In order to investigate the influence of particle shape on the shear instability characteristics of sand,the particle shape analysis of quartz sand with the same gain size and gradation,but with differ-ent shape was firstly made by using the microscopic image acquisition and processing techniques.Then the undrained triaxial shear tests were conducted under stress controlled condition,with a instability criterion established based on the strain rate increment(ΔSR).Finally,the collapse tests of granular columns with different particle shape were simulated by PFC2D and the mechanism of destabilization was examined.The results show that ΔSR can be used as a new means to determine whether the sand is instable or not.When the value of ΔSR is continuously shaken,the sample has a large cumulative de-formation,and the sample becomes instable.The instability point is also the peak point in the sand samples with regular particle shape.And the samples exhibit a"false instability point",which shows that the shear stress of the samples decreases and increases suddenly with the development of strain during the shear process.On the other hand,the peak point of the irregularly-shaped sand samples lagged behind the instability point.Under stress controlled condition,the stress path of the regular-shaped sand samples is in a"jagged"pattern,and the excess pore pressure and axial strain are in"stepped"patterns,but the test curves of the irregular sand samples do not show any sudden changes.The difference of instability of sand samples with different shapes is related to the energy conversion mechanism and contact motion formed between particles.The research results could provide a reference for slope stability analysis and a guidance for prevention of geological disasters such as landslides.
关键词
砂/颗粒形状/失稳/应力控制/三轴试验
Key words
sand/particle shape/instability/stress control/triaxial test
维普
万方数据