Study on optimization and field application of static and dynamic mechanical properties of different steel fiber reinforced concrete

Floor heave in coal mine roadways is a key technical challenge restricting the safe and efficient mining of deep coal mines. Conventional concrete support materials suffer from poor toughness and low impact resistance, making them difficult to adapt to the complex static loads and dynamic disturbance loads acting on the surrounding rock of roadways, and thus leading to unsatisfactory floor heave control effects. To address this problem, standard uniaxial static compression tests and split Hopkinson pressure bar (SHPB) dynamic impact tests were carried out on plain concrete specimens and steel fiber reinforced concrete specimens with four typical fiber morphologies (straight, milled, end-hooked, and crimped) at the same dosage (1.2% mass fraction) in this paper. The core mechanical indicators of different specimens, including static compressive strength, elastic modulus, peak strain, dynamic impact strength, energy absorption capacity and failure mode, were systematically compared and analyzed. The steel fiber type with the optimal comprehensive performance was selected by combining the linear normalization method with the analytic hierarchy process (AHP). The results show that end-hooked steel fiber reinforced concrete exhibits the optimal post-peak ductility, energy absorption capacity and toughness index under static loads, achieves the highest peak strength of 123.7 MPa with a unique "strain rebound" phenomenon under dynamic impacts. The strain rebounds from 0.0251 to 0.0223 after reaching the peak, and the stress recovery amplitude reaches 8.6 MPa (a relative recovery of 6.9%), and also presents the optimal micro-interface anchoring strength and damage resistance. The optimized end-hooked steel fiber reinforced concrete was applied to the field industrial test for floor heave control in the deep roadway of a coal mine. Monitoring data indicate that the maximum floor heave of the roadway is controlled within 50 mm, the floor heave control efficiency is increased by 95% compared with the original plain concrete support method, the stability of the floor support structure is significantly enhanced, and the maintenance cost of a single roadway is reduced by more than 90%, which effectively solves the problem of repeated treatment of roadway floor heave. The research results provide a new type of high-performance support material and technical reference for the floor heave control of coal mine roadways, and have good engineering promotion value.