Study on calculation of nonlimit passive earth pressure of unsaturated soil behind retaining wall

The accurate calculation of soil pressure behind retaining walls is essential for their design and construction. Currently, research on the non-limit soil pressure of unsaturated soil behind retaining walls is limited. Therefore, it is initially assumed that the backfill behind the wall comprises cohesionless soil. Subsequently, based on the unified strength theory of double shear, a calculation model for non-limit passive earth pressure of unsaturated soil is developed, which considers intermediate principal stress, soil arching effects, and internal horizontal shear stress, resulting in an analytical solution. By comparing the calculated results with experimental data, the following conclusions are derived: (1) When considering the effects of intermediate principal stress, the computed results of non-limit passive earth pressure in unsaturated soil correspond more closely to the experimental findings. (2) As the intermediate principal stress coefficient b and the displacement ratio η behind the wall increase, the mobilized value of the effective internal friction angle φ'_m increases. Conversely, when the matrix suction value decreases, the internal friction angle φ^b_m associated with matrix suction increases. (3) When the intermediate principal stress coefficient b increases, both the limit and non-limit passive earth pressure values diminish. Conversely, when the matrix suction value increases, the horizontal earth pressure exerted on the retaining wall escalates. The significance of this study lies in providing a theoretical foundation for retaining wall design under unsaturated soil conditions, facilitating more accurate earth pressure calculations in engineering practice.