Abstract: The implementation of the western development strategy has led to a surge in underground engineering projects. To protect ecological environment and reduce engineering costs, crushed strongly weathered rock is utilized in combination with loess, cement, bentonite, and pumping agent to create solidified and improved fluid filling materials. Based on a foundation pit backfilling project in northwest China, compression tests were conducted on fluid-solidified soil with varying proportions using orthogonal design. The optimal proportions of different factors were determined. The influencing factors and their significance on the compressive modulus of fluid-solidified soil made from strongly weathered rock were analyzed. Additionally, the microstructural changes and water stability of fluid-solidified soil were also investigated. Results demonstrate that the pumping agent is the most significant factor affecting the compressive modulus, followed by the dosage of coarse aggregate of strongly weathered rock. The influence of various factors on the compressive modulus can be ranked in the following order from large to small: pumping agent dosage, coarse aggregate content, bentonite dosage, cement dosage, loess dosage, and fine aggregate content. Moreover, the reduction rate of compressive modulus of improved samples decreases with age after being immersed in water. This indicates significant improvements in water stability and overall performance. Microscopic analysis reveals that a pumping agent dosage of 0.4% yields better sample cementation. The research findings hold valuable reference for evaluating the feasibility of using strongly weathered rock as fluid filling material.

Key words: strongly weathered rock, fluid-solidified soil, orthogonal test, compression characteristics, water stability, microstructure, significance analysis