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Editor Work2023 Vol. 31, No. 2
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2023, 31(2): 351-357.
Abstract
3087KB
The natural fractures generated by geological movement can form the lattice structure pattern in the sedimentary rocks. Crystal growth of carbonate mineral in these pre-existing fractures result in the calcite sealing in the limestone. In this study, mineralogical composition was analyzed and the concerns include hard minerals and water sensitive minerals. Water saturation can affect the minerals content and lead to water sensitive damage. Uniaxial compression experiment was carried out on the cylinder-shaped samples of the Carboniferous limestone containing calcite veins. Complete stress-strain relationship of the compression experiment combined with CT scanning results reflect two aspects for the role of calcite vein in the mechanical behavior of limestone under compression conditions. One aspect is the structural effect played by the interface between calcite vein and host rock, and another aspect is the joining of the thick calcite vein together with the host rock to resist compression. Significant brittleness of the limestone containing thin calcite veins is illuminated through the experimental results. More plasticity and lower strength are shown with thickness increase of the calcite vein in the limestone.
The natural fractures generated by geological movement can form the lattice structure pattern in the sedimentary rocks. Crystal growth of carbonate mineral in these pre-existing fractures result in the calcite sealing in the limestone. In this study, mineralogical composition was analyzed and the concerns include hard minerals and water sensitive minerals. Water saturation can affect the minerals content and lead to water sensitive damage. Uniaxial compression experiment was carried out on the cylinder-shaped samples of the Carboniferous limestone containing calcite veins. Complete stress-strain relationship of the compression experiment combined with CT scanning results reflect two aspects for the role of calcite vein in the mechanical behavior of limestone under compression conditions. One aspect is the structural effect played by the interface between calcite vein and host rock, and another aspect is the joining of the thick calcite vein together with the host rock to resist compression. Significant brittleness of the limestone containing thin calcite veins is illuminated through the experimental results. More plasticity and lower strength are shown with thickness increase of the calcite vein in the limestone.
2023, 31(2): 358-367.
In the environment of engineering geology,high temperatures accelerate drying of the soil mass that is also subject to wetting by rainfall. Dry-wet cycles tends to cause degradation of the soil mass,which can seriously damage the infrastructure and buildings on the soil mass. Investigation of dry-wet cycling on deformation behavior of compacted loess is indispensable to evaluate the stability of basement and subgrade in the engineering practice. In the present work,we fabricated three groups of samples with one water content of 11% and three different dry densities(1.5,1.6 and 1.7 g·cm-3). The samples were desiccated at 80 ℃,followed by wetting at an ambient temperature through immersing the samples into deionized water until a designated dry-wet cycling number. Upon cycling,electrical resistivity was measured by a digital LCR meter to characterize the structure change of the samples. Besides,the photographs of the sample surface after desiccation were taken to observe crack evolution. At the end of the cycles,constant rate of strain(CRS)was imposed on the saturated samples to determine the deformation parameters of the compacted loss. Results shows that the electrical resistivity increases due to the increase of crack ratio as the cycling numbers increase. Since the vertical stress is zero,the volume of the unsaturated compacted samples decrease as undergoing initial drying in high temperature,followed by expansion as the samples are immersed into water. Subsequently,expansion continues in the process of desiccating the samples at 80 ℃ and shrinkage then occurs after saturating the samples. Besides,as dry-wet cycling numbers increases,the elastic compressibility index increases,and the plastic compressibility index decreases and the yield pressure increases for samples with low density but the tendency is opposite for samples with high density. This study can provide a theoretical basis for post-construction settlement analysis in the engineering practice.
In the environment of engineering geology,high temperatures accelerate drying of the soil mass that is also subject to wetting by rainfall. Dry-wet cycles tends to cause degradation of the soil mass,which can seriously damage the infrastructure and buildings on the soil mass. Investigation of dry-wet cycling on deformation behavior of compacted loess is indispensable to evaluate the stability of basement and subgrade in the engineering practice. In the present work,we fabricated three groups of samples with one water content of 11% and three different dry densities(1.5,1.6 and 1.7 g·cm-3). The samples were desiccated at 80 ℃,followed by wetting at an ambient temperature through immersing the samples into deionized water until a designated dry-wet cycling number. Upon cycling,electrical resistivity was measured by a digital LCR meter to characterize the structure change of the samples. Besides,the photographs of the sample surface after desiccation were taken to observe crack evolution. At the end of the cycles,constant rate of strain(CRS)was imposed on the saturated samples to determine the deformation parameters of the compacted loss. Results shows that the electrical resistivity increases due to the increase of crack ratio as the cycling numbers increase. Since the vertical stress is zero,the volume of the unsaturated compacted samples decrease as undergoing initial drying in high temperature,followed by expansion as the samples are immersed into water. Subsequently,expansion continues in the process of desiccating the samples at 80 ℃ and shrinkage then occurs after saturating the samples. Besides,as dry-wet cycling numbers increases,the elastic compressibility index increases,and the plastic compressibility index decreases and the yield pressure increases for samples with low density but the tendency is opposite for samples with high density. This study can provide a theoretical basis for post-construction settlement analysis in the engineering practice.
2023, 31(2): 368-378.
As an important external factor,temperature has an important influence on the strength and fracture properties of red clay.Direct shear test and desiccation tests were conducted under different drying temperatures on unsaturated red clay with different initial state to investigate the effects of drying temperature,dry density and water content on strength and cracking characteristics.The evolutionary rules of the strength and fracture under different temperatures are analyzed.The relationship between shear strength index (cohesion and internal friction angle) and fracture geometry parameter (joint rate) are discussed in this paper.The results show that total joint length,nodes and joint rate increase with the increase of temperature.The amplitudes have significant increases when the water content is the maximum moisture content and the dry density is the minimum dry density.Tensile stress field in soils is the main mechanical cause of cracking.Cohesion increases firstly and then decreases with increasing temperature and the attenuation amplitude is related to dry density.Internal friction angle becomes lower firstly and then higher when the temperature is rising.The lower the water content,the more obvious the increase.As the joint rate increases,the cohesion becomes larger firstly,and then smaller,and then internal friction angle continuously increases.
As an important external factor,temperature has an important influence on the strength and fracture properties of red clay.Direct shear test and desiccation tests were conducted under different drying temperatures on unsaturated red clay with different initial state to investigate the effects of drying temperature,dry density and water content on strength and cracking characteristics.The evolutionary rules of the strength and fracture under different temperatures are analyzed.The relationship between shear strength index (cohesion and internal friction angle) and fracture geometry parameter (joint rate) are discussed in this paper.The results show that total joint length,nodes and joint rate increase with the increase of temperature.The amplitudes have significant increases when the water content is the maximum moisture content and the dry density is the minimum dry density.Tensile stress field in soils is the main mechanical cause of cracking.Cohesion increases firstly and then decreases with increasing temperature and the attenuation amplitude is related to dry density.Internal friction angle becomes lower firstly and then higher when the temperature is rising.The lower the water content,the more obvious the increase.As the joint rate increases,the cohesion becomes larger firstly,and then smaller,and then internal friction angle continuously increases.
2023, 31(2): 379-385.
Acid rain can react with carbonate formed in the process of MICP mineralization,destroy the structural strength of materials and release the fixed heavy metal ions again.However,the research on this technology in acid rain condition is less,and the acid corrosion resistance is not clear.Therefore,it is of practical significance to study the leaching characteristics of MICP solidified heavy metal contaminated soil under acid rain infiltration.In this paper,three typical acid rain conditions with a pH of 3.5,4.5 and 5.6 were designed.Deionized water with a pH of 7.5 was used as a control.The experimental study on MICP solidified lead-contaminated soil was carried out by using soil column leaching method.The influence of pH value of acid rain on strength,pH value,leaching amount of Pb2+,Ca2+ and occurrence form of Pb2+ was analyzed.The results show that: as the pH value of acid solution decreases,the strength of MICP solidified sample decreases,But as the pH value of leaching solution decreases,the leaching amount of Pb2+ and Ca2+ increases,When the exchangeable Pb2+ in solidified sample increases,and the Pb2+ in carbonate bound,iron manganese oxide bound,organic matter bound and residue state would decrease.The sample would be less affected by acid rain of 5.6 pH,while the pH value is 3.5,the sample change significantly.
Acid rain can react with carbonate formed in the process of MICP mineralization,destroy the structural strength of materials and release the fixed heavy metal ions again.However,the research on this technology in acid rain condition is less,and the acid corrosion resistance is not clear.Therefore,it is of practical significance to study the leaching characteristics of MICP solidified heavy metal contaminated soil under acid rain infiltration.In this paper,three typical acid rain conditions with a pH of 3.5,4.5 and 5.6 were designed.Deionized water with a pH of 7.5 was used as a control.The experimental study on MICP solidified lead-contaminated soil was carried out by using soil column leaching method.The influence of pH value of acid rain on strength,pH value,leaching amount of Pb2+,Ca2+ and occurrence form of Pb2+ was analyzed.The results show that: as the pH value of acid solution decreases,the strength of MICP solidified sample decreases,But as the pH value of leaching solution decreases,the leaching amount of Pb2+ and Ca2+ increases,When the exchangeable Pb2+ in solidified sample increases,and the Pb2+ in carbonate bound,iron manganese oxide bound,organic matter bound and residue state would decrease.The sample would be less affected by acid rain of 5.6 pH,while the pH value is 3.5,the sample change significantly.
2023, 31(2): 386-396.
