Surrounding rock control mechanism in the gob-side retaining entry in thin coal seams, and its application

Huang

Energy Science & Engineering

et al. 2021

Recently, concerns regarding coal resource waste and safety mining have grown worldwide. The no-pillar mining method without advance tunneling, known as the N00 longwall mining method, represents a rational alternative in this regard.Since the 20th century, coal mining technology has undergone long-term development in China. The mining methods used in China's coal industry can be classified into three types: longwall mining, gob-side entry retaining, and N00 longwall mining.The longwall mining method, which originated in Britain during the early 18th century, was first used in China in the 1930s and has been developed for approximately 90 years. It has become one of the landmark achievements in the field of coal mining in China. 1,2 However, a large coal pillar measuring 20-50 m and double advance tunneling roadways should be set up before stopping a working face when using this mining method. This results in low coal recovery rates and mining productivity. Hence, the contradiction between this mining method and China's energy characteristics has become more prominent.

mentioning

confidence: 99%

Validation study of no‐pillar mining method without advance tunneling: A case study of a mine in China

Huang

Energy Science & Engineering

et al. 2021

“…By substituting Eqs. (6), (7) and (8) into Eq. (5), the static equilibrium calculation formula for the final roof subsidence position of gob-side entry retaining is obtained as follows:…”

Section: Analysis Of Roof Subsidence Of the Gob-side Entry Retainingmentioning

confidence: 99%

“…The roof of the gob-side entry retaining is shared by the solid roadside and the roadside filling body, and the cutting form of the roof can be divided into three situations [1][2][3][4]. One is to cut into the solid roadside, and forming the internal stress field at the same time; second, cut off in the roadway; the third is to cut off directly above the roadside filling body [5][6][7][8]. A large number of studies have shown that [9][10][11][12][13]: only in the first case, the overlying strata along the gob-side entry retaining will form a relatively stable large and small structure.…”

Section: Introductionmentioning

confidence: 99%

Discussion on stability analysis and support technology of surrounding rock of gob-side entry retaining

Zheng¹,

Duan²

2019

J. vibroeng.

In order to further analyze the stability and control mechanism of surrounding rock in the gob-side entry retaining, the slip instability coefficient and compression failure coefficient are proposed by the mechanical analysis of the established filling body mechanics model, and when both and are less than 1, the roadside filling body can keep stable. The mechanical model of main roof is analyzed by the static equilibrium method, and the formula for calculating the maximum roof subsidence is deduced. Based on the data of haulage gateway of No. 21201 coal face of Juncheng Coal Mine, using the formula to calculate the amount of roof subsidence at the junction point of filling body and the roof, and proposes two methods to reduce roadway floor heave by increasing the roadside filling width and transferring the surrounding rock stress to the gob. Finally, the corresponding surrounding rock control technology is proposed according to the surrounding rock deformation characteristics during roadway excavation, roadway retention and roadway reuse, and then carries out field monitoring and evaluation. The results show that after adopting the corresponding supporting technology, the surrounding rock of the gob-side entry retaining has been effectively controlled from the excavation to the reuse period with the coal face advancing, the roof-to-floor convergence of roadway solid coal side is less than 220 mm, the roof-to-floor convergence of filling body side is less than 280 mm, and the convergence on the both sides of the roadway is about 190 mm. At the same time, the calculated roof subsidence with the junction point of filling body and the roof is similar to the field monitoring results, which achieves the expected control effect, and the research contents provides a certain reference for the support technology of the gob-side entry retaining.

“…China has a large number of coal resources in the "threesoft" geological condition [29]. e roof of these coal seams is soft and has low strength [30].…”

Section: Introductionmentioning

confidence: 99%

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

Advances in Materials Science and Engineering

Zhang

2020

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.