Estimation challenges of lateral pressures in retaining structures using granular recycled tire aggregates as backfill

The civil engineering community is a leader in national and international efforts toward sustainability, recycling, and reuse of materials. For example, asphalt is the most recycled material on earth, which is approximately 13 times the newsprint recycling and 27 times the glass bottles recycling. Recycled materials that have been used as borrow materials for embankment construction and retaining wall backfills include recycled asphalt, recycled concrete, tire-derived aggregates (TDA), blast furnace slag, steel slag, coal bottom ash/ boiler slag, flue gas desulfurization scrubber, cullet glass, and roofing shingles. Some of these recycled materials offer potential environmental, technical, and economical benefits for retaining-wall applications. For example, when compared with natural soils, many may offer the advantage of reduced lateral earth pressures and foundation settlement due to smaller unit weight and potentially higher drainage capacity. However, implicit in some of these options is the applicability of conventional soil mechanical principles in the design and technical assessment. In this paper we present experimental data from laboratory and model tests (centrifuge and model retaining walls) that highlight the challenges involved when trying to predict lateral pressures induced by a recycled wall backfill composed of tire derived aggregate. A key difference of this type of granular material is related to the nature of their particles, which are deformable and can exhibit viscous behavior. The experimental results are compared with classical lateral earth theories for active, passive, and at-rest conditions. The manuscript also includes an assessment of the time dependency of the at-rest pressures induced by TDA backfill.