循环荷载下红黏土的变形演化分析

Deformation Evolution of Disturbed Red Clay Under Cyclic Loading

为了给施工场地沉降量的预测工作及安全性评估提供依据,以南宁某高速公路的红黏土回填为背景,进行双向循环动三轴试验,研究扰动红黏土在循环荷载下的变形行为,分析围压、循环应力比(CSR)和加载频率对土体动弹性模量的影响规律。依据试验数据绘制滞回曲线、永久应变(εp)-循环次数(N)关系曲线,分析土体弹性应变、永久应变的演化发展规律。并对永久应变曲线进行了非线性拟合,建立满足稳定型和临界型的永久应变预测方程,最后通过试验验证该累积变形模型的可行性以及对模型参数进行分析。结果表明:土样经过一定次数循环后,其应力-应变滞回曲线形状基本保持不变。弹性模量衰减速率与围压、CSR大小呈正相关,且弹性模量随循环次数的增加呈先快后慢的非线性衰减趋势。土样永久应变受围压、CSR和加载频率的影响显著,围压、CSR和加载频率越大累积应变越多;但随循环次数的增加,永久应变曲线逐渐收敛,应变量趋于稳定。永久应变预测方程能较好预测重塑红黏土不同变形状态的累积塑性变形。

A series of bi-directional cyclic dynamic triaxial tests were carried out using red clay backfill of a highway in Nanning as a practical engineering application scenario.The deformation behavior of disturbed red clay under cyclic loading was investigated,and the influence laws of confining pressure,CSR and loading frequency on the dynamic elastic modulus of the soil were analyzed.Hysteresis curves andε_p-N relationship curves are plotted based on the test results,and the development and evolution rules of soil′s elastic and permanent strains are specifically examined.The results show that after a certain number of cycles,the shape of the stress-strain hysteresis curve of the soil sample basically remains unchanged,so the elastic modulus tends to be stabilized.The decay rate of the resilient modulus of the soil is positively correlated with the confining pressure and the size of the CSR.Additionally,the resilient modulus shows a nonlinear decay trend with the increase of the number of cycles in a fast and then slow manner.The permanent strain of soil samples is significantly affected by the confining pressure,CSR,loading frequency.With the increase of confining pressure,CSR and loading frequency,the rate of permanent strain accumulation increases,producing greater deformation.However,with the increase of the number of cycles,the permanent strain curve gradually converges and the strain stabilizes.Combined with the permanent strain curves,the permanent strain prediction equations satisfying the stable and critical types were established to better predict the cumulative plastic deformation of different deformation states of the remodeled red clay.The test also confirmed the viability of the cumulative deformation model and led to an analysis of the model parameters that yielded the influence law of the cyclic loading conditions on the model parameters.The purpose of this test is to give a theoretical foundation for the dynamic stability analysis of slopes under short-term loading and unloading,as well as a basic reference for the forecast work and safety evaluation of the settlement of the building site.