According to a field investigation,expansive soil disasters such as building damage and slope failure happened in the area of Nanyang Basin in Henan Province as a result of extreme climate condition—persistent rains and drought,threatening people's property and lives. This paper aims to study the effect of calcium lignosulphonate for improving the swelling and shrinkage characteristics of weak expansive soil. The soil specimens mixed with calcium lignosulphonate at various percentages(0.5%,0.75%,1%,1.25%) by dry weight,and the free swell test were performed after specimens cured for 0,3,7,11,14,and 28 days to explore the optimum value of calcium lignosulphonate. The laboratory test results indicate that the specimen mixed with 0.75% calcium lignosulphonate and cured for 14 days has the lowest free swelling ratio. Based on the optimum values of calcium lignosulphonate(0.75%),unloaded expansion test and shrinkage test were conducted under cyclic drying and wetting condition. The results show that the addition of calcium lignosulfonate can effectively reduce the absolute expansion rate and the absolute shrinkage rate of weak expansive soil during the wetting-drying cycle. The maximum absolute expansion rate decreases from 29% to 3%,and the maximum absolute shrinkage rate decreases from 17% to 2%. The relative expansion rate and shrinkage rate of ameliorated soils keep steady with the increase of the wetting-drying cycle,which indicates that calcium lignosulfonate can effectively ameliorate the stability of swelling and shrinkage property of weak expansive soil during wetting and drying cycles. The increased drying-wetting cycle has no effect on the improved effectiveness of calcium lignosulphonate. By analyzing the crack development pattern of test specimens,calcium lignosulfonate primarily inhibits crack development,improves soil cementation ability,and causes the soil to form a more compact structure,allowing weak expansive soil to maintain its swelling and shrinkage characteristics stability during the drying-wetting cycle.
According to a field investigation,expansive soil disasters such as building damage and slope failure happened in the area of Nanyang Basin in Henan Province as a result of extreme climate condition—persistent rains and drought,threatening people's property and lives. This paper aims to study the effect of calcium lignosulphonate for improving the swelling and shrinkage characteristics of weak expansive soil. The soil specimens mixed with calcium lignosulphonate at various percentages(0.5%,0.75%,1%,1.25%) by dry weight,and the free swell test were performed after specimens cured for 0,3,7,11,14,and 28 days to explore the optimum value of calcium lignosulphonate. The laboratory test results indicate that the specimen mixed with 0.75% calcium lignosulphonate and cured for 14 days has the lowest free swelling ratio. Based on the optimum values of calcium lignosulphonate(0.75%),unloaded expansion test and shrinkage test were conducted under cyclic drying and wetting condition. The results show that the addition of calcium lignosulfonate can effectively reduce the absolute expansion rate and the absolute shrinkage rate of weak expansive soil during the wetting-drying cycle. The maximum absolute expansion rate decreases from 29% to 3%,and the maximum absolute shrinkage rate decreases from 17% to 2%. The relative expansion rate and shrinkage rate of ameliorated soils keep steady with the increase of the wetting-drying cycle,which indicates that calcium lignosulfonate can effectively ameliorate the stability of swelling and shrinkage property of weak expansive soil during wetting and drying cycles. The increased drying-wetting cycle has no effect on the improved effectiveness of calcium lignosulphonate. By analyzing the crack development pattern of test specimens,calcium lignosulfonate primarily inhibits crack development,improves soil cementation ability,and causes the soil to form a more compact structure,allowing weak expansive soil to maintain its swelling and shrinkage characteristics stability during the drying-wetting cycle.
2023, 31(2): 397-408.
The waste clay has poor engineering properties and is difficult to be used as subgrade material for resource utilization. This paper studies the effects of different amounts of ground granulated blast furnace slag-desulfurization gypsum-calcium carbide slag(GDC)soil stabilizer on the mechanical properties and micro mechanism of marine clay. Firstly,the unconfined compressive strength,splitting tensile strength and water stability tests were used to evaluate the macroscopic mechanical properties of GDC solidified soil. Then the interaction mechanism between the curing agent and marine clay was analyzed by SEM and XRD,and compared with the traditional cement curing scheme with the same content. The results show that the unconfined compressive strength of GDC solidified clay and cement solidified clay increases with the increase of curing agent content and curing age. Compared with cement solidified soil,GDC solidified soil has better water stability. With the growth of curing age,GDC solidified soil shows higher compressive strength,splitting resistance and lower brittleness;SEM and XRD analysis shows that GDC solidified soil would continuously generate cementitious hydrates such as hydrated calcium silicate(C-S-H),hydrated calcium aluminate(C-A-H) and expansive hydrated product ettringite(Aft) during curing,which can effectively wrap and connect clay particles and fill soil micro pores. Compared with cement stabilized soil,GDC solidified soil at the age of 28 days has a denser microstructure and a wider coverage of hydrated products. GDC soil stabilizer has remarkable effect on the modification of waste marine clay and has a good application prospect.
The waste clay has poor engineering properties and is difficult to be used as subgrade material for resource utilization. This paper studies the effects of different amounts of ground granulated blast furnace slag-desulfurization gypsum-calcium carbide slag(GDC)soil stabilizer on the mechanical properties and micro mechanism of marine clay. Firstly,the unconfined compressive strength,splitting tensile strength and water stability tests were used to evaluate the macroscopic mechanical properties of GDC solidified soil. Then the interaction mechanism between the curing agent and marine clay was analyzed by SEM and XRD,and compared with the traditional cement curing scheme with the same content. The results show that the unconfined compressive strength of GDC solidified clay and cement solidified clay increases with the increase of curing agent content and curing age. Compared with cement solidified soil,GDC solidified soil has better water stability. With the growth of curing age,GDC solidified soil shows higher compressive strength,splitting resistance and lower brittleness;SEM and XRD analysis shows that GDC solidified soil would continuously generate cementitious hydrates such as hydrated calcium silicate(C-S-H),hydrated calcium aluminate(C-A-H) and expansive hydrated product ettringite(Aft) during curing,which can effectively wrap and connect clay particles and fill soil micro pores. Compared with cement stabilized soil,GDC solidified soil at the age of 28 days has a denser microstructure and a wider coverage of hydrated products. GDC soil stabilizer has remarkable effect on the modification of waste marine clay and has a good application prospect.
2023, 31(2): 409-420.
On the basis of three issues,namely,the high moisture content,the high plasticity index and the poor construction performance of the waste drilling mud,this paper aims to design and select the quicklime and limestone powder as pretreatment agent materials. We conducted a series of tests in the laboratory. The effect of modification was characterized by the dehydration speed,variation range of Atterberg Limits,particle state as well as degree of crushing difficulty. Thereafter,we used the unconfined compressive strength(qu),water stability coefficient(γw),California bearing ratio(CBR) and the compressive modulus of resilience(Ec) as indices to determine the optimal ratio of waste soil,quicklime,limestone powder and WSS. These materials are selected to make modified compaction soil used in construction of roads. After that,we studied the influence of the aggregate size on the strength,broken shape and water stability. The results show that pretreatment can effectively reduce the moisture content of the waste soil,increase the drying rate,improve the Atterberg Limits and enhance the mixing effect with the powdered curing agent. The performance of quicklime-limestone powder-WSS(QLW) is far better than the cement. Pretreatment can not only improve the construction performance of the soil,but also promote the curing effect. In addition,the test clarified that with the decrease of Dmax,the strength and water stability of the QLW solidified soil gradually increased,and the failure mode changes from brittle shear failure to plastic compression failure.
On the basis of three issues,namely,the high moisture content,the high plasticity index and the poor construction performance of the waste drilling mud,this paper aims to design and select the quicklime and limestone powder as pretreatment agent materials. We conducted a series of tests in the laboratory. The effect of modification was characterized by the dehydration speed,variation range of Atterberg Limits,particle state as well as degree of crushing difficulty. Thereafter,we used the unconfined compressive strength(qu),water stability coefficient(γw),California bearing ratio(CBR) and the compressive modulus of resilience(Ec) as indices to determine the optimal ratio of waste soil,quicklime,limestone powder and WSS. These materials are selected to make modified compaction soil used in construction of roads. After that,we studied the influence of the aggregate size on the strength,broken shape and water stability. The results show that pretreatment can effectively reduce the moisture content of the waste soil,increase the drying rate,improve the Atterberg Limits and enhance the mixing effect with the powdered curing agent. The performance of quicklime-limestone powder-WSS(QLW) is far better than the cement. Pretreatment can not only improve the construction performance of the soil,but also promote the curing effect. In addition,the test clarified that with the decrease of Dmax,the strength and water stability of the QLW solidified soil gradually increased,and the failure mode changes from brittle shear failure to plastic compression failure.
2023, 31(2): 421-431.
In order to replace the landfill treatment mode of underground excavated sludge in Wenzhou,the solidified effect of quicklime on the sludge is explored. The solidified effect of quicklime on sludge in Wenzhou is provided with direct reference data for engineering. The solidification research of the sludge in Wenzhou is carried out in the laboratory. The influence of quicklime on various physical properties of the sludge is mainly explored. Besides,the solidification of the sludge is studied at field. The bearing capacity characteristic value of the solidified sludge is detected by cone penetration test of single bridge and plate loading test. The laboratory test shows that the addition of quicklime has an effect on many physical properties of the sludge,and the engineering and mechanical properties of the sludge are improved. When the content of quicklime is 4%,the UCS of the solidified sludge can reach 116 kPa. The cone penetration test in field shows that the solidified effect of quicklime on the sludge is obvious. When the content of quicklime is 1% ~5%,the average value of specific penetration resistance of the solidified sludge is 0.439~0.773 MPa. According to the plate loading test at field,when the content of quicklime is 1% ~5%,the characteristic value of the solidified sludge bearing capacity is between 126~330 kPa. In the project,quicklime can be used to solidify sludge,and the characteristic value of its bearing capacity can be predicted by the linear equation in this study.
