method. Source code of the numerical simulation is shared online(http://matdem.com), with which a three-dimensional model can be built quickly. This paper provides an alternative approach for the study of mechanism of high-speed long-runout landslide and the evaluation of corresponding disaster effects.
This paper examines the seismic response of soil landslide supported with micropiles. It is based on tests of large-scale shaking table. A landslide model with a scale of 8: 1 is made. The El Centro wave, Wenchuna wave, Kobe wave and Sinusoidal wave are regarded as the seismic excitation. The landslide failure characteristics and acceleration response under the seismic waves were analyzed. The test results indicate the following findings. (1) The failure pattern of micropile after earthquake shows the reverse "S"-type, which is similar to that under static loads. The destruction area of micropile mainly distributes in 1.4-4 times pile diameter above the sliding surface and 1.4-3.4 times pile diameter below the sliding surface. (2) Acceleration response is different under different seismic waves with different spectrum characteristics. The closer excitation frequency to the natural frequency of landslide, the stronger the dynamic response of the landslide. The acceleration response of the landslide with micropiles has obvious elevation amplification effect. The higher the excitation frequency is, the more significant the elevation effect is. (3) Micropiles can suppress seismic waves. The acceleration in landslide surface that supported by micropiles is weaker than that inside the landslide(especially the landslide toe). However, with the increase of height, it ends to weaken, consequently, the upper part without supporting structure has surface effect. This paper examines the seismic response of soil landslide supported with micropiles. It is based on tests of large-scale shaking table. A landslide model with a scale of 8: 1 is made. The El Centro wave, Wenchuna wave, Kobe wave and Sinusoidal wave are regarded as the seismic excitation. The landslide failure characteristics and acceleration response under the seismic waves were analyzed. The test results indicate the following findings. (1) The failure pattern of micropile after earthquake shows the reverse "S"-type, which is similar to that under static loads. The destruction area of micropile mainly distributes in 1.4-4 times pile diameter above the sliding surface and 1.4-3.4 times pile diameter below the sliding surface. (2) Acceleration response is different under different seismic waves with different spectrum characteristics. The closer excitation frequency to the natural frequency of landslide, the stronger the dynamic response of the landslide. The acceleration response of the landslide with micropiles has obvious elevation amplification effect. The higher the excitation frequency is, the more significant the elevation effect is. (3) Micropiles can suppress seismic waves. The acceleration in landslide surface that supported by micropiles is weaker than that inside the landslide(especially the landslide toe). However, with the increase of height, it ends to weaken, consequently, the upper part without supporting structure has surface effect.
In order to analyse the influence of topographic parameters on the motion parameters of slope-toe landslide including maximum horizontal movement distance (Lmax), horizontal movement distance beyond slope toe (L) and equivalent friction coefficient (f), the non-linear statistical model is used to establish the motion parameters models of different landslide scales for the inversion analysis. The main results of inversion analysis are as follows:(1) The discrepancy in elevation of landslide (H) and slope gradient (α) have significant influence on Lmax, L and f under different landslide scales. (2) With the increase of landslide scale, the influence of angle of slope-toe (β) on Lmax and L is gradually weakened which indicates that the blocking effect of slope toe is weakened, but the influence of angle of slope-toe (β) on f is gradually increased. (3) With the increase of landslide scale, the influence of slope of accumulation area (γ) on Lmax and f is gradually increased, which indicates that the micro geomorphic effect of the accumulation area is significantly enhanced. Finally, the prediction model of the maximum horizontal movement distance considering the main terrain parameters (H, α, β, γ) and landslide scale (V) has higher prediction accuracy and certain applicability. In order to analyse the influence of topographic parameters on the motion parameters of slope-toe landslide including maximum horizontal movement distance (Lmax), horizontal movement distance beyond slope toe (L) and equivalent friction coefficient (f), the non-linear statistical model is used to establish the motion parameters models of different landslide scales for the inversion analysis. The main results of inversion analysis are as follows:(1) The discrepancy in elevation of landslide (H) and slope gradient (α) have significant influence on Lmax, L and f under different landslide scales. (2) With the increase of landslide scale, the influence of angle of slope-toe (β) on Lmax and L is gradually weakened which indicates that the blocking effect of slope toe is weakened, but the influence of angle of slope-toe (β) on f is gradually increased. (3) With the increase of landslide scale, the influence of slope of accumulation area (γ) on Lmax and f is gradually increased, which indicates that the micro geomorphic effect of the accumulation area is significantly enhanced. Finally, the prediction model of the maximum horizontal movement distance considering the main terrain parameters (H, α, β, γ) and landslide scale (V) has higher prediction accuracy and certain applicability.
