Experimental Study On Dynamic Characteristics And Transitional Failure Of Sand-clay Mixed Fine-grained Soil Based On Mineral Composition

When the sand meets certain conditions,liquefaction will occur under the action of cyclic load.When the clay meets certain conditions,cyclic mobility will occur under the action of cyclic load,while the low-plasticity fine-grained soil may have a transitional failure which is a failure type between liquefaction and cyclic mobility.There have been many cases of failure of fine-grained soil which occur under the action of seismic loads.A large number of researchers have conducted experimental studies on undisturbed fine-grained soils,sand-clay mixed soils,and silt-clay mixed soils in the earthquake area,and have found many factors that could have effect on liquefaction sensitivity of these fine-grained soils such as fine content,clay content and plasticity index,etc.They have also done lots of researches on the relationship between different microstructures of the soil and specific failure modes,and made lots of achievements.Though the unique dynamic characteristics of low-plasticity fine-grained soil have attracted people's attention and researches,there are still few studies based on mineral composition and transitional failure.In this paper,we mixed toyora sand with specific clay minerals and non-clay minerals to turn it into sand-clay mixed fine-grained soil with different mineral components.Aiming at this material,this paper carried out lateral compression test and one-way dynamic triaxial test to study its compression and dynamic characteristics.The focus of this study is the influence of mineral composition on the dynamic characteristics of sand-clay mixed fine-grained soil and the transitional failure of soil under certain conditions.The main conclusions are summarized as follows:(1)Mineral composition plays an important role on the dynamic characteristics of the soil.Sand-clay mixed fine-grained soils with different mineral compositions can exhibit different failure modes under the action of cyclic loading.For example,failure induced by pore-pressure or structual failure induced by cyclic stress.It is inadequate to apply a single index such as plasticity index or clay content to evaluate the dynamic characteristics of the soil body.To study the dynamic characteristics of the soil body,the mineral composition of the soil must be taken into consideration.(2)In the sand-clay mixed fine-grained soil with the same plastic index which is composited mainly with montmorillonite and talc,the sand-clay mixed fine-grained soil with high montmorillonite content obtain higher dynamic strength than that with low low or no montmorillonite.and it also has higher resistence to pore pressure failure.(3)There is a peak point in the viscous energy dissipation ratio of the soil where the failure mode is transitional failure.After passing the peak point,the viscous energy dissipation ratio will decline sharply and be accompanied by rapid changes in other indicators,which is the characteristic of the energy expression of the transitional failure.The value of its peak point shows an upward trend with the increase of cyclic stress ratio.(4)As the mineral content of the high plastic clay in the sand-clay mixed fine-grained soil increases,the viscous energy dissipation ratio of the soil that undergoes transitional failure will appear to decline first and then increase after going through the peak point,and the soil failure mode change from "sand-like" to "clay-like".