Research and Development of Steel Fiber Reinforced Concrete Filling Material and Its Application in Gob-Side Entry Retaining Technology in Deep Mines

Abstract

Against the background of the prevailing green development paradigm, numerous coal mines have embraced the adoption of gob-side entry retaining mining technology. The most commonly employed form of gob-side entry retaining involves building an artificial wall along the edge of the goaf behind the working face to maintain the roadway. The pivotal challenge in gob-side entry retaining lies in the roadside support. Currently, commonplace concrete serves as the predominant material for the roadside filling body. Nevertheless, traditional concrete exhibits drawbacks, including inadequate tensile strength and poor toughness, leading to wall cracks or even collapses in the retaining wall. Steel fiber, a frequently employed reinforcement and toughening agent in concrete, has found widespread application in the construction sector and other fields. However, its use as a roadside filling material in underground coal mines remains infrequent. Therefore, in this paper, the flow and mechanical properties of steel fiber concrete were tested and analyzed, and field industrial tests were conducted. Results of indoor experiments show that steel fibers reduce the slump of concrete. The addition of steel fibers shifted the pore compacting stage, linear elasticity stage, and destabilization stage forward and improved the post-peak bearing capacity. The addition of steel fibers makes the concrete compressive and tensile strength show a “first increase and then decrease” trend; both peaked at 1.5%, and the increase in tensile strength is more pronounced. Steel fibers enhance the strength of compressive strength of concrete at an early age, weaker at a late age, and tensile strength inversely. The addition of steel fiber can change the concrete matrix from tensile damage to shear damage, and the toughness index shows the trend of “first increase and then decrease”, and reaches the peak value when the dosage is 1.5%. Industrial test results show that steel fiber concrete as a roadside filling body can reduce the surrounding rock surface displacement and bolt (cable) force.