南宁膨胀土非线性剪切应力松弛特性试验

利用四联装等应变直剪仪，对南宁非饱和重塑膨胀土进行一系列室内剪切应力松弛试验，探讨南宁非饱和重塑膨胀土的剪切应力松弛特性，得到诸多有益的结论。试验结果表明，不同初始条件下的剪切应力松弛曲线均属于不完全衰减型，剪切应力逐渐减少并趋于一个稳定值；膨胀土的松弛曲线都可以明显的分成3个阶段：瞬间松弛阶段、衰减松弛阶段、稳定松弛阶段。不同初始条件下不同时刻的剪切应力-应变等时关系曲线都是非线性的曲线，说明南宁膨胀土具有明显的非线性流变特性，是弹、黏、塑性体。膨胀土的含水率越高，或者竖向荷载越小，或者初始应变越大，或者时间越长，则膨胀土的流变特性及其非线性程度就越高。对试验结果的分析，通过改进剪切应力对数与时间对数的线性关系，建立南宁膨胀土在直剪条件下的非线性剪切应力松弛经验方程，能较好地拟合试验结果。非线性经验模型考虑了应变水平对应力松弛的影响，直观地反映出南宁膨胀土的非线性应力松弛特性，更加符合工程实际，可为膨胀土非线性应力松弛问题的计算分析提供理论依据。

Experimental study of nonlinear shear stress relaxation characteristics of Nanning expansive soil

On the basis of a series of indoor shear stress relaxation tests for unsaturated remolded expansive soils by using a quadruple load equal strain-controlled direct shear apparatus，the shear stress relaxation characteristics of this kind of soils were researched. Many useful conclusions are obtained. The results show that shear stress relaxation curves under different initial conditions are all incomplete attenuation type; but the shear stress decreased gradually and eventually tending to stable values. The relaxation curves can be clearly divided into three stages, i.e. the instantaneous relaxation stage, attenuation relaxation stage and stable relaxation stage. Shear stress-strain curve at different moments is nonlinear under different initial conditions, which indicates that expansive soil in Nanning is nonlinear, indeed bomb, sticky, as well as plastic. The conclusions show that the soil is the higher the nonlinear degree of the rheological properties of expansive soil with higher the moisture content, or the smaller the vertical load, or the greater initial strain, or the longer the time. Based on the analysis of tested results, an empirical shear stress relaxation equation of Nanning expansive soils under the condition of direct shearing has been established by improving the linear relationship between logarithm of shear stress and time. The regression curves of empirical relaxation equation are in good agreement with those of the observed data. The strain level of stress relaxation was taken into nonlinear empirical models. It intuitively reflect the nonlinear stress relaxation properties of Nanning expansive soils. The model is more corresponded with the actual engineering, so as to provide a theory for analytical calculation of nonlinear stress relaxation problems of expansive soils.