分级加载条件下泥炭质土滞回曲线演化规律试验研究

Experimental study on evolution law of hysteretic curves of peaty soil under stepped axial cyclic loading

针对目前泥炭质土滞回特性研究缺乏的现状,通过一系列不同围压、固结比、加载频率等条件下的分级加载动三轴试验,采用滞回圈的整体斜率k、中心偏移距离d、包围面积S等参数定量分析昆明泥炭质土滞回曲线的形态特征、影响因素及其演化规律,并与其他土进行对比。研究结果表明:泥炭质土滞回曲线呈长梭形,k即土体刚度随动载振幅呈对数关系衰减,随围压、固结比增大而增大,加载频率对k影响较小;d即土体塑性变形量和S即能量耗散在初始加载阶段增长缓慢,后随动载振幅以指数关系快速增长;加载频率和围压越小,d和S越大;对泥炭质土塑性变形而言,存在某一临界固结比,且非等压固结条件下(K_c≠1.0)塑性变形明显比同振级等压固结条件下(K_c=1.0)的大;围压、加载频率(1~5 Hz)对d和S影响较显著;与海洋软土等相比,泥炭质土对动载振幅和加载频率更加敏感,塑性变形和损伤更容易累积。

A series of staged cyclic loading triaxial tests were performed at different confining pressure,consolidation ratio,and loading frequency to study the hysteretic curves of peaty soils,so as to overcome the lack in current researches.The morphological characteristics and influencing factors of hysteretic curves of peaty soils in Kunming were quantitatively analyzed by using three defined parameters,i.e.,the gradient k,the center offset distance d and the area S of hysteretic curves.Furthermore,a comparison of hysteretic curves between peaty soils and other soils was carried out.The results show that the shapes of hysteretic curves of peaty soils are approximated to long spindles;k,namely stiffness of soil decreases logarithmically with the amplitude of dynamic load and increases with confining pressure and consolidation ratio;as loading frequency increasing,k goes through a process of increasing,decreasing and finally stabilizing;d,namely plastic deformation and S,namely energy consumption increase exponentially with the amplitude of dynamic load at high loading levels,while they grow very slowly at low loading levels first;the smaller the loading frequency is,the greater the value of d and S are;there exists a critical consolidation ratio at which d reaches the maximum;the value of d under nonisotropic consolidation(Kc≠1.0)is significantly greater than that of under isotropic consolidation(Kc=1.0);loading frequency has little effect on k but notable on d and S;both confining pressure and consolidation ratio have significant effect on k,d and S.Compared with marine soft soils,peat soils are more sensitive to dynamic loading amplitude and loading frequency and their plastic deformation and damage are more easily to develop.