Settlement Mechanism and Reinforcement Analysis of Soft Soil Subgrades Based on Anisotropic Constitutive Model

Abstract:

Taking the deep soft soil subgrade project of the South Extension of Wanhuan West Road as the background， the K₀-MCC model was embedded into the finite element software ABAQUS through secondary development of a UMAT subroutine to establish a finite element model of deep soft soil subgrades considering soil anisotropy. Settlements， pore water pressures， and horizontal displacements caused by subgrade filling were calculated. The model’s validity was verified by comparison with field-measured data. The settlement and deformation mechanisms of deep soft soil subgrades were analyzed. Furthermore， by comparing the effectiveness of cement-mixed piles and prestressed pipe piles in controlling settlement， reinforcement methods suitable for deep soft subgrades were proposed. The results indicate that the initial stress anisotropy of the soil and stress-induced anisotropy have significant effects on the settlement and deformation of soft soil subgrades. The settlement during the two-stage surcharge of the deep soft soil subgrade reached 0.337 m， while the consolidation settlement occurring during the construction interval after the first surcharge was only 0.005 m. Within one year after the surcharge， as excess pore water pressure dissipated and the subgrade continued to bear load， settlement further developed， reaching a total of 0.366 m， with settlement generated during surcharge construction accounting for 92 % of the total. After subgrade filling， settlements were larger at shallower depths and closer to the subgrade center. Compared with cement-mixed piles， prestressed pipe pile reinforcement is more effective in controlling construction settlement of deep soft soil subgrades， particularly in terms of total and long-term settlement control.