Analysis Of Pore Structure Evolution And Strength Characteristics Of Nanjing Silty Sand

Ground instability and landslides caused by static liquefaction have received widespread attention.Most of the research results have focused on spherical sand particles,while the Nanjing silt silty-fine sand in the middle and lower reaches of the Yangtze River is widely distributed.In this paper,we studied the pore structure evolution and strength characteristics of Nanjing silt during triaxial compressionBased on the synchrotron radiation micro-CT scan,the triaxial compression test obtained a real-time scanning image of the pore structure of the sample during loading under different confining pressures.We reconstruct the three-dimensional model of the sample and analyze the evolution of the pore structure during loading.The following conclusions are obtained:(1)The permeability of Nanjing silt sand samples is 4.988×10-5mm2 based on capillary bundle model,Through laboratory constant head test,the permeability of Nanjing silt sand is 5.538×10-5 mm2,the error between capillary bundle model and constant head test is 9.93%.This shows that the pore size fractal dimension characterization method of permeability has a higher characterization accuracy.(2)When Nanjing silt sand sample is statically liquefied,average pore coordination number of REV has little change compared with initial state of the sample in the same position,but the average pore diameter increases by about 2.5 times,indicating that the number of large-size pores increases obviously under the state of static liquefaction.(3)Numerical simulation of discrete elements shows that the shear strength of the long-sized particles is the largest,and the shear strength of the circular particles is the smallest.This is due to the fact that the biting interaction between the round particles is not caused by the other three kinds of abnormal particles.(4)The micro-pores in Nanjing silt sand particles has obvious influence on the connectivity of pore structure.Compared with spherical particles,the porosity of acicular particles and flake particles is larger than that of spherical particles.The number of genus of particles in non-spherical particles is significantly smaller than that of spherical particles,which indicates that the pore space structure of spherical particles is more complex.(5)Based on grey correlation degree analysis method,the order of impact of pore structure parameters on permeability is:average pore radius,porosity,average coordination number of pore throats,average shape factor of pore cross-sectional area,average length of throat,average throat radius,hole-to-throat ratio.(6)After the zoned damage occurred in Nanjing silt samples,the cross-sectional shape of the throat in the failure zone was more regular than that of the pores.The axial stress in the test resulted in the inter-grainal misalignment,which leads to more regular shape of the pore cross section.