Utilization of excavated loess and gravel soil in controlled low strength material: Laboratory and field tests

This study investigates the engineering properties of cement-fly ash solidified controlled low strength material (CLSM) containing excavated collapsible loess and gravel soil. The workability (flowability and bleeding rate), physical and mechanical properties (compressive strength and permeability) and collapsibility of CLSM were analyzed by adjusting the fine-to-coarse aggregate ratio (F/C), water-to-solid ratio (W/S), binder-to-aggregate ratio (B/A) and sandy soil to fine aggregate ratio (SS/F). Results show that improved flowability and compressive strength can be achieved by reducing collapsible loess content through decreasing the F/C ratio or increasing the SS/F ratio, with decreased or increased permeability respectively. The addition of fly ash as an admixture increases the long-term strength of CLSM, while the increased B/A ratio improves the strength, reduces the flowability, bleeding rate and permeability. Specimens with B/A of 0.06 can be proportioned to obtain 28-day compressive strength of up to 0.849 MPa and permeability coefficient of less than 1 × 10-6 cm/s. The results also show that the collapsibility of CLSM has been eliminated during the preparation process. Finally, the optimal mixture ratio was proposed and the field test was carried out, which proves the feasibility of the proposed CLSM for trench backfilling.