In order to replace the landfill treatment mode of underground excavated sludge in Wenzhou,the solidified effect of quicklime on the sludge is explored. The solidified effect of quicklime on sludge in Wenzhou is provided with direct reference data for engineering. The solidification research of the sludge in Wenzhou is carried out in the laboratory. The influence of quicklime on various physical properties of the sludge is mainly explored. Besides,the solidification of the sludge is studied at field. The bearing capacity characteristic value of the solidified sludge is detected by cone penetration test of single bridge and plate loading test. The laboratory test shows that the addition of quicklime has an effect on many physical properties of the sludge,and the engineering and mechanical properties of the sludge are improved. When the content of quicklime is 4%,the UCS of the solidified sludge can reach 116 kPa. The cone penetration test in field shows that the solidified effect of quicklime on the sludge is obvious. When the content of quicklime is 1% ~5%,the average value of specific penetration resistance of the solidified sludge is 0.439~0.773 MPa. According to the plate loading test at field,when the content of quicklime is 1% ~5%,the characteristic value of the solidified sludge bearing capacity is between 126~330 kPa. In the project,quicklime can be used to solidify sludge,and the characteristic value of its bearing capacity can be predicted by the linear equation in this study.
2023, 31(2): 432-440.
Cement solidified soft soil is a common foundation treatment method in engineering. However,many engineering practices have shown that the early strength of soft soil reinforced by cement alone is low,and the volume of cement solidified soil shrinks with the growth of the curing age. They are likely to cause settlement and cracking of the engineering soil mass. We used basalt fibers to solidify soft soils with cement to explore the effect of basalt fibers on the strength and shrinkage performance. We prepared the different cement and basalt fibers solidified soil samples in this experiment. Under various age conditions,we tested the unconfined compressive strength and volume shrinkage property of the specimens to determine the optimum cement and fibers dosage. From the microstructural characteristics of the specimens,we analyzed the fibers mechanism on the strength and shrinkage distortion of cement solidified soil. The results show that the addition of fibers can effectively improve the strength and shrinkage of the cement soil. The fibers are randomly distributed in the specimen. The presence of fibers can play a "bridge" role,filling the pores of the soil sample together with the hydration products of cement,making the soil particles fully connected,limiting the displacement between the particles,improving the strength of the specimen,inhibiting the shrinkage of the specimens,and improving the overall stability of the soil mass. The research results can provide theoretical and practical references for the effective solidified treatment and efficient utilization of soft soils.
Cement solidified soft soil is a common foundation treatment method in engineering. However,many engineering practices have shown that the early strength of soft soil reinforced by cement alone is low,and the volume of cement solidified soil shrinks with the growth of the curing age. They are likely to cause settlement and cracking of the engineering soil mass. We used basalt fibers to solidify soft soils with cement to explore the effect of basalt fibers on the strength and shrinkage performance. We prepared the different cement and basalt fibers solidified soil samples in this experiment. Under various age conditions,we tested the unconfined compressive strength and volume shrinkage property of the specimens to determine the optimum cement and fibers dosage. From the microstructural characteristics of the specimens,we analyzed the fibers mechanism on the strength and shrinkage distortion of cement solidified soil. The results show that the addition of fibers can effectively improve the strength and shrinkage of the cement soil. The fibers are randomly distributed in the specimen. The presence of fibers can play a "bridge" role,filling the pores of the soil sample together with the hydration products of cement,making the soil particles fully connected,limiting the displacement between the particles,improving the strength of the specimen,inhibiting the shrinkage of the specimens,and improving the overall stability of the soil mass. The research results can provide theoretical and practical references for the effective solidified treatment and efficient utilization of soft soils.
2023, 31(2): 441-448.
This paper explores the improving effect and strengthening mechanism of xanthan gum and guar gum on tailing sand. It examines the interaction between different water-soluble plant gums and tailing sand by unconfined compressive strength,scanning electron microscopy and industrial CT scanning tests. The test results show that the optimal ratio of xanthan gum and guar gum to soil is 1%,and the compressive strength increased with the increase of the curing age. After 28 days and compared to untreated tailing sand,the strengths of xanthan gum and guar gum-improved soils increased by 266.84% and 262.33%,respectively. The microscopic tests show that as the curing age grows,colloids in the soil change into "small cemented and wrapped granular particles",and the internal cracks and pores gradually decrease. The porosity of tailing sand is 14.55% while the porosities of 28 d xanthan gum and guar gum soils are 3.08% and 3.26%,respectively. Moreover,the influence of the colloid-polymer optimal mixture ratio and curing age on the compressive strength,microstructures,and internal fracture pores of soil are obtained and presented.
This paper explores the improving effect and strengthening mechanism of xanthan gum and guar gum on tailing sand. It examines the interaction between different water-soluble plant gums and tailing sand by unconfined compressive strength,scanning electron microscopy and industrial CT scanning tests. The test results show that the optimal ratio of xanthan gum and guar gum to soil is 1%,and the compressive strength increased with the increase of the curing age. After 28 days and compared to untreated tailing sand,the strengths of xanthan gum and guar gum-improved soils increased by 266.84% and 262.33%,respectively. The microscopic tests show that as the curing age grows,colloids in the soil change into "small cemented and wrapped granular particles",and the internal cracks and pores gradually decrease. The porosity of tailing sand is 14.55% while the porosities of 28 d xanthan gum and guar gum soils are 3.08% and 3.26%,respectively. Moreover,the influence of the colloid-polymer optimal mixture ratio and curing age on the compressive strength,microstructures,and internal fracture pores of soil are obtained and presented.
2023, 31(2): 449-459.
Since the impoundment of the Three Gorges Reservoir at 175 m,the water level has periodically fluctuated,causing the strength of the bank slope to decrease and gradually deteriorate,which easily leads to instability and destruction of the rocky bank slope. So it has attracted widespread attention. The deterioration of the rock mass is related to the fluctuation of the reservoir water level,and the area of damage and deterioration must have a certain relationship with the scope of hydraulic adjustment. This paper presents for the first time a spatial analysis method of rock mass degradation based on the seepage difference of the fracture network model. The Beacher model is used to simulate the spatial distribution of rock mass fractures in combination with the fracture geometric parameter distribution probabilistic model. Based on the equal cross-sectional area of the fractures,the surface seepage in the fracture network is simplified as a pipeline flow,and the seepage space diagram of the fracture network is constructed. At the same time,the topological relationship is used to solve the water head distribution area in the seepage space of the rock mass fracture network in the actual working condition. The space where the rock mass degradation may occur through the seepage difference area under different water levels is used to obtain the new seepage area with the same hydraulic difference and the new water level change. Based on theoretical analysis and numerical simulation,it is concluded that the area with hydraulic difference and the newly added seepage area are the area of rock mass deterioration. This prediction method can have important guiding significance for quantifying the spatial strength of rock mass deterioration and bank slope stability in the Three Gorges Reservoir area.
Since the impoundment of the Three Gorges Reservoir at 175 m,the water level has periodically fluctuated,causing the strength of the bank slope to decrease and gradually deteriorate,which easily leads to instability and destruction of the rocky bank slope. So it has attracted widespread attention. The deterioration of the rock mass is related to the fluctuation of the reservoir water level,and the area of damage and deterioration must have a certain relationship with the scope of hydraulic adjustment. This paper presents for the first time a spatial analysis method of rock mass degradation based on the seepage difference of the fracture network model. The Beacher model is used to simulate the spatial distribution of rock mass fractures in combination with the fracture geometric parameter distribution probabilistic model. Based on the equal cross-sectional area of the fractures,the surface seepage in the fracture network is simplified as a pipeline flow,and the seepage space diagram of the fracture network is constructed. At the same time,the topological relationship is used to solve the water head distribution area in the seepage space of the rock mass fracture network in the actual working condition. The space where the rock mass degradation may occur through the seepage difference area under different water levels is used to obtain the new seepage area with the same hydraulic difference and the new water level change. Based on theoretical analysis and numerical simulation,it is concluded that the area with hydraulic difference and the newly added seepage area are the area of rock mass deterioration. This prediction method can have important guiding significance for quantifying the spatial strength of rock mass deterioration and bank slope stability in the Three Gorges Reservoir area.
2023, 31(2): 460-468.
This paper takes siltstone,granite and marble with a diameter of 20~50 mm and a height-diameter ratio of 2︰1 as research objects. It examines the influence of size change and lithology on the stress-strain curve,the failure,the uniaxial compressive strength,the elastic modulus and the Poisson's ratio of the rock samples,and analyzes the causes of size effect. The test results show that with the increase of the size,the coincidence degree of the stress-strain curves of the three rock samples increases gradually. The failure mode of siltstone and marble develops from single inclined plane shear failure to X-shaped conjugate plane shear failure. The granite is mainly the X-shaped conjugate plane shear failure,and the failure degree increases gradually. The uniaxial compressive strength and elastic modulus of the three rock samples increase as a whole,and the increase rate is larger between 20 and 30 mm,and smaller between 30 and 50 mm. The failure modes of different rock samples are roughly the same,but the dispersion of stress-strain curve,the stress-strain curve characteristics after peak,and the degree of damage vary. Poisson's ratio has no definite size effect. The local measurement method of resistance strain gauge can not well reflect the deformation characteristics of rock specimen. The main reason for the size effect is the heterogeneity of rock sample,followed by the end effect.
This paper takes siltstone,granite and marble with a diameter of 20~50 mm and a height-diameter ratio of 2︰1 as research objects. It examines the influence of size change and lithology on the stress-strain curve,the failure,the uniaxial compressive strength,the elastic modulus and the Poisson's ratio of the rock samples,and analyzes the causes of size effect. The test results show that with the increase of the size,the coincidence degree of the stress-strain curves of the three rock samples increases gradually. The failure mode of siltstone and marble develops from single inclined plane shear failure to X-shaped conjugate plane shear failure. The granite is mainly the X-shaped conjugate plane shear failure,and the failure degree increases gradually. The uniaxial compressive strength and elastic modulus of the three rock samples increase as a whole,and the increase rate is larger between 20 and 30 mm,and smaller between 30 and 50 mm. The failure modes of different rock samples are roughly the same,but the dispersion of stress-strain curve,the stress-strain curve characteristics after peak,and the degree of damage vary. Poisson's ratio has no definite size effect. The local measurement method of resistance strain gauge can not well reflect the deformation characteristics of rock specimen. The main reason for the size effect is the heterogeneity of rock sample,followed by the end effect.
