Experimental Study Of The Dynamic Properties Of Clay In Nanchang Area Under Intermittent Cyclic Dynamic Loading

Under the action of long-term cyclic load,clay foundation is easy to produce large settlement,which seriously affects the safety and stability of superstructure.In the past studies on the dynamic characteristics of soil mass,sinusoidal and half-sinusoidal wave forms of continuous cyclic loading are used.In fact,the common dynamic loads,such as traffic loads and earthquake loads,have a certain interval in the loading process.The drainage and reconsolidation behavior of clay during the intermittent period will change the dynamic characteristics of clay and affect the development trend of its cumulative deformation.In order to establish an empirical formula which can accurately reflect the settlement deformation of foundation under long-term dynamic load,the influence of intermittent effect on the dynamic characteristics of soil should be considered.Taking the clay in Nanchang area as the research object,a series of triaxial consolidated undrained shear tests,resonant column tests and periodic intermittent dynamic triaxial tests were carried out to study the strain development and dynamic characteristics evolution of Nanchang reshaped clay under intermittent cyclic load.The test results are mainly divided into the following two parts:1.Based on the analysis of the resonant column test results,it is found that the shear modulus of the soil under the cyclic loading of small strain goes through the softening and recovery process repeatedly,and the dynamic load,water content and confining pressure have obvious effects on the softening and recovery of the clay.The softening and recovering properties of clay stiffness under small strain loading were studied by the modulus evolution model.The influences of different factors on the modulus evolution could be quantitatively described by the model parameters a,b and c.With the increase of voltage,the initial softening rate and softening degree of the sample increase(parameters a and c increase),while the recovery rate decreases(parameters a and c decrease).The influence of moisture content on the softening and recovery of soil modulus has a peak value.The internal structure of soil is readjusted under intermittent dynamic load and the modulus evolution tends to be stable.2.The results of intermittent triaxial test were analyzed to study the development of total axial strain,pore water pressure,hysteresis curve and elastic modulus under different stress amplitudes and water content.It is found that the axial strain of soil has a small amplitude rebound in the intermittent period,and the stress amplitude and the number of loading stages have a significant effect on the strain rebound.It is found that the clay reconsolidation behavior during intermittent loading changes the strain accumulation mode during subsequent loading.Based on the experimental results,the empirical formula of cumulative plastic deformation of clay under intermittent cyclic loading in Nanchang area is established.The accumulation and dissipation of excess pore water pressure in soil under intermittent loading mode are obtained.The moisture content has significant influence on the variation trend of elastic modulus.