循环荷载下砂与钢板界面的弱化机制

Degenerate mechanism of sand-steel interface under cyclic loading

针对桩-土界面的循环弱化机制,采用自主研发的大尺度恒刚度界面剪切仪,进行不同剪切位移幅值和初始法向应力下砂与钢板界面的循环剪切试验研究.研究结果表明,界面剪切应力、法向应力与剪切位移关系曲线分别呈"滞回环"和"阶梯"状发展,且随循环次数的增加趋于"扁平",相邻循环应力应变曲线趋于重合,两者的循环弱化速率均随初始法向应力和剪切位移幅值的增加而增大;同组试验不同循环下的最大剪切应力随循环次数的增加近似呈对数型弱化;循环剪切过程中界面摩擦角的发展趋势与剪切位移幅值密切相关;循环剪切形成毗邻界面1cm厚剪切带,剪切带内砂土颗粒破碎率达5%以上.

The self-developed large-scale constant normal stiffness（CNS）interface shear apparatus was used to conduct a series of the cyclic shear tests occurred at the sand-steel plate interface,in order to investigate the degenerate mechanism that occurred at the pile-soil interface under cyclic loading.In the mean time,these tests experienced different shear displacement amplitudes and initial normal stresses.Results show that the relationship of interface shear stress-shear displacement behavior presents a‘hysteretic＇loop,while the curve of normal stress-shear displacement develops as‘stair-step＇shape.The curve becomes‘flat＇and the adjacent curves tend to be overlapped as the number of loops increases.At the same time,the rate of cyclic degeneration raises with the increase of initial normal stress and the amplitude of shear displacement.When the same experiment is under different cycles,the maximum shear stresses degenerate approximately logarithmically with cyclic number.In the process of cyclic shear tests,the development of the interface friction angle is closely related to the shear displacement amplitude.The cyclic shear band thickness adjacent to the interface is 1 cm after cyclic shear tests,moreover,the percentage of sand particle breakage in the shear band is more than 5%.