Ancient outwash accumulations, deposited in Pleistocene with complicated sedimentary characteristics, are discovered in the midstream valley of Dadu River, Southwestern China. Their sedimentation characteristics are i...Ancient outwash accumulations, deposited in Pleistocene with complicated sedimentary characteristics, are discovered in the midstream valley of Dadu River, Southwestern China. Their sedimentation characteristics are investigated for gaining a deep insight into the dependency of Paleoclimate changes in this area. This is achieved by means of detailed site investigation, sampling and laboratory tests （grain size distribution and Electron Spin Resonance dating tests） for two representative outwash accumulations. Based on the present study, several main conclusions are drown out as follows： 1） The accumulations are composed mainly of coarse soils （coarse fraction is over 50%） and very coarse soils （coarse fraction is about 20%-35%, and very coarse fraction is over 55%）; 2） The coarse soils are sub-rounded well-sorted and sub-stratified to well-stratified, while the very coarse soils exhibit sub-rounded to sub-angular and poorly-sorted; 3） The accumulations are postulated to have been intermittently deposited in three time periods. This is evidenced by two layers of weathered/ residual clay, purple to brick red in color; and 4） It is inferred that the temperature in the study area increased over three time periods, i.e., 280 ka B.P. to 120 ka B.P., 110 ka B.P. to 80 ka B.P. and 70 ka B. P. to 25 ka B.P., and declined twice at 120 ka B.P. and 77 ka B.P. respectively.展开更多
Outwash deposit is a unique type of geological materials, and its features such as heterogeneity, discontinuity and nonlinearity determine the complexity of mechanical characteristics and failure mechanism. In this wo...Outwash deposit is a unique type of geological materials, and its features such as heterogeneity, discontinuity and nonlinearity determine the complexity of mechanical characteristics and failure mechanism. In this work, random meso-structure of outwash deposits was constructed by the technique of computer random simulation based on characteristics of its meso-structure in the statistical sense and some simplifications, and a series of large direct shear tests on numerical samples of outwash deposits with stone contents of 15%, 30%, 45% and 60% were conducted using the discrete element method to further investigate its mechanical characteristics and failure mechanism under external load. The results show that the deformation characteristics and shear strength of outwash deposits are to some extent improved with the increase of stone content, and the shear stress–shear displacement curves of outwash deposits show great differences at the post-peak stage due to the random spatial distribution and content of stones. From the mesoscopic view, normal directions of contacts between "soil" and "stone" particles undergo apparent deflection as the shear displacement continues during the shearing process, accompanying redistribution of the magnitude of contact forces during the shearing process. For outwash deposits, the shear zone formed after shear failure is an irregular stripe due to the movements of stones near the shear zone, and it expands gradually with the increase of stone content. In addition, there is an approximately linear relation between the mean increment of internal friction angle and the stone content lying between 30% and 60%, and a concave nonlinear relation between the mean increment of cohesion and stone content, which are in good agreement with the existing research results.展开更多
The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. Acco...The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. According to the results of laboratory direct shear test on the remolded samples, the soil particle parameters of numerical model based on in-situ particle size cumulative curves and 3D granular discrete element method were determined. Then, numerical experiments on different lithology, stone content and gradation composition were conducted. The results show that it is not a flat surface but a shear band that yields in the sample. The curve of particle velocity vs distance from the designed shear surface of test model that is taken as a datum plane in the vertical section of sample shows in "S" shape. The shear disturbance area is about twice the maximum diameter of stone blocks. The greater the stiffness of stone is, the rougher the shear surface is. The shear strength of outwash deposits is largely controlled by lithology and stone content, and the bite force between stone blocks is the root reason of larger friction angle. It is also shown that strain hardening and low shear dilatancy occur under high confining pressure as well as possibility of shear shrinkage. But it is easy to behave shear dilatation and strain softening under low confining pressure. The relationship between particle frictional coefficient and stone content presents an approximately quadratic parabola increase. The strain energy first increases and then drops with the increase of frictional energy. The cohesion increases with soil stiffness increasing but decreases with stone stiffness increasing. Numerical results are consistent with the laboratory test results of remolded samples, which indicate that this method can be a beneficial supplement to determine the parameters of engineering deposit bodies.展开更多
Outwash deposit is one of the major threats to the safety and stability of railway transit engineering in the Sichuan–Tibet area.In this paper,different samples of outwash deposits were prepared based on the random s...Outwash deposit is one of the major threats to the safety and stability of railway transit engineering in the Sichuan–Tibet area.In this paper,different samples of outwash deposits were prepared based on the random structure method,and a series of large-scale direct shear tests were carried out under different normal stresses.The influence of stone content and the spatial distribution of stone blocks on the physical and mechanical properties of outwash deposits were studied.The results show that with the increase of stone content,the shear stress-displacement curve changs from strain softening to strain hardening.The shear zone is larger,and its shape is more tortuous due to the movement and rotation of stone blocks.The internal frictional angle increases linearly while the cohesion diseases with the increase of stone content.The main influence of the spatial distribution of stone blocks on the mechanical properties of outwash deposits is the peak stress.The shear zone is mainly determined by the distribution of the stone blocks near the shear zone.展开更多
基金financially supported by the Young People's Foundation of State Key Laboratory of Geo-hazard Prevention and Geo-environment Protection (SKLGP2010Z007)
文摘Ancient outwash accumulations, deposited in Pleistocene with complicated sedimentary characteristics, are discovered in the midstream valley of Dadu River, Southwestern China. Their sedimentation characteristics are investigated for gaining a deep insight into the dependency of Paleoclimate changes in this area. This is achieved by means of detailed site investigation, sampling and laboratory tests （grain size distribution and Electron Spin Resonance dating tests） for two representative outwash accumulations. Based on the present study, several main conclusions are drown out as follows： 1） The accumulations are composed mainly of coarse soils （coarse fraction is over 50%） and very coarse soils （coarse fraction is about 20%-35%, and very coarse fraction is over 55%）; 2） The coarse soils are sub-rounded well-sorted and sub-stratified to well-stratified, while the very coarse soils exhibit sub-rounded to sub-angular and poorly-sorted; 3） The accumulations are postulated to have been intermittently deposited in three time periods. This is evidenced by two layers of weathered/ residual clay, purple to brick red in color; and 4） It is inferred that the temperature in the study area increased over three time periods, i.e., 280 ka B.P. to 120 ka B.P., 110 ka B.P. to 80 ka B.P. and 70 ka B. P. to 25 ka B.P., and declined twice at 120 ka B.P. and 77 ka B.P. respectively.
