Strength demand of cemented backfill guided by backfilling ratio control in coal mines

The cemented backfill is an environment⁃friendly mining technology widely used in coal mines. However，there is no systematically scientific method to design the strength demand of cemented backfill. In this paper，the strength demand of cemented backfill in coal mines guided by ground control is studied by using the labora⁃ tory test and theoretical analysis methods. The relationship between the uniaxial compressive strength (UCS) and the compressibility under the confined condition of cemented backfill is obtained. The scientific connotation of backfilling ratio in coal mines is clarified，and the bearing mechanism of cemented backfill in the goaf is revealed. The backfilling ratio characterization model of the cemented backfill is established，and the effect of the cemented backfill strength on the backfilling ratio is presented. The calculation principle of the target backfilling ratio is established， which can be used for multiple application scenarios. The dynamic design method of the strength demand of cemented backfill guided by backfilling ratio control is proposed. The results show that 1 In the confined compressive test，the UCS of cemented backfill is monotonically negatively correlated with the compressibility，which can be characterized by the Allometric function of the upper and lower boundaries. The sensitivity of compressibility to UCS decreases with the increase of UCS，which means increasing the strength of cemented backfill after reaching a certain level has little effect on its compressibility. 2 The coupling relationships among vertical stress，compressibility，and UCS of ce⁃ mented backfill are obtained. Theoretical characterization methods for UCS and compressibility of cemented backfill under different mining depth conditions are developed. The mathematical characterization theoretical model of backfill⁃ ing ratio for the cemented backfill in coal mines is established. 3 The backfilling ratio characterization model is used for various application scenarios including roof deformation control，water flowing fractured zone control，and surface subsidence control. The design method of strength demand of cemented backfill guided by target backfilling ratio con⁃ trol is obtained. The research findings are applied to a mine of Kailuan Group，the average strength demand of cemen⁃ ted backfill is 3.00 MPa. In addition，based on the roadway layout and the variation of mining geological conditions such as coal thickness and burial depth in the backfill mining area，the dynamic distribution of cemented backfill strength demand in each mining area is obtained.