粗粒土卸载－再加载力学特性试验研究

进行了3种不同粗粒土的常规三轴加载－卸载－再加载的剪切试验，对粗粒土的卸载－再加载的力学特性进行了分析。结果表明：粗粒土存在卸载体缩现象，且随着应力水平的增加，卸载体缩量增加；随着围压的增加，卸载体缩量减小。根据试验数据总结了卸载体缩量与应力水平、围压之间关系式。回弹模量随应力水平的增加呈驼峰型曲线，即应力水平在0.7左右时最大，小于或大于0.7时的弹性模量均较小。平均回弹模量与单调加载时的初始弹性模量的比值随围压呈幂函数降低，母岩硬度大的土料，该比值较大，相反，母岩较软的土料，该比值较小。由单调加载得出的邓肯模型参数k、n和卸载回弹确定的kur、nur的大致关系为kur=(2.64～4.60) 、nur =(0.540～0.885) n。

Experimental study of mechanical behaviour of coarse-grained soil in unloading and reloading

The test results of three different coarse-grained soils are obtained with conventional triaxial cyclic loading test.Based on these results,some useful conclusions are drawn from the discussion and analysis of the phenomenon of volume-contraction in unloading of coarse-grained soils: The phenomenon of the volume-contraction in unloading of coarse-grained soil is more obvious with the increasing of stress level and with the decreasing of confining pressure.According to the test data,a relationship formula among volume contraction in unloading and stress level and confining pressure is obtained.Rebound modulus presents the curve of hump shape with the increasing of stress level and the maximum is obtained when stress level is 0.7.The ratio of average rebound modulus and initial elastic modulus with monotonic loading present decrease of a power function,this ratio of soil material whose mother rock is high hardness is larger and the ratio of soil material whose mother rock is soft is smaller.The general relationship between kur and nur which is obtained from rebound in unloading and k and n which is obtained from monotonic loading is that kur is approximately from 2.46 times to 4.60 times of k and nur is approximately from 0.540 times to 0.885 times of n respectively.