Field Test Study on Dynamic Characteristics of Lateritic Soil Expressway Subgrade Under Wetting Action
In this study,the dynamic response and accumulative deformation characteristics of expressway lateritic soil subgrade were investigated under varying moisture contents by performing vehicle and vibration tests on a section of the Nanzhan expressway.Different axle loads,vehicle speeds,and subgrade wetting conditions were considered in the vehicle test,and different excitation forces,times,and subgrade wetting conditions were considered in the vibration tests.Moreover,the variation laws of the dynamic stresses,dynamic accelerations,and dynamic displacements of the subgrade were analyzed,and the accumulative deformation and the attenuation of dynamic characteristics along the depth and transverse directions of the subgrade were determined.The results show that subgrade immersion significantly reduces the attenuation ability of the subgrade to dynamic stress,dynamic acceleration,and dynamic displacement,leading to an increase in the dynamic response and accumulative deformation.When the moisture content increases by 2.8％and 4.2％,the dynamic response increases by 7％and 13％,respectively,and the accumulative deformation increases by 28％and 54％,respectively.The dynamic stress,dynamic acceleration,and dynamic displacement also increase with increasing axle load,vehicle speed,and excitation force,whereas the influence distance of the dynamic response of the subgrade exhibits an exponential attenuation along the direction away from the action point of the dynamic load.Moreover,the attenuation rate of the dynamic response can reach 80％at a distance of 1.3 m from the roadbed surface,and the effective influence depth of the subgrade increases with an increase in the moisture of the subgrade,axle load,and vehicle speed.The influence of the axle load on the subgrade is also significantly higher than that of the moisture of the subgrade and vehicle speed at an axle load of 10 t,20 t,and 30 t,respectively,and effective influence depth of 1.3 m,2.3 m,and 3.3 m,respectively.The accumulative deformation of the subgrade first rapidly increases before gradually stabilizing with an increase in the moisture content and vibration times.Furthermore,the accumulative deformation of the subgrade after wetted twice and wetted once are 1.46 and 1.86 times higher than those during pre-wetting,respectively,and the accumulative deformation of the first 1 million cycles accounts for 60％of the total deformation under the same moisture conditions.Therefore,these results provide a reference for the service performance evaluation of expressway subgrades improved using lateritic soil.
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