Comparison of Analytical and Numerical Analysis Results of Deep Excavation for Nhon – Hanoi Urban Railway Project in Hanoi, Vietnam

Abstract

Deep excavation is an indispensable part of constructions on subsoil in Hanoi, Vietnam. There are 8 urban railways which were constructed with many deep foundations in the main terminals in Hanoi. The 8^th terminal at the Nhon – Hanoi Station route is more complex than others due to the configuration of the terminal. The terminal is about 8 m deep. Bored piles with 1.2 m in diameter were constructed at the bottom of the pit. In order to ensure stability of the pit, Larsen IV steel sheet piles were constructed with a length of 12 m. In addition, two rows of soil anchors with 14 m in length and 15.2 mm in diameter have also been adopted to strengthen the foundation pit.

Analytical method using the Geo5 program was conducted to design the steel sheet piles at the site. Numerical method using the Plaxis program was also conducted to verify the design of the steel sheet piles. In the analytical analysis, exact solutions are obtained by solving differential equations directly with some assumptions and limitations, meanwhile in the numerical analysis the derivatives in different equations are replaced by some sort of approximation and solutions. Comparison of the deformation of steel sheet piles, internal forces on the piles, and internal forces on the anchors obtained from the analytical and numerical methods were provided in the paper. It was concluded that the predicted values obtained from the analytical method should be more conservative than those obtained from the numerical analysis.