Dynamic Response Of Sand-clay Layer Based On Transparent Soil

At present,most of the foundations in China are laminated soil layers formed by contact combinations of soils with different properties,and the study of laminated soil layers equivalent to a single nature soil no longer meets the needs of engineering safety,and the contact mechanical behavior of soil interface is essential to the study of dynamic stress transfer law,while there are few reports on the study of soil visualization at the soil interface.Based on the similar material of transparent soil,indoor model tests and numerical simulation analysis were carried out for the problem of interfacial effect at soil interface,which revealed the dynamic response mechanism of sand-clay layer interface and provided a technical reference for the study of layered foundation stability.The transparent sandy soil and transparent clay were formulated with similar soil materials,the aggregates（soil particles）were fused silica sand and precipitated silica,and the pore fluid was n-dodecane and No.15 white oil.The physical and mechanical indices of transparent sand and transparent clay were measured by shear test and consolidation test;and the microscopic contact mechanism of soil interface was elaborated by scanning electron microscope test,and then it was proved that the transparent soil could simulate the natural soil layer approximately.An indoor model of sand-clay layer was prepared to meet the transparency requirements,and the dynamic response mechanism of the soil interface under ramming load and machine vibration load was investigated to confirm the phenomenon of sudden change of dynamic stress at the soil interface.Particle image velocimetry was used to reveal the mechanism of this phenomenon,and the movement of particles in the soil layer under the ramming load and machine vibration load was observed and recorded.At the soil interface,the particles were in vibration state,and the particle velocity increased compared with the upper soil layer,and the particles had a tendency to move laterally along the soil interface.The above phenomenon indicates that the soil interface has produced some depletion to the transfer of load energy.In order to further elucidate the influence of the elastic modulus ratio of soil layer on the interface effect of soil layer,the sand-clay layer was modeled with the aid of particle flow PFC^2Ddiscrete element software,and the change data of stress,velocity,displacement and force chain at each monitoring point of soil layer under disturbance were monitored and recorded by arranging the built-in measurement circle of the software.The numerical simulation results show that the particle force chain at the soil interface is enhanced by the increase of contact force,and with the increase of the elastic modulus ratio above and below the soil layer,the greater the sudden change coefficient of dynamic stress at the soil interface is,the more obvious the interface effect is.