Experimental, numerical, and case study on soil-based CLSM as backfill materials in the foundation excavation

Abstract

Deep foundation pits, pipe gallery troughs, culverts, and other infrastructure often require backfilling operations. Soil-based controlled low-strength material (soil-based CLSM), with its advantages of self-compaction, self-leveling, and self-hardening, has garnered significant attention in recent years and shows potential as a replacement for traditional rolling compaction backfill materials. Based on the backfill project of the pipe gallery at the Xihong Bridge in Ningbo, this study investigates the unconfined compressive strength, permeability coefficient, compression characteristics, and flow behavior of soil-based CLSM with varying curing agent ratios, assessing its engineering feasibility through field testing. The results demonstrate that soil-based CLSM, particularly with polycarboxylate superplasticizer agent, exhibits substantially improved strength, permeability, construction workability, and other service performance. Additionally, a detailed simulation of the entire pipe gallery foundation pit construction process—including pipe gallery construction, trench backfilling, support removal, and road construction—was performed using the Hardening soil with small strain stiffness model of the soil. The deformation characteristics were analyzed under different backfill conditions to assess the suitability of soil-based CLSM for trench backfilling. The analysis also considered soil deformation under varying curing ages and upper load conditions. The optimized backfilling solution for soil-based CLSM was obtained and validated with field test data. The findings suggest that using soil-based CLSM for foundation trench backfilling can effectively mitigate settlement issues.