This paper studies the karst collapse prediction method in the karst area. It bases on a large number of karst collapse examples. It identifies six typical influencing factors in the karst area. They are lithology coefficient(RQC), rock mass structure coefficient(RMSC), groundwater coefficient(GWC), overlap factor(SSC), topographic coefficient(LPC) and environmental condition factor(ECC). It combines the cloud theory to establish an entropy weight normal cloud model. The model can predict the possibility of collapse in the karst area by calculating the weight of each impact factor in the subsidence area. The model is used to predict the data before the collapse of the karst collapse in the west of Guilin. The prediction result is close to the actual collapse. This proves that the model has good applicability and reliability for karst collapse prediction analysis. It provides new method for predicting and judging the nonlinearity and complexity of karst collapse in karst development areas. This paper studies the karst collapse prediction method in the karst area. It bases on a large number of karst collapse examples. It identifies six typical influencing factors in the karst area. They are lithology coefficient(RQC), rock mass structure coefficient(RMSC), groundwater coefficient(GWC), overlap factor(SSC), topographic coefficient(LPC) and environmental condition factor(ECC). It combines the cloud theory to establish an entropy weight normal cloud model. The model can predict the possibility of collapse in the karst area by calculating the weight of each impact factor in the subsidence area. The model is used to predict the data before the collapse of the karst collapse in the west of Guilin. The prediction result is close to the actual collapse. This proves that the model has good applicability and reliability for karst collapse prediction analysis. It provides new method for predicting and judging the nonlinearity and complexity of karst collapse in karst development areas.
Two large landslide-debris avalanches occurred in Jinsha River at the junction of Baige Village, Bolo Township, Jiangda County, Tibet and Sichuan Province in October and November 2018, respectively. The volumes of the two landslides were about 2400×104 m3 and 850×104 m3, respectively. The two landslides moved down an average distance of 1400 m, blocked the Jinsha River and formed a barrier lake. The first natural outburst of the dam caused no casualties. However, the second landslide blocked the natural crater of the first landslide and resulted in a rapid increase in the storage capacity of the barrier lake to 3.85×108 m3. The government immediately carried out emergency measures to discharge floods by building spillways, which greatly reduced the risk of flood. In this article, a particle flow code in three dimensions(PFC3D) is adopted to simulate the occurrence, movement and accumulation of the two landslides. Based on the inversion results, we predict the movement path and accumulation scope of the potential dangerous sliding mass in Baige landslide, as well as evaluate its risk scientifically. The results show the follows. (1) Under gravity, in addition to being affected by the initial potential energy, the micro-geomorphology of the landslide is also one of the key factors determining the movement path and the distance of the particles. (2) The PFC3D particle flow numerical simulation method is suitable for landslides similar to the debris avalanche type such as Baige landslide, and the accumulation scope and thickness obtained from the two simulated landslides are basically consistent with these of the reality. (3) Using the parameters obtained from the inversion of the two events, we predict the instability process of the potentially unstable part of the source area. The unstable slope bodies can collapse and form a barrier dam with a thickness of about 70 m at the Jinsha River, which is possible to block the river again. Two large landslide-debris avalanches occurred in Jinsha River at the junction of Baige Village, Bolo Township, Jiangda County, Tibet and Sichuan Province in October and November 2018, respectively. The volumes of the two landslides were about 2400×104 m3 and 850×104 m3, respectively. The two landslides moved down an average distance of 1400 m, blocked the Jinsha River and formed a barrier lake. The first natural outburst of the dam caused no casualties. However, the second landslide blocked the natural crater of the first landslide and resulted in a rapid increase in the storage capacity of the barrier lake to 3.85×108 m3. The government immediately carried out emergency measures to discharge floods by building spillways, which greatly reduced the risk of flood. In this article, a particle flow code in three dimensions(PFC3D) is adopted to simulate the occurrence, movement and accumulation of the two landslides. Based on the inversion results, we predict the movement path and accumulation scope of the potential dangerous sliding mass in Baige landslide, as well as evaluate its risk scientifically. The results show the follows. (1) Under gravity, in addition to being affected by the initial potential energy, the micro-geomorphology of the landslide is also one of the key factors determining the movement path and the distance of the particles. (2) The PFC3D particle flow numerical simulation method is suitable for landslides similar to the debris avalanche type such as Baige landslide, and the accumulation scope and thickness obtained from the two simulated landslides are basically consistent with these of the reality. (3) Using the parameters obtained from the inversion of the two events, we predict the instability process of the potentially unstable part of the source area. The unstable slope bodies can collapse and form a barrier dam with a thickness of about 70 m at the Jinsha River, which is possible to block the river again.
