Online Submission
Manuscript Tracking
Peer Review
Editor Work2023 Vol. 31, No. 1
Previous Issue
2023, 31(1): 1-11.
Abstract
8639KB
This paper aims to study the influence of high temperature on the physical-mechanical properties and acoustic emission characteristics of sandstone. It uses Brazilian splitting test on sandstone treated at 25~900℃. Meanwhile, it exames the changes in tensile strength, volume expansion ratio, mass loss ratio, P-wave velocity, macro and micro failure characteristics, acoustic emission characteristics and other properties in combination with scanning electron microscope(SEM) and acoustic emission(AE). The results show the following four findings. (1)After high temperature treatment, the mass, P-wave velocity, tensile strength and residual tensile strength of sandstone decrease to different degrees, and the volume also expands; (2)In the 200~400℃, the tensile strength decreases greatly, indicating that the threshold temperature of thermal damage is in this range; (3)The failure of sandstone is mainly caused by a single main crack, and the formation of secondary cracks is less and the brittleness of sandstone is more significant with the increase of temperature; (4)The results of SEM show that there are a large number of micro-cracks and micro-pores in the sandstone after the high-temperature treatment. The extension length, opening width, density, connectivity and extended range of the cracks are changed with the increase of temperature, leading to the decrease of mineral integrity; (5)AE characteristics of sandstone after heating are different, showing obvious characteristics of stage. Moreover, the AE activity become more stable with increasing temperature, and the peak value of AE events precedes the occurrence of sandstone failure, which can better monitor the failure of sandstone.
This paper aims to study the influence of high temperature on the physical-mechanical properties and acoustic emission characteristics of sandstone. It uses Brazilian splitting test on sandstone treated at 25~900℃. Meanwhile, it exames the changes in tensile strength, volume expansion ratio, mass loss ratio, P-wave velocity, macro and micro failure characteristics, acoustic emission characteristics and other properties in combination with scanning electron microscope(SEM) and acoustic emission(AE). The results show the following four findings. (1)After high temperature treatment, the mass, P-wave velocity, tensile strength and residual tensile strength of sandstone decrease to different degrees, and the volume also expands; (2)In the 200~400℃, the tensile strength decreases greatly, indicating that the threshold temperature of thermal damage is in this range; (3)The failure of sandstone is mainly caused by a single main crack, and the formation of secondary cracks is less and the brittleness of sandstone is more significant with the increase of temperature; (4)The results of SEM show that there are a large number of micro-cracks and micro-pores in the sandstone after the high-temperature treatment. The extension length, opening width, density, connectivity and extended range of the cracks are changed with the increase of temperature, leading to the decrease of mineral integrity; (5)AE characteristics of sandstone after heating are different, showing obvious characteristics of stage. Moreover, the AE activity become more stable with increasing temperature, and the peak value of AE events precedes the occurrence of sandstone failure, which can better monitor the failure of sandstone.
2023, 31(1): 12-20.
Clay is the main component of loess particle group, and also the most active part of loess activity. The addition of salt makes the agglomeration and physical and mechanical properties of clay in loess obviously different, which also means that salt content plays a dominant role in many factors affecting aggregation. Loess was taken as the research object. The influence and mechanism of salt on the aggregation of clay particles in loess was studied. The loess salted soil was taken as the research object to study the influence and mechanism of salt on the aggregation of clay particles in loess. In this paper, the artificial sulfate saline soils with different mass ratios(0, 0.3%, 0.5%, 3%, 5.0%, 8.0%) were prepared on the basis of salt washing. Based on the grain size analysis and Atterberg limits tests, the macroscopic token of sulfate on the aggregation of clay particles was studied. Based on the compaction test, the microstructure and physicochemical mechanisms of the aggregation of clay particles were studied by combining XRD, SEM, EDS and BET. The results show that with the increase of salt content, the content of clay decreases, the liquid limit and plasticity index decrease, and the plasticity limit remains unchanged. When the salt content is more than 0.3%(saline soil stage), with the increase of salt content, too much sodium sulfate can not be dissolved and precipitated in the form of crystal. The precipitated crystal further absorbs water molecules and finally forms mirabilite crystal, the volume can increase sharply, resulting in the decrease of the maximum dry density, and the strong hydration can increase the optimum water content. Due to the agglomeration of sulfate on clay, when the salt content increases, the diffraction peak of sodium sulfate crystal is enhanced, the content of aggregate increases, and the specific surface area decreases, and compressing and thinning the diffusion layer, which leads to a decrease in the liquid limit and plasticity index.
Clay is the main component of loess particle group, and also the most active part of loess activity. The addition of salt makes the agglomeration and physical and mechanical properties of clay in loess obviously different, which also means that salt content plays a dominant role in many factors affecting aggregation. Loess was taken as the research object. The influence and mechanism of salt on the aggregation of clay particles in loess was studied. The loess salted soil was taken as the research object to study the influence and mechanism of salt on the aggregation of clay particles in loess. In this paper, the artificial sulfate saline soils with different mass ratios(0, 0.3%, 0.5%, 3%, 5.0%, 8.0%) were prepared on the basis of salt washing. Based on the grain size analysis and Atterberg limits tests, the macroscopic token of sulfate on the aggregation of clay particles was studied. Based on the compaction test, the microstructure and physicochemical mechanisms of the aggregation of clay particles were studied by combining XRD, SEM, EDS and BET. The results show that with the increase of salt content, the content of clay decreases, the liquid limit and plasticity index decrease, and the plasticity limit remains unchanged. When the salt content is more than 0.3%(saline soil stage), with the increase of salt content, too much sodium sulfate can not be dissolved and precipitated in the form of crystal. The precipitated crystal further absorbs water molecules and finally forms mirabilite crystal, the volume can increase sharply, resulting in the decrease of the maximum dry density, and the strong hydration can increase the optimum water content. Due to the agglomeration of sulfate on clay, when the salt content increases, the diffraction peak of sodium sulfate crystal is enhanced, the content of aggregate increases, and the specific surface area decreases, and compressing and thinning the diffusion layer, which leads to a decrease in the liquid limit and plasticity index.
2023, 31(1): 21-31.
It is an important task to identify the moisture content of loess from deep layers in situ, which establishes underpinnings to reveal the disaster mechanism for major loess projects and provide a warn for the disaster. Based on convolutional neural network, an intelligent identification method is proposed to detect moisture content of loess in-situ by holes. An indoor experimental platform was built to collect the image information of 7 kinds of loess with different water contents at an interval of 2%, which was used to generate the data set for neural network training. Under the transfer learning framework, multiple types of transfer convolutional neural network models were established. The identification accuracy of moisture content of loess was compared and analyzed for different transfer learning models, and their reliability and effectiveness were evaluated by confusion matrix visualization. Comparative results show that: for the established image data sets of moisture content of loess, the test accuracy rate of the deep migration network models based on VGG19、ResNet101、DesNe201 are below 90%, which unveils an over-fitting phenomenon. If this method was applied directly, there would be a false positive rate of over 10%. The lightweight migration network models based on Xception, MobileNet, and NASNetMobile have good generalization ability after transfer training, and their test accuracies are above 90%. Among them, the test accuracy of the migration network model based on Xception achieves highest gains up to 94.6%. The lightweight migration network model achieves high recognition accuracy and fast calculation speed simultaneously, which provides a favorable algorithm support for the development of a robot vision system with in-situ detection of quality information of loess.
It is an important task to identify the moisture content of loess from deep layers in situ, which establishes underpinnings to reveal the disaster mechanism for major loess projects and provide a warn for the disaster. Based on convolutional neural network, an intelligent identification method is proposed to detect moisture content of loess in-situ by holes. An indoor experimental platform was built to collect the image information of 7 kinds of loess with different water contents at an interval of 2%, which was used to generate the data set for neural network training. Under the transfer learning framework, multiple types of transfer convolutional neural network models were established. The identification accuracy of moisture content of loess was compared and analyzed for different transfer learning models, and their reliability and effectiveness were evaluated by confusion matrix visualization. Comparative results show that: for the established image data sets of moisture content of loess, the test accuracy rate of the deep migration network models based on VGG19、ResNet101、DesNe201 are below 90%, which unveils an over-fitting phenomenon. If this method was applied directly, there would be a false positive rate of over 10%. The lightweight migration network models based on Xception, MobileNet, and NASNetMobile have good generalization ability after transfer training, and their test accuracies are above 90%. Among them, the test accuracy of the migration network model based on Xception achieves highest gains up to 94.6%. The lightweight migration network model achieves high recognition accuracy and fast calculation speed simultaneously, which provides a favorable algorithm support for the development of a robot vision system with in-situ detection of quality information of loess.
2023, 31(1): 32-42.
This paper aims to characterize the swelling-shrinkage and slaking features of the expansive red clay under the different initial moisture content condition. The weak expansive red clay from high-speed railway tunnel in Qingyang, Gansu Province, were tested with swelling-shrinkage and slaking tests in laboratory. Its slaking differentiation was examined through video, photographs, and images by optical and scanning electron microscope. The swelling-shrinkage, slaking changes and its fractal features of the expansive red clay were studied under different moisture contents of 3%, 8%, 13%, and 18%, respectively. Total expansion capacity has a piecewise function relationship with the initial moisture content, acquiring that the minimum swelling-shrinkage change value is located at 11.6% moisture content. The slaking time is earlier and slaking rate is increased with decreasing moisture content. The fracture development degree of expansive red clay in slaking test prensents the characteristics of rapid increase, slow increase, and stable trend with increasing immersion time. The maximum crack development degree can be up to 4.6 under the minimum moisture content condition. Maximum crack width index value is upward increased in the first half immersion time, but oscillatory decreased in rest parts of immersion time. The expansive red clay with low moisture content is more prone to macroscopic slaking than that with high moisture content, which is mainly due to the scattered agglomeration units and high percentage micro-pores in the expansive red clay under the low moisture content condition. The fractal dimension of porosity is positively correlated as a quadratic function with the initial moisture content, which resulted in the slaking more complete and slaking time shorter with lower fractal dimension.
This paper aims to characterize the swelling-shrinkage and slaking features of the expansive red clay under the different initial moisture content condition. The weak expansive red clay from high-speed railway tunnel in Qingyang, Gansu Province, were tested with swelling-shrinkage and slaking tests in laboratory. Its slaking differentiation was examined through video, photographs, and images by optical and scanning electron microscope. The swelling-shrinkage, slaking changes and its fractal features of the expansive red clay were studied under different moisture contents of 3%, 8%, 13%, and 18%, respectively. Total expansion capacity has a piecewise function relationship with the initial moisture content, acquiring that the minimum swelling-shrinkage change value is located at 11.6% moisture content. The slaking time is earlier and slaking rate is increased with decreasing moisture content. The fracture development degree of expansive red clay in slaking test prensents the characteristics of rapid increase, slow increase, and stable trend with increasing immersion time. The maximum crack development degree can be up to 4.6 under the minimum moisture content condition. Maximum crack width index value is upward increased in the first half immersion time, but oscillatory decreased in rest parts of immersion time. The expansive red clay with low moisture content is more prone to macroscopic slaking than that with high moisture content, which is mainly due to the scattered agglomeration units and high percentage micro-pores in the expansive red clay under the low moisture content condition. The fractal dimension of porosity is positively correlated as a quadratic function with the initial moisture content, which resulted in the slaking more complete and slaking time shorter with lower fractal dimension.
