循环荷载下黏土应变积累积强化模型研究

Study of strain accumulation strengthened model for clay under cyclic loadings

循环加载历史是影响土的动力特性的一个重要因素。通过对一种原状粉质黏土进行高循环次数单剪试验,研究了黏土体应变随剪应变幅值及循环次数的变化规律,以及由于体应变的累积对黏土动力特性产生的影响。试验结果表明,黏土的体应变随着循环次数的增多和循环剪应变幅值的增大而增大,而土的动力特性则随着体应变的不断累积而出现强化现象,表现为动剪模量增加,阻尼比减小。对累积体应变与动剪模量、阻尼比之间的关系进行了研究,提出了相应的强化关系式。在常用的非线性模型基础上,通过引入动剪模量的强化系数和阻尼比的衰减系数,建立了一种能考虑循环应变历史影响的土动力模型。

Cyclic loading history is an important parameter to the further dynamic characteristics of soils. A series of draining cyclic simple shear tests on an undisturbed silty clay are carried out; and the development of volumetric strains with the change of load cycles and shear strain amplitude is found out, as well as the correlation between the accumulated volumetric strain and the further dynamic characteristics. The test results show that the volumetric strains increase with the development of cyclic load cycles and the improvement of cyclic shear strain amplitude, and further more with the accumulation of volumetric strain, the dynamic characteristics of the clay soil are strengthened, which means that the dynamic shear modulus goes up and the damping ratio degrades The effects of accumulated volumetric strains on dynamic shear modulus and damping ratio are analyzed; and some relevant correlation equations are proposed. With the adoption of two coefficients, respectively the coefficient of modulus strengthening and the coefficient of damping degrading, a constitutive model which can take the effect of cyclic load history into account is constructed based on a normal nonlinear model.