2023, 31(2): 469-478.
The acoustic parameters of ultrasonic shear waves in rocks are closely related to mechanical parameters. The mechanical parameters of rocks can be inverted by using the propagation characteristics of ultrasonic shear waves. However,there are few relevant research results at present,so it is necessary to carry out in-depth research on the propagation characteristics of ultrasonic shear waves in rocks. Taking grey,red and yellow sandstone as the research objects,carry out ultrasonic shear wave propagation experiments at frequencies of 50,100 and 200 kHz. We extract acoustic parameters such as wave speed,dominant frequency and maximum amplitude to study the propagation characteristics of ultrasonic shear waves in sandstone. The results show that in the three types of sandstones,the shear wave velocity and dominant frequency all show a nonlinear increasing trend with the increase of the incident frequency and elastic modulus,and the maximum amplitude decreases with the incident frequency. Through homogenization,the sensitivity of the three acoustic parameters to the change of elastic modulus is analyzed. The results show that in the three kinds of sandstone,the shear wave velocity,dominant frequency and maximum amplitude increase nonlinearly with the increase of incident frequency and elastic modulus,while the effects of elastic modulus and incident frequency on the change rates of three acoustic parameters show different laws. The overall analysis shows that the maximum amplitude is the most sensitive to the change of the elastic modulus of sandstone. Three estimation formulas for the elastic modulus of sandstone are established based on the maximum amplitude. 50 kHz is the incident frequency for ultrasonic shear wave testing of this type of sandstone. The research results can provide reference for the development of ultrasonic testing technology.
The acoustic parameters of ultrasonic shear waves in rocks are closely related to mechanical parameters. The mechanical parameters of rocks can be inverted by using the propagation characteristics of ultrasonic shear waves. However,there are few relevant research results at present,so it is necessary to carry out in-depth research on the propagation characteristics of ultrasonic shear waves in rocks. Taking grey,red and yellow sandstone as the research objects,carry out ultrasonic shear wave propagation experiments at frequencies of 50,100 and 200 kHz. We extract acoustic parameters such as wave speed,dominant frequency and maximum amplitude to study the propagation characteristics of ultrasonic shear waves in sandstone. The results show that in the three types of sandstones,the shear wave velocity and dominant frequency all show a nonlinear increasing trend with the increase of the incident frequency and elastic modulus,and the maximum amplitude decreases with the incident frequency. Through homogenization,the sensitivity of the three acoustic parameters to the change of elastic modulus is analyzed. The results show that in the three kinds of sandstone,the shear wave velocity,dominant frequency and maximum amplitude increase nonlinearly with the increase of incident frequency and elastic modulus,while the effects of elastic modulus and incident frequency on the change rates of three acoustic parameters show different laws. The overall analysis shows that the maximum amplitude is the most sensitive to the change of the elastic modulus of sandstone. Three estimation formulas for the elastic modulus of sandstone are established based on the maximum amplitude. 50 kHz is the incident frequency for ultrasonic shear wave testing of this type of sandstone. The research results can provide reference for the development of ultrasonic testing technology.
2023, 31(2): 479-492.
Baihetan Hydropower Station is the second largest hydropower station after the Three Gorges hydropower station in China. There are many residential areas in Hulukou Xiangbiling reservoir bank section of the reservoir area. The stability of the reservoir bank is the focus of attention. Due to the influence of topography,tectonics and complex strata in this reservoir section,there can be active landslides with small deformation and hidden high position before impoundment. During impoundment and operation of the reservoir,such landslides can further aggravate the deformation and seriously threaten the life and property safety of surrounding residents. Therefore,it is of great significance to effectively identify and analyze the active landslide in the reservoir section before impoundment. In this study,the active landslides in this key reservoir section are effectively identified by using Sentinel-1A ascending and ALOS-1 ascending satellites and SBAS-InSAR(Small Baseline Subset-InSAR)technology based on terrain visibility. A total of 27 active landslides are identified,and 23 are finally determined through field verification,of which 12 slopes have their toe involving water level lines. Statistics show that active landslides in the study area develop most when the slope direction is northeast and northwest and the relative height difference is less than 500 m. Most of them are controlled by faults. The rock stratum strength of landslide disasters not controlled by faults is low. The research results are conducive to the prevention and early warning of landslides during the operation of the reservoir. The overall technical process and identification and analysis method can also provide an important reference basis for the identification and analysis of regional active landslides under complex terrain in the future.
Baihetan Hydropower Station is the second largest hydropower station after the Three Gorges hydropower station in China. There are many residential areas in Hulukou Xiangbiling reservoir bank section of the reservoir area. The stability of the reservoir bank is the focus of attention. Due to the influence of topography,tectonics and complex strata in this reservoir section,there can be active landslides with small deformation and hidden high position before impoundment. During impoundment and operation of the reservoir,such landslides can further aggravate the deformation and seriously threaten the life and property safety of surrounding residents. Therefore,it is of great significance to effectively identify and analyze the active landslide in the reservoir section before impoundment. In this study,the active landslides in this key reservoir section are effectively identified by using Sentinel-1A ascending and ALOS-1 ascending satellites and SBAS-InSAR(Small Baseline Subset-InSAR)technology based on terrain visibility. A total of 27 active landslides are identified,and 23 are finally determined through field verification,of which 12 slopes have their toe involving water level lines. Statistics show that active landslides in the study area develop most when the slope direction is northeast and northwest and the relative height difference is less than 500 m. Most of them are controlled by faults. The rock stratum strength of landslide disasters not controlled by faults is low. The research results are conducive to the prevention and early warning of landslides during the operation of the reservoir. The overall technical process and identification and analysis method can also provide an important reference basis for the identification and analysis of regional active landslides under complex terrain in the future.
2023, 31(2): 493-501.
After having collected a large number of loess landslides data in Tianshui City,Gansu Province through extensive site investigation,we constructed a multivariate probability distribution model for loess landslide data via Johnson's system of distribution. We used the model to predict the width,length,and area of potential slides in an unstable loess slope. The results show that the prediction from the proposed model is reasonably accurate. The upper boundary of the 90% confidence interval of the prediction results is used as the safety value of the impact range to derive the potential impact of the unstable loess slope in the survey area. After having verified with the same type of loess landslide data outside the survey area,it is found that the prediction formula has certain applicability to the evaluation of the same type of loess landslide in other areas in Tianshui City. Only the height of the unstable slope in the prediction formula is used as independent variables,which provides a great convenience for rapid on-site assessment of the hazard and impact range of unstable loess slopes. The proposed method therefore provides a vehicle for quantifying the impact of unstable loess slopes,and hence offers basis for quantitative evaluation of loess slope hazards in the region of Tianshui City.
After having collected a large number of loess landslides data in Tianshui City,Gansu Province through extensive site investigation,we constructed a multivariate probability distribution model for loess landslide data via Johnson's system of distribution. We used the model to predict the width,length,and area of potential slides in an unstable loess slope. The results show that the prediction from the proposed model is reasonably accurate. The upper boundary of the 90% confidence interval of the prediction results is used as the safety value of the impact range to derive the potential impact of the unstable loess slope in the survey area. After having verified with the same type of loess landslide data outside the survey area,it is found that the prediction formula has certain applicability to the evaluation of the same type of loess landslide in other areas in Tianshui City. Only the height of the unstable slope in the prediction formula is used as independent variables,which provides a great convenience for rapid on-site assessment of the hazard and impact range of unstable loess slopes. The proposed method therefore provides a vehicle for quantifying the impact of unstable loess slopes,and hence offers basis for quantitative evaluation of loess slope hazards in the region of Tianshui City.
2023, 31(2): 502-513.
A fragmentable discrete element landslide model takes into account the unique structure of loess and is built on the basis of PFC2D in order to investigate the impact of slide fragmentation on the dynamics of loess landslides. The landslide occurrence process under various fragmentation rates is simulated. The impact of fragmentation on the landslide velocity,mobility,and accumulation features is examined in order to replicate the whole process of the Dangchuan 8-meter landslide from beginning to end. The results show the follows. (1)The peak velocity of the slide is inversely related to the fragmentation rate,as evidenced by the fact that the maximum velocity of the slide movement falls as a power function with an increase in fragmentation rate. (2)There could be a cutoff point for the fragmentation-based encouragement of landslide mobility,below which the effective friction coefficient rapidly declines and does not change appreciably when the fragmentation rate rises above it. (3)As the degree of fragmentation increases,the landslide accumulation thickness decreases,sorting decreases,the horizontal dispersion broadens,the distribution of pores becomes more homogeneous,and the highest accumulation thickness is frequently found in low-lying terrain. (4)The Dangchuan 8-meter landslide had a fragmentation rate of 19%,a maximum local velocity of around 17 m·s-1,a maximum sliding distance of roughly 195 m,and a total duration from destabilization to cease movement of 28 s. It demonstrates how fragmentation affects a landslide's dynamic process,providing some useful context for those looking into the subject.
A fragmentable discrete element landslide model takes into account the unique structure of loess and is built on the basis of PFC2D in order to investigate the impact of slide fragmentation on the dynamics of loess landslides. The landslide occurrence process under various fragmentation rates is simulated. The impact of fragmentation on the landslide velocity,mobility,and accumulation features is examined in order to replicate the whole process of the Dangchuan 8-meter landslide from beginning to end. The results show the follows. (1)The peak velocity of the slide is inversely related to the fragmentation rate,as evidenced by the fact that the maximum velocity of the slide movement falls as a power function with an increase in fragmentation rate. (2)There could be a cutoff point for the fragmentation-based encouragement of landslide mobility,below which the effective friction coefficient rapidly declines and does not change appreciably when the fragmentation rate rises above it. (3)As the degree of fragmentation increases,the landslide accumulation thickness decreases,sorting decreases,the horizontal dispersion broadens,the distribution of pores becomes more homogeneous,and the highest accumulation thickness is frequently found in low-lying terrain. (4)The Dangchuan 8-meter landslide had a fragmentation rate of 19%,a maximum local velocity of around 17 m·s-1,a maximum sliding distance of roughly 195 m,and a total duration from destabilization to cease movement of 28 s. It demonstrates how fragmentation affects a landslide's dynamic process,providing some useful context for those looking into the subject.
