Numerical Modelling of Tiered Retaining Walls

Tiered retaining walls tend to be constructed on property boundaries to address planning requirements with respect to excavations on the boundary, and/or for aesthetics (e.g., improve sunlight, reduce mass, etc.), and may be constructed independently as adjacent sites are developed. The interaction between tiered cantilevered pole walls is not well researched. This paper summarises the finding of the author’s masters research, which consisted of numerical analysis of tiered retaining walls using two finite element analysis software programmes, RocScience RS2 (finite element analysis software) and WALLAP (pseudo-finite element software). The numerical analysis was undertaken in three parts. Analysis of single retaining walls to establish baseline results, utilising both RS2 and WALLAP to calculate the internal forces (bending moments and shear forces) and associated deflections; analysis of the variation in internal forces and deflections with changes to the in-plane spacing between tiered retaining walls utilising RS2; and analysis of equivalent tiered walls loads using WALLAP. The results showed that the effective retained height of the lower wall approaches the combined retained height of the tiered retaining walls as the spacing between the walls approaches zero. This increase in the effective retained height can be detrimental to the stability of the walls, particularly in situations where the interaction has not been considered.