Effects of Soil Improvement by Mass Mixing on the Lateral Capacity of Pile Group Using Finite Element Method

Mass mixing is one of main soil improvement methods by mixing the native soil and grout spoil to a relatively homogeneous mixture to increase the soil resistance. Numerical study using finite element method (FEM) of soil improvement effects by mass mixing on the lateral capacity of pile group in soft clay is presented. The clay is modeled by three-dimensional (3D) nonlinear pressure-independent elastoplastic solid elements, and the piles are modeled by one-dimensional (1D) linear elastic beam-column elements. The gapping between the soil and pile is taken into account using non-extension zero-length spring elements. The mass mixing block is also modeled as 3D linear elastic solid elements due to its relatively higher stiffness and strength than the surrounding virgin soft clay. The soil parameters are calibrated by simulating the lateral behavior of single pile in virgin weak clay, and of pile groups in virgin and improved soil. A series of parameter study including the depth and length effect of mass mix block, the effect of strength of mass mix on the lateral resistance of soil are preformed using the calibrated soil parameters and validated FEM model. Analyses show significant effect of mix depth and length and less significant effect of mix strength on the lateral capacity of pile group in soft clay.