2020 Vol. 28, No. 1

Others
The internal pores of red beds soft rock are random and diversified. Their changing characteristics can affect the macroscopic mechanical properties of the soft rock. The mesoscopic structure images of the rock samples at different saturation time are obtained by Scanning Electron Microscope and are used to calculate the fractal dimension by box dimension method. It is found that the fractal dimension of pores increases with the increase of saturation time. Basing on the quantity and size of pores,the distribution characteristics of pores in the rock samples at different saturation times are obtained. The multifractal theory is used to quantitatively evaluate pore structure. The results show that the distribution function of pore structure tends to be linear with q order,which verifies its self-similarity and scale-less property. The generalized fractal dimension of D(0)>D(1)>D(2) reveal the multifractal characteristics of pores,and the irregularity and complexity of pore structure are analyzed by multifractal spectrum parameters,which can characterize the distribution of different pore sizes. Combining the multifractal characteristics of pore structure with the compressive strength of the rock samples,the relationship between the change of pore structure and its mechanical properties is established,which has certain guiding significance for studying the damage process of the red beds soft rock. The internal pores of red beds soft rock are random and diversified. Their changing characteristics can affect the macroscopic mechanical properties of the soft rock. The mesoscopic structure images of the rock samples at different saturation time are obtained by Scanning Electron Microscope and are used to calculate the fractal dimension by box dimension method. It is found that the fractal dimension of pores increases with the increase of saturation time. Basing on the quantity and size of pores,the distribution characteristics of pores in the rock samples at different saturation times are obtained. The multifractal theory is used to quantitatively evaluate pore structure. The results show that the distribution function of pore structure tends to be linear with q order,which verifies its self-similarity and scale-less property. The generalized fractal dimension of D(0)>D(1)>D(2) reveal the multifractal characteristics of pores,and the irregularity and complexity of pore structure are analyzed by multifractal spectrum parameters,which can characterize the distribution of different pore sizes. Combining the multifractal characteristics of pore structure with the compressive strength of the rock samples,the relationship between the change of pore structure and its mechanical properties is established,which has certain guiding significance for studying the damage process of the red beds soft rock.
As an important parameter to characterize the fracture characteristics of rock mass,we characterize the fracture rate from the linear,surface and volumetric perspective. However,the available linear measurement method and statistical window method,which obtain the linear and surface fracture rate from 1-D or 2-D perspective,have the disadvantages of randomness of measurement results and limited application conditions. And the existing method of volumetric fracture rate also has some problems such as poor practical application and high cost. There is still a lack of easy-to-operate method to measure the rate of fissures in the field. Therefore,a new sphere method is proposed to measure volumetric fracture rate of rock mass in the field. Due to the unique tectonic and statistical regularity of the structure and diagenetic fissures,the sphere method observes each group of fracture occurrences from different directions. The development of the rock mass can be statistically inferred by measuring the developmental characteristics of each group of cracks on the limited exposed surface of rock mass. And its value can better reflect the development degree of the internal crack of the local rock mass. In addition,the spherical method can obtain the true value of the gap width and the gap spacing data along the normal direction of the fracture surface by using the patented instrument at the field. And the flatness of the exposed surface of the rock mass affect the measurement result hardly. Taking Dalongshan quarry in Anqing as the study area,field measurements of spheroid method show that the average volumetric fracture rate is 2.286% and the overall difference is concentrated in 1% ~4%. The method can realize rapid measurement on the basis of more convenient operation in the field. Combining the actual situation of the study area and the results of error analysis,the sphere method can reflect the degree of fracture development at each measurement point in the study area. As an important parameter to characterize the fracture characteristics of rock mass,we characterize the fracture rate from the linear,surface and volumetric perspective. However,the available linear measurement method and statistical window method,which obtain the linear and surface fracture rate from 1-D or 2-D perspective,have the disadvantages of randomness of measurement results and limited application conditions. And the existing method of volumetric fracture rate also has some problems such as poor practical application and high cost. There is still a lack of easy-to-operate method to measure the rate of fissures in the field. Therefore,a new sphere method is proposed to measure volumetric fracture rate of rock mass in the field. Due to the unique tectonic and statistical regularity of the structure and diagenetic fissures,the sphere method observes each group of fracture occurrences from different directions. The development of the rock mass can be statistically inferred by measuring the developmental characteristics of each group of cracks on the limited exposed surface of rock mass. And its value can better reflect the development degree of the internal crack of the local rock mass. In addition,the spherical method can obtain the true value of the gap width and the gap spacing data along the normal direction of the fracture surface by using the patented instrument at the field. And the flatness of the exposed surface of the rock mass affect the measurement result hardly. Taking Dalongshan quarry in Anqing as the study area,field measurements of spheroid method show that the average volumetric fracture rate is 2.286% and the overall difference is concentrated in 1% ~4%. The method can realize rapid measurement on the basis of more convenient operation in the field. Combining the actual situation of the study area and the results of error analysis,the sphere method can reflect the degree of fracture development at each measurement point in the study area.