基金Project(2011CB013504) supported by the National Basic Research Program(973 Program)of ChinaProject(2013BAB06B01) supported by the National Science&Technology Pillar Program during the Twelfth Five-year Plan Period+2 种基金Projects(11772118,51479049,51709282) supported by the National Natural Science Foundation of ChinaProject(2017M620838) supported by the Postdoctoral Science Foundation of ChinaProject(487237) supported by the Natural Sciences and Engineering Research Council of Canada
文摘Outwash deposit is a unique type of geological materials, and its features such as heterogeneity, discontinuity and nonlinearity determine the complexity of mechanical characteristics and failure mechanism. In this work, random meso-structure of outwash deposits was constructed by the technique of computer random simulation based on characteristics of its meso-structure in the statistical sense and some simplifications, and a series of large direct shear tests on numerical samples of outwash deposits with stone contents of 15%, 30%, 45% and 60% were conducted using the discrete element method to further investigate its mechanical characteristics and failure mechanism under external load. The results show that the deformation characteristics and shear strength of outwash deposits are to some extent improved with the increase of stone content, and the shear stress–shear displacement curves of outwash deposits show great differences at the post-peak stage due to the random spatial distribution and content of stones. From the mesoscopic view, normal directions of contacts between "soil" and "stone" particles undergo apparent deflection as the shear displacement continues during the shearing process, accompanying redistribution of the magnitude of contact forces during the shearing process. For outwash deposits, the shear zone formed after shear failure is an irregular stripe due to the movements of stones near the shear zone, and it expands gradually with the increase of stone content. In addition, there is an approximately linear relation between the mean increment of internal friction angle and the stone content lying between 30% and 60%, and a concave nonlinear relation between the mean increment of cohesion and stone content, which are in good agreement with the existing research results.
基金Project(2011CB013504) supported by the National Basic Research Program of ChinaProjects(50911130366, 11172090) supported by the National Natural Science Foundation of ChinaProject supported by Central University Basic Research Special Fund, China
文摘The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. According to the results of laboratory direct shear test on the remolded samples, the soil particle parameters of numerical model based on in-situ particle size cumulative curves and 3D granular discrete element method were determined. Then, numerical experiments on different lithology, stone content and gradation composition were conducted. The results show that it is not a flat surface but a shear band that yields in the sample. The curve of particle velocity vs distance from the designed shear surface of test model that is taken as a datum plane in the vertical section of sample shows in "S" shape. The shear disturbance area is about twice the maximum diameter of stone blocks. The greater the stiffness of stone is, the rougher the shear surface is. The shear strength of outwash deposits is largely controlled by lithology and stone content, and the bite force between stone blocks is the root reason of larger friction angle. It is also shown that strain hardening and low shear dilatancy occur under high confining pressure as well as possibility of shear shrinkage. But it is easy to behave shear dilatation and strain softening under low confining pressure. The relationship between particle frictional coefficient and stone content presents an approximately quadratic parabola increase. The strain energy first increases and then drops with the increase of frictional energy. The cohesion increases with soil stiffness increasing but decreases with stone stiffness increasing. Numerical results are consistent with the laboratory test results of remolded samples, which indicate that this method can be a beneficial supplement to determine the parameters of engineering deposit bodies.
基金supported by the Open Research Fund of State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin(China Institute of Water Resources and Hydropower Research),Grant No.IWHRSKL-KF202016Natural Science Foundation of Hunan Province(CN),Grant No.2020JJ5732+3 种基金National Natural Science Foundation of China(Grant No.51679069)National Key R&D Program of China,Grant No.2017YFC1501100Open Fund of State Key Laboratory of Hydraulics and Mountain River Engineering(Sichuan University),Grant No.SKHL1725Water Conservancy Science and Technology Research and Extension Project of Shanxi Province,Grant No.2021LS034.
文摘Outwash deposit is one of the major threats to the safety and stability of railway transit engineering in the Sichuan–Tibet area.In this paper,different samples of outwash deposits were prepared based on the random structure method,and a series of large-scale direct shear tests were carried out under different normal stresses.The influence of stone content and the spatial distribution of stone blocks on the physical and mechanical properties of outwash deposits were studied.The results show that with the increase of stone content,the shear stress-displacement curve changs from strain softening to strain hardening.The shear zone is larger,and its shape is more tortuous due to the movement and rotation of stone blocks.The internal frictional angle increases linearly while the cohesion diseases with the increase of stone content.The main influence of the spatial distribution of stone blocks on the mechanical properties of outwash deposits is the peak stress.The shear zone is mainly determined by the distribution of the stone blocks near the shear zone.