2023, 31(1): 43-50.
A large number of tests have shown that after the saturated soil sample enters the hygroscopic stage in the dehumidification process, residual gas would be distributed in the pore of the soil sample in the form of closed bubbles in the high-saturation area. At this time, the soil sample shows great compressibility. When the matric suction is 0kPa after the hygroscopic process, the soil sample would not reach full saturation state. Wei et al. (2008) put forward the constitutive model of unsaturated soil without considering the influence of the residual gas content, and considering the soil sample after moisture absorption process could still achieve fully saturated state, which has certain deviation with the actual situation. In order to simulate the real situation more accurately, this paper proposes a modified constitutive model for unsaturated soils with different residual gas contents. The modified model is based on the theory of capillary hysteresis internal variables and the hydraulic coupling constitutive model for unsaturated soils. The modified model is verified with the measured data and can well simulate the influence of any wet and dry path on the mechanical properties of unsaturated soil.
A large number of tests have shown that after the saturated soil sample enters the hygroscopic stage in the dehumidification process, residual gas would be distributed in the pore of the soil sample in the form of closed bubbles in the high-saturation area. At this time, the soil sample shows great compressibility. When the matric suction is 0kPa after the hygroscopic process, the soil sample would not reach full saturation state. Wei et al. (2008) put forward the constitutive model of unsaturated soil without considering the influence of the residual gas content, and considering the soil sample after moisture absorption process could still achieve fully saturated state, which has certain deviation with the actual situation. In order to simulate the real situation more accurately, this paper proposes a modified constitutive model for unsaturated soils with different residual gas contents. The modified model is based on the theory of capillary hysteresis internal variables and the hydraulic coupling constitutive model for unsaturated soils. The modified model is verified with the measured data and can well simulate the influence of any wet and dry path on the mechanical properties of unsaturated soil.
2023, 31(1): 51-59.
This paper took the soil samples in Qian'an area of Jilin Province as the research object and tested them with the dispersion test and scanning electron microscope(SEM)test. The fissures of soil samples were quantitatively treated by MATLAB image processing software and CIAS fissures quantitative analysis program. The dispersion variation characteristics and micro mechanism of original and modified soil samples under the freeze-thaw cycle condition were explored and the relationship between soil sample dispersion and fissure parameters was analyzed. The results show that: (1)The dispersion of the samples without alum modification increases with the increase of freeze-thaw cycles, while the dispersion of the samples with alum modification does not change under the condition of limited 20 freeze-thaw cycles. (2)The structural unit of soil samples is broken under the action of freeze-thaw cycle, which increases the fine-grained content in the soil sample, thus enhancing the dispersion of the soil. Meantime, the newly formed fissures cut soil into blocks of different sizes and shapes, which further increases the dispersion of the soil. (3)Among the fissure parameters, the fractal dimension of fissures has a good correlation with the grade value of soil dispersion, followed by the fissures rate. (4)The aluminum ion in alum replaces the sodium ion on the surface of the soil particles, increases the attraction between the soil particles, thus reduces the dispersion of the soil, and the dispersion of the sample is less affected by the freeze-thaw cycle conditions. Therefore, alum can be used as a good modifier for the treatment of the seasonally frozen differentiated bulk soil.
This paper took the soil samples in Qian'an area of Jilin Province as the research object and tested them with the dispersion test and scanning electron microscope(SEM)test. The fissures of soil samples were quantitatively treated by MATLAB image processing software and CIAS fissures quantitative analysis program. The dispersion variation characteristics and micro mechanism of original and modified soil samples under the freeze-thaw cycle condition were explored and the relationship between soil sample dispersion and fissure parameters was analyzed. The results show that: (1)The dispersion of the samples without alum modification increases with the increase of freeze-thaw cycles, while the dispersion of the samples with alum modification does not change under the condition of limited 20 freeze-thaw cycles. (2)The structural unit of soil samples is broken under the action of freeze-thaw cycle, which increases the fine-grained content in the soil sample, thus enhancing the dispersion of the soil. Meantime, the newly formed fissures cut soil into blocks of different sizes and shapes, which further increases the dispersion of the soil. (3)Among the fissure parameters, the fractal dimension of fissures has a good correlation with the grade value of soil dispersion, followed by the fissures rate. (4)The aluminum ion in alum replaces the sodium ion on the surface of the soil particles, increases the attraction between the soil particles, thus reduces the dispersion of the soil, and the dispersion of the sample is less affected by the freeze-thaw cycle conditions. Therefore, alum can be used as a good modifier for the treatment of the seasonally frozen differentiated bulk soil.
2023, 31(1): 60-67.
Active heating optical fiber method(AHFO)can realize the distributed measurement of soil moisture content in situ. But due to the complex environment of the site, the test results obtained by the interpretation of the existing moisture content calculation model are prone to large errors. Based on the experimental research, this paper explored the effect of soil dry density on the calculation of water content of AHFO method, and introduced support vector regression(SVR)algorithm into the calculation model of water content. The numerical result was compared with the traditional calculation model. The research results show that the dry density of the soil is an important factor that affects the accuracy of the water content calculation model. The larger the dry density fluctuation, the larger the calculation error of the traditional calculation model. The higher the soil content, the lower the sensitivity of the calculation model. Compared with the traditional water content calculation model, the radial basis kernel support vector regression method considering the influence of dry density has a higher calculation accuracy, and it is recommended to be applied in the test of the water content AHFO method.
Active heating optical fiber method(AHFO)can realize the distributed measurement of soil moisture content in situ. But due to the complex environment of the site, the test results obtained by the interpretation of the existing moisture content calculation model are prone to large errors. Based on the experimental research, this paper explored the effect of soil dry density on the calculation of water content of AHFO method, and introduced support vector regression(SVR)algorithm into the calculation model of water content. The numerical result was compared with the traditional calculation model. The research results show that the dry density of the soil is an important factor that affects the accuracy of the water content calculation model. The larger the dry density fluctuation, the larger the calculation error of the traditional calculation model. The higher the soil content, the lower the sensitivity of the calculation model. Compared with the traditional water content calculation model, the radial basis kernel support vector regression method considering the influence of dry density has a higher calculation accuracy, and it is recommended to be applied in the test of the water content AHFO method.
2023, 31(1): 68-77.
The creep of the aquifer during ground subsidence cannot be ignored. This paper examines the effects of particle size, grading, and particle shape on the creep behaviour of quartz sand. The mechanism of creep is qualitatively and quantitatively analyzed from a mesoscopic perspective by establishing a relationship with macroscopic deformation. The results show that the creep process of sand is divided into three stages: stable creep, decelerating creep, and decay creep. The particle size, gradation, and particle shape of sand affect the creep behaviour as follows: the larger particle size, the better grading, and the more complex particle shape, may induce greater creep rate at any moment, as well as the greater the final creep strain. Sand mesostructured parameters have good correlations with the creep characteristics as follows: the larger final creep strain of sand may induce a higher degree of particle breakage, the greater final average shape factor of the particles, as well as the greater change in porosity and the greater final area probability. On this basis, the creep potential evaluation index of sand soil is introduced to evaluate the creep potential of different sand layers in ground settlement by using the characteristics of sand particles and pores.
The creep of the aquifer during ground subsidence cannot be ignored. This paper examines the effects of particle size, grading, and particle shape on the creep behaviour of quartz sand. The mechanism of creep is qualitatively and quantitatively analyzed from a mesoscopic perspective by establishing a relationship with macroscopic deformation. The results show that the creep process of sand is divided into three stages: stable creep, decelerating creep, and decay creep. The particle size, gradation, and particle shape of sand affect the creep behaviour as follows: the larger particle size, the better grading, and the more complex particle shape, may induce greater creep rate at any moment, as well as the greater the final creep strain. Sand mesostructured parameters have good correlations with the creep characteristics as follows: the larger final creep strain of sand may induce a higher degree of particle breakage, the greater final average shape factor of the particles, as well as the greater change in porosity and the greater final area probability. On this basis, the creep potential evaluation index of sand soil is introduced to evaluate the creep potential of different sand layers in ground settlement by using the characteristics of sand particles and pores.
2023, 31(1): 78-89.
The contact surface of the silt soil and the new fill in the raising earth dam from upstream is the weak part of the whole dam body. This paper studied the progressive shear failure characteristics of the contact interface under different working conditions. It took the raising earth dam project from upstream deposited mud in Nanchuan Reservoir, Xiji County, the southern mountainous area of Ningxia, China as the research object. On the basis of improving the conventional strain-type direct shear instrument, using the electron microscope scanning technology, the microscopic analysis of the progressive shear of the contact interface was explained by controlling the shear displacement increment. Finally, the stepwise regression analysis method was used to obtain the significant variable of the micro-structure that affected the strength of the contact interface. Their regression equation was established. The results show that the silt soil in different compaction states causes interface particle cementation and structural changes, which is the main reason for increasing the interface shear strength. There is an interface "optimal adhesion" state. Meanwhile, with the increase of shear displacement, the interfacial soil particles are gradually developed into a flaky structure arranged in face-to-face and edge-to-face contact orientation from the independently distributed single-grain structure contact form. Finally they formed an incompressible block shaped pellet structure. And the change law of interface pore micro-structure parameters is related to the change of macroscopic cohesion and internal friction angle. Therefore, the results of this study can provide a certain reference for the construction of silt surface dam.
The contact surface of the silt soil and the new fill in the raising earth dam from upstream is the weak part of the whole dam body. This paper studied the progressive shear failure characteristics of the contact interface under different working conditions. It took the raising earth dam project from upstream deposited mud in Nanchuan Reservoir, Xiji County, the southern mountainous area of Ningxia, China as the research object. On the basis of improving the conventional strain-type direct shear instrument, using the electron microscope scanning technology, the microscopic analysis of the progressive shear of the contact interface was explained by controlling the shear displacement increment. Finally, the stepwise regression analysis method was used to obtain the significant variable of the micro-structure that affected the strength of the contact interface. Their regression equation was established. The results show that the silt soil in different compaction states causes interface particle cementation and structural changes, which is the main reason for increasing the interface shear strength. There is an interface "optimal adhesion" state. Meanwhile, with the increase of shear displacement, the interfacial soil particles are gradually developed into a flaky structure arranged in face-to-face and edge-to-face contact orientation from the independently distributed single-grain structure contact form. Finally they formed an incompressible block shaped pellet structure. And the change law of interface pore micro-structure parameters is related to the change of macroscopic cohesion and internal friction angle. Therefore, the results of this study can provide a certain reference for the construction of silt surface dam.
