Verification of soil parameters of hardening soil model with small-strain stiffness for deep excavations in medium dense sand in Ho Chi Minh City, Vietnam

Accurate prediction of wall displacements induced by deep excavations is essential to guarantee stability and safety of the excavation as well as to prevent any harm and damage to the adjacent structures. This paper proposes and validates a set of equations for determining soil parameters of hardening soil model with small-strain stiffness (HS-small model) for medium dense sand in Ho Chi Minh City (HCMC), Vietnam. The study was based on back-analysis of diaphragm walls’ displacements from three well-documented excavation cases and data from twenty boreholes. Good agreements between finite element analysis (FEA) results and field observations were obtained by assuming the E50 stiffness value to 2500N (kPa) (N is the SPT value), the small-strain shear modulus, G0, to 7000ρN0.7 (kPa) and the shear strain at which the shear modulus is reduced to 70% of small-strain modulus, γ0.7, to 0.0002. The comparisons with field measurements indicated that HS-small model can better predict the diaphragm walls’ displacements than hardening soil model (HS model). Additionally, the field displacements of diaphragm walls in medium dense sand are in the range of 0.1–0.3%H (H is excavation depth).