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The problem of mud pumping in saturated subgrade seriously affects the safe operation of trains on railways. There are relatively few research results on the characteristics of subgrade mud pumping, and those that do exist dispute the precise mechanism of the mud pumping. In this paper, a new test model is designed to study the important characteristics of subgrade mud pumping. The model can monitor not only the evolution of subgrade mud pumping but excess pore water pressure and dynamic stress in soil as well. In particular, we study the mud pumping of Lean Clay. Our results show that with the increase in the number of cycles, the axial strain of samples increases rapidly and then slowly. The axial strain increases with the increase in cyclic loading amplitude and decreases with the increase in loading frequency and initial dry density of Lean Clay. We also find that the excess pore water pressure first increases rapidly and then decreases slowly with the increase in the number of cycles. Furthermore, with the increase in cyclic loading amplitude, excess pore water pressure increases, and with the increase in the initial dry density, the excess pore water pressure decreases. We find that the loading frequency has little effect on excess pore water pressure. After the test procedure, we find that an increase in cyclic loading amplitude aggravates the degree of Lean Clay subgrade mud pumping and that an increase in loading frequency and increase in initial dry density of subgrade soil reduces the degree of mud pumping. We further find that the upward migration of fine particles driven by excess pore water pressure gradient is the main mechanism of subgrade mud pumping. However, the generation of an interlayer can also promote the occurrence of subgrade mud pumping.

来源平台：GEOMECHANICS AND ENGINEERING