基于大三轴试验的粗粒土剪胀性研究

Study of dilatancy behaviors of coarse-grained soils in large-scale triaxial test

采用大三轴剪切仪对3种不同相对密度的双江口心墙坝覆盖层料进行固结排水剪切试验,重点研究粗粒土的剪胀特性,分析粗粒土的剪胀性与围压、相对密度之间的关系,并检验修正剑桥模型的剪胀方程、Rowe剪胀方程对粗粒土的适用性。结果表明,粗粒土在低围压下表现出明显的剪胀趋势,随着围压的增加,逐渐由剪胀向剪缩过渡;随着密度的增大,粗粒土的剪胀性明显增强;相变应力比是粗粒土剪胀强弱的一个重要影响因素,其随密度的增加而增加,随围压的增大则呈线性减小趋势;粗粒土的剪胀性与相对密度、围压关系密切,根据试验数据得出最大剪胀率d f与相对密度Dr、围压3之间的关系式;修正剑桥模型的剪胀方程不能反映粗粒土的剪胀性;Rowe剪胀方程在一定程度上能反映粗粒土的剪胀性,但高围压下在压缩阶段低估了其压缩性,而在剪胀阶段则高估了其剪胀性。

Using large-scale shearing device, isotropic consolidated-drained triaxial tests under different confining pressures are performed for three relative densities overburden material of Shuangjiangkou earth dam. The dilatancy of coarse-grained materials is investigated; the relationship among dilatancy, relative density and confining pressure are discussed; and applicability of dilatancy equation of modified Cam-clay model and Rowe dilatancy equation for coarse-grained soils are tested. It is found that the confining pressure and initial density influence dilatancy evidently; that is, under low confining pressure coarse-grained soils are characterized by volumetric dilatancy; and with the increasing of confining pressure they exhibit volumetric compression. The increasing of density results in the increase of dilatancy. Phase transformation stress ratio is an important factor affecting dilatancy, which exhibit increasing with the increase of density and linear decrease with the increase of confining pressure. According to the test data, a relationship formula among dilatancy ratio and relative density and confining pressure is obtained. Dilatancy equation of modified Cam-clay model cannot reflect the dilatancy; and Rowe dilatancy equation can reflect the dilatancy of the coarse-grained materials; but when confining pressure is higher it underestimate the compression during compression stage and overestimate the dilatancy during shearing stage.