Experimental Study On Dynamic Characteristics And Cumulative Deformation Of Clayey Sand In Qingdao Area

Under the long-term cyclic train load,the stability of subgrade and the safety of railway operation will be seriously affected by the typical clay bearing sandy soil foundation in Qingdao area.Many scholars at home and abroad have studied the dynamic characteristics and permanent deformation of soft soil and sand under cyclic load,and accumulated rich research results and experience,but few have studied the dynamic characteristics and deformation mechanism of sand with clay under cyclic train load.Based on the GDS resonant column,this paper studies the effects of effective confining pressure,dry density and clay content on the G-?,D-? curves and shear wave velocity of the dynamic characteristics of clay;based on the GDS dynamic triaxial and other test instruments,it studies the effects of cyclic vibration number,vibration frequency and effective confining pressure on the permanent deformation of clay bearing sand under cyclic train load.The main research contents and test results are as follows:(1)The remolded samples were made by Fujian standard sand and Malaysian kaolin,and their physical and mechanical properties were tested in laboratory.The test results show that the Malay pressure kaolin belongs to the medium compressibility and has very low permeability.(2)The dynamic shear modulus of clayey sandy soil decreases with the increase of strain,increases with the increase of dry density and effective confining pressure,and decreases with the increase of clay content;the damping ratio of clayey sandy soil increases with the increase of strain,and increases with the increase of clay content;the relationship between confining pressure and damping ratio of clayey sandy soil is not clear with the increase of dynamic strain,but there is an increasing trend.In the case of small strain,the change of damping ratio with dry density is not obvious,but with the increase of strain,there is an increasing trend;Hardin drnevich model can better fit the G-? curve;shear wave velocity increases with the increase of effective confining pressure and dry density,and decreases first and then increases with the increase of clay content.(3)comparison of clayey sand and non clayey sand: under different confining pressures,the dynamic shear modulus of non clayey sand is higher than that of clayey sand;the damping ratio of clayey sand in Qingdao increases with the increase of confining pressure,dry density and clay content;the damping ratio and dynamic strain of clayey sand and non clayey sand The damping ratio of clayey sand is higher than that of non clayey sand.The trend of normalized test points is consistent with that before normalization;the dispersion range of non cohesive sand is smaller than that of cohesive sand;and with the increase of dynamic strain,the ratio of dynamic shear modulus changes from linear to nonlinear.(4)according to the cumulative strain growth trend of each soil layer,the fifth layer and the twelfth layer are classified as stable clay bearing sand layer,and the ninth layer is defined as critical type.The cumulative deformation process of sand layer with clay can be divided into two stages: the first stage is vibration 0-2000 times;the axial cumulative strain develops fastest,and the cumulative strain can reach the final total deformation of 60%-80%;the second stage,after vibration more than 2000 times,the cumulative strain growth rate slows down.Compared with Barksdale model and Monismith model,it is found that Barksdale model has better fitting effect on experimental data.