Model Experimental Study on Dynamic Performance of Special Soil Subgrade Reinforced with Composite Geomembrane Seal Layer

To analyze the protective effect of a composite geomembrane seal layer on special soil subgrades, two full-scale models of ballast track-special soil subgrade were developed. In this study, the dynamic performance of ballast track-special soil subgrades with and without a composite geomembrane seal layer were investigated under both soaked and unsoaked conditions. The test results show that the vibration in the model without a composite geomembrane seal layer is more severe than the vibration in the model with a composite geomembrane seal layer for the same loading frequency and level. Under cyclic loading in unsoaked conditions, the accumulative settlement of the models with and without a composite geomembrane seal layer tends to stabilize at cyclic loading greater than 80,000 cycles. Under cyclic loading in soaked conditions, the accumulative settlement of the model without a composite geomembrane seal layer continually increases, while the accumulative settlement of the model with a composite geomembrane seal layer gradually stabilizes. When the cyclic loading reaches 1,400,000 cycles, the moisture content of the special soil is increased by 41%, while the K30 value at the top of the bottom layer of the subgrade is reduced by 39% in the model without a composite geomembrane seal layer. However, the moisture content of the special soil and K30 values for the model with a composite geomembrane seal layer remain basically unchanged. The composite geomembrane used for protecting the special soil of a subgrade bed can effectively intercept water seeping into the subgrade bottom of a bed filled with special soil, which can prevent the special soil from softening. Therefore, the ballast track-special soil subgrade demonstrates favorable long-term dynamic stability when subjected to cyclic loading.