Numerical Analysis on Effects of Soil Improvement on Pile Forces on Existing High-Rise Building

Nowadays, seismic codes are regularly updated with new knowledge and a better understanding
of the earthquake phenomenon. With these updates, existing buildings require a reevaluation
of their stability and a process of reinforcement and/or retrofitting. This study investigated
the effects of two types of ground improvement which use cement-mixing soil surrounding the
foundation structure to reduce and redistribute forces acting on piles. This is especially important
when the reevaluation of high-rise buildings leads to increased forces in the piles. Typically, buildings
are designed while assuming fixed base boundary conditions at the foundation level, without considering
soil–pile–structure interaction (SPSI). SPSI significantly influences the response of high-rise
buildings supported by soft soil. Increasing the lateral resistance of the surrounding soil can reduce
the influence of SPSI. In this study, a detailed dynamic numerical analysis was used to investigate the
dynamic response of an SPSI system of a high-rise building under seismic load. A dynamic analysis
was conducted on a modified layout of a real building, using real-time earthquake motion. The finite
element program DIANA FEA was used to perform nonlinear 3D FEM numerical simulations, taking
into account the essential SPSI phenomena, gap-slip between the piles and the soil, and free-field
boundary conditions. A comparison of the data suggests that the bending moment and shear forces
in the piles are reduced in magnitude and evenly distributed along the upper part of the pile, which
reduces the stress concentration of the bending moment and shear forces at the contact between the
piles and the pile cap.