膨胀土侧向卸荷试验研究及归一化特性分析

Experimental study on expansive soil lateral unloading and analysis on its normalized characteristics

【目的】为探究膨胀性黏土在侧向卸荷应力路径下的应力-应变特性,【方法】以合肥地区典型膨胀土为研究对象,开展了侧向卸荷应力路径三轴试验,分析了卸荷应力路径下合肥膨胀土的破坏形态、应力-应变特征和强度指标,并基于Kondner双曲线模型,获得了膨胀土卸荷模型参数,对其卸荷应力-应变曲线进行了归一化分析,建立了其归一化方程。【结果】结果显示:在侧向卸荷路径下,膨胀土在不同围压下呈现出剪切、鼓胀劈裂和鼓胀3种破坏形态;膨胀土卸荷应力路径下应力—应变曲线呈双曲线型,为典型应变硬化型土;卸荷路径下膨胀土的黏聚力c=68.4 kPa,明显小于常规加载黏聚力c=101.7 kPa。基于Kondner双曲线模型,建立了以幂因子σ0.466为归一化因子的膨胀土卸荷归一化经验方程,通过试验验证,该归一化经验方程对合肥地区典型膨胀土卸载应力-应变拟合度达到99%以上,【结论】采用该模型预测合肥地区典型膨胀土在卸荷路径下的应力-应变曲线较为理想。研究结果可为合肥地区典型膨胀土的卸荷工程提供理论支持。

[Objective] In order to explore the stress-strain characteristics of expansive clay under lateral unloading stress path, [Methods]the typical expansive soil in Hefei area is taken as the study object to carry out the triaxial test of lateral unloading stress path for studying the failure mode, stress-strain characteristics and strength index of the expansive soil within the area of Hefei, while the parameters of the expansive soil unloading model are obtained based on Kondner hyperbolic model, and then its unloading stress-strain curve is normalized and the normalized equation is established as well. [Results] The results show that the expensive soil exhibits three failure patterns under different confining pressures, i.e. shearing failure, swelling-splitting failure and swelling failure, under lateral unloading path, while the stress-strain curve of the expansive soil under unloading stress path exhibits a hyperbolic type, thus it is a typical strain hardening soil. Under unloading path, the cohesive force of c=68.4 kPa of the expansive soil is obviously less than the conventional loading cohesive force of c=101.7 kPa. Based on Kondner hyperbolic model, the normalized empirical equation with the power factor of σ0.466as the normalization factor of the expansive soil unloading is established. Through the relevant experimental verification, the fitting degree of the normalized empirical equation to the typical unloading stress-strain of the expansive soil in Hefei area reaches to more than 99%, [Conclusion] and then predicting the stress-strain curve under unloading path for the typical expansive soil in Hefei area with this model is relatively ideal. The study result can provide the relevant theoretical support for the unloading project of the typical expansive soil in Hefei area.