There exists the issue of overreliance on the empirical multiplicative relationship between the modulus parameters of the hardening soil model with small strain (HSS) and the compression modulus E_s1-2, as well as the neglect of the confining pressure dependence of the shear modulus reduction parameter γ_0.7, in the context of Tianjin soft soil area. The ultra-deep subway excavation of Xiawafang Station on Tianjin Metro Line 8 was taken as a case study. The Xiawafang station was currently the deepest metro station in soft soil areas in China, with an excavation depth of 38.3 m. By utilizing extensive laboratory and field test data, particularly the small-strain shear modulus G₀ obtained from in-situ wave velocity tests, a statistical relationship between G₀, the initial void ratio, and confining pressure was established. The variation of γ_0.7 with soil depth was considered and a statistical relationship between the tangent modulus for primary oedometer loading $ E_{{\text{oed}}}^{{\text{ref}}} $ and E_s1-2 was established. As a result, the HSS parameters applicable to soils in the Tianjin area were finally determined. A detailed three-dimensional finite element model of the Xiawafang Station excavation was established using PLAXIS 3D, and the results of lateral displacement of the retaining wall and surface settlement outside the pit were compared with the field measured data. The results demonstrate that the proposed HSS parameter determination is reasonable, with calculated excavation deformations closely matching measured values. These findings can provide an engineering reference for the design of deep excavations and the selection of geotechnical soil parameters in the Tianjin soft soil area.