The long-term stability of rock in the alpine area of Qinghai-Tibet Plateau is significantly affected by freeze-thaw action. Accordingly it is necessary to study the time-dependent mechanical characteristics of the rock under freeze-thaw cycles. In this study,we conducted the uniaxial creep experiments on the red sandstone samples subjected to different freeze-thaw cycles. We further analysed the previous studies about quartz sandstone and investigated the effect of freeze-thaw cycles on each creep stage of sandstone. The results show the follows. The creep time of the samples during the deceleration creep decreases with an increasing number of freeze-thaw cycles under the condition of non-yield stress,corresponding to the increase of creep deformation and rate. The threshold stress for the rock samples entering accelerated creep decreases gradually with increasing freeze-thaw cycles under the condition of yield stress,the corresponding time from stable creep to acceleration creep gets more shorter,and the accumulated strain becomes more greater when rock failure. The macro-failure mode of the samples gradually evolves from a single oblique shear failure mode to a conjugate section tension-shear composite failure mode with increasing freeze-thaw cycles. The damage evolution equation about unsteady viscoelastic coefficient with the characteristics of freeze-thaw damage and time-dependent deterioration was proposed based on the experimental results. We introduced the Nishihara model to establish the creep constitutive model of sandstone considering freeze-thaw damage. The parameters of the model were identified by using the creep experimental data of red sandstone. The comparisons verify the correctness and applicability of the model. By fitting and analysing the identified parameters of the model,the law of viscoelastic coefficients varying with freeze-thaw cycles was revealed. The damage parameters under long-term load which plays an important role in controlling the amplitude of accelerated creep was shown. The research results have certain significance for long-term stability evaluation of rock mass in alpine area. The long-term stability of rock in the alpine area of Qinghai-Tibet Plateau is significantly affected by freeze-thaw action. Accordingly it is necessary to study the time-dependent mechanical characteristics of the rock under freeze-thaw cycles. In this study,we conducted the uniaxial creep experiments on the red sandstone samples subjected to different freeze-thaw cycles. We further analysed the previous studies about quartz sandstone and investigated the effect of freeze-thaw cycles on each creep stage of sandstone. The results show the follows. The creep time of the samples during the deceleration creep decreases with an increasing number of freeze-thaw cycles under the condition of non-yield stress,corresponding to the increase of creep deformation and rate. The threshold stress for the rock samples entering accelerated creep decreases gradually with increasing freeze-thaw cycles under the condition of yield stress,the corresponding time from stable creep to acceleration creep gets more shorter,and the accumulated strain becomes more greater when rock failure. The macro-failure mode of the samples gradually evolves from a single oblique shear failure mode to a conjugate section tension-shear composite failure mode with increasing freeze-thaw cycles. The damage evolution equation about unsteady viscoelastic coefficient with the characteristics of freeze-thaw damage and time-dependent deterioration was proposed based on the experimental results. We introduced the Nishihara model to establish the creep constitutive model of sandstone considering freeze-thaw damage. The parameters of the model were identified by using the creep experimental data of red sandstone. The comparisons verify the correctness and applicability of the model. By fitting and analysing the identified parameters of the model,the law of viscoelastic coefficients varying with freeze-thaw cycles was revealed. The damage parameters under long-term load which plays an important role in controlling the amplitude of accelerated creep was shown. The research results have certain significance for long-term stability evaluation of rock mass in alpine area.
Accurately evaluation of brittleness characteristics of granite under different water content is of great significance to rock mass stability evaluation. The existing rock brittleness evaluation indices are summarized. The indices based on stress-strain curve are analyzed in detail. The brittleness of granite decreases with the increase of water content under uniaxial compression,but experiment results show that the indices which based on the stress-strain curve are difficult to accurately reflect the brittleness characteristics of granite under different water contents. So a new brittleness index Bd is proposed and can fully reflect the whole process of granite deformation and failure. Considering the whole process stress-strain curve and the post peak failure time,the new index Bd uses the peak strain to characterize the pre-peak brittleness characteristics and uses the post peak stress drop rate and the post peak strain growth rate to characterize the post-peak brittleness characteristics. It is proved by experiments that the index Bd can accurately reflect the trend that the granite brittleness decreases with the increase of water content. The new index Bd has superiority over the other brittleness indices. The research results can provide some references and help to enrich and improve the rock brittle characteristics evaluation methods. Accurately evaluation of brittleness characteristics of granite under different water content is of great significance to rock mass stability evaluation. The existing rock brittleness evaluation indices are summarized. The indices based on stress-strain curve are analyzed in detail. The brittleness of granite decreases with the increase of water content under uniaxial compression,but experiment results show that the indices which based on the stress-strain curve are difficult to accurately reflect the brittleness characteristics of granite under different water contents. So a new brittleness index Bd is proposed and can fully reflect the whole process of granite deformation and failure. Considering the whole process stress-strain curve and the post peak failure time,the new index Bd uses the peak strain to characterize the pre-peak brittleness characteristics and uses the post peak stress drop rate and the post peak strain growth rate to characterize the post-peak brittleness characteristics. It is proved by experiments that the index Bd can accurately reflect the trend that the granite brittleness decreases with the increase of water content. The new index Bd has superiority over the other brittleness indices. The research results can provide some references and help to enrich and improve the rock brittle characteristics evaluation methods.
The shear characteristics of soil-rock mixture(S-RM)control the stability of the high fill slope. The special structure,material and particle size composition of soil-rock mixture are extremely complicated. This paper explores the influencing factors and laws of shear properties of soil-rock mixture on the basis of laboratory experiments. It constructs the particle discrete element numerical models with PFC2D to study the influence of particle gradation,initial porosity,rock size and rock shape on the shear characteristics of soil-rock mixture. The results shows that: the shear stress-shear displacement curves of soil-rock mixture can be divided into four phases including elastic,local shear,shear failure and residual deformation. The rock shape,particle gradation and initial porosity have no significant influence on the failure mode of soil-rock mixture,and the failure mode is strain softening. When the particle gradation of soil-rock mixture is poor,the shear stress fluctuates largely with the raising of shear displacement,and the curve shows obvious"jump" phenomenon. When the rock content is constant,under the same normal stress condition,the larger the stone size,the larger the shear strength of the S-RM. As the normal stress increases,the difference in shear strength between the test groups of different rock sizes increases,and the effect of rock size on the shear strength of soil-rock mixture is more obvious. The shear characteristics of soil-rock mixture(S-RM)control the stability of the high fill slope. The special structure,material and particle size composition of soil-rock mixture are extremely complicated. This paper explores the influencing factors and laws of shear properties of soil-rock mixture on the basis of laboratory experiments. It constructs the particle discrete element numerical models with PFC2D to study the influence of particle gradation,initial porosity,rock size and rock shape on the shear characteristics of soil-rock mixture. The results shows that: the shear stress-shear displacement curves of soil-rock mixture can be divided into four phases including elastic,local shear,shear failure and residual deformation. The rock shape,particle gradation and initial porosity have no significant influence on the failure mode of soil-rock mixture,and the failure mode is strain softening. When the particle gradation of soil-rock mixture is poor,the shear stress fluctuates largely with the raising of shear displacement,and the curve shows obvious"jump" phenomenon. When the rock content is constant,under the same normal stress condition,the larger the stone size,the larger the shear strength of the S-RM. As the normal stress increases,the difference in shear strength between the test groups of different rock sizes increases,and the effect of rock size on the shear strength of soil-rock mixture is more obvious.
