Consolidation analysis of an impervious multi-pile composite ground under rigid foundation

The multi-pile composite ground with fully penetrated long rigid piles and partially penetrated impervious or pervious short piles is a new type of soft soil improvement technology. Based on the equal vertical strain assumption, the governing equations for average excess pore water pressures within the surrounding soil of the composite ground with long rigid piles and impervious short piles are derived under ramp loading. The corresponding analytical solutions are developed based on the one dimensional consolidation theory of a double-layer ground, and overall average degree of consolidation of the composite ground is presented. The accuracy of the proposed solution is examined by FEM. A parametric study on the consolidation behaviour of the composite ground is performed using the proposed solutions. The results show that the consolidation rate of the composite ground increases with increasing the constrained modulus and the area replacement ratio of the long piles. In addition, it increases with increasing the modulus ratio of the subsoil below short piles to that above the tip of the short piles. The variations of the length, the constrained modulus and the area replacement ratio of the impervious short piles have negligible influence on the consolidation rate of the composite ground.