Experimental Study On Resilient Characteristics Of Coarse Granular Materials Under Three-dimensional Stress State

The coarse granular materials in road base and subbase layers are subjected to long-term traffic loading after opening to the traffic.Most of the road diseases,such as the rutting,cracking and excessive permanent deformation are strongly related to the uneven resilient deformational response of road base and subbase layers,which affects the service performance of the road and cause the increase of maintenance cost.In geotechnical application,the stress state of soil is three-dimensional.Firstly,owing to the difference of pavement structure,construction process,location and surrounding environment,the initial stress state of granular materials are usually three-dimensional anisotropy.Secondly,under the traffic loading,the cyclic dynamic stress on soil element is also in a three-dimensional state,which is manifested by the coupling effects of cyclic major principal stress,intermediate principal stress and minor principal stress.Meanwhile,few researches were proposed to study the resilient characteristics of coarse granular materials in three-dimensional stress state.Based on the factors above,in this study,a series of multi-stage resilient deformation tests were conducted by a true triaxial apparatus,considering the effects of initial anisotropic stress state,effective confining pressure,amplitude of cyclic shear stress and coefficient of cyclic intermediate principal stress in three-dimensional stress state,and the modified model is established to predict the resilient modulus of coarse granular materials in three-dimensional stress state.In addition,the difference of resilient characteristics of coarse granular materials under various moisture content and clay content are also studied.The main results are as follow:(1)In the condition of three-dimensional cyclic stress state,the resilient deformation response of coarse granular materials are different from that of axisymmetric stress state.The resilient modulus are significantly correlated with the amplitude of cyclic shear stress and cyclic coefficient of intermediate principal stress.(2)In the condition of initial anisotropic stress state,the resilient modulus and initial shear stress shows a linear relationship when the initial stress ratio is less than 0.8.And the influence of coefficient of intermediate principal stress on resilient modulus is significantly related to moisture content.(3)The variation of clay content is considered to affect the inherent structure of coarse granular materials greatly,and there appears to exist a critical value of clay content,at which the resilient modulus changes the variation trend from increasing to decreasing.(4)On the basis of a large number of test data,the modified model is established to predict the resilient modulus of coarse granular materials in three-dimensional stress state,and the predicted model under the coupling condition of three-dimension dynamic and static stress state is further discussed.