2023, 31(1): 90-101.
This paper used the variable head permeability test and measured the hydraulic conductivity values of the mixtures of quartz powder and bentonite in distilled water and NaCl and CaCl2 solution with different concentrations. It further used the magnetic resonance test(MRI) and the environmental scanning electron microscope(ESEM) and analyzed the pore distribution characteristics of the mixture saturated with different pore fluid salinity. It investigated the effect of pore fluid salinity and bentonite content on the hydraulic conductivity of the mixtures. The results show that the hydraulic conductivity of the mixture of quartz powder increases obviously under the action of salt solution, and the pore distribution also has obvious difference. At last, using the concept of clay porosity ratio(eb) was adopted and established a new characterization formula of hydraulic conductivity of quartz powder bentonite mixture under the action of salt solution. Compared with the existing formula, the new formula can better predict the hydraulic conductivity of quartz powder-bentonite mixture under the action of salt solution.
This paper used the variable head permeability test and measured the hydraulic conductivity values of the mixtures of quartz powder and bentonite in distilled water and NaCl and CaCl2 solution with different concentrations. It further used the magnetic resonance test(MRI) and the environmental scanning electron microscope(ESEM) and analyzed the pore distribution characteristics of the mixture saturated with different pore fluid salinity. It investigated the effect of pore fluid salinity and bentonite content on the hydraulic conductivity of the mixtures. The results show that the hydraulic conductivity of the mixture of quartz powder increases obviously under the action of salt solution, and the pore distribution also has obvious difference. At last, using the concept of clay porosity ratio(eb) was adopted and established a new characterization formula of hydraulic conductivity of quartz powder bentonite mixture under the action of salt solution. Compared with the existing formula, the new formula can better predict the hydraulic conductivity of quartz powder-bentonite mixture under the action of salt solution.
2023, 31(1): 102-112.
This paper investigates the relationship between the mechanical strength of the cement-slag-fly ash solidified silt excited by gypsum and the evolution of the water conversion process, and aims to essentially reveal the curing mechanism. Both the unconfined compressive strength test(UCS) and direct shear strength test(DST)were conducted to explore the effects of cementslagfly ash ratio, curing agent dosage and curing age on the strength of solidified silt. In addition, the nuclear magnetic resonance(NMR)relaxation analysis, X-ray diffraction(XRD) and scanning electron microscopy(SEM)were applied to observe the soil-water characteristics and analyze the mineral composition and the microstructure of hydration products. From the test results, the functional relationships among unconfined compression strength(qu), shear strength parameters(c, tan φ) and the combined water content(Cw)were established. Results show that during 14 days of age, the strength of solidified soil with a higher cement ratio(20%) is significantly higher than that of the low cement ratio(5%). The early developed strength effect can be attributed to hydrate formation and the greatly increasing amount of combined water. After 14 days, the strength of low cement solidified soil increases rapidly and exceeds the strength of high cement solidified soil. From the perspective of macro-mechanical strength in the specimen with higher cement content(20%), the strength parameters(qu, c, tan φ)all show a linear growth relationship with curing age(lg t), while the specimen with low cement content(5%)has a power function relationship with lg t. In contrast, from the perspective of microscopic water conversion, the relationship among the combined water content Cw, the compressive strength and the shear strength are identical in high and low cement ratio solidified soil, where, qu-Cw and tan φ-Cw increase as a power function, and c-Cw exists a linear relationship. The mechanical strength of solidified soil is not only related to the amount of combined water, but also to the structure of hydrate. The flocculated hydrate C-A-S-H gradually forms a spatial network structure, which makes the micropore structure denser and reduces the porosity.
This paper investigates the relationship between the mechanical strength of the cement-slag-fly ash solidified silt excited by gypsum and the evolution of the water conversion process, and aims to essentially reveal the curing mechanism. Both the unconfined compressive strength test(UCS) and direct shear strength test(DST)were conducted to explore the effects of cementslagfly ash ratio, curing agent dosage and curing age on the strength of solidified silt. In addition, the nuclear magnetic resonance(NMR)relaxation analysis, X-ray diffraction(XRD) and scanning electron microscopy(SEM)were applied to observe the soil-water characteristics and analyze the mineral composition and the microstructure of hydration products. From the test results, the functional relationships among unconfined compression strength(qu), shear strength parameters(c, tan φ) and the combined water content(Cw)were established. Results show that during 14 days of age, the strength of solidified soil with a higher cement ratio(20%) is significantly higher than that of the low cement ratio(5%). The early developed strength effect can be attributed to hydrate formation and the greatly increasing amount of combined water. After 14 days, the strength of low cement solidified soil increases rapidly and exceeds the strength of high cement solidified soil. From the perspective of macro-mechanical strength in the specimen with higher cement content(20%), the strength parameters(qu, c, tan φ)all show a linear growth relationship with curing age(lg t), while the specimen with low cement content(5%)has a power function relationship with lg t. In contrast, from the perspective of microscopic water conversion, the relationship among the combined water content Cw, the compressive strength and the shear strength are identical in high and low cement ratio solidified soil, where, qu-Cw and tan φ-Cw increase as a power function, and c-Cw exists a linear relationship. The mechanical strength of solidified soil is not only related to the amount of combined water, but also to the structure of hydrate. The flocculated hydrate C-A-S-H gradually forms a spatial network structure, which makes the micropore structure denser and reduces the porosity.
2023, 31(1): 113-123.
MICP technology cements loose soil particles into a stone body with a certain strength through the induced calcium carbonate. The morphology, size and crystal type of calcium carbonate would affect its filling and cementing effect in the soil, and then affect the mechanical properties of the cemented soil. On the basis of the related research about the reinforcement of the adverse soil mass by MICP technology, we screened the urease-producing bacteria from the soil in the southern moist heat areas for ultraviolet mutagenesis treatment. Then we selected the bacteria after UV mutagenesis, and got the mutant strain YB7 with high urease production. After that, we applied the mutant strain YB7 to the MICP laboratory grouting test of four soil samples. Combined with scanning electron microscope and energy spectrometer, we compared and analyzed the crystallization phenomenon of calcium carbonate in each sample. Finally, we carried out the direct shear test and uniaxial compression test on the grouting samples of the mutant strain YB7. Combining macroscopic mechanical characteristics and mesoscopic growth characteristics analysis of calcium carbonate, we studied the effect of the mutant strain YB7 on soil reinforcement systematically. The results showed that the novel urease producing bacteria in the southern warm wet area are feasible to reinforce the poor soil, but the structure of the soil can affect the formation of calcium carbonate. The formation effect of calcium carbonate in the soil with suitable particle gradation and suitable mineral morphology is better, and the cementation effect of the corresponding grouting sample is also better. The structure of the soil, the growth of calcium carbonate, and the cementation effect between the calcium carbonate and the soil particles can affect the mechanical properties of the sample. The results can provide a research basis for the further promotion and application of this technology.
MICP technology cements loose soil particles into a stone body with a certain strength through the induced calcium carbonate. The morphology, size and crystal type of calcium carbonate would affect its filling and cementing effect in the soil, and then affect the mechanical properties of the cemented soil. On the basis of the related research about the reinforcement of the adverse soil mass by MICP technology, we screened the urease-producing bacteria from the soil in the southern moist heat areas for ultraviolet mutagenesis treatment. Then we selected the bacteria after UV mutagenesis, and got the mutant strain YB7 with high urease production. After that, we applied the mutant strain YB7 to the MICP laboratory grouting test of four soil samples. Combined with scanning electron microscope and energy spectrometer, we compared and analyzed the crystallization phenomenon of calcium carbonate in each sample. Finally, we carried out the direct shear test and uniaxial compression test on the grouting samples of the mutant strain YB7. Combining macroscopic mechanical characteristics and mesoscopic growth characteristics analysis of calcium carbonate, we studied the effect of the mutant strain YB7 on soil reinforcement systematically. The results showed that the novel urease producing bacteria in the southern warm wet area are feasible to reinforce the poor soil, but the structure of the soil can affect the formation of calcium carbonate. The formation effect of calcium carbonate in the soil with suitable particle gradation and suitable mineral morphology is better, and the cementation effect of the corresponding grouting sample is also better. The structure of the soil, the growth of calcium carbonate, and the cementation effect between the calcium carbonate and the soil particles can affect the mechanical properties of the sample. The results can provide a research basis for the further promotion and application of this technology.
STUDY ON MECHANICAL PROPERTIES OF LARGE DEFORMATION OF SOLIDIFIED LIGHTWEIGHT SOIL WITH SODA RESIDUE
2023, 31(1): 124-133.
People stacked or discharged soda residue into the sea directly, which caused environment pollution. It is imperative to convert alkali slag into geotechnical materials that can be directly used in engineering and realize waste utilization. In this paper, we used the 7-day unconfined compressive strength as an index to determine the optimal ratio of coastal soft soil, alkali slag, cement, quicklime, fly ash and self-made foaming agent. These materials were selected to make solidified lightweight soil with soda residue. We conducted indoor experiment on the new mixture. The results show that the solidified light soil with soda residue has strong structural properties. After the curing age exceeds 28 days, the increase in unconfined compressive strength slows down, and 28 days can be regarded as the critical curing time. The large-deformation mechanical properties of the alkali slag light solidified soil were studied with the ring shear. Under static load and the same normal stress, the peak strength and residual strength of the sample increase with the increase of the density, and the softening phenomenon is also greater obvious. At the same density, with the increase of normal stress, both the peak strength and residual strength increase, but the softening is less obvious. Under dynamic load, when the maximum normal stress is greater than the yield stress of the soil structure, the amplitude, frequency and vibration frequency have a greater impact on the residual strength of the sample. This research provides a reference for the effective treatment of alkali slag and has certain engineering application value.
People stacked or discharged soda residue into the sea directly, which caused environment pollution. It is imperative to convert alkali slag into geotechnical materials that can be directly used in engineering and realize waste utilization. In this paper, we used the 7-day unconfined compressive strength as an index to determine the optimal ratio of coastal soft soil, alkali slag, cement, quicklime, fly ash and self-made foaming agent. These materials were selected to make solidified lightweight soil with soda residue. We conducted indoor experiment on the new mixture. The results show that the solidified light soil with soda residue has strong structural properties. After the curing age exceeds 28 days, the increase in unconfined compressive strength slows down, and 28 days can be regarded as the critical curing time. The large-deformation mechanical properties of the alkali slag light solidified soil were studied with the ring shear. Under static load and the same normal stress, the peak strength and residual strength of the sample increase with the increase of the density, and the softening phenomenon is also greater obvious. At the same density, with the increase of normal stress, both the peak strength and residual strength increase, but the softening is less obvious. Under dynamic load, when the maximum normal stress is greater than the yield stress of the soil structure, the amplitude, frequency and vibration frequency have a greater impact on the residual strength of the sample. This research provides a reference for the effective treatment of alkali slag and has certain engineering application value.
