Abstract
When gob side entry retaining is carried out in backfill mining, the roof will show different subsidence morphology due to the difference of compactness and supporting force of the backfill body at different positions. This paper analyzed the immediate roof subsidence structure under two extreme conditions, constructed the roof segmented subsidence structure and the mechanical model of roadside backfill body, and used FLAC3D software to investigate the roof migration and the force law of the roadside backfill body under the conditions of different goaf backfilled rates, different width and strength of roadside backfill body. Finally, the backfill practice of a mine in Shandong Province of China is taken as an example for analysis. The results show that the segmented subsidence structure of the immediate roof is related to the mechanical properties of the roadside backfill body and the goaf backfill body. When the backfilled rate of goaf decreases from 95% to 70%, the width of roadside backfill body decreases from 5 m to 1 m, and the elastic modulus decreases from 10 GPa to 0.5 GPa, the greater difference in the subsidence and inclination of the immediate roof on both sides of the roadside backfill body is, the more obvious the segmented subsidence structure characteristics of the immediate roof are, and the greater force on the roadside backfill body will be, the more unfavorable it is to maintain the stability of the roadway surrounding rock and the roadway backfill body. Therefore, when gob side entry retaining is carried out in backfill mining, the surrounding rock structure and the force on roadside backfill body should be considered comprehensively.
Highlights
As a non-pillar mining technology, gob side entry retaining has significant advantages such as high coal recovery rate and less roadway excavation amount, which is widely used in mines with traditional caving method (Liu et al, 2020; Zhang et al, 2012; Zhou et al, 2012)
The surrounding rock structure and deformation characteristics of gob side entry retaining in backfill mining are different from those of gob side entry retaining by caving method (Kang et al, 2011)
Based on the movement characteristics of the overlying strata, Quan et al (2018) established an immediate roof mechanical model of gob side entry retaining in backfill mining, deduced the formula for the width of the roadside backfill body and the length of the elastoplastic zone in the coal bank, and conducted an engineering example analysis
Summary
As a non-pillar mining technology, gob side entry retaining has significant advantages such as high coal recovery rate and less roadway excavation amount, which is widely used in mines with traditional caving method (Liu et al, 2020; Zhang et al, 2012; Zhou et al, 2012). In the project of retaining roadway along the backfilling area, the roadside backfill body is closely connected with the goaf backfill body and controls the roof cooperatively They are independent due to different strength and compressibility in the process of roof subsidence, forming two supporting structures of roadside backfill body and goaf backfill body. The immediate roof subsidence is not synchronous at the position of roadside backfill body and goaf, forming a segmented structure The supporting effect of the goaf backfill body is far less than that of the roadside backfill body, and it has greater compressibility, the immediate roof in goaf presents an obvious subsidence morphology, and the subsidence angle hx formed by the immediate roof and the horizontal plane is related to the deflection of the immediate roof
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