The performance of subgrade soil can decay during long-term service. The moisture content and compaction degree are important control indicators for subgrade construction. Therefore,soil moisture content control and compaction quality are the key factors in the performance evaluation of subgrade. The research results can provide a theoretical basis for the detection and evaluation of the engineering properties of subgrade soil. In order to make up for the deficiencies of the existing detection methods,we developed a rapid indoor test device for soil physical parameters based on the quadrupole electric measurement method,while we changed the water content between the different compactions. We carried out a series of laboratory tests on the resistivity and polarizability of soil samples and obtained the correlation and change trend. We analyzed the influence of water content and compaction on electrical parameters and proposed the soil moisture content and compaction degree. We calculated the calculation formula of resistivity and polarizability and discussed the feasibility of the test method. The results show that the resistivity of soil in different regions decreases with the increase of water content and compaction. The polarizability of soil increases with the increase of water content and compaction. Under different compaction degrees,the resistivity and polarity of soil shows a similar index and logarithmic characteristics with the change of water content. For the loam of Wangqingtuo area in Tianjin,when the compaction degree ranged from 84.47% to 94.41% and the water content changed from 15% to 20%,the resistivity falls to original 1/3~1/2 times and the polarizability falls to 1.4~2.3 times. And we obtain the indoor fitting formula. In practical engineering,the resistivity method is more suitable for soil moisture detection,and the polarizability method is more suitable for soil compaction detection. The comprehensive resistivity and polarizability index have good prospects for roadbed engineering. The research results can provide a theoretical basis for the detection and evaluation of the engineering properties of subgrade soil. The performance of subgrade soil can decay during long-term service. The moisture content and compaction degree are important control indicators for subgrade construction. Therefore,soil moisture content control and compaction quality are the key factors in the performance evaluation of subgrade. The research results can provide a theoretical basis for the detection and evaluation of the engineering properties of subgrade soil. In order to make up for the deficiencies of the existing detection methods,we developed a rapid indoor test device for soil physical parameters based on the quadrupole electric measurement method,while we changed the water content between the different compactions. We carried out a series of laboratory tests on the resistivity and polarizability of soil samples and obtained the correlation and change trend. We analyzed the influence of water content and compaction on electrical parameters and proposed the soil moisture content and compaction degree. We calculated the calculation formula of resistivity and polarizability and discussed the feasibility of the test method. The results show that the resistivity of soil in different regions decreases with the increase of water content and compaction. The polarizability of soil increases with the increase of water content and compaction. Under different compaction degrees,the resistivity and polarity of soil shows a similar index and logarithmic characteristics with the change of water content. For the loam of Wangqingtuo area in Tianjin,when the compaction degree ranged from 84.47% to 94.41% and the water content changed from 15% to 20%,the resistivity falls to original 1/3~1/2 times and the polarizability falls to 1.4~2.3 times. And we obtain the indoor fitting formula. In practical engineering,the resistivity method is more suitable for soil moisture detection,and the polarizability method is more suitable for soil compaction detection. The comprehensive resistivity and polarizability index have good prospects for roadbed engineering. The research results can provide a theoretical basis for the detection and evaluation of the engineering properties of subgrade soil.
Pore network controls important engineering properties of the soil such as seepage,drainage consolidation and matrix suction. This article introduces the basic principle and algorithm of the maximal ball algorithm used in establishing the pore network model of the soil space. Taking the Nanjing silty sand specimen fabricated by vibrating-dry method and scanned by micro-CT as an example,we use the maximal ball algorithm to extract the spatial pore network ball-stick model for Representative Element Volume(REV)in the three-dimensional reconstruction model of the specimen,and calculates the pore network parameters at REV scale. Statistical results shows that the pore parameters such as pore radius,throat radius,pore coordination number,area shape factor of pore,area shape factor of throat and throat length approximately obey the normal distribution,the pore volume approximately obeys the attenuation exponential distribution. The pore radius and throat radius distributes within 100 μm and 65 μm respectively,and their mathematical expectations are 40 μm and 18 μm; the pore coordination number distributes within 25 and the mathematical expectation is 5.1; the area shape factor of pore and area shape factor of throat distributes in the range of 0.01~0.04 and 0.01~0.05 respectively,and their mathematical expectations are 0.019 and 0.033; the throat length distributes in the range of 100~800 μm and the mathematical expectation is 292.22 μm. Meanwhile,we find that the number of small pore with volume less than1.5×107 μm3 is more than 90%. This method can be used to the quantitative characterization of micro pore structure of soil. Pore network controls important engineering properties of the soil such as seepage,drainage consolidation and matrix suction. This article introduces the basic principle and algorithm of the maximal ball algorithm used in establishing the pore network model of the soil space. Taking the Nanjing silty sand specimen fabricated by vibrating-dry method and scanned by micro-CT as an example,we use the maximal ball algorithm to extract the spatial pore network ball-stick model for Representative Element Volume(REV)in the three-dimensional reconstruction model of the specimen,and calculates the pore network parameters at REV scale. Statistical results shows that the pore parameters such as pore radius,throat radius,pore coordination number,area shape factor of pore,area shape factor of throat and throat length approximately obey the normal distribution,the pore volume approximately obeys the attenuation exponential distribution. The pore radius and throat radius distributes within 100 μm and 65 μm respectively,and their mathematical expectations are 40 μm and 18 μm; the pore coordination number distributes within 25 and the mathematical expectation is 5.1; the area shape factor of pore and area shape factor of throat distributes in the range of 0.01~0.04 and 0.01~0.05 respectively,and their mathematical expectations are 0.019 and 0.033; the throat length distributes in the range of 100~800 μm and the mathematical expectation is 292.22 μm. Meanwhile,we find that the number of small pore with volume less than1.5×107 μm3 is more than 90%. This method can be used to the quantitative characterization of micro pore structure of soil.