2023, 31(1): 134-144.
Owing to the unprompted and short time span of natural hazards, such as rockfalls and rockslides, it is difficult to conduct real-time monitoring and rapid event analysis. Correspondently, environmental seismology can well solve those defects. Based on the analysis of emitted seismic signal, the characteristics of rockfalls or landslides including volume, duration time and kinetics parameters can quickly be obtained. We conducted a series of laboratory experiments simulating the process of granular flow impact the ground. Then, the correlations between the seismic parameters and the initial condition and kinetic parameters of granular flow were studied via the analysis of recorded seismic signal during experiments. Experimental results showed that:(1)The bandwidth of seismic signal gradually decreases as the volume of granular flow increases; (2)The peak ground acceleration, duration time, Arias intensity and the seismic energy are gradually increasing with the increasing of granular volume, which have good correlations; (3)The ratio between the seismic energy and the potential energy lost range from 3.09×10-2 to 7.2×10-1 and mostly increases with increasing in the granular flow volume. In this paper, we established the relationship between the characteristic parameters of landquake and the initial conditions as well as kinematic parameters of granular flow, which provides a theoretical basis for the monitoring and emergency response of mountainous rockfalls and landslides.
Owing to the unprompted and short time span of natural hazards, such as rockfalls and rockslides, it is difficult to conduct real-time monitoring and rapid event analysis. Correspondently, environmental seismology can well solve those defects. Based on the analysis of emitted seismic signal, the characteristics of rockfalls or landslides including volume, duration time and kinetics parameters can quickly be obtained. We conducted a series of laboratory experiments simulating the process of granular flow impact the ground. Then, the correlations between the seismic parameters and the initial condition and kinetic parameters of granular flow were studied via the analysis of recorded seismic signal during experiments. Experimental results showed that:(1)The bandwidth of seismic signal gradually decreases as the volume of granular flow increases; (2)The peak ground acceleration, duration time, Arias intensity and the seismic energy are gradually increasing with the increasing of granular volume, which have good correlations; (3)The ratio between the seismic energy and the potential energy lost range from 3.09×10-2 to 7.2×10-1 and mostly increases with increasing in the granular flow volume. In this paper, we established the relationship between the characteristic parameters of landquake and the initial conditions as well as kinematic parameters of granular flow, which provides a theoretical basis for the monitoring and emergency response of mountainous rockfalls and landslides.
2023, 31(1): 145-153.
On June 24,2017,a large rockslide occurred in Xinmo Village,Maoxian County,Sichuan Province. In approximate 2 minutes,the rockslide traveled with more than 2500 m horizontally. The field investigation indicates that the kinetic process of the Xinmo rockslide was divided into four stages: the initiation of ejection,flying,scraping,stopping and accumulating. To investigate the possible initiation mechanism,we carried out a physical model test. Monitoring data of rockslide acceleration showed that the sliding body was subjected to a shaking force in the direction normal to the rupture surface,and the value of acceleration was up to 0.94g when the locked segment is broken. The failure behaviours show that the strong vibration effects triggered by the release of strain energy at the same instant within the brittle locked segment. and a shaking force played an important role in the initial stage of Xinmo rockslide. Under the dynamic model,the rockslide ejected along the 15.5° direction to the horizontal plane. Considering the strong vibration effects,the software Rockfall was used to simulate and analyze the motion characteristics of the sliding rock by assuming a variety of initial velocities(at 0,10 20,30,40 and 50 m ·s-1). It is observed that the rock avalanches arrived at the opposite side of the Songping gully,when the values of initial velocity were larger than 30 m ·s-1. Furthermore,we estimated the total duration of the main sliding process and the mean value of the velocity of the mobile rock mass. The estimation results are about 60 s and 45 m ·s-1,respectively.
On June 24,2017,a large rockslide occurred in Xinmo Village,Maoxian County,Sichuan Province. In approximate 2 minutes,the rockslide traveled with more than 2500 m horizontally. The field investigation indicates that the kinetic process of the Xinmo rockslide was divided into four stages: the initiation of ejection,flying,scraping,stopping and accumulating. To investigate the possible initiation mechanism,we carried out a physical model test. Monitoring data of rockslide acceleration showed that the sliding body was subjected to a shaking force in the direction normal to the rupture surface,and the value of acceleration was up to 0.94g when the locked segment is broken. The failure behaviours show that the strong vibration effects triggered by the release of strain energy at the same instant within the brittle locked segment. and a shaking force played an important role in the initial stage of Xinmo rockslide. Under the dynamic model,the rockslide ejected along the 15.5° direction to the horizontal plane. Considering the strong vibration effects,the software Rockfall was used to simulate and analyze the motion characteristics of the sliding rock by assuming a variety of initial velocities(at 0,10 20,30,40 and 50 m ·s-1). It is observed that the rock avalanches arrived at the opposite side of the Songping gully,when the values of initial velocity were larger than 30 m ·s-1. Furthermore,we estimated the total duration of the main sliding process and the mean value of the velocity of the mobile rock mass. The estimation results are about 60 s and 45 m ·s-1,respectively.
2023, 31(1): 154-164.
In 2017, the initiation of Xinmocun landslide in Maoxian, Sichuan had obvious "locking section" effect. On the basis of field investigation, we adopt high strength brittle material to make slope model, and used it to carry out physical simulation test for reproducing the process of landslide deformation and failure. We analyze the initiation mechanism of Xinmocun landside under the control of the anti-dip joint and the potential slip fracture surface. We combined the deformation and failure characteristics of the rock mass of the "locking section", and the deformation monitoring data and acoustic emission signals. We found some precursors of landslide. The experiment showed the follows: Due to the push of the upper slide, the rock mass of the "locking section" in the front of the sliding source area expanded and sheared along the anti-dip joints, which formed a bulging fracture on the slope surface and a downslope tension crack surface in the interior of the slope. Next the two groups of fractures were combined to form a stepped failure surface, which formed the boundary condition of rock mass failure in the "locking section". Under the pushing of the upper slide, the middle part of the slope formed the ejection block with high speed. Within the meantime, the lower dumping block toppled over the outside. Subsequently the landslide failed. Therefore, we conclude that the bulging cracks that were formed along the anti-dip joints can be regarded as the macroscopic precursors of this kind of landslides. At the same time, in the yield stage of the "locking section", the displacement ratio between the slope surface and the top increases rapidly and then flattens out with time, representing the gradual penetration of the slide surface. Hence, the ratio tends to be stable with time, which can be used as a precursor of the landslide. The research conclusions have theoretical and practical significance for warning of instability of bedding slopes with anti-dipping joints.
In 2017, the initiation of Xinmocun landslide in Maoxian, Sichuan had obvious "locking section" effect. On the basis of field investigation, we adopt high strength brittle material to make slope model, and used it to carry out physical simulation test for reproducing the process of landslide deformation and failure. We analyze the initiation mechanism of Xinmocun landside under the control of the anti-dip joint and the potential slip fracture surface. We combined the deformation and failure characteristics of the rock mass of the "locking section", and the deformation monitoring data and acoustic emission signals. We found some precursors of landslide. The experiment showed the follows: Due to the push of the upper slide, the rock mass of the "locking section" in the front of the sliding source area expanded and sheared along the anti-dip joints, which formed a bulging fracture on the slope surface and a downslope tension crack surface in the interior of the slope. Next the two groups of fractures were combined to form a stepped failure surface, which formed the boundary condition of rock mass failure in the "locking section". Under the pushing of the upper slide, the middle part of the slope formed the ejection block with high speed. Within the meantime, the lower dumping block toppled over the outside. Subsequently the landslide failed. Therefore, we conclude that the bulging cracks that were formed along the anti-dip joints can be regarded as the macroscopic precursors of this kind of landslides. At the same time, in the yield stage of the "locking section", the displacement ratio between the slope surface and the top increases rapidly and then flattens out with time, representing the gradual penetration of the slide surface. Hence, the ratio tends to be stable with time, which can be used as a precursor of the landslide. The research conclusions have theoretical and practical significance for warning of instability of bedding slopes with anti-dipping joints.
2023, 31(1): 165-175.
The study of landslide susceptibility is of great practical significance to the risk management of geological hazards and disasters prevention. Currently,the coupling of different evaluation methods is commonly adopted worldwide,but few of them applied the combination of the weight of evidence model(WOE) and other models to assess landslides susceptibility. Taking Yongjia County of Zhejiang Province as an example,nine evaluation factors were elected as the evaluation indices. They include elevation,slope,aspect,distance to river,distance to road,distance to faults,stratum lithology,land cover,and the normalized difference vegetation index(NDVI). The state of each evaluation factor was graded based on the contrast values calculated with WOE,the grading grid ratio and landslide grid ratio. We applied logistic regression model to obtain the weight of each factor. Based on the grid operation function of GIS,we combined weight of states and weight of evaluation factors weight determined by the two models and calculated the probability of landslide occurrence in each evaluation unit obtained a zoning map of landslide susceptibility. The results indicate that the evaluation results of the coupling model is more reasonable and has higher precision. High and extremely high susceptibility of landslide areas are mainly distributed in the water extension area,fault concentration area and lithology weakness area. Landslide susceptibility mapping has a certain reference meaning to landslide risk management and urban disaster prevention planning.
The study of landslide susceptibility is of great practical significance to the risk management of geological hazards and disasters prevention. Currently,the coupling of different evaluation methods is commonly adopted worldwide,but few of them applied the combination of the weight of evidence model(WOE) and other models to assess landslides susceptibility. Taking Yongjia County of Zhejiang Province as an example,nine evaluation factors were elected as the evaluation indices. They include elevation,slope,aspect,distance to river,distance to road,distance to faults,stratum lithology,land cover,and the normalized difference vegetation index(NDVI). The state of each evaluation factor was graded based on the contrast values calculated with WOE,the grading grid ratio and landslide grid ratio. We applied logistic regression model to obtain the weight of each factor. Based on the grid operation function of GIS,we combined weight of states and weight of evaluation factors weight determined by the two models and calculated the probability of landslide occurrence in each evaluation unit obtained a zoning map of landslide susceptibility. The results indicate that the evaluation results of the coupling model is more reasonable and has higher precision. High and extremely high susceptibility of landslide areas are mainly distributed in the water extension area,fault concentration area and lithology weakness area. Landslide susceptibility mapping has a certain reference meaning to landslide risk management and urban disaster prevention planning.
2023, 31(1): 176-187.
