Penglu Cui

As an effective technology for the rapid treatment of soft-soil foundations, geosynthetic encased stone column (GESC) composite foundations are commonly used in various embankment engineerings, including those situated on sloped soft foundations. Nevertheless, there is still a scarcity of stability studies for sloped GESC composite foundations. Several 3D numerical models for sloped GESC composite foundations were established using an equivalent method. The influences of the area replacement ratio and the tensile strength of geosynthetic encasement on the stability were investigated. The results showed that the stability increased nonlinearly with the area replacement ratio, and there existed an optimal area replacement ratio (e.g., 24.56% in this study) to balance the safety and economic requirements. The stability increased linearly with the tensile strength of geosynthetic encasement at low tensile strength levels (lower than 105 kN/m in this study), and the impact was relatively limited compared with that of the area replacement ratio. In addition, the stability generally decreased nonlinearly as the foundation slope decreased, and high-angle (foundation slope close to 30°) sloped GESC composite foundations are recommended to be treated with multiple reinforcement techniques. The relationship between the minimum area replacement ratio and the foundation slope was further quantified by an exponential function, allowing for the determination of the area replacement ratio of various sloped GESC composite foundations and providing theoretical guidance for engineering practice.

The vacuum preloading method effectively strengthens soft soil foundations with vertical drainage, which produces a smear effect when laying sand drains. Meanwhile, the seepage of pore water and soil deformation during consolidation exhibit nonlinear characteristics. Therefore, based on Gibson’s 1D large-strain consolidation theory, this paper developed a more generalized large-strain radical consolidation model of sand-drained soft foundations under free-strain assumptions. In this system, the double logarithmic compression permeability relationships for soft soils with large-strain properties, the variation in the radical permeability coefficient in the smear zone, and the effect of the non-Darcy flow were all included. Then, the partial differential control equations were numerically solved by the finite difference method and validated with existing radical consolidation test results and derived analytical solutions. Finally, the influences of relevant model parameters on consolidation are discussed. The analysis shows that the greater the maximum dimensionless vacuum negative pressure P₀, the faster the consolidation rate of sand-drained foundations. Meanwhile, the decrease in the negative pressure transfer coefficient k₁ will result in a decreasing final settlement amount. Moreover, the consolidation rate of sand-drained foundations is slower considering the non-Darcy flow, but the final settlement is unaffected.

The elastic viscoplastic properties are non‐negligible factors of clays that cause the deviation between the theoretical and the measured values, which were rarely incorporated in layered consolidation problems. Thus, this paper extended a generalized bi‐layered one‐dimensional (1D) consolidation model for soft ground under ramp load, simultaneously incorporating elastic viscoplastic deformation, non‐Darcy flow (NDF), and time‐dependent drainage boundary (TDB) condition. The finite volume technique was employed to numerically solve the control equation. Then, the proposed method solutions were verified by comparing with degenerated cases, including oedometer experimental results, analytical and semi‐analytical solutions with different boundary conditions. Furthermore, parametric studies were conducted on the bi‐layered clay creep consolidation characteristics by investigating the effect of the loading rate, interface and flow parameters, and the relative soil layer properties. The results demonstrate that the entire dissipation rate of the excess pore‐water pressure (EPWP) and settlement rate in the bi‐layered ground become faster as the soil thickness with high permeability or low compressibility increases. When considering the viscosity of soft clay, the EPWP exceeding the overlying construction load value can occur in poorly drained locations. Neglecting loading rate, time‐dependent drainage boundary (TDB), and NDF can result in a significant overestimation of consolidation and settlement proceedings.

To further investigate the nonlinear creep properties of soft soils and the effect of variable loading, a one‐dimensional (1D) nonlinear creep consolidation system of soft soils under construction load is established, including time‐dependent drainage (TDD) boundary, elastic‐viscous‐plastic deformation, non‐Darcy flow (NDF), and self‐weight stress. The consolidation problem is presented by virtue of the finite volume method, and the associated calculation program is compiled. The efficiency of the numerical solutions is validated by comparing the degenerated solution against analytical, semi‐analytical, and numerical solutions. Then the influences of construction load and nonlinear creep model parameters on consolidation are studied. The results show that TDD boundary and construction load significantly affect consolidation, and the larger the loading rate and interface parameter, the faster soil's overall dissipation process of excess pore‐water pressure (EPP). Meanwhile, at the earlier consolidation stage, considering the secondary consolidation effect will cause an increase in excess pore‐water pressure (EPP). Prolonging the construction period, decreasing the interface parameter, considering the self‐weight stress, or increasing the non‐Newtonian index will all aggravate this phenomenon. Additionally, the TDD boundary, construction load, and non‐Newtonian index flow (NNIF) are not a determinant for final soil settlement.

The nonlinear flow law and soil boundaries greatly affect the dissipation process of soil consolidation. Thus, to study the impact of nonlinear flow under impeded drainage boundaries, the classical non-Darcian flow model described by non-Newtonian index was introduced. The numerical solutions are derived in detail by the finite difference method (FDM) for one-dimensional (1-D) consolidation incorporating the impeded boundaries, and the computer program is compiled. Then, comparing two analytical solutions based on Darcy’s law and a numerical case of Forchheimeer’s flow, the validity of the present method was verified. The numerical results indicate that there is a critical depth phenomenon for the non-Darcian flow incorporating impeded drainage boundaries. The excess pore water pressure of the soil below the critical depth dissipates more slowly than that of Darcy’s law, whereas the pore pressure of the soil above the critical depth dissipates more quickly than that of Darcy’s law. Moreover, considering that the non-Darcian flow with the non-Newtonian index will still delay the overall consolidation rate of the soft ground, the greater the nondimensional parameter I₀ is, the more obvious the lagging phenomenon of the overall dissipation of pore pressure is.

Considering the nonlinear rheological properties of saturated clay, the modified unified hardening (UH) constitutive relation was introduced to describe the nonlinear rheological deformation. Meanwhile, Swartzendruber's flow law was used to simulate the non‐Darcian flow of pore water in the progress of rheological consolidation. Consequently, a nonlinear rheological consolidation model (NRCM), for one‐dimensional consolidation, that simultaneously incorporates nonlinear stress‐strain‐time relationship, Swartzendruber's flow, self‐weight stress, and variable permeability coefficient has been developed here. The finite volume method (FVM) was utilized to solve the NRCM system, and its effectiveness was verified by comparing with the existing consolidation data. The parametric analysis results indicate that the soil's nonlinear rheological effect induced the excess pore water pressure (EPWP)’s accumulation in the initial loading. This phenomenon became more significant when considering the self‐weight stress or as the initial overconsolidated parameter, soil thickness, and seepage parameter increased. In contrast, it weakened with the increase of external loading. Additionally, considering the self‐weight stress slowed down the whole dissipation of EPWP in the initial period of loading. Nevertheless, it accelerated the nonlinear consolidation process in the middle and late loading stages.