The variables of the soil-water characteristic curve(air-entry value, residual suction and slope at the inflection point) are very critical parameters in the strength theory, percolation theory and volume change behavior of unsaturated soil. It is often obtained by conventional graphical method, which is subjective and inaccurate. This study presents the methods for determining the variables of unimodal and bimodal SWCC based on VG model using the measured SWCC data of the four layers of undisturbed loess in Luochuan standard section. SWCC data were measured by filter paper method and best fitted using Van Genuchten's equation. Consequently the best fitting parameters were obtained, and the proposed methods were validated using the measured unimodal and bimodal SWCC data. The water evaporation test in the natural state was carried out. Then the evaporation residual saturation Srzf was determined according to the relationship between the mass moisture content and the evaporation time. According to the relative errors between Sr1, Sr2 and Srzf(Sr1 and Sr2 were acquired from the two methods for determining the residual state, respectively), the comparison was made between the two methods for determining the residual state. The results suggest that the proposed methods can produce reasonable variables and determine the residual state effectively related to the unimodal and bimodal SWCC. The variables of the soil-water characteristic curve(air-entry value, residual suction and slope at the inflection point) are very critical parameters in the strength theory, percolation theory and volume change behavior of unsaturated soil. It is often obtained by conventional graphical method, which is subjective and inaccurate. This study presents the methods for determining the variables of unimodal and bimodal SWCC based on VG model using the measured SWCC data of the four layers of undisturbed loess in Luochuan standard section. SWCC data were measured by filter paper method and best fitted using Van Genuchten's equation. Consequently the best fitting parameters were obtained, and the proposed methods were validated using the measured unimodal and bimodal SWCC data. The water evaporation test in the natural state was carried out. Then the evaporation residual saturation Srzf was determined according to the relationship between the mass moisture content and the evaporation time. According to the relative errors between Sr1, Sr2 and Srzf(Sr1 and Sr2 were acquired from the two methods for determining the residual state, respectively), the comparison was made between the two methods for determining the residual state. The results suggest that the proposed methods can produce reasonable variables and determine the residual state effectively related to the unimodal and bimodal SWCC.
Coral sand, as a special bioclastic sediment, is widely distributed in the South China Sea. It has many engineering characteristics such as porous, heterogeneous and discontinuous. As the basis of island filling materials and engineering construction, the mechanical properties of the dredged coral sand are the key scientific issues in the research of coral island and reef engineering. The South China Sea has a large amount of rainfall. The dredged coral sand has good permeability and high engineering bearing capacity. The influence of water content and high load on the shear mechanical properties of the sand is very significant. Based on the analysis of gradation and composition, the conditions of different compactness and water content were studied by using a self-developed large-scale shear mechanical testing machine for soil rock mixture and an island reef in Nansha, China. The results show that:(1)The increase of water content leads to the decrease of shear strength, which has a negative correlation; the increase of compactness leads to the increase of shear strength, which has a positive correlation; (2)The influence of water content on the angle of internal friction is significant, showing a negative correlation. When the water content is greater than 10%, the angle of internal friction decreases slightly; when the density is 90%, the water content is greater than 5%, and the cohesion decreases slightly; (3)The influence of the compactness on the cohesion of the coral sand is not obvious, and the influence of the compactness on the angle of internal friction is significant, when the water content is greater than 5%, with the increase of the compactness internal friction angle increases significantly; (4)Under the high load, the influence of water content and compactness on the shear mechanical properties of sand is significant. The sand with small water content and large compactness has the strongest shear properties, which is of guiding significance for the design of the island filling project and the modification of site conditions. Coral sand, as a special bioclastic sediment, is widely distributed in the South China Sea. It has many engineering characteristics such as porous, heterogeneous and discontinuous. As the basis of island filling materials and engineering construction, the mechanical properties of the dredged coral sand are the key scientific issues in the research of coral island and reef engineering. The South China Sea has a large amount of rainfall. The dredged coral sand has good permeability and high engineering bearing capacity. The influence of water content and high load on the shear mechanical properties of the sand is very significant. Based on the analysis of gradation and composition, the conditions of different compactness and water content were studied by using a self-developed large-scale shear mechanical testing machine for soil rock mixture and an island reef in Nansha, China. The results show that:(1)The increase of water content leads to the decrease of shear strength, which has a negative correlation; the increase of compactness leads to the increase of shear strength, which has a positive correlation; (2)The influence of water content on the angle of internal friction is significant, showing a negative correlation. When the water content is greater than 10%, the angle of internal friction decreases slightly; when the density is 90%, the water content is greater than 5%, and the cohesion decreases slightly; (3)The influence of the compactness on the cohesion of the coral sand is not obvious, and the influence of the compactness on the angle of internal friction is significant, when the water content is greater than 5%, with the increase of the compactness internal friction angle increases significantly; (4)Under the high load, the influence of water content and compactness on the shear mechanical properties of sand is significant. The sand with small water content and large compactness has the strongest shear properties, which is of guiding significance for the design of the island filling project and the modification of site conditions.
