重工业厂房长期堆卸载会引起黏土地基沉降过大等病害问题。揭示病害机制需探明低频循环三轴试验中软黏土力学特性。本文对此开展了一系列不同围压、循环荷载幅值、排水方式、加卸载方式下的单向低频循环三轴试验,对土样的累积轴向应变、超孔隙水压及循环后抗剪强度等进行研究。结果表明: (1) 黏土累积轴向应变εp与循环次数N的关系可用对数函数模型描述,且εp随着循环应力比( Cyclic Stress Ratio, CSR)增大而增大; (2) 峰值偏应力在应变控制加载的循环中衰减,衰减率在30%以内; (3)超孔隙水压力比U与CSR存在线性关系,可据CSR等指标计算U的取值; (4) 排水循环后土体抗剪强度增加至1.5~2倍且应力路径右移,而不排水循环后应力路径左移,但均贴近临界状态线。本文研究可为长周期重复加卸载条件下软土地基长期力学特性预测提供参考。
The long-term heap unloading of heavy industrial plants will cause problems such as excessive accumulated settlement of clay foundation. To reveal the disease mechanism, it is necessary to explore the mechanical properties of soft clay in low-frequency cyclic triaxial tests. In this paper, a series of one-way low-frequency cyclic triaxial tests under different confining pressures, cyclic load amplitudes, drainage methods, and loading-unloading methods were carried out to study the accumulated axial strain, excess pore water pressure, and post-cyclic undrained shear strength of soil samples. The test results reveal that: (1) The relationship between the axial strain of clay and the number of cycles can be described by logarithmic function model. The accumulated axial strain increases with the increase of Cyclic Stress Ratio (CSR). (2) During the strain-controlled loading cycle stage, the peak deviatoric stress drops continually, with an attenuation rate of less than 30%. (3) Excess pore water pressure ratio U and CSR have a linear connection. According to CSR and other indicators, the excess pore water pressure ratio may be expected. (4) The undrained strength of the soil sample increases to 1.5~2 times after the drainage cycle, and the stress path shifts to the right. The stress path shifts to the left after the undrained cycle, but both are near the critical state line. The test results can provide a reference for the prediction of the long-term mechanical properties of soft soil foundation under the condition of long-term repeated loading and unloading.
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