Field evaluation of the three-dimensional dynamic stress state of the subgrade induced by the heavy-haul train load

Abstract

The three-dimensional stress state of subgrade soil elements plays a crucial role in railway subgrade design and service life evaluation, especially in heavy-haul railways. To solve the complex problem of the field test of three-dimensional stress state in subgrade induced by train vehicles, a novel regular dodecahedron soil pressure sensor (RDSPS) was developed and applied to field tests, which can measure dynamic stress components, including normal stress and shear stress in ×,y and z directions. Then the field test of total stress components of subgrade was carried out on the Datong-Qinhuangdao heavy-haul railway. The dynamic stress, including three normal stresses and three shear stresses, was determined at seven points in the subgrade for trains with 25 t axle load at different speeds (45, 55, and 60 km/h). The result indicates that the distributions of dynamic stresses of railway subgrade show periodic fluctuation subjected to moving train load, and each bogie can be regarded as a loading point for the field test section. Meanwhile, the stress path of soil elements in the subgrade changes continuously during the passage of a heavy-haul train, and the maximum principal stress angle changes between -π/2 and π/2. The normal stress in the × and y directions decreases first slowly and then rapidly with the depth of subgrade, while the attenuation law of normal stress in the z-direction with the depth of subgrade is just the opposite. Due to the stress superposition effect, the normal stress in the y-direction of the measuring points below the track centerline is greater than that at other measuring points. A calculation model of vertical normal stress was proposed based on the measured data. The empirical model for the attenuation coefficient of normal stress in the ×, y, and z directions was established to predict the stress attenuation coefficient more accurately. In this paper, the total stress components of the railway subgrade were measured for the first time during the passage of the train, which can provide helpful guidance for a better understanding of the dynamic response of the subgrade.