Experimental study on mechanical characteristics of coarse-grained materials of subgrade under static-dynamic loading

The coarse-grained soil is widely used as the filling materials in subgrade construction due to its excellent mechanical properties. However, the significant deformation of the filling materials caused by long-term loading severely impacts the safe operation of the roadbed structures. In order to reveal the deformation and strength evolution of the coarse-grained soil under typical subgrade stress levels and traffic loading conditions, a series of static-dynamic characteristic tests on the coarse-grained soil are conducted. Furthermore, an in-depth analysis is performed on the differences in the breakage characteristics under static-dynamic loading. The research indicates that under low confining pressure, a smaller axial strain can reach the peak stress state, and the increase in the confining pressure can significantly enhance the peak strength of the filling materials. Under different confining pressures, the fill materials exhibit shear expansion during the shearing process, with the final volumetric strain of samples under the confining pressures less than 300 kPa all exceeding 0. In the dynamic tests, the axial accumulation of the filling materials increases with the dynamic deviator stress, decreases with the confining pressure under the same load cycles, and the axial strain generated by the first 500 loading cycles constitutes 80% of the total strain. The particle breakage pattern in the filling materials under static and dynamic loading differs significantly. Under static loading, the particle breakage primarily occurs in the form of edge fractures and overall rupture. Conversely, under dynamic loading, it predominantly involves surface abrasion and slight edge fractures.