Rapid flow-like landslides are characterized by their high mobility and catastrophic consequences. These landslides tend to entrain a great amount of loose materials along their travelling paths, resulting in the enlargement of landslide volume and covering area. This phenomenon is called bed entrainment/scouring in literatures. Although previous studies showed that bed entrainment was a significant factor influencing the mobility of rapid flow-like landslides, few of them considered its impact on the rheology of the sliding mass, and needless to say quantifying this impact in numerical modeling. Therefore, this paper proposes an improved finite difference model based on momentum conservations of both the landslide and erodible mass. In this model, the influence of bed entrainment on the rheology of a landslide is quantified by modifying the rheological parameters of the landslide according to the calculated entrainment depth. Then the Ximiaodian landslide, a typical rapid flow-like landslide located at the south bank of the Jinghe River in Shaanxi Province, is simulated by the new model. It shows that the run-out process of this landslide can be divided into the rapid acceleration stage(0~5 s) and the slow deceleration stage(5~14 s). During the acceleration stage, the extent of entrainment is small, so its impact on the motion of this landslide is slight. However, the entrainment obviously promotes the mobility of this landslide at the deceleration stage by reducing the basal resistance. In addition, the modeling results of considering and not considering bed entrainment show totally different patterns. The simulated covering area and final deposit agree well with the measured data when adopting the improved model, while those neglecting the impact of bed entrainment-induced rheology change are obviously smaller than that of the fact. It turns out that the new model proposed here is more suitable for simulating those rapid flow-like landslides with similar bed entrainment phenomenon. Rapid flow-like landslides are characterized by their high mobility and catastrophic consequences. These landslides tend to entrain a great amount of loose materials along their travelling paths, resulting in the enlargement of landslide volume and covering area. This phenomenon is called bed entrainment/scouring in literatures. Although previous studies showed that bed entrainment was a significant factor influencing the mobility of rapid flow-like landslides, few of them considered its impact on the rheology of the sliding mass, and needless to say quantifying this impact in numerical modeling. Therefore, this paper proposes an improved finite difference model based on momentum conservations of both the landslide and erodible mass. In this model, the influence of bed entrainment on the rheology of a landslide is quantified by modifying the rheological parameters of the landslide according to the calculated entrainment depth. Then the Ximiaodian landslide, a typical rapid flow-like landslide located at the south bank of the Jinghe River in Shaanxi Province, is simulated by the new model. It shows that the run-out process of this landslide can be divided into the rapid acceleration stage(0~5 s) and the slow deceleration stage(5~14 s). During the acceleration stage, the extent of entrainment is small, so its impact on the motion of this landslide is slight. However, the entrainment obviously promotes the mobility of this landslide at the deceleration stage by reducing the basal resistance. In addition, the modeling results of considering and not considering bed entrainment show totally different patterns. The simulated covering area and final deposit agree well with the measured data when adopting the improved model, while those neglecting the impact of bed entrainment-induced rheology change are obviously smaller than that of the fact. It turns out that the new model proposed here is more suitable for simulating those rapid flow-like landslides with similar bed entrainment phenomenon.
