Abstract:

 In order to enhance the ground strength and accelerate the consolidation rate, the technique of combined composite ground has been widely utilized in ground improvement projects. However, there are few theoretical investigations on the nonlinear consolidation behavior of this combined technique. To fill this gap, the logarithm models of are incorporated to describe the nonlinear consolidation characteristics of soils, then an analytical model for the nonlinear consolidation of composite ground with combined use of granular columns and impervious columns is established by accounting for the variation of the column-soil compression modulus ratio with consolidation. Further, the consolidation deformation of granular columns is considered by introducing a new flow continuity relationship. Based on the equal strain assumption and Darcy’s law, the governing equations and analytical solutions are then obtained with consideration of the well resistance of granular columns, disturbance effects of both impervious columns and granular columns and the coupled radial-vertical seepage within soil. Moreover, the present solutions under different loading schemes are adopted to investigate the influence of several crucial parameters on the nonlinear consolidation behavior of composite ground. Furthermore, the accuracy of the current model is verified by comparing it with the existing solutions and applying it to analyze two tests. The results reveal that ignoring column consolidation deformation leads to an overestimate of consolidation rate, with maximum error reaching up to 10.5% as the replacement ratio increases. Neglecting the nonlinearity will underestimate the consolidation rate when the soil’s compressive indices C_c are smaller than the permeability indices C_kh(v). Additionally, the variation of C_c/C_kv has little influence on the consolidation rate and can be ignored when compared with C_c/C_kh. Factors such as a denser construction site layout, a higher column-soil compression modulus ratio, a larger permeability coefficient, or a smaller smear zone area of granular columns will accelerate the consolidation of composite ground.

Key words: nonlinear consolidation, composite ground, granular column, impervious column, ground improvement