Gob-Side Entry Retaining Technology with Advanced Empty Hole Butterfly-Shaped Weakening in Three-Soft Coal Seam in China

Abstract EN

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.