Landslides are often the most common and serious secondary disasters induced by earthquakes,and can cause the massive property losses even casualties. Therefore,the stability analysis of slope and the effectiveness of reinforcement measures have become one of the important topics in the field of engineering geology. According to Bainigou landslide in Qiaojia County,the numerical model is created using the two-dimensional finite difference program FLAC and the reinforcement effect of the landslide under different support structures is investigated based on the numerical results. As this landslide belongs to a huge thick bedrock landslide with huge sliding force,three support structures are employed and included double-row anti-slide piles,anchor cable anti-slide piles and anchor cables,and continuous pile-plug structure. The reinforcement effect of three support structures is explored. The computed results show that the double-row anti-slide piles can bear the sliding force,but the sliding force for the double-row anti-slide piles is still relatively large,which can cause that the pile top pushes the surrounding soil downwards. Anchor cable reinforcement can provide the greater anti-sliding force and,reduce the downward slide trend of the slope. Anchor cable with prestressing can effectively restrain the displacement of the pile top and improve the bearing capacity of pile shaft. The inner force distribution using the continuous pile-plug structure is reasonable,and it has better integrity,which plays a beneficial role on anti-sliding. Among the three support structures,the continuous pile-plug structure has the best reinforcement effect.
Landslides are often the most common and serious secondary disasters induced by earthquakes,and can cause the massive property losses even casualties. Therefore,the stability analysis of slope and the effectiveness of reinforcement measures have become one of the important topics in the field of engineering geology. According to Bainigou landslide in Qiaojia County,the numerical model is created using the two-dimensional finite difference program FLAC and the reinforcement effect of the landslide under different support structures is investigated based on the numerical results. As this landslide belongs to a huge thick bedrock landslide with huge sliding force,three support structures are employed and included double-row anti-slide piles,anchor cable anti-slide piles and anchor cables,and continuous pile-plug structure. The reinforcement effect of three support structures is explored. The computed results show that the double-row anti-slide piles can bear the sliding force,but the sliding force for the double-row anti-slide piles is still relatively large,which can cause that the pile top pushes the surrounding soil downwards. Anchor cable reinforcement can provide the greater anti-sliding force and,reduce the downward slide trend of the slope. Anchor cable with prestressing can effectively restrain the displacement of the pile top and improve the bearing capacity of pile shaft. The inner force distribution using the continuous pile-plug structure is reasonable,and it has better integrity,which plays a beneficial role on anti-sliding. Among the three support structures,the continuous pile-plug structure has the best reinforcement effect.
2023, 31(1): 188-198.
There are many mountains in Guizhou Province. Due to the characteristics of karst landforms,collapses,landslides and other geological disasters occur frequently,which is one of the most serious geological disasters in China. There were many collapses in the development process of Xujiadabang collapse in Sinan County. The existing dangerous rock mass is on a large scale and a serious threat to the life and property safety of Xujiadabang residents. So it is urgent and necessary to carry out corresponding risk assessment. In this paper,the high precision DEM of Xujiadabang collapse area after vegetation removal was obtained with UAV Lidar technology. The 3D terrain model was constructed by 3D real scene modeling technology. Considering the situation of rock fall from two empty surfaces,three typical particle sizes of 0.3 m,1.5 m and 2.5 m were selected for random numerical simulation. The motion trajectories and dynamic characteristics of three kinds of particle size were obtained. Four evaluation factors of falling rock energy,frequency,acceleration and bouncing height are selected to comprehensively evaluate the risk of collapse in Xujiadabang. The weight of each evaluation factor is calculated with entropy weight method. The risk range distribution of Xujiadabang collapse is obtained using spatial grid analysis technology based on ArcGIS software. The collapse risk range of Xujiadabang was divided into four grades: extremely high risk area,high risk area,medium risk area and low risk area. The research ideas and technical methods adopted in this paper can provide reference for the risk assessment and scope division of other monomer collapse disasters.
There are many mountains in Guizhou Province. Due to the characteristics of karst landforms,collapses,landslides and other geological disasters occur frequently,which is one of the most serious geological disasters in China. There were many collapses in the development process of Xujiadabang collapse in Sinan County. The existing dangerous rock mass is on a large scale and a serious threat to the life and property safety of Xujiadabang residents. So it is urgent and necessary to carry out corresponding risk assessment. In this paper,the high precision DEM of Xujiadabang collapse area after vegetation removal was obtained with UAV Lidar technology. The 3D terrain model was constructed by 3D real scene modeling technology. Considering the situation of rock fall from two empty surfaces,three typical particle sizes of 0.3 m,1.5 m and 2.5 m were selected for random numerical simulation. The motion trajectories and dynamic characteristics of three kinds of particle size were obtained. Four evaluation factors of falling rock energy,frequency,acceleration and bouncing height are selected to comprehensively evaluate the risk of collapse in Xujiadabang. The weight of each evaluation factor is calculated with entropy weight method. The risk range distribution of Xujiadabang collapse is obtained using spatial grid analysis technology based on ArcGIS software. The collapse risk range of Xujiadabang was divided into four grades: extremely high risk area,high risk area,medium risk area and low risk area. The research ideas and technical methods adopted in this paper can provide reference for the risk assessment and scope division of other monomer collapse disasters.
2023, 31(1): 199-206.
Rockfall is a serious geo-hazard in mountainous area. The shed tunnel is one of the main engineering measures to prevent rockfall. It has the great actual meaning to study the dynamic response characteristics of the shed tunnel under the impact of rockfall. Based on Hertz theory,the impact mechanics model of rockfall is established assuming that the rockfall is a rigid spherical body and the shed is a beam. Then the maximum impact force of rockfall impacting on the shed slab with different thickness cushion are derived at different speeds. Moreover the limit punching shear velocity of rockfall is obtained. The results show that the impact force of rockfall on the shed slab decreases with the increase of cushion thickness,while the cushion with finite thickness can only bear a certain limit of impact energy,The larger the rockfall size and impact velocity is,the greater the stress of the shed plate becomes. When the impact energy exceeds the ultimate bearing strength of cushion material,the cushion would no longer dissipate energy,furthermore,the small impact velocity of rockfall could cause the shed tunnel without cushion damaged,and the reasonable cushion thickness is of great significance to prevent rockfall.
Rockfall is a serious geo-hazard in mountainous area. The shed tunnel is one of the main engineering measures to prevent rockfall. It has the great actual meaning to study the dynamic response characteristics of the shed tunnel under the impact of rockfall. Based on Hertz theory,the impact mechanics model of rockfall is established assuming that the rockfall is a rigid spherical body and the shed is a beam. Then the maximum impact force of rockfall impacting on the shed slab with different thickness cushion are derived at different speeds. Moreover the limit punching shear velocity of rockfall is obtained. The results show that the impact force of rockfall on the shed slab decreases with the increase of cushion thickness,while the cushion with finite thickness can only bear a certain limit of impact energy,The larger the rockfall size and impact velocity is,the greater the stress of the shed plate becomes. When the impact energy exceeds the ultimate bearing strength of cushion material,the cushion would no longer dissipate energy,furthermore,the small impact velocity of rockfall could cause the shed tunnel without cushion damaged,and the reasonable cushion thickness is of great significance to prevent rockfall.
2023, 31(1): 207-216.
Due to the complex topographic conditions and dense vegetation development in Jiuzhaigou region, it is difficult for the traditional manual geological disaster investigation methods to achieve a detailed investigation in a short time. Airborne LiDAR technology has the technical advantage of being able to penetrate through plant gaps and detect microscopic damage to geological objects. InSAR technology has the technical advantage of detecting deformation and damage of geological bodies from macroscopic perspective. Therefore, the two technologies are combined to assist in field verification. By building a macro-to micro-scale geohazard investigation model, it can reduce the workload of manual investigation, improve the identification of potential hazards, and improve the efficiency of geohazard investigation.Based on the above, an internationally advanced high-performance LiDAR scanner was used in this study to achieve the objective of acquiring high-density laser point clouds within 230km2 of the study area. High-accuracy digital elevation model(DEM)data of the study area was obtained through a combination of data pre-processing, point cloud denoising, automatic classification and manual vegetation classification operations. The DEM data did not do microtopography removal, but instead retained the microtopography for disaster hazard identification. Based on the data, a three-dimensional interpretation environment was set up. The identification of major geological hazards under the vegetation was carried out by combining the DEM-derived results, optical remote sensing data and the results of previous geological hazard investigations. Meanwhile, the surface deformation monitoring of 230km2 in the study area was carried out based on ALOS-2 L-band data and Sentinel-1 data and data processing operations. The integration and interpretation of the airborne LiDAR survey results, the InSAR results and the optical remote sensing image results, enhanced the field verification work, and the field investigation of the difficult hidden hazards, which helped further enrich and optimize the practical effect of the technology system. Ultimately, the identification of geological hazards in the study area was completed. The study demonstrated that the multi-source remote sensing technologies such as airborne LiDAR and InSAR can significantly increase the accuracy and efficiency of geohazard investigation, as well as effectively solve the problem of identifying geohazard hazards in complex terrain and high vegetation cover areas.
Due to the complex topographic conditions and dense vegetation development in Jiuzhaigou region, it is difficult for the traditional manual geological disaster investigation methods to achieve a detailed investigation in a short time. Airborne LiDAR technology has the technical advantage of being able to penetrate through plant gaps and detect microscopic damage to geological objects. InSAR technology has the technical advantage of detecting deformation and damage of geological bodies from macroscopic perspective. Therefore, the two technologies are combined to assist in field verification. By building a macro-to micro-scale geohazard investigation model, it can reduce the workload of manual investigation, improve the identification of potential hazards, and improve the efficiency of geohazard investigation.Based on the above, an internationally advanced high-performance LiDAR scanner was used in this study to achieve the objective of acquiring high-density laser point clouds within 230km2 of the study area. High-accuracy digital elevation model(DEM)data of the study area was obtained through a combination of data pre-processing, point cloud denoising, automatic classification and manual vegetation classification operations. The DEM data did not do microtopography removal, but instead retained the microtopography for disaster hazard identification. Based on the data, a three-dimensional interpretation environment was set up. The identification of major geological hazards under the vegetation was carried out by combining the DEM-derived results, optical remote sensing data and the results of previous geological hazard investigations. Meanwhile, the surface deformation monitoring of 230km2 in the study area was carried out based on ALOS-2 L-band data and Sentinel-1 data and data processing operations. The integration and interpretation of the airborne LiDAR survey results, the InSAR results and the optical remote sensing image results, enhanced the field verification work, and the field investigation of the difficult hidden hazards, which helped further enrich and optimize the practical effect of the technology system. Ultimately, the identification of geological hazards in the study area was completed. The study demonstrated that the multi-source remote sensing technologies such as airborne LiDAR and InSAR can significantly increase the accuracy and efficiency of geohazard investigation, as well as effectively solve the problem of identifying geohazard hazards in complex terrain and high vegetation cover areas.
2023, 31(1): 217-227.