The irregular shape of coral sand particles is a major feature that distinguishes it significantly from the ordinary terrigenous soil. In order to research the influence of coral sand particle shape on the compression property of coarse grained calcareous soil, different coral sand particles(block, branch, rod, flake) were selected manually. Based on the block particles, mixed with any of the other three different shapes of coral sand particles, the different particle shape ratios were controlled to make coarse grained calcareous soil samples, and the indoor compression tests were complete. The particle shape parameters such as roundness, length-width ratio, flatness and convexity of coral sand particles before and after the test were compared and analyzed. The effects of particle shape on the compressibility were evaluated. The test results show that:(1)The compression modulus of coarse grained calcareous soil with diameters of 10~20mm is from 4 to 5.5MPa, and the rebound coefficient is from 42 to 53; (2)With the increase of the amount of branch, rod or flake particles(0, 10%, 20%, 30%), the compressive modulus of the sample changed slightly, and the rebound coefficient continued to decrease. (3)The stress-strain curves of each loading range include one stable point and three sections which are rapid growth stress section, synchronous increase of stress and strain section, strain growth section; (4)With the increase of the amount of branch particles, the length-width ratio and the convexity of the sample increased gradually, while the roundness and flatness were unchanged substantially. Due to the influence of particle breakage, the length-width ratio and flatness of the sample increased after the test, while the roundness and concavity decreased. When selecting coarse grained calcareous soil foundation, its compressibility should be considered to avoid rapid loading at the beginning of construction. The irregular shape of coral sand particles is a major feature that distinguishes it significantly from the ordinary terrigenous soil. In order to research the influence of coral sand particle shape on the compression property of coarse grained calcareous soil, different coral sand particles(block, branch, rod, flake) were selected manually. Based on the block particles, mixed with any of the other three different shapes of coral sand particles, the different particle shape ratios were controlled to make coarse grained calcareous soil samples, and the indoor compression tests were complete. The particle shape parameters such as roundness, length-width ratio, flatness and convexity of coral sand particles before and after the test were compared and analyzed. The effects of particle shape on the compressibility were evaluated. The test results show that:(1)The compression modulus of coarse grained calcareous soil with diameters of 10~20mm is from 4 to 5.5MPa, and the rebound coefficient is from 42 to 53; (2)With the increase of the amount of branch, rod or flake particles(0, 10%, 20%, 30%), the compressive modulus of the sample changed slightly, and the rebound coefficient continued to decrease. (3)The stress-strain curves of each loading range include one stable point and three sections which are rapid growth stress section, synchronous increase of stress and strain section, strain growth section; (4)With the increase of the amount of branch particles, the length-width ratio and the convexity of the sample increased gradually, while the roundness and flatness were unchanged substantially. Due to the influence of particle breakage, the length-width ratio and flatness of the sample increased after the test, while the roundness and concavity decreased. When selecting coarse grained calcareous soil foundation, its compressibility should be considered to avoid rapid loading at the beginning of construction.
Particles breakage under normal stress levels distinguishes calcareous sand from other sands and is one of the important properties of calcareous sands. Due to particle breakage, the mechanical behavior of calcareous sands cannot be well simulated using the traditional constitutive models. Therefore, based on the Duncan-Chang E-B model, this paper proposes a constitutive model that can be used for calcareous sands by considering particle breakage. The specific method is as follows. Firstly, this paper uses the relative breakage Br proposed by Hardin to measure the degree of particle breakage. Moreover, the influence of particle breakage on Duncan-Chang model parameters including internal friction angle, secant modulus E50 and bulk modulus B is obtained. Then, the relative breakage Br, which cannot be directly determined in each state, is related to the determinable stress-strain state by the relationship between particle breakage and input energy. Finally, a modified Duncan-Chang E-B model for calcareous sand considering particle breakage is proposed in this paper. In order to verify the accuracy and applicability of the model, this model is used to simulate the triaxial drainage behavior of calcareous sands with four particle sizes. It is shown that the simulation results agree well with the experimental ones, and the modified model is significantly better than the conventional Duncan-Chang E-B model in the case of large particle breakage. Particles breakage under normal stress levels distinguishes calcareous sand from other sands and is one of the important properties of calcareous sands. Due to particle breakage, the mechanical behavior of calcareous sands cannot be well simulated using the traditional constitutive models. Therefore, based on the Duncan-Chang E-B model, this paper proposes a constitutive model that can be used for calcareous sands by considering particle breakage. The specific method is as follows. Firstly, this paper uses the relative breakage Br proposed by Hardin to measure the degree of particle breakage. Moreover, the influence of particle breakage on Duncan-Chang model parameters including internal friction angle, secant modulus E50 and bulk modulus B is obtained. Then, the relative breakage Br, which cannot be directly determined in each state, is related to the determinable stress-strain state by the relationship between particle breakage and input energy. Finally, a modified Duncan-Chang E-B model for calcareous sand considering particle breakage is proposed in this paper. In order to verify the accuracy and applicability of the model, this model is used to simulate the triaxial drainage behavior of calcareous sands with four particle sizes. It is shown that the simulation results agree well with the experimental ones, and the modified model is significantly better than the conventional Duncan-Chang E-B model in the case of large particle breakage.
Dynamic elastic modulus and damping ratio are important mechanical parameters in soil dynamics analysis. Considering the characteristics of heavy-duty railway loads, the dynamic modulus and damping ratio of cement-stabilized expansive soil are less. Based on the background of the railway coal transportation channel(hereinafter referred to as Meng-Hua Railway) in the central area of the city of Tolemon and the central China, the dynamic modulus and damping ratio of 3% and 5%cement reinforced expansive soils were studied and compared with the expanded soil from Dashanzhai expansive soil in Dengzhou City, Nanyang, under the consolidation with different frequencies, confining pressure, ratio and dynamic stress amplitude. The results were compared with expansive soils. The results show that the maximum dynamic modulus of cement modified with 3% and 5%modified expansive soil is about 3-4 times that of expansive soil. When the dynamic strain is less than 0.002, the dynamic elastic modulus has a steep drop and decreases by 70%. In the dynamic elastic modulus-strain curve, when the dynamic strain is greater than 0.002, the decrease is small, and the dynamic elastic modulus tends to be stable with the dynamic strain. The dynamic elastic modulus increases as the confining pressure, the frequency and the cement content increase. Damping ratio decreases as the confining pressure and consolidation ratio increase. At low strain levels, the consolidation ratio is positively correlated with the dynamic modulus. At high strain levels, the consolidation ratio is inversely related to the dynamic modulus. At the same time, the dynamic modulus and damping ratio are normalized and analyzed, and an empirical formula for estimating the dynamic modulus and damping ratio is established. Dynamic elastic modulus and damping ratio are important mechanical parameters in soil dynamics analysis. Considering the characteristics of heavy-duty railway loads, the dynamic modulus and damping ratio of cement-stabilized expansive soil are less. Based on the background of the railway coal transportation channel(hereinafter referred to as Meng-Hua Railway) in the central area of the city of Tolemon and the central China, the dynamic modulus and damping ratio of 3% and 5%cement reinforced expansive soils were studied and compared with the expanded soil from Dashanzhai expansive soil in Dengzhou City, Nanyang, under the consolidation with different frequencies, confining pressure, ratio and dynamic stress amplitude. The results were compared with expansive soils. The results show that the maximum dynamic modulus of cement modified with 3% and 5%modified expansive soil is about 3-4 times that of expansive soil. When the dynamic strain is less than 0.002, the dynamic elastic modulus has a steep drop and decreases by 70%. In the dynamic elastic modulus-strain curve, when the dynamic strain is greater than 0.002, the decrease is small, and the dynamic elastic modulus tends to be stable with the dynamic strain. The dynamic elastic modulus increases as the confining pressure, the frequency and the cement content increase. Damping ratio decreases as the confining pressure and consolidation ratio increase. At low strain levels, the consolidation ratio is positively correlated with the dynamic modulus. At high strain levels, the consolidation ratio is inversely related to the dynamic modulus. At the same time, the dynamic modulus and damping ratio are normalized and analyzed, and an empirical formula for estimating the dynamic modulus and damping ratio is established.
