Abstract
With the mining depth getting deeper and deeper, surrounding rock control technology has become a difficult issue in the development of modern mining, especially the mining roadways affected by mining. It is very difficult to control the surrounding rock due to the intense mining of the last working faces. In order to alleviate the impact of dynamic pressure on the gob-side entry retained, solve the ventilation difficulties caused by the commonly used method of the gob-side entry retained without leaving coal pillars, and solve the disadvantages of the inability to effectively isolate water and harmful gases, this paper proposes a small coal pillar gob-side entry retained technology based on the key stratum, that is, cutting the key stratum above the top plate, transferring lateral support pressure from the workings further up the seam to the depths of the coal seam, and then protecting gob-side entry retained method. In the final method of precracking and cutting joints by blasting with D-type polytunnel, we directionally cut the lower key stratum above the roadway in the designed direction and position. The theoretical analysis, numerical simulation and field test, and the method of the blasting broken roof pressure release effect are analyzed. Compared to the unloaded pressure method, the relatively complete direct roof is conducive to the maintenance of the surrounding rock on the gob-side entry retained. At the same time, the pressure relief caused by the fracture of the lower key stratum of the coal roof significantly improves the stress environment. The stress is no longer concentrated on the small coal pillars and the gob-side entry retained, and the required roadway support strength is greatly reduced and no longer needs to carry out the construction of roadside support system. This technology reduces labor intensity and production costs.
Highlights
When shallow coal resources become increasingly depleted, mining depths are increasing year on year
A is the lateral pressure coefficient; φ is the angle of internal friction; γ is the gravitational density of the rock formation; H is the mining depth (m); C0 is the cohesion of the coal seam at the junction with the roof and floor; Px is the preload force of the anchor against the roof; and M is the mining height (m)
In order to facilitate the overall coherence analysis and simulation, this chapter used the numerical simulation of mechanical model mentioned above, to continue using FLAC3D finite difference software to continue the simulation, and analyzed the roof cutting and pressure releasing and not roof cutting and pressure releasing under the condition of two kinds of working condition of small coal pillar along the gob-side entry retained for the surrounding rock stress variation of the arrangement
Summary
When shallow coal resources become increasingly depleted, mining depths are increasing year on year. Under the influence of high ground pressure and mining, the effect of retained entry is poor, and the entry roof fall and side slope appear Under this background, a method of deep mine small coal pillar gob-side entry retained based on broken roof pressure relief is proposed; that is, the lower part key stratum above the entry roof is cut off while the direct roof is relatively intact. The working principle and test effect of this technology are studied and analyzed by various means, and the stress distribution state and surrounding rock failure law of broken roof pressure relief gob-side entry retained are obtained, verifying the feasibility of the gob-side entry retained method of small coal pillars in deep wells based on broken roof pressure relief key stratum The research results can provide useful reference for entry stability control under similar conditions. In the process of mining in the working face, the gravity from the lower part key stratum of the coal seam roof to the surface rock layer is transferred from the thick and hard part key stratum above the lower part key stratum to the solid coal, as shown in Figure 2, so that the small coal pillars and gob-side entry retained are under lower supporting pressure, which is beneficial to the bearing stability of the small coal pillars and the maintenance of the gob-side entry retained
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