2023, 31(2): 514-525.
In Yanqing Competition Area of Winter Olympic Games Beijing 2022,the snow making and water diversion project is an important supporting project,which is responsible for water storage and water supply in the competition area. Due to engineering functions and topography conditions,the engineering site area is a favorable geological environment for debris flow disaster,and the main hydraulic facilities are faced with high risk of debris flow. At present,it is difficult to use debris flow dynamic numerical simulation method to simulate and predict sediment erosion thickness under multiple rainfall conditions. In terms of this issue,we propose two indexes: the mean thickness of water yield in debris flow gully and the mean thickness of stone produced by source under different rainfall recurrence periods. And we simulate and predicte the potential debris flow disaster in engineering area with UAV measurement,remote sensing interpretation,field investigation and Massflow. The results show that hydraulic facilities(damp and pumping stations) at different elevations face different debris flow threats,under different rainfall recurrence periods. The debris flow risk of 1050 dam is the highest,facing the double damage of siltation and alluvial,followed by the debris flow risk of 900 pumping station and 1290 reservoir. The former is mainly siltation damage,the latter is mainly alluvial damage. The risk of debris flow is low at pump station 900 and pump station 1050. Based on simulation analysis and field investigation,it is suggested to build a sand dam upstream of 1050 reservoir,a diversion channel on the east side of 1290 reservoir,and a sand settling basin at the end of 900 reservoir to ensure long-term safety operation of hydraulic facilities.
In Yanqing Competition Area of Winter Olympic Games Beijing 2022,the snow making and water diversion project is an important supporting project,which is responsible for water storage and water supply in the competition area. Due to engineering functions and topography conditions,the engineering site area is a favorable geological environment for debris flow disaster,and the main hydraulic facilities are faced with high risk of debris flow. At present,it is difficult to use debris flow dynamic numerical simulation method to simulate and predict sediment erosion thickness under multiple rainfall conditions. In terms of this issue,we propose two indexes: the mean thickness of water yield in debris flow gully and the mean thickness of stone produced by source under different rainfall recurrence periods. And we simulate and predicte the potential debris flow disaster in engineering area with UAV measurement,remote sensing interpretation,field investigation and Massflow. The results show that hydraulic facilities(damp and pumping stations) at different elevations face different debris flow threats,under different rainfall recurrence periods. The debris flow risk of 1050 dam is the highest,facing the double damage of siltation and alluvial,followed by the debris flow risk of 900 pumping station and 1290 reservoir. The former is mainly siltation damage,the latter is mainly alluvial damage. The risk of debris flow is low at pump station 900 and pump station 1050. Based on simulation analysis and field investigation,it is suggested to build a sand dam upstream of 1050 reservoir,a diversion channel on the east side of 1290 reservoir,and a sand settling basin at the end of 900 reservoir to ensure long-term safety operation of hydraulic facilities.
2023, 31(2): 526-537.
Taking Yongji County of Jilin Province as a study area,we investigated the application of the geographic information similarity based absence sample sampling method to debris flow susceptibility mapping,and explored the influence of the selected negative samples under different value ranges on the final susceptibility mapping results. We selected 14 factors including elevation,slope,aspect,plane curvature,profile curvature,mean annual precipitation,normalized difference vegetation index,topographic wetness index,fault density,road density,water system density,population density,land-use,and geotechnical type. Then,we used different methods to calculate single-factor similarity based on two classifications: discrete and continuous. After synthetically obtaining the region-wide geographical information similarity,we sampled negative samples according to their different thresholds. Subsequently,we chose the support vector machine model as the base model,and three methods(ROC,positive sample accuracy and forecast efficiency curves) as evaluate system. The results show that: Firstly,the geographical information similarity based absence sample sampling method can effectively improve the quality of negative samples. Secondly,when the value of geographical information similarity of negative samples gradually increases,the model accuracy and positive sample accuracy gradually decrease,the forecast efficiency first increases and then decreases. At last,the negative sample selected within the geographic information similarity range of 0 to 0.5 balances model accuracy with land-use value and has the highest predictive efficiency,making it an excellent negative sample sampling strategy. The sampling strategy of negative samples based on the similarity of geographical information effectively improves the quality of negative samples,enhances the prediction efficiency,reasonably balances the contradiction between the division of susceptibility zones and land-use,and provides a new way of thinking on the evaluation of regional debris flow susceptibility.
Taking Yongji County of Jilin Province as a study area,we investigated the application of the geographic information similarity based absence sample sampling method to debris flow susceptibility mapping,and explored the influence of the selected negative samples under different value ranges on the final susceptibility mapping results. We selected 14 factors including elevation,slope,aspect,plane curvature,profile curvature,mean annual precipitation,normalized difference vegetation index,topographic wetness index,fault density,road density,water system density,population density,land-use,and geotechnical type. Then,we used different methods to calculate single-factor similarity based on two classifications: discrete and continuous. After synthetically obtaining the region-wide geographical information similarity,we sampled negative samples according to their different thresholds. Subsequently,we chose the support vector machine model as the base model,and three methods(ROC,positive sample accuracy and forecast efficiency curves) as evaluate system. The results show that: Firstly,the geographical information similarity based absence sample sampling method can effectively improve the quality of negative samples. Secondly,when the value of geographical information similarity of negative samples gradually increases,the model accuracy and positive sample accuracy gradually decrease,the forecast efficiency first increases and then decreases. At last,the negative sample selected within the geographic information similarity range of 0 to 0.5 balances model accuracy with land-use value and has the highest predictive efficiency,making it an excellent negative sample sampling strategy. The sampling strategy of negative samples based on the similarity of geographical information effectively improves the quality of negative samples,enhances the prediction efficiency,reasonably balances the contradiction between the division of susceptibility zones and land-use,and provides a new way of thinking on the evaluation of regional debris flow susceptibility.
2023, 31(2): 538-551.
To address the lack of historical disaster data in high-precision geological disaster research,we proposed a geological disaster susceptibility evaluation model. This model couples grey relational degree(GRD) and analytic hierarchy process(AHP). We obtained and classified the states of 9 factors by engineering survey and remote sensing interpretation according to the disaster mechanism. We analyzed the relational degrees between 9 factors and historical disasters and constructed three discriminant matrices of AHP based on the values,the index scale values,and the ranking of the relational degrees,respectively. Three GRD-AHP coupling models(G-A1,G-A2,and G- A3) and a classical GRD model(G)were established. The coupling model G-A1 shows a more reasonable susceptibility index distribution,a higher prediction accuracy,and a larger high-susceptibility intensity index. This new model is recommended as the evaluation model of geological hazard susceptibility in Chongtou Town and southwest Zhejiang Province. This work provides an effective coupled model for high-precision geological disaster research.
To address the lack of historical disaster data in high-precision geological disaster research,we proposed a geological disaster susceptibility evaluation model. This model couples grey relational degree(GRD) and analytic hierarchy process(AHP). We obtained and classified the states of 9 factors by engineering survey and remote sensing interpretation according to the disaster mechanism. We analyzed the relational degrees between 9 factors and historical disasters and constructed three discriminant matrices of AHP based on the values,the index scale values,and the ranking of the relational degrees,respectively. Three GRD-AHP coupling models(G-A1,G-A2,and G- A3) and a classical GRD model(G)were established. The coupling model G-A1 shows a more reasonable susceptibility index distribution,a higher prediction accuracy,and a larger high-susceptibility intensity index. This new model is recommended as the evaluation model of geological hazard susceptibility in Chongtou Town and southwest Zhejiang Province. This work provides an effective coupled model for high-precision geological disaster research.
2023, 31(2): 552-561.
In Kenyan part of the East African Rift,the magmatism related to asthenosphere intrusion and lithospheric thinning leads to frequent volcanic activities. The ground fissures caused by volcanic activity directly threaten the engineering facilities in the study area. The purposes of this paper are (a) to determine the distribution characteristics of the ground fissures,(b) to analyze the correlation between ground fissures and volcanic activities,and (c) to explore the formation mechanism of the ground fissures. Through field investigation and geophysical exploration,this paper summarizes the plane distribution characteristics and failure characteristics of the ground fissures,analyzes the relationship between the bedrock fissures and the ground fissures. The results show that the ground fissures are mainly distributed at the bottom of the rift,accompanied by volcanoes. The strikes of ground fissures are mainly NE-NNE and NW,extending linearly on the ground surface. The characteristics of surface failure are mainly horizontal tension. The ground fissures in sediments are connected with the bedrock fissures. The bedrock fissures determine the development location and scale of the ground fissures. The relationship between volcanic activity and the ground fissures is examined by crustal deformation data and the Mogi point source model. The formation mechanism of the ground fissures under volcanic activity is summarized. The widespread discontinuous deformation is caused by volcanic eruption resulted in bedrock rupture. The formation mechanism of the ground fissures in Kenya Rift Valley can be summarized as volcanic eruption-bedrock rupture-sediment destruction.
