Cumulative effects of cyclic train loading on strains in reinforced soils around tunnels

Metro tunnels often experience uneven settlement of the soil beneath them during operation, a problem that is especially pronounced in soft soil layers such as silt. This uneven settlement negatively affects the operational safety of subways, prompting engineers to use soil reinforcement techniques to mitigate ground deformation. However, there is a lack of research on the cumulative deformation of reinforced soils under cyclic train loading. In this study, dynamic triaxial tests were conducted to obtain the deformation parameters of silty reinforced soils under cyclic loading. The principal dynamic relationship was summarized, and the effect of loading frequency on soil deformation was analyzed. The results indicated that as the loading frequency increased, the cumulative deformation of the soil decreased. Using the dynamic constitutive relationship derived from the tests, the finite element method was employed to model the interaction system between the load, tunnel, and strata, as well as the dynamic modulus attenuation behavior of the reinforced soil layer. This approach was used to investigate the cumulative deformation characteristics of reinforced soils under cyclic loading. The findings indicated that the dynamic modulus of the reinforced soil decayed rapidly at the beginning of the loading period, leading to an accelerated increase in the cumulative deformation. Additionally, the cumulative deformation was measured at different train speeds, revealing that when the speeds exceeded 80 km/h, the cumulative strain of the soil increased gradually with speed.