# Experimental Study on Permeability Characteristics of
## 1 Introduction
[20] conducted permeability tests on tailing-cemented backfill materials, tested the porosity of solidified tailing-cemented backfill materials through electron microscopy, and obtained the effect of the cement-sand ratio and gangue dosage on the internal porosity and overall permeability of tailing-cemented backfill materials. [PERSON] et al. [21] conducted rheological, mechanical, and permeability tests on modified magnesium-coal-based solid waste backfill materials and investigated the influence of different dosages and lengths of polypropylene fibers on the properties of modified magnesium-coal-based solid waste backfill materials. The research results indicate that the transmission pathway between the connecting pores of polypropylene fibers is the main reason for the change in permeability. [PERSON] et al. [22] used aeolian sand as a filling aggregate, cement and fly ash as bonding materials, and quicklime and water-reducing  
Figure 1: Schematic diagram of gangue grouting and backfilling technique. agents as additives and explored the seepage characteristics of sand-based bonding backfill materials under the interaction of multiple factors, obtaining the significance degree of each factor's influence. [PERSON] et al. [23] conducted nuclear magnetic resonance and centrifugal tests on tailing-cemented backfill materials, found a high correlation between fractal dimension and the permeability of backfill material based on fractal theory, and analyzed the permeability changes of the backfill materials with the curing age and ash-sand ratio. [PERSON] et al. [24] summarized the influence of axial and confining pressures on the permeability of sand-based cementitious backfill materials and revealed the permeability change mechanism of these backfill materials through laboratory permeation meters, particle size analyzers, scanning electron microscopes, and X-ray diffractometers. In summary, research on the permeability of backfill materials mostly focuses on solid bulk or cementitious materials, and there is less research on pure gangue slurry. Moreover, the study on the preparation method of compacted backfilling system and permeability characteristics of gangue slurry is rarely involved. Considering the application prospects of gangue slurry grouting and backfilling technology for water-preserved mining, the pressure bleeding characteristics, permeability changes, and waterproof optimization methods of gangue slurry were analyzed in this study. Specifically, a multi-field coupled seepage test system for backfill materials was developed, and a laboratory preparation method for the CBB of gangue slurry was proposed. The staged pressure bleeding characteristics of gangue slurry were analyzed, and the influence of axial pressure, particle size range, and cement dosage on the permeability of the CBB was obtained; the determination method for the permeability level of the CBB and its optimization method were provided. This research provides a theoretical basis for improving the waterproof performance of gangue slurry and enriching the theoretical framework for water preserve mining.