Particle Shape Quantification And Static Liquefaction Behavior Of Nanjing Sand

As static liquefaction is considered to be responsible for some landslides, much more researches are conducted on it. Meanwhile, most of those researches are about worldwide spherical quartz sands. A kind of schistose sand distributes widely along middle and lower Yangtze River valley. It consists of quartz, feldspar and a little chlorite, muscovite, other clay minerals and metallic minerals. It is quite different from quartz sands in mineral composition, particle size distribution, and particle shape.This paper focuses on the schistose sands in Nanjing. Through testing research, the influence of mineral composition, particle size distribution, density and particle shape on static liquefaction behavior of sand is analyzed. The main results of this dissertation is as follows:(1) The mineral composition, particle size distribution and dry density of ISO Sand (A) and Nanjing Sand (B, C, D) are tested. Sand A consists of quartz, while Sand B, C and D consist of more than50%quartz,20～35%feldspar and a little other minerals. In contrast to Sand B, C and D, Sand A is better graded, and has higher limitation dry densities and lower limitation void ratios.(2) Micro-photos of particles within every size ranges are taken to get parameters of particle shapes. Particles within0.075～0.1mm and1～2mm have little Aspect Ratio (AR) meaning poor elongation and large Form Factor (FF) meaning better roundness. Based on the assumption that particles within different size ranges have same particle density, the parameters of different sands could be calculated. Sand A has small AR, while ARs of Sand B, C and D are larger. Sand A and C have bigger FF than Sand B and D.(3) Particles within0.075～2mm of those four kinds of sands are conducted CU triaxial tests under different confining pressures and different relative densities. Deformation, strength and pore pressure are analyzed to describe the shearing behavior of different sands. It is found out that Sand B, C and D show the behavior of dense sand under lower relative densities than Sand A.(4) Nanjing Sand B, C and D have large liquefaction potential under low confining pressure (<400kPa). The liquefaction potential of ISO Sand A is large under confining pressure of50kPa and decreases quickly while the confining pressure increases. The liquefaction potential of Sand B, C and D are more sensitive to relative density.(5) Based on steady state theory, the steady state lines of Sand B, C and D are on top of that of Sand A in e-(p’/pa)a plain. This is because the limitation void ratios of Sand B, C and D are bigger than their counterparts of Sand A. The order of the steady state lines is as same as that of the coefficient of uniformity (Cu).(6) The internal friction angles of loose sands correlates with Aspect Ratio (AR) and Form Factor (FF). The bigger the AR and the smaller the FF is, the larger the internal friction angle will be. The friction angle at steady state correlates to AR. The bigger the AR is, the larger the angle will be. This is because of the secondary anisotropy during the triaxial tests. Before quasi-steady-state, the structures between particles are strongly rebuilt, the friction angle is influenced by AR and FF. After quasi-steady-state, the oriented structure near shear zone leads to the crucial influence of AR.