Most of the loess landslides induced by irrigation own obvious sudden characteristics. The deformation and displacement during slope failure process are small and the time of duration is short, which is of great risk. Due to such loess landslides undergo a short time in accelerated deformation stage, it is difficult for traditional monitoring methods, such as GNSS system and crack gauge, to obtain complete monitoring data in accelerated deformation stage and to predict the sudden landslide occurrence. With respect to this problem, a self-adaptive frequency conversion acquisition monitoring method is designed to monitor the deformation of sudden loess landslides, which adjust automatically the frequency sampling according to the speed of landslide deformation. To meet the needs for risk mitigation and management of slope sudden failure, it is of practical significance to develop a self-adaptive frequency conversion acquisition monitoring method and establish a real-time automatic early warning system. The new artificial intelligence by the authors' institute can obtain entire monitoring data in accelerated deformation stage and to predict the sudden failure occurrence time. Taking deformation rate threshold and the improved tangent angle as the early warning parameters of comprehensive warning model, a four-level early warning criterion is established. The real-time automatic early warning of the landslide is realized through the self-developed "real-time monitoring and early warning system of geological hazards". The early warning information is released in the local group defense information platform, which provides a direct gauge for disaster prevention and emergency avoidance. Since 2017, it has been successfully warned six times of loess slope sudden failure on the Heifangtai terrace, which avoided heavy casualties and achieved remarkable disaster prevention and mitigation effect. Most of the loess landslides induced by irrigation own obvious sudden characteristics. The deformation and displacement during slope failure process are small and the time of duration is short, which is of great risk. Due to such loess landslides undergo a short time in accelerated deformation stage, it is difficult for traditional monitoring methods, such as GNSS system and crack gauge, to obtain complete monitoring data in accelerated deformation stage and to predict the sudden landslide occurrence. With respect to this problem, a self-adaptive frequency conversion acquisition monitoring method is designed to monitor the deformation of sudden loess landslides, which adjust automatically the frequency sampling according to the speed of landslide deformation. To meet the needs for risk mitigation and management of slope sudden failure, it is of practical significance to develop a self-adaptive frequency conversion acquisition monitoring method and establish a real-time automatic early warning system. The new artificial intelligence by the authors' institute can obtain entire monitoring data in accelerated deformation stage and to predict the sudden failure occurrence time. Taking deformation rate threshold and the improved tangent angle as the early warning parameters of comprehensive warning model, a four-level early warning criterion is established. The real-time automatic early warning of the landslide is realized through the self-developed "real-time monitoring and early warning system of geological hazards". The early warning information is released in the local group defense information platform, which provides a direct gauge for disaster prevention and emergency avoidance. Since 2017, it has been successfully warned six times of loess slope sudden failure on the Heifangtai terrace, which avoided heavy casualties and achieved remarkable disaster prevention and mitigation effect.
How to use the time schedule in case of heavy precipitation and undertaking intensive excavation of the retaining wall pit, and then upward backfilling the slope as permanent reinforcement, is the priority countermeasure in the tail canal project. The information construction depends on the analysis results of the deformation process and displacement vector relationship, from the primary landslide and then transformed to the cut slope. This paper takes the right bank slope of Gaobei Key Water Control Project as an example. It analyzes the monitoring data during the excavation of retaining wall foundation pit of the tail canal, It obtains the three-dimensional vector space-time variation relations of 55 monitoring points. It reveals the mechanism of clockwise compression-shearing consolidation drainage failure in the process of slope deformation. It bases on the correlation of precipitation data and obtains the corresponding relationship between slope deformation and precipitation, as well as excavation in 4 different stages. The statistical relationship between the average daily displacement rate and the daily precipitation is approximately as v=103.45ln(p)-82.821. The paper infers that during the period of non-strong rainfall, the displacement rate caused by excavation of the slope foot reached 200mm ·d-1, which is the key parameter of information construction. The above failure modes and monitoring analysis results provide a basis for the information construction of retaining wall beside the tail canal. As a result the landslide was mitigated and cut slope was reinforced as designed in a rainy season. How to use the time schedule in case of heavy precipitation and undertaking intensive excavation of the retaining wall pit, and then upward backfilling the slope as permanent reinforcement, is the priority countermeasure in the tail canal project. The information construction depends on the analysis results of the deformation process and displacement vector relationship, from the primary landslide and then transformed to the cut slope. This paper takes the right bank slope of Gaobei Key Water Control Project as an example. It analyzes the monitoring data during the excavation of retaining wall foundation pit of the tail canal, It obtains the three-dimensional vector space-time variation relations of 55 monitoring points. It reveals the mechanism of clockwise compression-shearing consolidation drainage failure in the process of slope deformation. It bases on the correlation of precipitation data and obtains the corresponding relationship between slope deformation and precipitation, as well as excavation in 4 different stages. The statistical relationship between the average daily displacement rate and the daily precipitation is approximately as v=103.45ln(p)-82.821. The paper infers that during the period of non-strong rainfall, the displacement rate caused by excavation of the slope foot reached 200mm ·d-1, which is the key parameter of information construction. The above failure modes and monitoring analysis results provide a basis for the information construction of retaining wall beside the tail canal. As a result the landslide was mitigated and cut slope was reinforced as designed in a rainy season.