In Kenyan part of the East African Rift,the magmatism related to asthenosphere intrusion and lithospheric thinning leads to frequent volcanic activities. The ground fissures caused by volcanic activity directly threaten the engineering facilities in the study area. The purposes of this paper are (a) to determine the distribution characteristics of the ground fissures,(b) to analyze the correlation between ground fissures and volcanic activities,and (c) to explore the formation mechanism of the ground fissures. Through field investigation and geophysical exploration,this paper summarizes the plane distribution characteristics and failure characteristics of the ground fissures,analyzes the relationship between the bedrock fissures and the ground fissures. The results show that the ground fissures are mainly distributed at the bottom of the rift,accompanied by volcanoes. The strikes of ground fissures are mainly NE-NNE and NW,extending linearly on the ground surface. The characteristics of surface failure are mainly horizontal tension. The ground fissures in sediments are connected with the bedrock fissures. The bedrock fissures determine the development location and scale of the ground fissures. The relationship between volcanic activity and the ground fissures is examined by crustal deformation data and the Mogi point source model. The formation mechanism of the ground fissures under volcanic activity is summarized. The widespread discontinuous deformation is caused by volcanic eruption resulted in bedrock rupture. The formation mechanism of the ground fissures in Kenya Rift Valley can be summarized as volcanic eruption-bedrock rupture-sediment destruction.
2023, 31(2): 562-573.
As a typical geological defect in Yebatan hydropower dam site area,the impact of multi-faults on the deformation and anti-slip stability of the high arch dam base cannot be ignored. Based on the development and distribution of faults in the dam area and their basic characteristics,this paper proposes the concept of multiple faults,and analyzes the geomechanical formation mechanism and spatial distribution characteristics of multiple faults in the foundation rock from the perspective of dynamic kinematics. It comes up with three basic combination patterns of multiple faults in the Yebatan hydropower dam site area. They are the parallel arrangement type,the conjugate shear type,and the primary & secondary intergrowth type,which simplifies the complex fault situation in the foundation rock. The combination of qualitative and quantitative methods is used to compare and analyze the degradation degree of faults on the quality of the foundation rock under different combination patterns. The degradation degree of the conjugate shear type and the primary & secondary intergrowth type is stronger,which degrades the quality of the rock body by one grade. The degradation degree of the parallel arrangement type is more general,which degrades the quality of the rock body by half grade. The relationship between the influence path of faults and the degradation degree under different patterns is discussed. The research results provide technical support for the excavation treatment and risk prevention and control of the foundation rock of Yebatan Hydropower Station.
As a typical geological defect in Yebatan hydropower dam site area,the impact of multi-faults on the deformation and anti-slip stability of the high arch dam base cannot be ignored. Based on the development and distribution of faults in the dam area and their basic characteristics,this paper proposes the concept of multiple faults,and analyzes the geomechanical formation mechanism and spatial distribution characteristics of multiple faults in the foundation rock from the perspective of dynamic kinematics. It comes up with three basic combination patterns of multiple faults in the Yebatan hydropower dam site area. They are the parallel arrangement type,the conjugate shear type,and the primary & secondary intergrowth type,which simplifies the complex fault situation in the foundation rock. The combination of qualitative and quantitative methods is used to compare and analyze the degradation degree of faults on the quality of the foundation rock under different combination patterns. The degradation degree of the conjugate shear type and the primary & secondary intergrowth type is stronger,which degrades the quality of the rock body by one grade. The degradation degree of the parallel arrangement type is more general,which degrades the quality of the rock body by half grade. The relationship between the influence path of faults and the degradation degree under different patterns is discussed. The research results provide technical support for the excavation treatment and risk prevention and control of the foundation rock of Yebatan Hydropower Station.
2023, 31(2): 574-583.
Landslide dams are formed by the blockage of river channel with soil and rock debris from rockfall,landslide and debris flow. Differ from the man-made dam,the materials of landslide dams have the characteristics of loose structure and uneven distribution. Hence,the landslide dams are prone to failure by overtopping,seepage damage and dam slope instability after their formation,which threatens the life and property safety of downstream people. Once the landslide dams are formed,their stability and failure mode are influence by the water in upstream and the aftershock. In this article,the Tangjiashan landslide dam induced by the Wenchuan earthquake is considered. The ABAQUS is used to establish the seepage and dynamic response analysis model. The stability of landslide dam under the action of seepage and aftershocks are analyzed. The influence of seepage and aftershock on the failure mode of landslide dam are discussed. The research results show that(1)the possibility of seepage failure of the Tangjiashan landslide dam is relatively small. But as the upstream water level rises,the probability of seepage failure of the landslide dam increases; (2)The dynamic response characteristics of the landslide dam shows that from top to bottom along the height of the dam,the acceleration magnification of the dam body gradually decreases,and the dynamic response presents an obvious"surface amplification" effect; (3)The Tangjiashan landslide dam would not fail under the action of aftershocks. The aftershocks can reduce the height of the landslide dam significantly,thereby accelerating the occurrence of overflow damage.
Landslide dams are formed by the blockage of river channel with soil and rock debris from rockfall,landslide and debris flow. Differ from the man-made dam,the materials of landslide dams have the characteristics of loose structure and uneven distribution. Hence,the landslide dams are prone to failure by overtopping,seepage damage and dam slope instability after their formation,which threatens the life and property safety of downstream people. Once the landslide dams are formed,their stability and failure mode are influence by the water in upstream and the aftershock. In this article,the Tangjiashan landslide dam induced by the Wenchuan earthquake is considered. The ABAQUS is used to establish the seepage and dynamic response analysis model. The stability of landslide dam under the action of seepage and aftershocks are analyzed. The influence of seepage and aftershock on the failure mode of landslide dam are discussed. The research results show that(1)the possibility of seepage failure of the Tangjiashan landslide dam is relatively small. But as the upstream water level rises,the probability of seepage failure of the landslide dam increases; (2)The dynamic response characteristics of the landslide dam shows that from top to bottom along the height of the dam,the acceleration magnification of the dam body gradually decreases,and the dynamic response presents an obvious"surface amplification" effect; (3)The Tangjiashan landslide dam would not fail under the action of aftershocks. The aftershocks can reduce the height of the landslide dam significantly,thereby accelerating the occurrence of overflow damage.
2023, 31(2): 584-595.
The arid northwestern China is fragile in ecological environment and is one of the most sensitive areas to global climate change. In recent years, the hydrological and ecological issues induced by the change of regional surface water runoff producing pattern have been more and more significant under the global warming. The present research took the hyper-arid Golmud River Basin on Tibetan Plateau as an example to get insights into the spatio-temporal characteristics of surface water runoff quantity evolution and its seepage infiltrating into the groundwater system of arid watershed under climate warming. It further conducted the SWAT simulation and the in-situ hydrological observed data analysis. The results show that the surface water runoff quantity of Golmud river at the mountain pass had a significant increasing trend from 1976 to 2014 with the annual average increasing rate up to 0.38 (m3·s-1)·a-1. The annual average increasing quantity of the surface water runoff at the mountain pass is approximately 1.66×108m3. The increase of surface water runoff quantity is more significant during the summer compared to the winter. Precipitation and temperature are the dominant meteorological factors governing the surface runoff quantity in the Golmud watershed. The increase of surface water runoff quantity has significantly changed the seepage condition of surface water into the groundwater system. The annual average seepage water quantity can be up to 9.89×108m3. The increase of river seepage water quantity would break the water balance of the regional groundwater system and trigger a series of hydrological and ecological issues, and furtherly threaten the sustainable development of the watershed. This study can provide scientific supports for our country to cope with the challenges of water resources and ecological environment in arid regions by global climate change.
The arid northwestern China is fragile in ecological environment and is one of the most sensitive areas to global climate change. In recent years, the hydrological and ecological issues induced by the change of regional surface water runoff producing pattern have been more and more significant under the global warming. The present research took the hyper-arid Golmud River Basin on Tibetan Plateau as an example to get insights into the spatio-temporal characteristics of surface water runoff quantity evolution and its seepage infiltrating into the groundwater system of arid watershed under climate warming. It further conducted the SWAT simulation and the in-situ hydrological observed data analysis. The results show that the surface water runoff quantity of Golmud river at the mountain pass had a significant increasing trend from 1976 to 2014 with the annual average increasing rate up to 0.38 (m3·s-1)·a-1. The annual average increasing quantity of the surface water runoff at the mountain pass is approximately 1.66×108m3. The increase of surface water runoff quantity is more significant during the summer compared to the winter. Precipitation and temperature are the dominant meteorological factors governing the surface runoff quantity in the Golmud watershed. The increase of surface water runoff quantity has significantly changed the seepage condition of surface water into the groundwater system. The annual average seepage water quantity can be up to 9.89×108m3. The increase of river seepage water quantity would break the water balance of the regional groundwater system and trigger a series of hydrological and ecological issues, and furtherly threaten the sustainable development of the watershed. This study can provide scientific supports for our country to cope with the challenges of water resources and ecological environment in arid regions by global climate change.
2023, 31(2): 596-606.
Factor of safety(FOS) is an important parameter to evaluate slope stability. Two common methods used for evaluating FOS are the limit equilibrium method(LEM) and the finite element method(FEM). Since the stress-strain relationship is not considered,the LEM cannot truly reflect the development of stress field,displacement field and plastic zone during soil failure. On the other hand,although the constitute model is considered in FEM,it may suffer from nonconvergence problem due to grid distortion in the calculation process. To solve this problem,the strength reduction material point method(SRMPM) is proposed to evaluate the slope stability. The relationship between dimensionless soil parameters and FOS is subsequently constructed and plotted by different curves to obtain the stability analysis chart. This method can quickly and conveniently determine the FOS of slope without any iterative process. The reliability of the method is verified by four typical examples. The results show that the FOS calculated by the proposed chart is close to that calculated by other methods. The proposed method is conservative and effective.