After occurrence of fires on slope ground, debris flow is the most hazardous secondary disaster in the burned area and closely linked to fire activity. Compared with traditional debris flow and post-earthquake debris flow, the post hill-fire debris flow features in its material initiation and hazard formation. This research conducts a detailed investigation in Ren'e Yong gully, so as to get better understanding of the post hill-fire debris flow. Ren'e Yong gully burned with area of 6.9 km2. Six tributary channels were affected by the forest fire, five of them generated post hill-fire debris flows during the following four years. Debris flows destroyed the country road and buried the houses. According to statistic analyze of cumulative channel entrainment, the generation of post hill-fire debris flows experienced three phases, including surface erosion, hyper-concentrated flow erosion and debris flow erosion. Enhanced overland flow after fire incised into cohesive sub-soil in critical condition, and subsequently started channel scour as hyper-concentrated flow. When hyper-concentrated flow transformed to debris flow, the yield rate of channel erosion increased dramatically with a magnification of 1.5~5.7. The collapse of log dams in channel and abrupt changes in channel geometry could promote the translation from hyper-concentrated flow to debris flow. Fire severity derived from remote sensing image of Landsat 8 and field survey was used to evaluate the effect of fire behavior on debris flow generation. As a consequence, significant surface erosion was only found in moderately and severely burned area, slightly burned and unburned area experienced little surface erosion. The erosion thickness in area with moderate and high fire severity equals to that during 20 to 30 years before fire. Fire severity also positively linked to the contribution area needed for the translation from surface erosion to channel incision, in which the angle of slope surface also matters positively. Statistical data shown the distribution density of landslides in burned area was obviously higher than that in unburned area, but little influence of fire intensity on landslides volume. Landslides volume was positively linked to height of free face following the law of meditation function. Multi-stage retrogressive landslide was found to be the most common mode of material initiation. After occurrence of fires on slope ground, debris flow is the most hazardous secondary disaster in the burned area and closely linked to fire activity. Compared with traditional debris flow and post-earthquake debris flow, the post hill-fire debris flow features in its material initiation and hazard formation. This research conducts a detailed investigation in Ren'e Yong gully, so as to get better understanding of the post hill-fire debris flow. Ren'e Yong gully burned with area of 6.9 km2. Six tributary channels were affected by the forest fire, five of them generated post hill-fire debris flows during the following four years. Debris flows destroyed the country road and buried the houses. According to statistic analyze of cumulative channel entrainment, the generation of post hill-fire debris flows experienced three phases, including surface erosion, hyper-concentrated flow erosion and debris flow erosion. Enhanced overland flow after fire incised into cohesive sub-soil in critical condition, and subsequently started channel scour as hyper-concentrated flow. When hyper-concentrated flow transformed to debris flow, the yield rate of channel erosion increased dramatically with a magnification of 1.5~5.7. The collapse of log dams in channel and abrupt changes in channel geometry could promote the translation from hyper-concentrated flow to debris flow. Fire severity derived from remote sensing image of Landsat 8 and field survey was used to evaluate the effect of fire behavior on debris flow generation. As a consequence, significant surface erosion was only found in moderately and severely burned area, slightly burned and unburned area experienced little surface erosion. The erosion thickness in area with moderate and high fire severity equals to that during 20 to 30 years before fire. Fire severity also positively linked to the contribution area needed for the translation from surface erosion to channel incision, in which the angle of slope surface also matters positively. Statistical data shown the distribution density of landslides in burned area was obviously higher than that in unburned area, but little influence of fire intensity on landslides volume. Landslides volume was positively linked to height of free face following the law of meditation function. Multi-stage retrogressive landslide was found to be the most common mode of material initiation.
