## 4 Results and Analysis
### Analysis
The results of the numerical simulation test show that under the conditions of \"any sand layer coefficient + mining height 3 m\" and \"any sand layer coefficient + mining height 5 m\", with the sand-mud ratio increasing from 6:4 to 8:2, the maximum development height of water-flowing fracture increases by 16.6-44 m and 39.7-59.5 m, respectively, with an average increase of 31.1 m and 47.9 m; that is, for every 1% increase in the proportion of total thickness of sandstone in bedrock, the maximum development height of water-flowing fracture increases by 1.56 m and 2.40 m. The theoretical calculation results of rock layer expansion show that under the conditions \"arbitrary sand layer coefficient + mining height 3 m\" and \"arbitrary sand layer coefficient + mining height 5 m\", as the sand-mud ratio increases from 6:4 to 8:2, the distance between the bearing layer and the coal seam increases by 40-76 m and 29.2-45 m, respectively, and the maximum development height of the water-conducting fracture increases by 31.1-44.5 m and 35.0-77.1 m, respectively, with an average increase of 36.7 m and 46.9 m. That is, for every 1% increase in the proportion of the total thickness of sandstone in the bedrock, the maximum development height of the water-conducting fracture increases by 1.84 m and 2.35 m, respectively. This is highly consistent with the results of the numerical simulation. The results of the two methods show that the increase in the sand-mud ratio of the overlying strata of the coal seam will amplify the positive effect of the increase in the mining height on the maximum development height of the water-conducting fracture of the overlying strata. 2. Large mining height will amplify the positive effect of the increase in sand-mud ratio on the maximum development height of water-conducting fractures. The results of the numerical simulation test show that the maximum development height of water-flowing fracture in overlying strata of coal seam is 48-134.2 m under the condition of \"sand-mud ratio of 6:4 + mining height of 3 m\", and the maximum development height of water-flowing fracture in overlying strata of coal seam is 64.6-178.2 m under the condition of \"sand-mud ratio of 8:2 + mining height of 3 m\", which is 31.1 m higher than that of the former. Under the condition of \"sand-mud ratio of 6:4 + mining height of 5 m\", the maximum development height of water-flowing fracture in overlying strata of coal seam is 78.5-133.2 m. Under the condition of \"sand-mud ratio of 8:2 + mining height of 5 m\", the maximum development height of water-flowing fracture in overlying strata of coal seam is 138-177.9 m, which is 47.9 m higher than that of the former. The theoretical calculation results of rock fragmentation and expansion show that the maximum development height of water-conducting fractures in overlying strata of coal seam is 57.1-147.5 m under the condition of \"sand-mud ratio of 6:4 + mining height of 3 m\", and the maximum development height of water-conducting fractures in overlying strata of coal seam is 90.6-183.1 m under the condition of \"sand-mud ratio of 8:2 + mining height of 3 m\", which is 36.7 m higher than the former on average. Under the condition of \"sand-mud ratio of 6:4 + mining height of 5 m\", the maximum development height of water-conducting fractures in overlying strata of coal seam is 82.7-147.9 m. Under the condition of \"sand-mud ratio of 8:2 + mining height of 5 m\", the maximum development height of water-conducting fractures in overlying strata of coal seam is 135.5-182.9 m, which is 46.9 m higher than the former on average. It can be seen that the results obtained by the two methods are very close, which together show that after the mining height increases from 3 m to 5 m, the increase in the sand-mud ratio makes the average increase in the maximum development height of water-conducting fractures by about 51.0%.