Abstract
China has a large number of coal resources in “three-soft” geological conditions. The roof of these coal seams is soft and has low strength. Under this condition, gob-side entry retaining can be carried out under the guidance of roof leading holes to achieve the goal of nonblasting roof cutting and roadway retaining. In this paper, the technology of void weakening, roof cutting, and pressure relief along gob retaining roadway is investigated. The force model of void is established, and the stress concentration of void and interference effect of stress superposition between holes is simulated by COMSOL numerical simulation software. The influence of different factors on stress distribution surrounding round holes is then studied by orthogonal experiment. The results show that the distribution of the plastic zone in circular holes varies with the lateral pressure ratio. With the increase of lateral pressure ratio, the shape of the plastic zone will gradually change from circular to elliptical, and eventually to butterfly, and the size of the butterfly plastic zone is positively correlated with the aperture. On this basis, the technology of “empty hole weakening + dense pillar” roof cutting and gob-side entry retaining is presented. The methodology is then applied to an auxiliary air intake roadway of 21309 working face in the Xiangshan Mine. Industrial testing of three-soft seams using advanced empty hole without blasting roof cutting and gob-side entry retaining is then successfully carried out. The advanced weakening hole replaces the original blasting cutting technology, omits the blasting cutting link in the existing gob-side entry retaining technology, shortens the retaining time, solves the problems such as large coal dust concentration and bad construction environment in the blasting process, and provides scientific theoretical basis for the gob-side entry retaining technology without blasting under such geological conditions.
Highlights
Efficient mining practices are becoming increasingly important as global coal market competition rises
Emerging mining techniques that do not require coal pillar are of great significance for improving resource recovery, reducing roadway heading and mining costs, and enhancing mine production safety [1,2,3,4]
Promoting mining techniques without coal pillar is vital for the technical transformation of production mines, the alleviation of mining relations, and mine life extension
Summary
Efficient mining practices are becoming increasingly important as global coal market competition rises. By analyzing the characteristics of strata behavior of gob-side entry retaining with direct thick and hard roof in a coal mine over 1000 m deep, structural optimization technology of overlying strata for gob-side entry retaining with hard roof conditions has been proposed [16], which is combined with roof caving optimization to advance the working face and pressure relief for hanging roof structure cutting along the gob side using deep-hole presplitting blasting. E roof of these coal seams is soft and has low strength [30] It can be cut off along the edge of the gob under the combined action of “self-gravity + empty hole weakening + roadside support,” making it possible to optimize the technique of nonblasting gob-side entry retaining. Upgrading and optimizing the technology of gobside entry soft roof retaining is aimed at reducing mining costs, simplifying the construction process, and improving the operating environment and is of great significance for mining under such geological conditions
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