Being a new multidisciplinary subject, planetary science was built in recent decades. Development and sustainable utilization of planetary resources has become a new frontier direction. In the midst of 50th anniversary of the Apollo 11 mission, several world powers embarked on the science and technology for deep space exploration again, for instance, America's return to space program, Russia's moon strategy and China's deep space exploration plan. Supplying theory and technique for planetary resources development, the subject of planetary geological resources and engineering is an important base for achieving these goals. Planetary geological resources and engineering(PGRE) is a branch of planetary geology subject, which is based on the theory of planetary science and the technology of planetary development. PGRE aims at the research and development of planetary geological resources and the technology of planetary geological engineering. The main research of PGRE contains exploration and exploitation of planetary geological resource and planetary geological engineering. Three important functions of PGRE are illustrated:promoting the progress of planetary science, reliving resources insufficient and cultivating talents of PGRE. The main tasks of PGRE are demonstrated:interdisciplinarity, planetary geologic survey, developing intelligent robot, adopting multi-scale test methods and techniques in planetary environment, subject building of PGRE and talent training. Being a new multidisciplinary subject, planetary science was built in recent decades. Development and sustainable utilization of planetary resources has become a new frontier direction. In the midst of 50th anniversary of the Apollo 11 mission, several world powers embarked on the science and technology for deep space exploration again, for instance, America's return to space program, Russia's moon strategy and China's deep space exploration plan. Supplying theory and technique for planetary resources development, the subject of planetary geological resources and engineering is an important base for achieving these goals. Planetary geological resources and engineering(PGRE) is a branch of planetary geology subject, which is based on the theory of planetary science and the technology of planetary development. PGRE aims at the research and development of planetary geological resources and the technology of planetary geological engineering. The main research of PGRE contains exploration and exploitation of planetary geological resource and planetary geological engineering. Three important functions of PGRE are illustrated:promoting the progress of planetary science, reliving resources insufficient and cultivating talents of PGRE. The main tasks of PGRE are demonstrated:interdisciplinarity, planetary geologic survey, developing intelligent robot, adopting multi-scale test methods and techniques in planetary environment, subject building of PGRE and talent training.
In order to resolve the issue of intensive resource during the reef highway construction, it is proposed to using cement stabilized/solidified coral reef and sand as pavement base materials. The experiments are carried out for their unconfined compressive strength, splitting strength, modulus of resilience, water stability, dry shrinkage and temperature shrinkage and examine their strength, stiffness, water stability and shrinkage characteristics. This research would provide theoretical basis and data foundation for the subsequent construction of reef engineering. The results show that under the standard curing conditions, compressive strength and splitting strength increase with the increase of cement dosage at the same curing age, and those strengths were also improved along with the age growth under the same cement dosage. The compressive strength follows an approximate liner relationship with the cement dosage. Modulus of resilience increases with the rising cement dosage, while the growth rate gradually decreases. Under the same age, saturation strength of the sample is relatively lower than the standard strength. The higher dosage of cement and the longer curing age induce lower intensity loss rate and higher performance of softening resisting. After 28 day curing, the strength loss rate increases 93% and the softening coefficient increases 101%, respectively, as the cement dosage decrease from 6% to 3%. For the dry shrinkage test, the water loss rate and dry shrinkage strain increase with rising the age and cement dosage. After 180 day curing, water loss rate and the drying shrinkage strain decrease 1.35 times and 1.27 times, respectively, as the cement dosage increase from 3% to 6%. The temperature shrinkage tests show that shrinkage strain and coefficient increase with rising cement dosage, whereas they fluctuate along the temperature drop. The temperature range of 30~45℃ is the most disadvantage reef construction of highway pavement, so high temperature construction needs to be avoid. In order to resolve the issue of intensive resource during the reef highway construction, it is proposed to using cement stabilized/solidified coral reef and sand as pavement base materials. The experiments are carried out for their unconfined compressive strength, splitting strength, modulus of resilience, water stability, dry shrinkage and temperature shrinkage and examine their strength, stiffness, water stability and shrinkage characteristics. This research would provide theoretical basis and data foundation for the subsequent construction of reef engineering. The results show that under the standard curing conditions, compressive strength and splitting strength increase with the increase of cement dosage at the same curing age, and those strengths were also improved along with the age growth under the same cement dosage. The compressive strength follows an approximate liner relationship with the cement dosage. Modulus of resilience increases with the rising cement dosage, while the growth rate gradually decreases. Under the same age, saturation strength of the sample is relatively lower than the standard strength. The higher dosage of cement and the longer curing age induce lower intensity loss rate and higher performance of softening resisting. After 28 day curing, the strength loss rate increases 93% and the softening coefficient increases 101%, respectively, as the cement dosage decrease from 6% to 3%. For the dry shrinkage test, the water loss rate and dry shrinkage strain increase with rising the age and cement dosage. After 180 day curing, water loss rate and the drying shrinkage strain decrease 1.35 times and 1.27 times, respectively, as the cement dosage increase from 3% to 6%. The temperature shrinkage tests show that shrinkage strain and coefficient increase with rising cement dosage, whereas they fluctuate along the temperature drop. The temperature range of 30~45℃ is the most disadvantage reef construction of highway pavement, so high temperature construction needs to be avoid.