Factor of safety(FOS) is an important parameter to evaluate slope stability. Two common methods used for evaluating FOS are the limit equilibrium method(LEM) and the finite element method(FEM). Since the stress-strain relationship is not considered,the LEM cannot truly reflect the development of stress field,displacement field and plastic zone during soil failure. On the other hand,although the constitute model is considered in FEM,it may suffer from nonconvergence problem due to grid distortion in the calculation process. To solve this problem,the strength reduction material point method(SRMPM) is proposed to evaluate the slope stability. The relationship between dimensionless soil parameters and FOS is subsequently constructed and plotted by different curves to obtain the stability analysis chart. This method can quickly and conveniently determine the FOS of slope without any iterative process. The reliability of the method is verified by four typical examples. The results show that the FOS calculated by the proposed chart is close to that calculated by other methods. The proposed method is conservative and effective.
2023, 31(2): 607-616.
Due to the limitations of the commonly used pseudo-static method,combining the more reasonable pseudo-dynamic method with the slope limit equilibrium analysis method has important theoretical and practical significance for the analysis of seismic slope stability. Based on the pseudo-dynamic method and the residual thrust method in the limit equilibrium analysis,we derive the pseudo-dynamic seismic force calculation formula and the residual thrust calculation formula of the seismic slope considering the vibration amplification effect. On this basis,a program was compiled with the help of MATLAB software to calculate the residual thrust and safety factor of the seismic slope. A new method of pseudo-dynamic seismic slope stability analysis was obtained. Using the developed program,through the analysis of calculation examples,the influences of ground motion characteristics,slope material characteristics,slope geometry,and topographic amplification effects on the stability of seismic slopes were discussed. Research results indicate that the safety factor of seismic slope fluctuates periodically with the initial phase of the input ground motion,and the soil amplification factor does not change its fluctuation period. The safety factor of seismic slope decreases with the increase of the seismic coefficient,soil amplification factor,and the ratio of seismic wave length to slope height. Regardless of the vibration amplification effect,when the value of λ/H is equal to 2,the pseudo-dynamic safety factor changes from a sharp decrease to a stable. The smaller the value of λ/H,the closer the pseudo-dynamic safety factor and the static safety factor. The larger the value of λ/H,the closer the pseudo-dynamic safety factor and the pseudo-static safety factor. When considering the effect of vibration amplification,the pseudo-dynamic safety factor appears to be smaller than the pseudo-static safety factor. Therefore,the pseudo-dynamic method is more reasonable than the pseudo-static method from the perspective of safety or economy,and it is the preferred method for seismic slope stability analysis.
Due to the limitations of the commonly used pseudo-static method,combining the more reasonable pseudo-dynamic method with the slope limit equilibrium analysis method has important theoretical and practical significance for the analysis of seismic slope stability. Based on the pseudo-dynamic method and the residual thrust method in the limit equilibrium analysis,we derive the pseudo-dynamic seismic force calculation formula and the residual thrust calculation formula of the seismic slope considering the vibration amplification effect. On this basis,a program was compiled with the help of MATLAB software to calculate the residual thrust and safety factor of the seismic slope. A new method of pseudo-dynamic seismic slope stability analysis was obtained. Using the developed program,through the analysis of calculation examples,the influences of ground motion characteristics,slope material characteristics,slope geometry,and topographic amplification effects on the stability of seismic slopes were discussed. Research results indicate that the safety factor of seismic slope fluctuates periodically with the initial phase of the input ground motion,and the soil amplification factor does not change its fluctuation period. The safety factor of seismic slope decreases with the increase of the seismic coefficient,soil amplification factor,and the ratio of seismic wave length to slope height. Regardless of the vibration amplification effect,when the value of λ/H is equal to 2,the pseudo-dynamic safety factor changes from a sharp decrease to a stable. The smaller the value of λ/H,the closer the pseudo-dynamic safety factor and the static safety factor. The larger the value of λ/H,the closer the pseudo-dynamic safety factor and the pseudo-static safety factor. When considering the effect of vibration amplification,the pseudo-dynamic safety factor appears to be smaller than the pseudo-static safety factor. Therefore,the pseudo-dynamic method is more reasonable than the pseudo-static method from the perspective of safety or economy,and it is the preferred method for seismic slope stability analysis.
2023, 31(2): 617-627.
The non-homogeneity and discontinuity of the height of spheroidal weathered granite type soil slopes and the complexity of the soil-ball contact interface cause their instability damage to be complex and variable. The failure mode of spherical weathered granite-like soil slopes is studied taking into account the action of content,spatial distribution,grain size composition and soil-sphere contact surface. The results show that the damage pattern of spheroidal weathered granite slopes is complex and variable. The presence of spheroidal weathering bodies makes the potential sliding surface of these slopes extremely irregular,and even multiple sliding surfaces appear. The weathered bodies located near the sliding surface hinder the development of the sliding surface,forcing the plasticity of "rock-winding,diversion or inclusion". As the content of spherical weathered bodies grows,it is more and more difficult to form a single sliding surface inside the slope body,and the safety factor gradually increases. The more the content of (0.22~0.3)Lc size weathering bodies,the larger the area occupied by the weathering bodies in Zone Ⅱ,the more favourable to slope stability. The soil-ball contact interface is most likely to develop into a sliding surface,and the interface contact type significantly affects the sliding surface of spherical weathered. The interface contact type significantly influences the destabilization evolution process of granite-like soil slopes. The research results can provide scientific basis and theoretical support for evaluating the stability of spheroidal weathered granitic soil slopes reasonably and accurately.
The non-homogeneity and discontinuity of the height of spheroidal weathered granite type soil slopes and the complexity of the soil-ball contact interface cause their instability damage to be complex and variable. The failure mode of spherical weathered granite-like soil slopes is studied taking into account the action of content,spatial distribution,grain size composition and soil-sphere contact surface. The results show that the damage pattern of spheroidal weathered granite slopes is complex and variable. The presence of spheroidal weathering bodies makes the potential sliding surface of these slopes extremely irregular,and even multiple sliding surfaces appear. The weathered bodies located near the sliding surface hinder the development of the sliding surface,forcing the plasticity of "rock-winding,diversion or inclusion". As the content of spherical weathered bodies grows,it is more and more difficult to form a single sliding surface inside the slope body,and the safety factor gradually increases. The more the content of (0.22~0.3)Lc size weathering bodies,the larger the area occupied by the weathering bodies in Zone Ⅱ,the more favourable to slope stability. The soil-ball contact interface is most likely to develop into a sliding surface,and the interface contact type significantly affects the sliding surface of spherical weathered. The interface contact type significantly influences the destabilization evolution process of granite-like soil slopes. The research results can provide scientific basis and theoretical support for evaluating the stability of spheroidal weathered granitic soil slopes reasonably and accurately.
2023, 31(2): 628-637.
Vegetation can effectively suppress shallow landslides. But landslide,debris flow and other disasters also occur in areas with good vegetation under special circumstances such as rainstorm. Due to the numerous factors affecting slope stability by different vegetations,it is difficult to assess slope stability and disaster risk. So there is no preferable evaluation or assessment method. In view of this situation,the Dadu River Basin is chosen as the research area. Through the regional terrain,slope,vegetation data extraction and slope division,the numerical calculation method of finite difference is adopted to calculate the stability of more than 40,000 slopes divided in the region. Then the factors of safety of slopes under different vegetation covers are obtained. Based on vegetation type,slope,it is found that different types of vegetation cover conditions of unstable slope gradient distribution have a normal slope stability of law. Based on the results of all potential unstable slope's vegetation type and grade of statistical analysis and distribution characteristic,we set up three different vegetation types of unstable slope development function relation between probability and slope. The calculation results show that as the slope increases,the number of stable slopes for different vegetation types decreases to different degrees. In general,arbor forests cover slopes have poor stability,followed by shrubs,and the meadows were better. In addition,the slope range with the highest probability of unstable slope development is different: 26.0°~37.0°for arbor forest,28.0~39.0°for shrub,and 31.0~39.0°for meadow. This study can provide a basis for the prevention and planning of landslide,debris flow and other geological disasters in the basin,and also provide more reliable data and ideas for the quantification of indexes and determination of weights in disaster risk assessment of good vegetation areas.
Vegetation can effectively suppress shallow landslides. But landslide,debris flow and other disasters also occur in areas with good vegetation under special circumstances such as rainstorm. Due to the numerous factors affecting slope stability by different vegetations,it is difficult to assess slope stability and disaster risk. So there is no preferable evaluation or assessment method. In view of this situation,the Dadu River Basin is chosen as the research area. Through the regional terrain,slope,vegetation data extraction and slope division,the numerical calculation method of finite difference is adopted to calculate the stability of more than 40,000 slopes divided in the region. Then the factors of safety of slopes under different vegetation covers are obtained. Based on vegetation type,slope,it is found that different types of vegetation cover conditions of unstable slope gradient distribution have a normal slope stability of law. Based on the results of all potential unstable slope's vegetation type and grade of statistical analysis and distribution characteristic,we set up three different vegetation types of unstable slope development function relation between probability and slope. The calculation results show that as the slope increases,the number of stable slopes for different vegetation types decreases to different degrees. In general,arbor forests cover slopes have poor stability,followed by shrubs,and the meadows were better. In addition,the slope range with the highest probability of unstable slope development is different: 26.0°~37.0°for arbor forest,28.0~39.0°for shrub,and 31.0~39.0°for meadow. This study can provide a basis for the prevention and planning of landslide,debris flow and other geological disasters in the basin,and also provide more reliable data and ideas for the quantification of indexes and determination of weights in disaster risk assessment of good vegetation areas.
2023, 31(2): 638-649.
As the most common cause of slope instability damage,rainfall has more complex influence characteristics in spheroidal weathered granite-type soil slopes with significant non-homogeneity and discontinuity characteristics. Based on ABAQUS and its secondary development,a study on the seepage characteristics and stability of spheroidal weathered granitic soil slopes under rainfall conditions was carried out by constructing a seepage model for spheroidal weathered granitic soil slopes and considering the influence of rainfall parameters. The results of the study show that the shallow soil of the slope is saturated more quickly under the influence of the spherical weathering body. The saturation rate is also controlled by the depth of burial of the weathering body,the cross-sectional area and content of the "rain-facing" surface. The potential sliding surfaces of the spherical weathering granite-like soil slope under rainfall conditions still show a significant complex diversity,and there are similar sliding surfaces to those in the rain-free state. The slope safety factor is negatively correlated with rainfall duration and intensity,and tends to level off as rainfall continues,but can also lose its leveling off trend and continue to decrease under the influence of spheroidal weathering bodies. Among the rainfall types,the gradual incremental type has the greatest influence on slope stability. The results of the study can provide a scientific basis for evaluating the stability of spherically weathered granite-like soil slopes under rainfall conditions.
