冻融循环作用下黄土累积塑性应变演变规律

Evolution of the cumulative plastic strain of loess under freeze-thaw cycles

摘要:

为探究黄土路基在冻融循环和交通荷载耦合作用下的累积塑性应变变化规律,选取西宁地区重塑黄土为研究对象,采用GDS双向动三轴测试系统对其进行一系列动三轴试验,研究不同冻融循环次数、围压、动应力幅值以及频率对累积塑性应变的影响规律,并通过引入拟合参数建立考虑多因素的累积塑性应变预测模型。结果表明:累积塑性应变随冻融循环次数的增大而增大,在6次冻融循环后增长速率减缓且趋于稳定;减小动应力幅值和增大围压能显著抑制累积塑性应变的发展;加载初期累积塑性应变随频率变化不明显,随着振次的增加,频率作用凸显,累积塑性应变随着频率的增大而减小;基于试样的累积塑性应变演变规律,分别采用幂指数模型和对数模型进行拟合,发现后者拟合效果好;综合考虑4种因素对累积塑性应变的影响,建立累积塑性应变预测模型,并对试验的实测值与预测值进行对比,验证模型的可行性。研究成果可为季冻区黄土路基永久变形的计算提供理论参考依据。

Abstract:

To explore the change law of cumulative plastic strain of loess subgrade under the coupling action of freeze-thaw cycles and traffic loads, remodeled loess in the Xining region was selected as the research object and a series of dynamic triaxial tests was performed using GDS bidirection dynamic triaxial test system. Effects of different freeze-thaw cycles, confining pressure, dynamic stress amplitude, and frequency on the cumulative plastic strain were investigated, and a prediction model for cumulative plastic strain with multiple factors was established by introducing fitting parameters. The results show that the cumulative plastic strain increases with the number of freeze-thaw cycles, and the growth rate slows down and stabilizes after six freeze-thaw cycles. Reducing the dynamic stress amplitude and increasing the confining pressure inhibits the development of cumulative plastic strain. The change in cumulative plastic strain with frequency is not possible at the initial stage of loading but becomes prominent with increasing vibration time, decreasing with increasing frequency. Based on the evolution law of the cumulative plastic strain of samples, the power exponential and logarithmic models were used for fitting, and the latter had a good fitting effect. Considering the influence of the abovementioned four factors on the cumulative plastic strain, a prediction model for the cumulative plastic strain was established, and the predicted value was compared with the measured values to verify the feasibility of the model. The research results provide a theoretical reference for calculating the permanent deformation of loess subgrade in seasonally frozen regions.