The rock mass structure controls the stability of the rock mass. Therefore, the geological cataloging of rock mass structure has always been an important part of rock mass engineering geology. The conventional method of cataloging the surface structure of open pit mines has the disadvantages of high risk and low efficiency. It is necessary to introduce new technologies to achieve safe and efficient geological cataloging. With the development of drones in recent years, the photos taken with the UAV-equipped camera can be used in the Structure-from -Motion to restore the 3D structure of the rock mass with the point cloud. The coordinate information of the point cloud can be used to achieve the interpretation of the occurrence of rock mass structure. Taking an open-pit mine slope in Zhejiang as an example, this paper expounds the application method and workflow of UAV photography technology in geological cataloging, and verifies the reliability of the application by comparing the occurrence of compass measurement and the occurrence of point cloud computing. It also divides the dominant occurrence of the structural plane and provides basic data support for analyzing the slope stability. The rock mass structure controls the stability of the rock mass. Therefore, the geological cataloging of rock mass structure has always been an important part of rock mass engineering geology. The conventional method of cataloging the surface structure of open pit mines has the disadvantages of high risk and low efficiency. It is necessary to introduce new technologies to achieve safe and efficient geological cataloging. With the development of drones in recent years, the photos taken with the UAV-equipped camera can be used in the Structure-from -Motion to restore the 3D structure of the rock mass with the point cloud. The coordinate information of the point cloud can be used to achieve the interpretation of the occurrence of rock mass structure. Taking an open-pit mine slope in Zhejiang as an example, this paper expounds the application method and workflow of UAV photography technology in geological cataloging, and verifies the reliability of the application by comparing the occurrence of compass measurement and the occurrence of point cloud computing. It also divides the dominant occurrence of the structural plane and provides basic data support for analyzing the slope stability.
The mechanical coupling between strain sensing optical cable and soil deformation is vital to determine the accuracy of distributed fiber-optic strain data. An anchored strain sensing optical cable is designed to enhance the cable-soil mechanical coupling for the use in geotechnical model test. Using a newly devised pullout apparatus, optical cable pullout tests are carried out to explore the influence and mechanism of anchor on the cable-soil coupling under low confining pressures. Test results show that the axial strain increases under increasing pullout displacements, but the strain propagation is limited to a length of 0.35 m. The anchored strain sensing optical cable requires more pullout forces than the unanchored cable under the same pullout displacement. The anchor averages the measured strain within a range of 0.05~0.075 m near the anchor. An increase ratio is proposed to characterize the effect of anchor on enhancing the cable-soil coupling. The ratio is calculated to be 97.41%in this test, which indicates that the anchor can effectively enhance the mechanical coupling between cable and soil. A mechanical model is proposed to simulate the pullout process of anchored strain sensing optical cable in loose sand, which accurately describes the relationship between pullout force and anchor force and surface friction of cable. This study provides a basis for the application of distributed fiber-optic monitoring technology in geotechnical model tests. The mechanical coupling between strain sensing optical cable and soil deformation is vital to determine the accuracy of distributed fiber-optic strain data. An anchored strain sensing optical cable is designed to enhance the cable-soil mechanical coupling for the use in geotechnical model test. Using a newly devised pullout apparatus, optical cable pullout tests are carried out to explore the influence and mechanism of anchor on the cable-soil coupling under low confining pressures. Test results show that the axial strain increases under increasing pullout displacements, but the strain propagation is limited to a length of 0.35 m. The anchored strain sensing optical cable requires more pullout forces than the unanchored cable under the same pullout displacement. The anchor averages the measured strain within a range of 0.05~0.075 m near the anchor. An increase ratio is proposed to characterize the effect of anchor on enhancing the cable-soil coupling. The ratio is calculated to be 97.41%in this test, which indicates that the anchor can effectively enhance the mechanical coupling between cable and soil. A mechanical model is proposed to simulate the pullout process of anchored strain sensing optical cable in loose sand, which accurately describes the relationship between pullout force and anchor force and surface friction of cable. This study provides a basis for the application of distributed fiber-optic monitoring technology in geotechnical model tests.