As the most common cause of slope instability damage,rainfall has more complex influence characteristics in spheroidal weathered granite-type soil slopes with significant non-homogeneity and discontinuity characteristics. Based on ABAQUS and its secondary development,a study on the seepage characteristics and stability of spheroidal weathered granitic soil slopes under rainfall conditions was carried out by constructing a seepage model for spheroidal weathered granitic soil slopes and considering the influence of rainfall parameters. The results of the study show that the shallow soil of the slope is saturated more quickly under the influence of the spherical weathering body. The saturation rate is also controlled by the depth of burial of the weathering body,the cross-sectional area and content of the "rain-facing" surface. The potential sliding surfaces of the spherical weathering granite-like soil slope under rainfall conditions still show a significant complex diversity,and there are similar sliding surfaces to those in the rain-free state. The slope safety factor is negatively correlated with rainfall duration and intensity,and tends to level off as rainfall continues,but can also lose its leveling off trend and continue to decrease under the influence of spheroidal weathering bodies. Among the rainfall types,the gradual incremental type has the greatest influence on slope stability. The results of the study can provide a scientific basis for evaluating the stability of spherically weathered granite-like soil slopes under rainfall conditions.
2023, 31(2): 650-660.
At present,most studies on earth pressure take the soil in the limit state as the research object,assume that the soil is in the saturated or dry state,and do not consider the influence of wall displacement and soil unsaturated characteristics on the earth pressure,which has limitations in practical engineering applications.This paper carries out the indoor model test of rigid retaining wall earth pressure of sand with different water contents behind the wall under active translation mode. The matrix suction and earth pressure at different depths are measured with seepage gauge and earth pressure box. The soil displacement of different retaining wall displacements is observed with DIC image correlation technology. The test results show that when the soil behind the wall is in a non-limit state,the failure surface of the soil always passes through the heel of the wall,and its shape is close to the plane. Secondly,on this basis,combined with the development characteristics of the frictional strength of the wall-soil under the non-limit state and the unsaturated soil strength criterion,a displacement-related unsaturated soil strength model is proposed. A calculation model of the unsaturated soil active earth pressure in the non-limit state is established. The comparison with the laboratory test results verifies the rationality of this model. Finally,the influence of wall displacement and matric suction on active earth pressure is discussed. The parametric analysis results show that the active earth pressure of unsaturated soil decreases gradually with the increase of the displacement of the retaining wall,but it first decreases and then increases with the increase of the matrix suction. There is a very small earth pressure value. The Rankine earth pressure and the Fredlund's extended Rankine earth pressure values are the special values of the model when the displacement reaches the limit state under saturated and unsaturated conditions,respectively.
At present,most studies on earth pressure take the soil in the limit state as the research object,assume that the soil is in the saturated or dry state,and do not consider the influence of wall displacement and soil unsaturated characteristics on the earth pressure,which has limitations in practical engineering applications.This paper carries out the indoor model test of rigid retaining wall earth pressure of sand with different water contents behind the wall under active translation mode. The matrix suction and earth pressure at different depths are measured with seepage gauge and earth pressure box. The soil displacement of different retaining wall displacements is observed with DIC image correlation technology. The test results show that when the soil behind the wall is in a non-limit state,the failure surface of the soil always passes through the heel of the wall,and its shape is close to the plane. Secondly,on this basis,combined with the development characteristics of the frictional strength of the wall-soil under the non-limit state and the unsaturated soil strength criterion,a displacement-related unsaturated soil strength model is proposed. A calculation model of the unsaturated soil active earth pressure in the non-limit state is established. The comparison with the laboratory test results verifies the rationality of this model. Finally,the influence of wall displacement and matric suction on active earth pressure is discussed. The parametric analysis results show that the active earth pressure of unsaturated soil decreases gradually with the increase of the displacement of the retaining wall,but it first decreases and then increases with the increase of the matrix suction. There is a very small earth pressure value. The Rankine earth pressure and the Fredlund's extended Rankine earth pressure values are the special values of the model when the displacement reaches the limit state under saturated and unsaturated conditions,respectively.
2023, 31(2): 661-670.
The size of the foundation pit affects the deformation characteristics of its supporting structure. The effect of long top beams in a long foundation pit is not quite clear. In order to clarify the force state,deformation form and the influence on other supporting structures,we studied the load conditions and restraint conditions of long and short top beams on the basis of previous studies,and obtained their main deformation characteristics. With the help of numerical simulation,we verified the long top beam's deformation form,and assessed effect of different level of integrity and the setting of prestress on the anchor rod. Then we proposed a new spliced top beam,based on the advantages and disadvantages of traditional top beam. Then we assessed its supporting effect and restrict ability on damage expansion by numerical methods. Study shows that the long top beams have more complete "wave characteristics" than the short top beams,which may deteriorate the stability conditions of local piles and hinder the function of prestressed anchors. The proposed new top beams are hinged and then rigidly connected,which weakens the "wave characteristics". It retains the function of the traditional top beam to strengthen the support structure and reduces the deformation and improves the effectiveness of bolt support. It turns out to be an optimized design.
The size of the foundation pit affects the deformation characteristics of its supporting structure. The effect of long top beams in a long foundation pit is not quite clear. In order to clarify the force state,deformation form and the influence on other supporting structures,we studied the load conditions and restraint conditions of long and short top beams on the basis of previous studies,and obtained their main deformation characteristics. With the help of numerical simulation,we verified the long top beam's deformation form,and assessed effect of different level of integrity and the setting of prestress on the anchor rod. Then we proposed a new spliced top beam,based on the advantages and disadvantages of traditional top beam. Then we assessed its supporting effect and restrict ability on damage expansion by numerical methods. Study shows that the long top beams have more complete "wave characteristics" than the short top beams,which may deteriorate the stability conditions of local piles and hinder the function of prestressed anchors. The proposed new top beams are hinged and then rigidly connected,which weakens the "wave characteristics". It retains the function of the traditional top beam to strengthen the support structure and reduces the deformation and improves the effectiveness of bolt support. It turns out to be an optimized design.
2023, 31(2): 671-679.
Based on the theory of maximum and minimum void ratios of granular materials,a new liquefaction potential index was used to predict the liquefaction resistance of binary sand silt mixtures with different particle gradations. By calculating the volume strain potential of sand silt mixtures in the existing literature data,the relationship among the fine particle content,the particle size ratio and the cyclic resistance ratio CRR of the mixture was analyzed. A new liquefaction potential index \begin{document}$\varepsilon_{\mathrm{v}}^{\prime}$\end{document} \begin{document}$\varepsilon_{\mathrm{v}}^{\prime}$\end{document} \begin{document}$\varepsilon_{\mathrm{v}}^{\prime}$\end{document} \begin{document}$\varepsilon_{\mathrm{v}}^{\prime}$\end{document} \begin{document}$\varepsilon_{\mathrm{v}}^{\prime}$\end{document} \begin{document}$\varepsilon_{\mathrm{v}}^{\prime}$\end{document} \begin{document}$\varepsilon_{\mathrm{v}}^{\prime}$\end{document} \begin{document}$\varepsilon_{\mathrm{v}}^{\prime}$\end{document}
2023, 31(2): 680-687.
Relying on the Dhaka Expressway in Bangladesh,the model test was conducted in this paper to analyze the stress and deformation characteristics of the geocell-reinforced retaining wall under static loads. The earth pressure,horizontal displacement and strain on the geocells were monitored. It is found that the maximum earth pressure is found at the heel of the wall and equals 24.8 kPa. The minimum earth pressure is at middle of the wall and equals 15.8 kPa. The earth pressure on the wall back is greater than that at half the width of the wall with the same height. The concave form is found for the earth pressure distribution. The maximum horizontal displacement of the wall is found at half the height(H/2) of the wall and equals 66 mm,accounting for 2.2% of the wall width. The horizontal displacement distribution is convex,which belongs to the drum form. The maximum cell strain is at the toe of the wall. In the area below H/2,the maximum strain line of the cell develops linearly from the toe to the back of the wall,with inclined angle of 34°to the horizontal plane. In the area above H/2,this line develops along the wall back to the top of the wall. The flexible retaining wall has an internal failure mode. The failure surface is a polyline. The test results can provide a guidance for the design of the flexible retaining wall.
Relying on the Dhaka Expressway in Bangladesh,the model test was conducted in this paper to analyze the stress and deformation characteristics of the geocell-reinforced retaining wall under static loads. The earth pressure,horizontal displacement and strain on the geocells were monitored. It is found that the maximum earth pressure is found at the heel of the wall and equals 24.8 kPa. The minimum earth pressure is at middle of the wall and equals 15.8 kPa. The earth pressure on the wall back is greater than that at half the width of the wall with the same height. The concave form is found for the earth pressure distribution. The maximum horizontal displacement of the wall is found at half the height(H/2) of the wall and equals 66 mm,accounting for 2.2% of the wall width. The horizontal displacement distribution is convex,which belongs to the drum form. The maximum cell strain is at the toe of the wall. In the area below H/2,the maximum strain line of the cell develops linearly from the toe to the back of the wall,with inclined angle of 34°to the horizontal plane. In the area above H/2,this line develops along the wall back to the top of the wall. The flexible retaining wall has an internal failure mode. The failure surface is a polyline. The test results can provide a guidance for the design of the flexible retaining wall.
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