Experimental Study on the Properties of Controlled Low-Strength Materials Prepared by Pipe Jacking Slag

As a byproduct of urban pipeline network construction, pipe jacking waste soil exhibits characteristics of massive volume, regional specificity, and complex composition. The presence of surface-active components impedes drainage consolidation, thereby restricting its resource utilization. This study developed self-compacting Controlled Low Strength Materials (CLSM) using waste soil from utility tunnel pipe jacking operations, investigating the effects of water-solid ratio, lime-soil ratio, and fly ash-to-cement ratio (F/C) on flowability, water secretion rate, and compressive strength. Experimental results demonstrate that: (1) Water–solid ratio predominantly governs CLSM flowability; (2) Compressive strength decreases with increasing F/C but enhances with higher lime-soil ratios; (3) Optimized mixtures achieved flowability (100–200 mm), water secretion rate (< 3%), and compressive strength (0.35–0.7 MPa) meeting trench backfill specifications. The developed CLSM exhibits self-compacting properties and high flowability, satisfying both operational performance and mechanical requirements for engineering applications. This research provides technical parameters for sustainable recycling of pipe jacking waste in urban underground engineering projects.