Considering the problems of traditional sensing technology, this paper conducts the long-term monitoring and analysis of deep deformation of the anti-slide pile of Majiagou landslide with Brillouin Optical Time Domain Reflectometry(BOTDR) technology. The deflection and internal forces of the anti-slide piles are estimated through the monitored strain data and comparison between the estimated and designed internal forces are made. Taking the hydrological factors into consideration, the working state of anti-slide piles is analyzed and evaluated from the internal and external perspectives. It is shown that there are two sliding surfaces in the Majiagou landslide at the depth of 19 m and 27 m, respectively. Before March 2015, the overall deformation of Majiagou landslide is small, signifying it is in a relative stable state. Then the piles gradually exerts its anti-sliding function. In addition, the shear force of the anti-slide pile is close to the designed value for the present. That is, the anti-slide pile is in an unstable state and needs to be strengthened. The deformation of the anti-slide pile is mainly controlled by the reservoir water level, while the precipitation has a minor effect. Seasonally, the anti-slide pile has an obvious pattern with large deformation when the reservoir water level decreases. Then there is a rapid transition to constant deformation as the reservoir level rises. BOTDR monitoring technology provides a very advanced monitoring means for long-term and meticulous evaluation of the stability state of anti-slide piles. Considering the problems of traditional sensing technology, this paper conducts the long-term monitoring and analysis of deep deformation of the anti-slide pile of Majiagou landslide with Brillouin Optical Time Domain Reflectometry(BOTDR) technology. The deflection and internal forces of the anti-slide piles are estimated through the monitored strain data and comparison between the estimated and designed internal forces are made. Taking the hydrological factors into consideration, the working state of anti-slide piles is analyzed and evaluated from the internal and external perspectives. It is shown that there are two sliding surfaces in the Majiagou landslide at the depth of 19 m and 27 m, respectively. Before March 2015, the overall deformation of Majiagou landslide is small, signifying it is in a relative stable state. Then the piles gradually exerts its anti-sliding function. In addition, the shear force of the anti-slide pile is close to the designed value for the present. That is, the anti-slide pile is in an unstable state and needs to be strengthened. The deformation of the anti-slide pile is mainly controlled by the reservoir water level, while the precipitation has a minor effect. Seasonally, the anti-slide pile has an obvious pattern with large deformation when the reservoir water level decreases. Then there is a rapid transition to constant deformation as the reservoir level rises. BOTDR monitoring technology provides a very advanced monitoring means for long-term and meticulous evaluation of the stability state of anti-slide piles.
