3D Finite Element Analysis of Pile Behavior Inside the Deep Excavation in Soft Soil

Abstract

A large excavation was carried out in the thick soft soil layer to construct the pile cap foundation and the basement floor for the 15 stories-building in Ho Chi Minh City. The soil profile consists of a 25-meter-thick of very soft clay with SPT value of zero laid on an 8.5-meter-thick of soft clay with SPT value of 3 and laid on a 13.9-meter-thick of medium dense fine sand with SPT value of 17. The excavation was supported by the system of 6-meter-depth SP -IV steel sheet piles with the tied-back rods on the top of the wall to the 6m H steel piles installed behind the wall. Before the excavation, the spun PHC pile with 600mm diameter and 100mm thick was installed to support the superstructure. As excavation to 3.8 meter depth, four piles with the distance 4.55m, 7.15m, 10.65m and 13.25m from the wall had the top pile displacement 63.5cm, 38.86cm, 19.5cm and 11.4cm, respectively. Furthermore, all these piles were determined to be cracked by using the PIT test. Base on the collected data, back analysis was carried out by using PLAXIS 3D Foundation with Hardening-Soil soil model to determine the response of these piles during excavation. In the results, the maximum bending moment of these piles was over its ultimate value, thereby, we can analyze the reason piles group in this building was failure and use the parameters in PLAXIS for expanding the analysis to other situations.