Interfacial enhancement of diaphragm walls through permeable polyurethane polymer grouting reinforcement: Laboratory test and field application case

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The interfacial integrity between diaphragm walls and surrounding soils is critical for the stability and waterproofing of deep excavations, yet it is frequently compromised by joint leakage and soil erosion. While grouting offers a promising remediation strategy, the reinforcement mechanisms and performance of permeable polymer grouts at the soil-concrete interface remain insufficiently quantified. This study presents laboratory direct shear tests, microstructural characterization, and a field case study on the interfacial enhancement achieved through permeation grouting using a permeable polyurethane polymers. The results demonstrate that the interfacial shear strength increases nearly linearly with vertical stress and roughness, and exhibits an optimum at a maximum within the tested moisture content range at approximately 13%. Microstructural analyses via SEM and MIP reveal that the polyurethane effectively fills soil pores, forms a cohesive transition layer at the interface, and reduces total porosity by over 50%, explaining the macroscopic strength enhancement. The failure mode transitions from interfacial slippage to soil matrix failure as roughness and optimal moisture content increase. A full-scale field application in a Hangzhou foundation pit with 20-m deep diaphragm wall joints confirmed the technique’s effectiveness: the grouted joints remained completely watertight throughout excavation, demonstrating excellent sealing and bonding performance. This work establishes that permeable polyurethane grouting restores interfacial shear resistance through combined physical filling and chemical bonding. The findings provide both mechanistic insight and practical validation for implementing polymer-based permeation grouting in geotechnical infrastructure repair.

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