Practice and experience in deep excavations in soft soil of Ho Chi Minh City, Vietnam

Deep excavations for the construction of basements and urban infrastructure have increased drastically in Vietnam. This study reviews 18 cases of deep excavations in 4-16-m-thick soft clay in central Ho Chi Minh City (HCMC), three of which experienced severe instability. Most reviewed cases applied internally braced Diaphragm Walls (DWs) whose maximum lateral wall deflections were 0.15%-1.0% of the excavation depth. In cases of a sheet pile wall or micro-bored pile wall, this value ranged 1.0%-2.4%. Among wall types used in HCMC, the DW was most effective in minimizing wall and ground movement. The wall deflection magnitude in cantilever mode at the first stage of excavation reached 35%-60% of total wall deflection in the final stage. Increasing the stiffness of the DW and bracing system is shown to be ineffective. The case studies suggest a need to: i) formulate local guidelines or codes of practice in association with damage assessment, and ii) improve numerical analysis in the assessment of wall system design, ground movements and risk of damage to adjacent buildings. Furthermore, for numerical analyses using the nonlinear hardening soil model of PLAXIS, more realistic soil parameters for HCMC soft clay are explored in laboratory testing.