The detection and monitoring of ground fissures is vital to understand their mechanism and the prevention and control of related hazards. Recently, high-and ultra-high-resolution distributed fiber optic sensing(DFOS) techniques have been developed and applied in the field of geoengineering. This provides a technological basis for improved detection and monitoring of ground fissures. This paper discusses a theoretical framework for ground fissure detection and sensing using the DFOS technique. Based on the tensile failure mode of soil during ground fissure formation and by considering that DFOS captures linear strains, a strain-based failure criterion is proposed as follows:Rs=ε3/εt, where εt is the ultimate tensile strain of soil and ε3 is the minimum principal strain. A value of Rs larger than 1 means that the absolute value of the minimum principal stress has exceeded the ultimate tensile strain of soil. Hence, tensile failure may occur. The ground fissure monitoring results are influenced by a combined effect of spatial resolution, fiber optic cable-soil interaction, strain localization, temperature variation, and strain transfer efficiency. These effects and their countermeasures are also analyzed and discussed. To improve the quality of DFOS-based monitoring, these effects should be carefully addressed according to different geologic conditions and monitoring schemes. The detection and monitoring of ground fissures is vital to understand their mechanism and the prevention and control of related hazards. Recently, high-and ultra-high-resolution distributed fiber optic sensing(DFOS) techniques have been developed and applied in the field of geoengineering. This provides a technological basis for improved detection and monitoring of ground fissures. This paper discusses a theoretical framework for ground fissure detection and sensing using the DFOS technique. Based on the tensile failure mode of soil during ground fissure formation and by considering that DFOS captures linear strains, a strain-based failure criterion is proposed as follows:Rs=ε3/εt, where εt is the ultimate tensile strain of soil and ε3 is the minimum principal strain. A value of Rs larger than 1 means that the absolute value of the minimum principal stress has exceeded the ultimate tensile strain of soil. Hence, tensile failure may occur. The ground fissure monitoring results are influenced by a combined effect of spatial resolution, fiber optic cable-soil interaction, strain localization, temperature variation, and strain transfer efficiency. These effects and their countermeasures are also analyzed and discussed. To improve the quality of DFOS-based monitoring, these effects should be carefully addressed according to different geologic conditions and monitoring schemes.
This is a review of the 2019 academic annual symposium of engineering investigation specialized committee of the Chinese Institute of Seismology and the 4th symposium on development strategies of marine engineering geology. From May 10 to 12, 2019, this symposium was successfully held in Ocean University of China. The symposium is mainly organized by the Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, and co-organized by Institute of Disaster Prevention Science and Technology and Division of Earth Sciences of National Natural Science Foundation of China. The symposium gathered more than 120 participants from 42 organizations including domestic universities, research institutes and the industries with theme of "Survey and prevention of ocean earthquake and its secondary disaster".Through 11 invited lectures and 9 oral lectures, this symposium reflected 4 aspects on the theoretical accumulation and academic achievements of marine engineering geology in China for several decades. In a harmonious atmosphere, all the attendees discussed the issues around symposium theme. In this symposium, new academic sparks were collided, and new academic thoughts were produced. It plays a positive role in making it clear that what is the mechanism of ocean earthquake and its secondary disaster and that how to prevent them. What's more, it provides a chance for marine engineering geologist to exchange their thoughts and share their research progress. This is a review of the 2019 academic annual symposium of engineering investigation specialized committee of the Chinese Institute of Seismology and the 4th symposium on development strategies of marine engineering geology. From May 10 to 12, 2019, this symposium was successfully held in Ocean University of China. The symposium is mainly organized by the Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, and co-organized by Institute of Disaster Prevention Science and Technology and Division of Earth Sciences of National Natural Science Foundation of China. The symposium gathered more than 120 participants from 42 organizations including domestic universities, research institutes and the industries with theme of "Survey and prevention of ocean earthquake and its secondary disaster".Through 11 invited lectures and 9 oral lectures, this symposium reflected 4 aspects on the theoretical accumulation and academic achievements of marine engineering geology in China for several decades. In a harmonious atmosphere, all the attendees discussed the issues around symposium theme. In this symposium, new academic sparks were collided, and new academic thoughts were produced. It plays a positive role in making it clear that what is the mechanism of ocean earthquake and its secondary disaster and that how to prevent them. What's more, it provides a chance for marine engineering geologist to exchange their thoughts and share their research progress.
Contents
2019, 27(6): 1488-1498.
Abstract(1071)
532KB(38)