Effect of Biopolymer-Based Soil Treatment on Lateral Earth Pressure in Sandy Soil Backfill: An Experimental Study Utilizing a Laboratory-Scale Soil Tank Apparatus and PIV Analysis
Materials meeting stringent criteria for retaining wall backfill typically result in increased wall volume to resist Earth pressure, which consequently drives up construction costs. Recently, due to the depletion of natural construction resources, locally sourced soils and sustainable materials are being investigated as alternative backfill materials. Studies are performed aiming to efficiently reduce lateral earth pressure using suitable materials. One innovative method is biopolymer-based soil treatment (BPST), recognized as an environmentally friendly geotechnical binder that improves soil strength. This study aims to employ biopolymers in retaining wall backfills to mitigate environmental concerns associated with the use of traditional soil improvers like cement in geotechnical engineering. The investigation of lateral earth pressure behavior for backfill reinforcement conditions was performed through laboratory tests and particle image velocimetry (PIV) analysis, including the introduction of a rotatable wall (rotation around the base) to support sandy soil. XG-BPST was formulated based on sand mass, 15% deionized water, and 1% xanthan gum biopolymer content and was classified into initial (wet) or dehydrated (dry) conditions. To address the weak strength of the initial (wet) condition of XG-BPST, a geogrid was encapsulated in the center of the XG-BPST layer. The reduction of lateral earth pressure and stability verification of retaining walls were investigated on backfills reinforced with XG-BPST and geogrid. Laboratory tests demonstrated that wall displacement reached a limit equilibrium state of approximately x/h 0.1% (active earth pressure), regardless of the backfill reinforcement conditions. In the initial (wet) state of XG-BPST, the variation in lateral earth pressure behavior was negligible compared to the untreated condition, due to a weak improvement in shear strength. However, significant reductions in lateral earth pressure were observed when the geogrid was integrated with the XG-BPST layer or in the dehydrated (dry) condition of XG-BPST, attributed to the restriction of ground deformation at the reinforcement position and the confinement effect on the surrounding soil. The laboratory test results confirmed that lowering active earth pressure enhances the external stability of the retaining wall. Moreover, the required wall width to satisfy safety guidelines decreased, indicating the feasibility of more economically efficient designs.