Landslide displacement prediction is one of important parts of landslide disaster prevention and mitigation. To improve the accuracy and precision of landslide displacement prediction is emphasis and difficulty. Outliers from monitoring samples are took into account in this research. By ignoring, reserving or correcting outliers to study on which is the best of three ways of landslide displacement prediction with outliers. The Zhujiadian Landslide in Three Gorges Reservoir Region is chosen as the case study on displacement prediction. Based on ARIMA(p, d, q) model, predictions are carried out using the accumulated displacement and the displacement rate time series, respectively. The research results show that: (1) The landslide prediction result with correcting outliers is between ignoring and reserving ones. (2)For ARIMA model, it is more suitable for using the displacement rate time series. (3)The prediction results of "step-like" displacement rates based on ARIMA(1, 0, 1) model for the displacement rate time series with correcting outliers are 79.0mm and 70.2mm in Jun. 2016 and 2017, and accumulated displacement is 1647.7mm until Aug. 2017. Landslide displacement prediction is one of important parts of landslide disaster prevention and mitigation. To improve the accuracy and precision of landslide displacement prediction is emphasis and difficulty. Outliers from monitoring samples are took into account in this research. By ignoring, reserving or correcting outliers to study on which is the best of three ways of landslide displacement prediction with outliers. The Zhujiadian Landslide in Three Gorges Reservoir Region is chosen as the case study on displacement prediction. Based on ARIMA(p, d, q) model, predictions are carried out using the accumulated displacement and the displacement rate time series, respectively. The research results show that: (1) The landslide prediction result with correcting outliers is between ignoring and reserving ones. (2)For ARIMA model, it is more suitable for using the displacement rate time series. (3)The prediction results of "step-like" displacement rates based on ARIMA(1, 0, 1) model for the displacement rate time series with correcting outliers are 79.0mm and 70.2mm in Jun. 2016 and 2017, and accumulated displacement is 1647.7mm until Aug. 2017.
The Nairobi-Malabar railway project is an important part of the "northern corridor" of East Africa. It is the trunk line of economic development in landlocked African countries. The railway line works pass through the rift valley. The volcanic landform, the fault belt and the tension fracture are extremely development. However, there is a lack of research data on railway construction in the rift valley. To study railway lines through the rift valley, firstly, this paper introduces the topography, landform, development mechanism and regional fault distribution of the east African rift valley, and then formulates three major railway routes through the east African rift valley based on the economic control points along the railway. We had compared the terrain and landform traversed by the three major routes, the stratum, fault and ground fractures, the earthquake and volcanic developments, and the adverse geological disasters. Finally, the investment, advantages and disadvantages of each route had been compared, and finally the southern route scheme was recommended. The scheme of the route was approved and adopted by the Kenyan government. At present, the Nairobi Malaba railway is in trial operation, and the practice shows that the selection of the rift section of Nairobi-Malabar railway is relatively successful, which can provide reference for similar projects. The Nairobi-Malabar railway project is an important part of the "northern corridor" of East Africa. It is the trunk line of economic development in landlocked African countries. The railway line works pass through the rift valley. The volcanic landform, the fault belt and the tension fracture are extremely development. However, there is a lack of research data on railway construction in the rift valley. To study railway lines through the rift valley, firstly, this paper introduces the topography, landform, development mechanism and regional fault distribution of the east African rift valley, and then formulates three major railway routes through the east African rift valley based on the economic control points along the railway. We had compared the terrain and landform traversed by the three major routes, the stratum, fault and ground fractures, the earthquake and volcanic developments, and the adverse geological disasters. Finally, the investment, advantages and disadvantages of each route had been compared, and finally the southern route scheme was recommended. The scheme of the route was approved and adopted by the Kenyan government. At present, the Nairobi Malaba railway is in trial operation, and the practice shows that the selection of the rift section of Nairobi-Malabar railway is relatively successful, which can provide reference for similar projects.
This paper takes the Datong-Xi'an passenger transport line subgrade orthogonally crossing ground fissure zone as research object. It establishes the foundation-ground fissure-embankment dynamic calculation model of high-speed railway with the finite element numerical method. It simulates and analyzes the dynamic response characteristics of subgrade on natural foundation with and without ground fissure zone under the action of high-speed train load. The results show that the response of dynamic displacement, acceleration and dynamic stratum stress of subgrade in natural site without ground fissure under train load is basically steady without obvious differences. In ground fissure site, the dynamic displacement of subgrade and the acceleration of embankment body both increases in the hanging wall and decreases in the footwall of active ground fissure zone, and the attenuation amplitude of dynamic displacement and acceleration of the subgrade in the footwall is greater than that of the hanging wall of ground fissure zone in perpendicular direction of train line. The critical influence depth of acceleration induced by ground fissure is about 15m below the ground. The dynamic stress in subgrade reduces in the hanging wall and increases in the footwall of ground fissure. The dynamic stress critical depth of subgrade in ground fissure site is 10m below the ground. The research results can provide scientific basis for the construction of high-speed railway and disaster prevention and mitigation in ground fissure development area in China. This paper takes the Datong-Xi'an passenger transport line subgrade orthogonally crossing ground fissure zone as research object. It establishes the foundation-ground fissure-embankment dynamic calculation model of high-speed railway with the finite element numerical method. It simulates and analyzes the dynamic response characteristics of subgrade on natural foundation with and without ground fissure zone under the action of high-speed train load. The results show that the response of dynamic displacement, acceleration and dynamic stratum stress of subgrade in natural site without ground fissure under train load is basically steady without obvious differences. In ground fissure site, the dynamic displacement of subgrade and the acceleration of embankment body both increases in the hanging wall and decreases in the footwall of active ground fissure zone, and the attenuation amplitude of dynamic displacement and acceleration of the subgrade in the footwall is greater than that of the hanging wall of ground fissure zone in perpendicular direction of train line. The critical influence depth of acceleration induced by ground fissure is about 15m below the ground. The dynamic stress in subgrade reduces in the hanging wall and increases in the footwall of ground fissure. The dynamic stress critical depth of subgrade in ground fissure site is 10m below the ground. The research results can provide scientific basis for the construction of high-speed railway and disaster prevention and mitigation in ground fissure development area in China.
