Numerical Analysis on the Mechanism of Bamboo Soil Nails and Bamboo Piles in Rows for Retaining Deep Foundation Pit

In this study, combined with an engineering case, nonlinear finite element (FE) analysis is adopted to explore the mechanism of a deep soft soil foundation pit supported by bamboo soil nails and bamboo piles in rows. Firstly, a plain strain model is built to analyze the stability of the pit excavated with a slope with 45° inclination angle and without a retaining system. It reveals that its factor of safety is so small that effective retaining measures should be taken. In order to reasonably analyze the working mechanism of this particular retaining structure, a high-fidelity simulation is carried out in the Super Computing Center of Fujian Province using three-dimensional (3-D) FE methods. That is to say, bamboo soil nails are modeled with solid elements instead of structural elements. In addition, the dense bamboo piles in rows are modeled with the equivalent diaphragm wall. Coulomb's frictions between the soils and bamboos, as well as soils and diaphragm wall, are considered. Mohr-Coulomb's constitutive model and strength reduction finite element technique are employed in the numerical analysis. In order to decrease the computational costs, displacement constraint and its release method are adopted to simulate the process before and after excavation. The study shows that an appropriate stability and structure analysis method for foundation pits supported by this kind of structure is presented. The research outcomes will facilitate this sort of environment-friendly, energy-saving and cost-saving retaining structure to be widely used in excavation engineering.