动力离心模型试验循环剪应力–剪应变反演方法对比

Evaluation of cyclic shear stress-strain using inverse analysis techniques in dynamic centrifuge tests

介绍了基于加速度阵列建立的3种循环剪应力–剪应变反演方法,分析了应用条件和影响因素。基于一组软黏土场地加固动力离心模型试验,探讨了试验加速度记录反演位移的信号处理方法,与多状态下实测位移对比,验证了有效性与可靠性。运用3种反演方法分别求取了两次试验、多种波激励下,自由场地和加固场地内土体剪应力–剪应变动态响应过程。结果表明,在传感器布设间距和采样率满足应用条件下,3种反演方法可获得基本一致结果并反映基本规律,上层土体剪应力小、剪应变大,土体剪切模量与围压密切联系;自由场地剪应变远大于加固场地,并因土体软化呈现强非线性。3种方法对比,三次样条法反演结果准确性对传感器布设间距和采样率较为敏感。

Evaluation of shear stress-strain characteristics in soils is paramount to the fundamental understanding of soil behavior in dynamic centrifuge tests. Three inverse analysis techniques for evaluating cyclic shear stress-strain response using data from accelerometer arrays are introduced and key factors that require consideration in the applied condition are discussed. Using a series of dynamic centrifuge tests on soft soil sites with stiff ground reinforcement, the data process for back-calculated displacements from acceleration records is presented. The back calculated displacements are compared to the recorded displacements in several cases with excellent agreements. The three inverse analysis techniques are used to estimate the dynamic shear stress-strain responses in the free field and with in the reinforced ground in two centrifuge tests with different shaking motions of varying magnitudes. The results demonstrate that as long as accelerometer spacing and sampling frequency are sufficient to the active mechanics, the calculated shear stress-strain responses from three inverse techniques are consistent and therefore likely accurately reflect the basic characteristics of interest. In these tests it is observed that shear stiffness decreased at shallower depths, consistent with the expected effects of confining pressure on shear stiffness. It was also observed that the amplitudes of shear strain in the free field are considerably larger, and stronger nonlinear features were observed in the stress-strain loops as compared to the motions with in the reinforced soil. With comparisons among the three inverse analysis techniques, the evaluation from cubic spline approach was more sensitive and the linear and weighted residual techniques produced more reasonably consistent results.