The NSFC proposals and grants of engineering geology field in 2019 are analyzed. The subjects include the engineering geological environment and disaster under the discipline of environmental geoscience and the engineering geology subordinate to the discipline of geology. The number of applications for funding projects in the field of engineering geology has increased rapidly, mainly due to the large increase in applications for General Program, Young Scientists Fund and Regional Science Funds. The number of applications for other types of fund programs remains stable. The statistics of the last ten years show that the peer-review referees well handled the peer-review scale on the proposals. The age structure of applicants for General Program tends to be younger, and that for the Youth Scientists Fund is reasonable. The field of engineering geology has been funded in a number of different project types, showing strong competitiveness. The NSFC proposals and grants of engineering geology field in 2019 are analyzed. The subjects include the engineering geological environment and disaster under the discipline of environmental geoscience and the engineering geology subordinate to the discipline of geology. The number of applications for funding projects in the field of engineering geology has increased rapidly, mainly due to the large increase in applications for General Program, Young Scientists Fund and Regional Science Funds. The number of applications for other types of fund programs remains stable. The statistics of the last ten years show that the peer-review referees well handled the peer-review scale on the proposals. The age structure of applicants for General Program tends to be younger, and that for the Youth Scientists Fund is reasonable. The field of engineering geology has been funded in a number of different project types, showing strong competitiveness.
The Second International Symposium on Marine Engineering Geology(ISMEG 2019)was successfully held from 18 to 20 October 2019 in Dalian, China. It is a global academic symposium on marine engineering geology sponsored by IAEG's Commission for Marine Engineering Geology(C34) and hosted by the State Key Laboratory of Coastal and Offshore Engineering(Dalian University of Technology) under the framework of International Association for Engineering Geology and the Environment(IAEG). The theme of the symposium was the exploration of marine resources and marine engineering geology. The symposium had a total of 10 plenary reports, 21 keynote reports and 71 academic reports focused on seven special topics. They include engineering properties of marine soils, marine geological hazards and preventions, in-situ exploration, monitoring and physical modelling, hydrodynamics and environmental interaction, exploration of gas hydrate, offshore foundations and flow-structure-seabed interaction. As a platform of communication, sharing, cooperation and innovation for marine engineering geological researchers at home and abroad, the International Symposium on Marine Engineering Geology has been successfully held twice in China. The two symposiums affirmed the rapid development of marine engineering geological research in China, and moreover, put forward higher requirements for the high-level achievements and achievements transformation of marine engineering geological research in China. The Second International Symposium on Marine Engineering Geology(ISMEG 2019)was successfully held from 18 to 20 October 2019 in Dalian, China. It is a global academic symposium on marine engineering geology sponsored by IAEG's Commission for Marine Engineering Geology(C34) and hosted by the State Key Laboratory of Coastal and Offshore Engineering(Dalian University of Technology) under the framework of International Association for Engineering Geology and the Environment(IAEG). The theme of the symposium was the exploration of marine resources and marine engineering geology. The symposium had a total of 10 plenary reports, 21 keynote reports and 71 academic reports focused on seven special topics. They include engineering properties of marine soils, marine geological hazards and preventions, in-situ exploration, monitoring and physical modelling, hydrodynamics and environmental interaction, exploration of gas hydrate, offshore foundations and flow-structure-seabed interaction. As a platform of communication, sharing, cooperation and innovation for marine engineering geological researchers at home and abroad, the International Symposium on Marine Engineering Geology has been successfully held twice in China. The two symposiums affirmed the rapid development of marine engineering geological research in China, and moreover, put forward higher requirements for the high-level achievements and achievements transformation of marine engineering geological research in China.
This paer summarizes the 6th International Forum on Opto-Electronic Sensor-Based Monitoring in Geo-Engineering(6th OSMG- 2017)held in Nanjing University on 3-5 November 2017 under the theme"Frontiers and Applications of Infrastructure Monitoring Technologies". Attended by over 350 delegates from nearly 20 countries/regions, the 3-day forum was organized around 35 invited presentations. The forum showed the recent breakthroughs achieved worldwide pertaining to geo-engineering monitoring:(1)opto-electronic demodulation technologies are undergoing numerous developments and the monitoring accuracy and reliability are significantly enhanced; (2)a host of new sensors have been recently developed for geo-engineering monitoring such as smart geotextiles with integrated plastic optical fibers; (3)opto-electronic sensing can provide huge data for health diagnosis of infrastructures including tunnels, dams, nuclear power plants, and bridges, hence insuring the safety operation of these infrastructures; and (4)opto-electronic sensing is playing an increasingly important role in monitoring and early warning of geohazards. Suggested future research includes the need for:(1)cost-effective demodulation techniques for distributed fiber optic sensing technology; (2)special opto-electronic sensors for geo-engineering monitoring and their field installation methods; and (3)real-time huge monitoring data processing and early warning system of natural and anthropogenic hazards. This paer summarizes the 6th International Forum on Opto-Electronic Sensor-Based Monitoring in Geo-Engineering(6th OSMG- 2017)held in Nanjing University on 3-5 November 2017 under the theme"Frontiers and Applications of Infrastructure Monitoring Technologies". Attended by over 350 delegates from nearly 20 countries/regions, the 3-day forum was organized around 35 invited presentations. The forum showed the recent breakthroughs achieved worldwide pertaining to geo-engineering monitoring:(1)opto-electronic demodulation technologies are undergoing numerous developments and the monitoring accuracy and reliability are significantly enhanced; (2)a host of new sensors have been recently developed for geo-engineering monitoring such as smart geotextiles with integrated plastic optical fibers; (3)opto-electronic sensing can provide huge data for health diagnosis of infrastructures including tunnels, dams, nuclear power plants, and bridges, hence insuring the safety operation of these infrastructures; and (4)opto-electronic sensing is playing an increasingly important role in monitoring and early warning of geohazards. Suggested future research includes the need for:(1)cost-effective demodulation techniques for distributed fiber optic sensing technology; (2)special opto-electronic sensors for geo-engineering monitoring and their field installation methods; and (3)real-time huge monitoring data processing and early warning system of natural and anthropogenic hazards.