At-Rest Lateral Earth Pressure on Retaining Walls Under Narrow Backfill Widths

Retaining walls are used for retaining soils at different levels on their two sides. A critical step in the design of retaining structures is to estimate the lateral earth pressure coefficient, which is often based on the classical well-established equations. It is noted that these solutions do not take the effect of the soil width on the lateral earth pressure into account. In practice, the backfill soil behind a retaining wall is often sufficiently wide so that its effect can be neglected. However, there are cases where a retaining wall supports backfill soils of limited width. In such cases, the horizontal earth pressure coefficient calculated using the classical equations is likely to lead to a conservative design and thus a less sustainable engineering solution. Although there are very limited studies looking into the effect of narrow backfill, much more research is required for a sound understanding. This motivated our research work where the values of the at-rest lateral earth pressure coefficient (K₀) are investigated under various key variables, including backfill width, wall depth and soil types. Our investigation is based on a set of numerical simulations using ABAQUS. The numerical model is first refined and validated using the data from the laboratory experiments reported in the literature, which is then applied to various simulation cases considered. For the narrow backfill widths considered (0.7, 0.5, 0.3, and 0.1 times the retaining wall height), it was found that the values of K₀ generally decreased with the reduced backfill widths and were smaller than those (i.e. the benchmark values) estimated using the classical equations. Along the ground depth, the values of K₀ appeared to decrease with increasing depth for narrow backfill width. It was also interesting to observe that when the backfill width was adequately large, the values of K₀ obtained in our simulations for sands and gravels were very close to those calculated using the classical equations.