This paper takes the steep bedding rock slope as the research object, uses shaking table model test and FLAC3D numerical simulation method and studies the dynamic response law and deformation failure mode of steep bedding rock slope under strong earthquake. Results show that the acceleration response of steep bedding rock slope on the surface and in the vertical direction shows elevation amplification effect, while the acceleration response in horizontal direction turns into surface effect. The type of input wave has significant influence on the acceleration response of slope model, and the acceleration response under sine wave is obviously stronger than that of natural seismic wave. The acceleration response of steep bedding rock slope under the action of sine wave is obviously stronger than that of natural seismic wave. The acceleration amplification coefficients increases first and then decreases with seismic wave amplitudes increasing. The influence of seismic wave duration on the acceleration response of steep bedding rock slope is small. Based on the analysis of the deformation and failure characteristics of the slope in the model test and numerical simulation, the failure mode of the steep bedding rock slope under strong earthquake action is described as (1)earthquake induction, (2)rock mass relaxation and tension fracture at the exposed part of the slope, then (3) tensile crack of the shoulder rock layer, then (4)appearance of shear cracks in the middle part of the slope-gradual coalescence of cracks, subsequently (5)the occurrence of high locality landslide.
This paper takes the steep bedding rock slope as the research object, uses shaking table model test and FLAC3D numerical simulation method and studies the dynamic response law and deformation failure mode of steep bedding rock slope under strong earthquake. Results show that the acceleration response of steep bedding rock slope on the surface and in the vertical direction shows elevation amplification effect, while the acceleration response in horizontal direction turns into surface effect. The type of input wave has significant influence on the acceleration response of slope model, and the acceleration response under sine wave is obviously stronger than that of natural seismic wave. The acceleration response of steep bedding rock slope under the action of sine wave is obviously stronger than that of natural seismic wave. The acceleration amplification coefficients increases first and then decreases with seismic wave amplitudes increasing. The influence of seismic wave duration on the acceleration response of steep bedding rock slope is small. Based on the analysis of the deformation and failure characteristics of the slope in the model test and numerical simulation, the failure mode of the steep bedding rock slope under strong earthquake action is described as (1)earthquake induction, (2)rock mass relaxation and tension fracture at the exposed part of the slope, then (3) tensile crack of the shoulder rock layer, then (4)appearance of shear cracks in the middle part of the slope-gradual coalescence of cracks, subsequently (5)the occurrence of high locality landslide.
2023, 31(1): 228-239.
"Red-bed" with complex composites and special structures, spreads widely in China and can induce geological hazards easily. This paper took the 82 mining area of Xinhu Coal Mine located in Huaibei, China as an example and studied the engineering geological characteristics induced by Huaibei Paleogene "red-bed". First, based on in situ investigations, the vertical overlying deposition of red bed lithology was classified. Second, the rock core was adopted to study the basic properties of "red bed" rock in aspects of mineral composition, microstructure, physical-mechanical property and water-physical property by laboratory tests. Third, 9 representative influential factors which might induce hazards were raised based on experimental analysis and in situ conditions. An engineering model concerning geological hazards relevant to red-bed was built on the basis of Analytic Hierarchy Process(AHP). Finally, the unfavorable geology was analyzed according to potential geological hazards induced by"red-bed" in the 82 mining area. Results show that the "red-bed" is dominated by mudstone and has low compressive strength, poor microstructure and poor stability. Besides, the "red-bed" contains a lot of hydrophilic minerals and has strong swelling and disintegrating properties. As a whole, the strata structure of the "red-bed" in the 82 mining area is relatively stable. The degree of potential geological hazards induced by the "red-bed" increases gradually from northwest to southeast. Among them, the hazard possibility is greatest in south, southeast parts and areas near faults in mining. Some parts of west are safer and most parts of north are more dangerous. The study can provide useful references for engineering design and mining.
"Red-bed" with complex composites and special structures, spreads widely in China and can induce geological hazards easily. This paper took the 82 mining area of Xinhu Coal Mine located in Huaibei, China as an example and studied the engineering geological characteristics induced by Huaibei Paleogene "red-bed". First, based on in situ investigations, the vertical overlying deposition of red bed lithology was classified. Second, the rock core was adopted to study the basic properties of "red bed" rock in aspects of mineral composition, microstructure, physical-mechanical property and water-physical property by laboratory tests. Third, 9 representative influential factors which might induce hazards were raised based on experimental analysis and in situ conditions. An engineering model concerning geological hazards relevant to red-bed was built on the basis of Analytic Hierarchy Process(AHP). Finally, the unfavorable geology was analyzed according to potential geological hazards induced by"red-bed" in the 82 mining area. Results show that the "red-bed" is dominated by mudstone and has low compressive strength, poor microstructure and poor stability. Besides, the "red-bed" contains a lot of hydrophilic minerals and has strong swelling and disintegrating properties. As a whole, the strata structure of the "red-bed" in the 82 mining area is relatively stable. The degree of potential geological hazards induced by the "red-bed" increases gradually from northwest to southeast. Among them, the hazard possibility is greatest in south, southeast parts and areas near faults in mining. Some parts of west are safer and most parts of north are more dangerous. The study can provide useful references for engineering design and mining.
2023, 31(1): 240-247.
Karst collapses are developed in Fujian Province and are second only to landslides and collapses. In order to study the evolution process of karst collapse, the typical covered karst collapse in Fujian Province is taken as the research object in this paper. On-site soil samples were taken. Fiber-optic grating strain sensors, pore water pressure gauges, settlement gauges, and other monitoring instruments were installed in a self-made physical model box to obtain stress and strain information of the overburden soil under different conditions. The response of the overburden soil is analysed. The development and evolution process of typical overburden karst collapse is proposed. The results show that: (1)Under the effect of the pore water fluctuations in the Quaternary overburden, the pore water pressure of the soil layer changes basically at the same amplitude. The largest deformation occurs in the top soil while the smallest deformation occurs in the subsoil. The fluctuation of the water level has little damage to the soil, and the soil cave has not formed yet. (2)In the process of the karst water level rising and falling repeatedly, the pore water pressure increases and decreases synchronously with the change of the seepage water level. The soil closer to the cave on the same horizontal plane produces greater strain. The higher the soil layer, the greater the strain difference. The deformation of the roof of the soil cave continues to develop upwards under the action of hydrodynamic force and vacuum erosion. When the deformation develops beyond the critical soil cave height of 40cm, the ground collapse occurs. (3)The evolution process of typical covered karst collapse can be divided into three stages: the first stage is the development and formation of soil caves, the second stage is the internal collapse, and the third stage is ground collapse. (4)The karst soil cave collapse in southwestern Fujian mostly occurs in the strong groundwater runoff drainage area on both sides of the intermountain basin and the valley. The overburden layer is thick, mostly composed of the Quaternary alluvial gravel, gravel-bearing clayey soil, and silty clay layer. The disaster mechanism has its regional characteristics.
Karst collapses are developed in Fujian Province and are second only to landslides and collapses. In order to study the evolution process of karst collapse, the typical covered karst collapse in Fujian Province is taken as the research object in this paper. On-site soil samples were taken. Fiber-optic grating strain sensors, pore water pressure gauges, settlement gauges, and other monitoring instruments were installed in a self-made physical model box to obtain stress and strain information of the overburden soil under different conditions. The response of the overburden soil is analysed. The development and evolution process of typical overburden karst collapse is proposed. The results show that: (1)Under the effect of the pore water fluctuations in the Quaternary overburden, the pore water pressure of the soil layer changes basically at the same amplitude. The largest deformation occurs in the top soil while the smallest deformation occurs in the subsoil. The fluctuation of the water level has little damage to the soil, and the soil cave has not formed yet. (2)In the process of the karst water level rising and falling repeatedly, the pore water pressure increases and decreases synchronously with the change of the seepage water level. The soil closer to the cave on the same horizontal plane produces greater strain. The higher the soil layer, the greater the strain difference. The deformation of the roof of the soil cave continues to develop upwards under the action of hydrodynamic force and vacuum erosion. When the deformation develops beyond the critical soil cave height of 40cm, the ground collapse occurs. (3)The evolution process of typical covered karst collapse can be divided into three stages: the first stage is the development and formation of soil caves, the second stage is the internal collapse, and the third stage is ground collapse. (4)The karst soil cave collapse in southwestern Fujian mostly occurs in the strong groundwater runoff drainage area on both sides of the intermountain basin and the valley. The overburden layer is thick, mostly composed of the Quaternary alluvial gravel, gravel-bearing clayey soil, and silty clay layer. The disaster mechanism has its regional characteristics.
2023, 31(1): 248-257.
Tunnels across mountain always go through fracture zones. With lack of knowledge of the mechanisms on rock faults, constructions on rock tunnels used to bring about quite an amount of collapse accidents with large deformations. This paper applied a combination of theoretical and numerical simulation with the on-site monitoring data. It considered the underground water in rock faults and examined the surrounded rock instability and collapse mechanism during the construction process. The result shows that the discontinuous structural plane is fully infilled with debris or clay when the tunnels going through water-rich fracture zones. Coupled with construction disturbances, the structural surfaces are prone to dislocation, causing groundwater flow with further damages. The formation of structural surface erosion reduces the integrity and mechanical strength of the surrounding rock. The lowers the shear strength of the fault fracture zone, the larger the range of loosening of the surrounding rock and the greater the probability and range of collapse. Based on the principle of "water resisting, drainage and strengthening surrounding rock", this paper proposes several measures letting tunnels go through fracture zones preventing collapse. These strategies can provide references for maintaining construction safety in upcoming project and include setting up detour pits, pre-reinforcement of the ground, increasing support strength, optimizing construction methods and strengthening monitoring measurement.
Tunnels across mountain always go through fracture zones. With lack of knowledge of the mechanisms on rock faults, constructions on rock tunnels used to bring about quite an amount of collapse accidents with large deformations. This paper applied a combination of theoretical and numerical simulation with the on-site monitoring data. It considered the underground water in rock faults and examined the surrounded rock instability and collapse mechanism during the construction process. The result shows that the discontinuous structural plane is fully infilled with debris or clay when the tunnels going through water-rich fracture zones. Coupled with construction disturbances, the structural surfaces are prone to dislocation, causing groundwater flow with further damages. The formation of structural surface erosion reduces the integrity and mechanical strength of the surrounding rock. The lowers the shear strength of the fault fracture zone, the larger the range of loosening of the surrounding rock and the greater the probability and range of collapse. Based on the principle of "water resisting, drainage and strengthening surrounding rock", this paper proposes several measures letting tunnels go through fracture zones preventing collapse. These strategies can provide references for maintaining construction safety in upcoming project and include setting up detour pits, pre-reinforcement of the ground, increasing support strength, optimizing construction methods and strengthening monitoring measurement.
2023, 31(1): 258-266.
