A spreadsheet-based technique to calculate the passive soil pressure based on the log-spiral method

This paper presents an efficient technique to calculate the passive earth pressure of a cohesionless sloping backfill on a rigid retaining wall which is an extension of the Terzaghi’s log-spiral approach. Moment equilibrium conditions are used to compute the minimum value of the passive pressure required to mobilize the passive failure. Terzaghi assumed that the pole of the log-spiral failure surface lies inside the soil mass, whereas the proposed technique and solutions show that the pole can lie inside or outside the soil mass. Thus, the developed technique has extended the log-spiral method reported by Terzaghi by providing a generalised solution. The distinctive feature of the proposed technique is the explicit and rigorous solutions developed which allow to evaluate the passive earth pressure with different friction angles for the soil and wall-soil interface, backfill slopes and wall inclination angles. These solutions are relatively simple to incorporate into a spreadsheet to derive the passive force and pressure. A series of experiments were carried out using a physical model and the Particle Image Velocimetry (PIV) technique to analyse the failure surface. The developed solutions were then validated with data obtained from model tests as well as experimental data found in the literature.