Failure test and strength model of high-porous low-cementitious waste backfilling material

In order to alleviate the shortage of underground aggregate sources and time cost of vibration and compaction during backfilling, a new type of high-porous low-cementitious waste backfilling material (HPLCM), which was composed of self-compacting slurry and loose packing waste with high porosity, was developed to achieve the purpose of low cementitious backfilling. Uniaxial compression tests were carried out on HPLCM in the laboratory, using orthogonal strength variables of cement slurry and waste aggregate, to study their failure strength characteristics and statistical laws. Considering the combined impact of solid waste and slurry strength, a generalized strength model of shear fracture was established based on the fracture statistical results. The coupled strength utilization ratio of solid waste aggregate and self-compacted slurry was defined, and the optimal ratio and cost of mix proportion of HPLCM were analyzed. The results indicate that the uniaxial compressive strength and failure mode of HPLCM are jointly controlled by the component strength of self-compacting cementitious slurry and solid waste aggregate. The strength of both components has a positive correlation with the strength of HPLCM, which is limited by the weaker component, and when one component grows stronger, the failure mode will be dominated by the other component. The uniaxial compressive test of HPLCM presents shear failure modes, including shear planes in single oblique and cross oblique patterns with an average angle of 55.4°. The density of loose packing aggregates can be reduced from 85% to 58% by using the proposed backfilling material, and the strength of cementitious slurry can be optimized within the optimal mixing range to maximize the utilization of filling material strength when the strength of in-situ solid waste aggregates is obtained. Thus, the compaction time of solid filling and the amount of single gangue can be reduced.