Assessing the Stress–Deformation and Safety Factor against Sliding in Reinforced Deep Urban Excavations in Unsaturated Soils

Abstract There has been limited research conducted to date on the role and significance of soil parameters in an unsaturated state on the amount of deformation and safety of reinforced deep urban excavations. This study investigates stress–deformations and static/pseudostatic safety factors against the general failure of an anchored deep excavated wall in an unsaturated soil deposit through two-dimensional finite-element modeling and limit equilibrium analysis, respectively. A suction-dependent elastic–plastic Mohr-Coulomb model is used in the analyses considering the effective stress approach in unsaturated soils. The results obtained from numerical modeling are validated against field monitoring data, including wall deformations and tensile forces in the anchors. A series of parametric studies are then performed assuming different groundwater levels, surcharge loads, and surcharge load distances from the wall crest to investigate their effects on the stability and deformation of the unsaturated soil excavation. Results are compared with those obtained from the corresponding routine analyses, in which the unsaturated state of the soil is not considered. The parametric study shows that the depth of the groundwater table is more influential on the results compared with the intensity and location of the surcharge load. The study demonstrates that unsaturated soil conditions result in a reduction of up to 37% in the maximum horizontal deformations of the excavation and increase the static and pseudostatic safety factors against general failure by 28% and 19%, respectively. In addition, taking unsaturated soil conditions into account during analysis leads to a decrease of up to 31% in the estimated tensile forces in the anchors. More importantly, it is shown that a more cost-effective stabilization plan can be developed for deep urban excavations by considering soil unsaturation effects, as demonstrated by comparing the results of the numerical analyses with the field data. Practical Applications Presenting a safe and economically feasible plan for stabilizing deep urban excavations is a significant challenge for geotechnical engineers. Traditionally, engineers have relied on classical methods that consider soil parameters under dry or saturated conditions. However, in practice, the soil above the water table is unsaturated, and its mechanical properties are greatly influenced by the saturation level. Contrary to common belief, rainfall or pipe leakage near an