Structural surfaces are generally developed widely in the loess slope,can not only alter the continuity of the soil,but also present a significant influence on the seepage,deformation,and stress fields,as well as the stability of the loess slope. In this study,the developmental characteristics and effects of structure surface of loess slope in southern Jing-Yang loess plateau were researched systematically through field investigations,experiments,and numerical simulations. The main results are presented as follows:(1)Considering the difference of formation and influence,the structural surface of the loess slope is classified from the perspective of macro,micro and micro multi-scales into 5 classes and 2 groups and 25 categories. (2)According to the results of the field investigation,the structural surfaces are mostly distributed near the slope shoulder,the orientation of the structural surface is generally in accordance with that of the loess slope. And the length,width,and displacement of the structural surface generally increase with the increase of distance from the slope shoulder. (3)The numerical simulation results show that the development characteristics and influence of the structural surface are various with the change of depth and location. The surface that is near the shoulder and shows large depth is easy to develop. The FOS of the loess slope decreases first and then increases to reach a stable value,with the increase of the distance of the surface from the shoulder. In addition,the FOS gradually decreases to reach a certain value with the increase of surface depth. The results of the paper can provide some basis for the stability evaluation of loess slopes.
Structural surfaces are generally developed widely in the loess slope,can not only alter the continuity of the soil,but also present a significant influence on the seepage,deformation,and stress fields,as well as the stability of the loess slope. In this study,the developmental characteristics and effects of structure surface of loess slope in southern Jing-Yang loess plateau were researched systematically through field investigations,experiments,and numerical simulations. The main results are presented as follows:(1)Considering the difference of formation and influence,the structural surface of the loess slope is classified from the perspective of macro,micro and micro multi-scales into 5 classes and 2 groups and 25 categories. (2)According to the results of the field investigation,the structural surfaces are mostly distributed near the slope shoulder,the orientation of the structural surface is generally in accordance with that of the loess slope. And the length,width,and displacement of the structural surface generally increase with the increase of distance from the slope shoulder. (3)The numerical simulation results show that the development characteristics and influence of the structural surface are various with the change of depth and location. The surface that is near the shoulder and shows large depth is easy to develop. The FOS of the loess slope decreases first and then increases to reach a stable value,with the increase of the distance of the surface from the shoulder. In addition,the FOS gradually decreases to reach a certain value with the increase of surface depth. The results of the paper can provide some basis for the stability evaluation of loess slopes.
2023, 31(1): 267-276.
It is an important way to accurately grasp the development mechanism and image characteristics of cracks and deduce the formation process of expansive landslide. In this paper,the expansive soil slope in Pishihang irrigation area of Anhui Province was taken as the research object. The in-situ test under the condition of rainfall plus dead weight was carried out to systematically study the image characteristics of soil surface cracks during the instability process. The emphasis was on the analysis of the relationship between the variation of crack degree,crack geometric characteristic parameters and slope instability. The results show that it is feasible to evaluate the slope risk through comprehensive analysis of soil surface crack images. In view of the expansive soil slope in this area,when the transverse cracks along the soft structural plane develop into the main control cracks,the slope would appear abnormal,and the early warning should be put forward.
It is an important way to accurately grasp the development mechanism and image characteristics of cracks and deduce the formation process of expansive landslide. In this paper,the expansive soil slope in Pishihang irrigation area of Anhui Province was taken as the research object. The in-situ test under the condition of rainfall plus dead weight was carried out to systematically study the image characteristics of soil surface cracks during the instability process. The emphasis was on the analysis of the relationship between the variation of crack degree,crack geometric characteristic parameters and slope instability. The results show that it is feasible to evaluate the slope risk through comprehensive analysis of soil surface crack images. In view of the expansive soil slope in this area,when the transverse cracks along the soft structural plane develop into the main control cracks,the slope would appear abnormal,and the early warning should be put forward.
2023, 31(1): 277-287.
With the continuous advancement of infrastructure construction,unreasonable stacking of excavated soil(spoil) has become one of the important problems in engineering construction. As the spoil ground increases in volume and height,the risk of instability within the deposit increases,which may result in water and soil erosion,ecological environment damage and other disasters. This paper takes the spoil ground in the loess gully region of a high-speed railway tunnel in Gansu Province as a research object and uses laboratory test,field test and numerical simulation research plan to explore and examine the mechanical properties,compaction degree and slope cutting type setting of deposit under different parameters. The results show that cohesion and internal friction angle of spoil soil have a positive correlation with dry density and a negative correlation with water content,but the internal friction angle is not affected by moisture content. The compaction during the layering process of spoil soil can significantly increase the surface compaction degree. The compaction degree of the middle and bottom layers increases significantly with increasing in the number of compaction. The average compaction degree increases rapidly in the early compaction process,but its change range decreases significantly with the increase of the number. The average moisture content shows a trend of decreasing at first,and then increasing in the compaction process. During the parameter setting of the slope steps,the magnitudes of stress and displacement deformation increase with increasing in height step and slope rate,and decrease with increasing in platform width. The stability coefficient of slope decreases with increasing in height step and slope rate,and increases with increasing in width platform. Through comprehensive analysis of curve,the slope stability shows that the sensitivity of step parameter setting in stress,displacement and stability coefficient from high to low is step slope,platform width,and step height in turn.
With the continuous advancement of infrastructure construction,unreasonable stacking of excavated soil(spoil) has become one of the important problems in engineering construction. As the spoil ground increases in volume and height,the risk of instability within the deposit increases,which may result in water and soil erosion,ecological environment damage and other disasters. This paper takes the spoil ground in the loess gully region of a high-speed railway tunnel in Gansu Province as a research object and uses laboratory test,field test and numerical simulation research plan to explore and examine the mechanical properties,compaction degree and slope cutting type setting of deposit under different parameters. The results show that cohesion and internal friction angle of spoil soil have a positive correlation with dry density and a negative correlation with water content,but the internal friction angle is not affected by moisture content. The compaction during the layering process of spoil soil can significantly increase the surface compaction degree. The compaction degree of the middle and bottom layers increases significantly with increasing in the number of compaction. The average compaction degree increases rapidly in the early compaction process,but its change range decreases significantly with the increase of the number. The average moisture content shows a trend of decreasing at first,and then increasing in the compaction process. During the parameter setting of the slope steps,the magnitudes of stress and displacement deformation increase with increasing in height step and slope rate,and decrease with increasing in platform width. The stability coefficient of slope decreases with increasing in height step and slope rate,and increases with increasing in width platform. Through comprehensive analysis of curve,the slope stability shows that the sensitivity of step parameter setting in stress,displacement and stability coefficient from high to low is step slope,platform width,and step height in turn.
2023, 31(1): 288-298.
In recent years,in order to expand the available land resources in the Loess Plateau area,people have carried out a wide range of engineering construction,such as gully filling and land building and city building. This paper aimed at the potential disaster hazard of the interface between high and steep original slope and filling slope and carried out the indoor physical model test. The results show that under continuous heavy rainfall,the loess slope would slip and lose stability along the high and steep filling interface. This paper further used finite element numerical simulation software and carried out a comparative analysis on working conditions including no weak zone,different weak zone thickness and weakening coefficient at the filling interface. It is found that the continuous development of soft zone reduces the stability coefficient of the filling slope and changes the position of the most dangerous sliding surface. The influence of the set weakening coefficient on the stability coefficient can be divided into three stages: no influence stage,equal speed steep descent control stage,equal speed slow descent control stage. This paper further defined the "key weakening factor". It is the critical weakening factor and has an initial impact on the stability of the slope. Measures in actual engineering should be taken to prevent the weakening factor of the weak zone from falling below its "key weakening factor". Under the influence of the weak zone of the high-steep intersection interface,the rainfall-induced instability mode of loess fill slopes can be summarized as: at first slope surface erosion and formation of gullies are developed,the multi-level local collapse of slope foot are present,then weak zone of cross-fill interface is gradually developed. The soil slips down along the interfill interface and the slope foot is sheared out shear cracks are penetrated and the fill slope is completely lost stable. The research results can provide theoretical support for the disaster prevention and mitigation work of loess-filled slopes built on steep slopes.
In recent years,in order to expand the available land resources in the Loess Plateau area,people have carried out a wide range of engineering construction,such as gully filling and land building and city building. This paper aimed at the potential disaster hazard of the interface between high and steep original slope and filling slope and carried out the indoor physical model test. The results show that under continuous heavy rainfall,the loess slope would slip and lose stability along the high and steep filling interface. This paper further used finite element numerical simulation software and carried out a comparative analysis on working conditions including no weak zone,different weak zone thickness and weakening coefficient at the filling interface. It is found that the continuous development of soft zone reduces the stability coefficient of the filling slope and changes the position of the most dangerous sliding surface. The influence of the set weakening coefficient on the stability coefficient can be divided into three stages: no influence stage,equal speed steep descent control stage,equal speed slow descent control stage. This paper further defined the "key weakening factor". It is the critical weakening factor and has an initial impact on the stability of the slope. Measures in actual engineering should be taken to prevent the weakening factor of the weak zone from falling below its "key weakening factor". Under the influence of the weak zone of the high-steep intersection interface,the rainfall-induced instability mode of loess fill slopes can be summarized as: at first slope surface erosion and formation of gullies are developed,the multi-level local collapse of slope foot are present,then weak zone of cross-fill interface is gradually developed. The soil slips down along the interfill interface and the slope foot is sheared out shear cracks are penetrated and the fill slope is completely lost stable. The research results can provide theoretical support for the disaster prevention and mitigation work of loess-filled slopes built on steep slopes.
2023, 31(1): 299-308.
The differential settlement of the hanging and footwall walls is the main activity mode of ground fissures in Xi'an. It is well accepted that the extraction of groundwater in confined aquifer is an important factor aggravating the differential settlement. The specific mechanism is not quite clear though. To clarify the mechanism,we performed the stress condition analysis and the soil-ground fissure coordinated deformation analysis on horizontal units,carried out numerical simulation,and explained how deformation differs by wall. Through fluid-structure coupling numerical simulation,we obtained settlement characteristics on the ground by different pumping condition and ground fissure permeability. The result shows that,the small-shear-modulus ground fissure causes relatively larger load on the top and larger reaction force on the bottom for units of hanging wall,nearby the fissure. However,when it comes to those of footwall,the situation is just the opposite. This is the foremost reason that the settlement is relatively larger in the hanging wall. Pumping condition and ground fissure permeability have influence on the mechanical disturbance caused by water-pumping,enlarging the deformation difference between two walls. The differential settlement is obvious when the well is located in the hanging wall,and more visible when the permeability of the ground fissure is poor.
The differential settlement of the hanging and footwall walls is the main activity mode of ground fissures in Xi'an. It is well accepted that the extraction of groundwater in confined aquifer is an important factor aggravating the differential settlement. The specific mechanism is not quite clear though. To clarify the mechanism,we performed the stress condition analysis and the soil-ground fissure coordinated deformation analysis on horizontal units,carried out numerical simulation,and explained how deformation differs by wall. Through fluid-structure coupling numerical simulation,we obtained settlement characteristics on the ground by different pumping condition and ground fissure permeability. The result shows that,the small-shear-modulus ground fissure causes relatively larger load on the top and larger reaction force on the bottom for units of hanging wall,nearby the fissure. However,when it comes to those of footwall,the situation is just the opposite. This is the foremost reason that the settlement is relatively larger in the hanging wall. Pumping condition and ground fissure permeability have influence on the mechanical disturbance caused by water-pumping,enlarging the deformation difference between two walls. The differential settlement is obvious when the well is located in the hanging wall,and more visible when the permeability of the ground fissure is poor.
