Optimization of the remaining ditch mode and parameters for end-wall covered of open pit coal mine with partition and inner dumping

The development of large open-pit coal fields with high safety and efficiency is the trend of open-pit coal development. With partitioned mining as the main development mode, the large open-pit coal field has the significant advantages of safety and efficiency, high recovery rate and short investment payback period. At the same time, it is possible to use the backfilling of stripped materials in the mined area to form an inner dumping field and reduce the pressure and damage of stripped materials on the land. To address the problem of large surface coal mines with large secondary stripping volume between adjacent mining areas derived from partitioned mining, the impact of different remaining ditch mode for end-wall covered on stripping and transportation systems is analyzed by adding height to the inner dumping on the basis of considering the impact of inner dumping remaining ditch mode for end-wall covered, combined with the restricted space conditions for outer dumping. The total cost model of inner dumping with end-wall fully covered and inner dumping with end-wall semi-covered is established, and the inverted triangular and inverted trapezoidal retention ditch patterns of the end-wall semi-covered are compared and analyzed. Based on the expense compensation method, a model for optimizing the ditch height of the inverted triangular ditching mode and the inverted trapezoidal ditching mode, as well as a model for optimizing the distance of the internal ditching bridges, was constructed based on the cost-least method, taking the full internal ditching of the inner dumping covering as a reference, and taking into account the capacity of the internal ditching under the condition that the stripped material would not be discharged. The optimization of the ditch height and transportation system between the first and second mining areas of Hequ open-pit coal mine was carried out. The results show that: the economic benefits of half inner dumping covering are significant, the total cost of inverted triangular retention ditch increases and then decreases with the increase of the height of retention ditch, and the total economic benefit decreases and then increases. The best trench height is 110 m, and the best distance to move the inner row bridge is 104 m, which saves 100.8 million yuan relative to the inner dumping covering; the total cost of the inner dumping covering inverted trapezoidal retention ditch first decreases and then increases with the increase of the retention ditch depth, and the total benefit first increases and then decreases, the best retention ditch height is 67 m, and the best displacement step of the inner drainage hitch is 264 m, which saves 245.4 million yuan compared with the full inner dumping covering. Under the condition of equal retention ditch area, the inverted triangular retention ditch mode has a greater retention ditch depth, which has a greater impact on the single-side stripping material transportation system The long length of the working line of the inter row field is generally applicable to open coal mines with tight inter row space; the inverted trapezoidal retention ditch mode has a smaller retention ditch depth and the row capacity is somewhat restricted, which is generally applicable to open coal mines with larger inter row space.