Abstract
Gob-side entry retaining formed by roof fracturing (GERRF) is a popular non-pillar mining method. The method uses crushed rocks in gob side to support and control the movements of the gob roof. These crushed rocks will deform under roof pressure and generate desirable lateral stress on support structures of gangue rib. In this study, the deformation behavior of crushed mudstones with different particle sizes under incremental loading was investigated with an innovative experimental device that simulated boundary conditions of the GERRF method. Influence of particle size of the crushed mudstones to the generation of lateral stress applied on support structures were concurrently observed and analyzed. Research outputs from the tests showed that: (1) The particle size exerted a significant influence on the accumulated axial deformation, period axial deformation, and lateral stress applied on support structure of crushed rocks. (2) Under the same axial stress, the larger the particle size, the smaller the accumulated axial deformation of the crushed rock; A skeletal loading-bearing effect was apparent in the rock samples with larger particles (S-2, S-3). The compressive deformation process of samples S-2, S-3 divided into structural adjustment, skeletal load-bearing and crushing cum filling phases. At skeletal loading-bearing phase, the crushed rocks showed better deformation resistance and stability than other phases; (3) Two types of periodic stress-strain curves were observed for crushed mudstones in the tests. The “down-concave” type implied the deformation for the crushed mudstones was primarily a consequence of the compression in the void spaces. While the “upper-convex” type curve was resulted in particle crushing cum filling again; (4) The lateral pressure generated by large-size samples was smaller than that of small-size samples. Additionally, a poor regularity of lateral stress was observed in compression test of large-size sample (S-3). The relationship between the axial stress and lateral stress generated on the support structure was found to be approximately linear relationship under the condition that lateral pressure shows good regularity.
Highlights
Gob-side entry retaining is one of the most commonly used mining method in nonpillar coal mining
The crushed rocks with this type stress-strain curve usually indicate that the sample has a certain initial bearing strength
When the axial stress is greater than the bearing strength of the crushed rock sample, a large number of particles crush and fill the void spaces
Summary
Gob-side entry retaining is one of the most commonly used mining method in nonpillar coal mining. In this method, the former entry is artificially retained as the tailgate for the mining panel by constructing a filling wall made of concrete blocks, pigsties, high-water packing material, and other fill materials, which can greatly improve resource 4.0/). (GERRF) is proposed [6,7] In this method, a pre-fracturing is constructed in the gob-side immediate roof before mining activities. The crushed rocks are of efficiently used to support and control the movement of gob roof [8,9], which make the GERRF method more flexible and effective. The conventional cables are difficult to adapt to thereduce large deformation of entryrate for [1,2]
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