2023, 31(1): 309-317.
In order to increase the capacity of a large municipal waste landfill in south China,increasing the height of the dam is required. With the restricting from the existing building around the old dam,the extended part of the dam is designed as a steep gravel dam reinforced with geotextiles. Based on this special engineering,experimental tests were carried out to examine the effect of the erosion of leachate on the limiting tensional stiffness of geotextiles. The centrifuge test was carried out to examine the stability of the dam considering the special design. Subsequently numerical simulations were conducted to examine the stability analysis with considering several potential operating conditions,in which the influence of strength of geotextiles and water levels were quantified by the numerical analysis. Furthermore,the influence of the slope safety factor by varying the specific parameters of those influencing factors,were conducted. The results show that the strength of the geotextiles and the water level in the landfill have significant influence on the stability of the geotextile-reinforced earth dam. The strength of geotextiles plays a significant role for the stability of the dam,compared to that induced by the variation of water level. The calculation results show that the safety factor of the dam cannot meet the design demand when the strength of geotextile reduced to 0 percent of the design strength. However,the factor of safety of the dam can meet that requirements with at least 50% of the design strength for geotextiles.
In order to increase the capacity of a large municipal waste landfill in south China,increasing the height of the dam is required. With the restricting from the existing building around the old dam,the extended part of the dam is designed as a steep gravel dam reinforced with geotextiles. Based on this special engineering,experimental tests were carried out to examine the effect of the erosion of leachate on the limiting tensional stiffness of geotextiles. The centrifuge test was carried out to examine the stability of the dam considering the special design. Subsequently numerical simulations were conducted to examine the stability analysis with considering several potential operating conditions,in which the influence of strength of geotextiles and water levels were quantified by the numerical analysis. Furthermore,the influence of the slope safety factor by varying the specific parameters of those influencing factors,were conducted. The results show that the strength of the geotextiles and the water level in the landfill have significant influence on the stability of the geotextile-reinforced earth dam. The strength of geotextiles plays a significant role for the stability of the dam,compared to that induced by the variation of water level. The calculation results show that the safety factor of the dam cannot meet the design demand when the strength of geotextile reduced to 0 percent of the design strength. However,the factor of safety of the dam can meet that requirements with at least 50% of the design strength for geotextiles.
2023, 31(1): 318-326.
This paper aims to accelerate the drainage consolidation process of bauxite tailings slurry. It proposes a method of adding horizontal and vertical drainage consolidation and combined with quicklime consolidation. The increasing the drainage path and the ballast effect of the sand layer can result in that the tailing mud can achieve better drainage consolidation effect in a short period of time. The solidification degree of tailing mud can be further enhanced by adding quicklime. Based on the model test,this paper further analyzes the change characteristics of pore water pressure,volume water content and water content along the depth of tailings slurry in the process of drainage and consolidation in the model with and without adding sand. It draws the following conclusions: sand adding layer has obvious improvement on the self weight drainage and consolidation effect of tailings slurry; water content of tailings slurry in the model of adding sand layer is higher than that in the model of without adding sand layer. Meanwhile,it is found that the addition of sand can promote the strength growth of quicklime solidified tailing slime. This study can provide some reference for the practical application of bauxite tailing slurry,sand and quicklime drainage and solidification.
This paper aims to accelerate the drainage consolidation process of bauxite tailings slurry. It proposes a method of adding horizontal and vertical drainage consolidation and combined with quicklime consolidation. The increasing the drainage path and the ballast effect of the sand layer can result in that the tailing mud can achieve better drainage consolidation effect in a short period of time. The solidification degree of tailing mud can be further enhanced by adding quicklime. Based on the model test,this paper further analyzes the change characteristics of pore water pressure,volume water content and water content along the depth of tailings slurry in the process of drainage and consolidation in the model with and without adding sand. It draws the following conclusions: sand adding layer has obvious improvement on the self weight drainage and consolidation effect of tailings slurry; water content of tailings slurry in the model of adding sand layer is higher than that in the model of without adding sand layer. Meanwhile,it is found that the addition of sand can promote the strength growth of quicklime solidified tailing slime. This study can provide some reference for the practical application of bauxite tailing slurry,sand and quicklime drainage and solidification.
2023, 31(1): 327-334.
Although the phenomenon of sand flowing around passive pile was observed,there is still a lack of systematical studies on the features of sand flowing as well as its related factors. Using the model experimental system designed and manufactured by Fuzhou University,the phenomenon of sand flowing around a circular passive pile was well tested and analyzed. The influence of pile diameter,loading velocity and sand density on the sand characteristic displacement and the pile drag force were studied. According to the test results,the sand flowing process around the passive pile could be divided into three stages: sand uplift on the head side,sand flowing around the pile and sand collapse on the back side. The increasing of pile diameter and sand density could hamper the sand flowing phenomenon around the pile,while the increasing of sand velocity could facilitate the sand flowing phenomenon. Furthermore,the position of sliding surface can be determined from the curve inflexion of drag force,the drag force above the sliding surface increased linearly with depth,and was always less than its counterpart calculated from the Shen-Zhujiang's formula.
Although the phenomenon of sand flowing around passive pile was observed,there is still a lack of systematical studies on the features of sand flowing as well as its related factors. Using the model experimental system designed and manufactured by Fuzhou University,the phenomenon of sand flowing around a circular passive pile was well tested and analyzed. The influence of pile diameter,loading velocity and sand density on the sand characteristic displacement and the pile drag force were studied. According to the test results,the sand flowing process around the passive pile could be divided into three stages: sand uplift on the head side,sand flowing around the pile and sand collapse on the back side. The increasing of pile diameter and sand density could hamper the sand flowing phenomenon around the pile,while the increasing of sand velocity could facilitate the sand flowing phenomenon. Furthermore,the position of sliding surface can be determined from the curve inflexion of drag force,the drag force above the sliding surface increased linearly with depth,and was always less than its counterpart calculated from the Shen-Zhujiang's formula.
2023, 31(1): 335-340.
This paper designed and processed flume model test,carried out pumping tests of single-hole complete wells with constant flow,combined with real-time dynamic monitoring of self-potentia(SP),and studied the groundwater level changes and SP response characteristics during the pumping process of phreatic aquifers. The results show that when pumping,both the groundwater level and SP decrease rapidly and gradually stabilize,but it takes a short time for the groundwater level to decrease to stability,and it takes a longer time for the SP to decrease to stability,with hysteresis. The greater the pumping flow,the greater the drop in groundwater level and SP; the farther away from the pumping well wall,the longer it takes for SP to stabilize. The self-potential difference(ΔSP) and the groundwater level drop depth(sw) satisfy the linear function relationship,and the ΔSP and the radial distance r both satisfy the exponential function relationship. According to the fitting formula,the groundwater level drop values at different positions in the model are calculated and compored with the observation values. The comparison of groundwater level and precipitation shows that the error between the calculated and observed values is relatively small,which indicate that this formula can be used to calculate and predict the groundwater level during pumping.
This paper designed and processed flume model test,carried out pumping tests of single-hole complete wells with constant flow,combined with real-time dynamic monitoring of self-potentia(SP),and studied the groundwater level changes and SP response characteristics during the pumping process of phreatic aquifers. The results show that when pumping,both the groundwater level and SP decrease rapidly and gradually stabilize,but it takes a short time for the groundwater level to decrease to stability,and it takes a longer time for the SP to decrease to stability,with hysteresis. The greater the pumping flow,the greater the drop in groundwater level and SP; the farther away from the pumping well wall,the longer it takes for SP to stabilize. The self-potential difference(ΔSP) and the groundwater level drop depth(sw) satisfy the linear function relationship,and the ΔSP and the radial distance r both satisfy the exponential function relationship. According to the fitting formula,the groundwater level drop values at different positions in the model are calculated and compored with the observation values. The comparison of groundwater level and precipitation shows that the error between the calculated and observed values is relatively small,which indicate that this formula can be used to calculate and predict the groundwater level during pumping.
2023, 31(1): 341-349.
In soft soil areas,there are two problems in checking the stability against basal heave using Prandtl foundation bearing capacity calculation formula. First,the formula can't reflect that the stability against basal heave increases with the increase of enclosure insertion depth; Secondly,it can't reflect the influence of foundation pit width on the safety factor of anti-uplift stability at the bottom of the wall. The analysis of the difference of mechanical boundary conditions between excavation and the bearing capacity by Prandtl formula indicated that the existing Prandtl formula is not enough to reflect the uplift failure sliding mode of foundation pit. According to the principle of limit equilibrium calculation,this paper proposes an improved calculation model considering the shear action of soil on both sides of foundation pit above the bottom of enclosure wall. The wide and narrow foundation pits are divided under the standard ratio 3 of foundation pit width-depth. The formulas for calculating the stability against basal heave of the wide and narrow foundation pits are given respectively. The calculation of engineering examples shows that the improved formula is consistent with the safety situation of successful engineering examples. It explains the law that the stability of foundation pit against basal heave is improved with the increase of enclosure insertion ratio in soft soil areas. According to the division of wide and narrow foundation pits,the safety factor of against basal heave stability of narrow foundation pits can be calculated reasonably. The research results of this paper can contribute to the calculation and evaluation of stability of foundation pit against basal heave in soft soil area,and to the structure optimization design of foundation pit. It also needs to be supplemented and improved by further theoretical research and verified by engineering practice.
In soft soil areas,there are two problems in checking the stability against basal heave using Prandtl foundation bearing capacity calculation formula. First,the formula can't reflect that the stability against basal heave increases with the increase of enclosure insertion depth; Secondly,it can't reflect the influence of foundation pit width on the safety factor of anti-uplift stability at the bottom of the wall. The analysis of the difference of mechanical boundary conditions between excavation and the bearing capacity by Prandtl formula indicated that the existing Prandtl formula is not enough to reflect the uplift failure sliding mode of foundation pit. According to the principle of limit equilibrium calculation,this paper proposes an improved calculation model considering the shear action of soil on both sides of foundation pit above the bottom of enclosure wall. The wide and narrow foundation pits are divided under the standard ratio 3 of foundation pit width-depth. The formulas for calculating the stability against basal heave of the wide and narrow foundation pits are given respectively. The calculation of engineering examples shows that the improved formula is consistent with the safety situation of successful engineering examples. It explains the law that the stability of foundation pit against basal heave is improved with the increase of enclosure insertion ratio in soft soil areas. According to the division of wide and narrow foundation pits,the safety factor of against basal heave stability of narrow foundation pits can be calculated reasonably. The research results of this paper can contribute to the calculation and evaluation of stability of foundation pit against basal heave in soft soil area,and to the structure optimization design of foundation pit. It also needs to be supplemented and improved by further theoretical research and verified by engineering practice.
微信 | 公众平台 
