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。 A series of indoor shear stress relaxation tests were carried out on the unsaturated remolded expansive soil in Nanning by means of a straight shear strain gauge such as a quadruple joint. The shear stress relaxation characteristics of the unsaturated remolded expansive soil in Nanning were discussed and many useful conclusions were obtained. The experimental results show that the shear stress relaxation curves under different initial conditions belong to the incomplete attenuation type and the shear stress decreases gradually and tends to a stable value. The relaxation curves of the expansive soil can be obviously divided into three phases: the moment relaxation phase , Decay relaxation phase, stable relaxation phase. The shear stress-strain curves at different times under different initial conditions are non-linear curve, indicating that Nanning expansive soil has obvious nonlinear rheological properties, which are elastic, viscous and plastic body. The higher the moisture content of expansive soil, or the smaller the vertical load, or the greater the initial strain, or the longer the rheological properties of expansive soil and its non-linearity is higher. Based on the analysis of the test results, the nonlinear shear stress relaxation empirical equation of Nanning expansive soil under direct shear condition is established by improving the linear relationship between the logarithm of shear stress and the logarithm of time, which can well fit the experimental results. The nonlinear empirical model considers the effect of strain level on stress relaxation and intuitively reflects the nonlinear stress relaxation characteristics of Nanning expansive soil, which is more in line with the engineering practice. It can provide a theoretical basis for the calculation and analysis of nonlinear stress relaxation of expansive soils.