Abstract
To solve the difficulty in controlling floor heave of a retained goaf-side roadway, a new control technique was investigated from the perspective of the pressure relief by roof cutting by combining mechanical analysis, numerical simulation, and engineering tests. The mechanical principle of controlling the floor heave based on pressure relief by roof cutting was attained by analyzing the movement of overlying strata and mechanical characteristics of key blocks before and after the roof cutting. A new technique for controlling the floor heave based on pressure relief by roof cutting was proposed. Research results have shown that after performing pressure relief by roof cutting, the caved gangues in the goaf can support the overlying strata and, thereby, change the movement law thereof and weaken the abutment pressure on the coal wall. Furthermore, the pressure exerted on the roadway floor by the coal wall is lowered to prevent plastic deformation of the floor, thus controlling floor heave in the roadway; a new integrated technique for controlling the floor heave based on pressure relief by roof cutting, flexible yielding, controlling with double-direction-control anchor bolts, and controlling with reinforcing anchor cables is developed, and the technological processes of support, cutting, and protection are summarised. The results of field testing showed that, after applying the new technique, the average floor heave amount of the roadway declines by 64% and the average speed of the floor heave up to 231 m behind the working face decreases by 61%.
Highlights
Gob-side entry retention (GER), as an important technique in coal mining system without pillars [1,2,3,4], can improve the recovery rate of coal resources, reduce the rate of tunnelling of roadways, and avoid the waste of resources [5], owing to which it has been widely used in various coal mines in countries such as China, Germany, Poland, and the United Kingdom and has achieved remarkable economic and social benefits [6]
Many researches indicate that roof cutting through bidirectional cumulative tensile blasting can optimize the stress state in the rock surrounding a roadway [25, 26], so it is expected to become a new technique for controlling floor heave in gobside entries
The mechanical principle of controlling floor heave by the virtue of pressure relief by roof cutting was obtained; (2) a new integrated technique for controlling floor heave combining pressure relief by roof cutting, flexible yielding, controlling with double-direction-control anchor bolts, and controlling with reinforcing anchor cables, based on pressure relief by roof cutting, was proposed; the technological processes of support, cutting, and protection were determined, and the field test was conducted; (3) the field monitoring revealed that the average floor heave amount of the retained goaf-side roadway with the new technique dropped by 64%, and the roadway can satisfy the requirement for reuse without undercutting, delivering a favorable control effect on the floor heave
Summary
Gob-side entry retention (GER), as an important technique in coal mining system without pillars [1,2,3,4], can improve the recovery rate of coal resources, reduce the rate of tunnelling of roadways, and avoid the waste of resources [5], owing to which it has been widely used in various coal mines in countries such as China, Germany, Poland, and the United Kingdom and has achieved remarkable economic and social benefits [6]. Many researches indicate that roof cutting through bidirectional cumulative tensile blasting can optimize the stress state in the rock surrounding a roadway [25, 26], so it is expected to become a new technique for controlling floor heave in gobside entries On this basis, against the background of a conveyor gateway in the working face of a retained goaf-side roadway by building concrete blocks beside in Faer Coal Mine, the aim of this study were threefold: (1) the movement of overlying strata and mechanical characteristics of the floor of the retained goaf-side roadway before and after pressure relief by roof cutting were explored through theoretical analysis and numerical simulation. The mechanical principle of controlling floor heave by the virtue of pressure relief by roof cutting was obtained; (2) a new integrated technique for controlling floor heave combining pressure relief by roof cutting, flexible yielding, controlling with double-direction-control anchor bolts, and controlling with reinforcing anchor cables, based on pressure relief by roof cutting, was proposed; the technological processes of support, cutting, and protection were determined, and the field test was conducted; (3) the field monitoring revealed that the average floor heave amount of the retained goaf-side roadway with the new technique dropped by 64%, and the roadway can satisfy the requirement for reuse without undercutting, delivering a favorable control effect on the floor heave
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