Experimental Study On Static-dynamic Characteristics Of Unsaturated Unbound Granular Materials

The unbound granular materials(UGMs)in road base and subbase courses are normally situated in an unsaturated state.Road base and roadbed filling layers,as the main load bearing layers of road,are not only bearing static load such as dead weight,but also experiencing long-term traffic cyclic loading.The strength,stiffness,and stability under static and dynamic load will directly affect the road service performance and service life.In order to study the influence of matric suction and fine particle content on static characteristic of granular materials,as well as the influence of matric suction,stress amplitude and the confining pressure on granular materials under long-term loading.A series of tests based on large triaxial apparatus which upgrated by unsaturated module were carried out.The axis-translation technique was adopted to control the suction in the specimens.The following are the main research contents:(1)A series of static tests were carried out to study the shearproperties of unbound granular materials in highway subgrade.The experimental results show that the increase of matric suction will increase the shear strength of UGMs.The increase of viscosity content from 3% to9% has less impact on peak strength than the increase of matric suction from 0kPa to 90 kPa on peak strength.(2)Based on a large triaxial device that can control the matric suction,a series of one-way cyclic triaxial tests are conducted to study the long-term cyclic behavior and resilient modulus of unbound granular materials under traffic loading.The influences of matric suction,stress amplitude and other factors on the accumulated axial strain and resilient modulus of unbound granular materials are revealed.The accumulated axial strain decreases with the increase of the matric suction,and the unsaturated specimen deforms less under the same cyclic stress amplitude than the saturated specimen.In semi-logarithmic coordinates,the accumulated strain has a good linear relationship with the number of loading cycles at low stress amplitude and a nonlinear relationship at high stress amplitude.The resilient modulus increases with the increase of the matric suction,and there is a linear relationship between the increase of the matric suction and the increase of the resilient modulus.(3)Based on the shakedown theory,the plastic stability and creep thresholds of saturated and unsaturated unbound granular materials are obtained,and it is found that the threshold value increases with theincrease of matric suction.(4)The influence of clay content on the long-term dynamic characteristics of unsaturated unbound granular materials was studied.In the saturated state,the resilient modulus decreases sharply with the increase of clay content.(5)Aiming at the unsaturated unbound granular materials which belongs to plastic creep behavior,a prediction model of long-term strain with cyclic vibration is proposed,which is simple in form and can accurately describe the long-term accumulated strain of UGMs filler under cyclic loading under different stress states,and can reflect the influence of stress state on the permanent accumulated strain.