Development and Applicability of High-Performance Fly Ash–Based Controlled Low-Strength Material: Laboratory Test, Numerical Analysis, and Field Test

Abstract The increasing occurrence of ground sinking in metropolitan cities due to excavation-induced backfill instability has raised significant safety concerns. Conventional compacted soils used for backfilling underground utilities often fail to provide adequate support, leading to infrastructure damage and ground sinking. This study presents the development and performance evaluation of a novel high-performance fly ash-based controlled low-strength material (HPFA-CLSM) designed to address these issues. The HPFA-CLSM was manufactured using calcium sulfoaluminate (CSA) cement, anhydrous gypsum, ordinary portland cement (OPC), fly ash, and selected additives to enhance flowability, reduce bleeding, and accelerate the setting time. Performance was assessed through comprehensive approaches, including laboratory tests, three-dimensional numerical analysis, and full-scale field tests. The HPFA-CLSM exhibited significantly higher flowability than the conventional fly ash-based CLSM while maintaining sufficient compressive strength. Excavation simulations based on laboratory tests and numerical analysis revealed that the HPFA-CLSM effectively minimized soil displacement and pipe movement, mitigating the risk of ground sinking. Field tests, including ground-penetrating radar surveys and excavation work, further confirmed the applicability of the HPFA-CLSM for void-filling and backfilling in urban environments. Overall, the developed CLSM (i.e., HPFA-CLSM) is a promising alternative for balancing high flowability, rapid strength, and long-term stability so that urban ground instability can be addressed during excavation work adjacent to underground utilities. In addition, the results of three approaches (i.e., laboratory tests, numerical analyses, and field tests) highlight the potential of HPFA-CLSM for widespread adoption in construction, particularly for backfilling underground utilities and mitigating excavation-related risks.