Research on Grouted Steel Pipe Supports Roof Cutting and Gob-Side Entry Retaining Support Technology for Fully-Mechanized Caving Face

Aiming at the roof control challenges of gob-side entry retaining in fully mechanized top-coal caving faces, traditional concrete-filled steel tube (CFST) support technology exhibits limitations such as slow strength development and complex construction equipment. This study, based on the 1311 fully mechanized caving face in Shanxi Runhong Coal Mine, proposes a gob-side entry retaining technology integrating roof cutting for pressure relief with support by grouted steel tubes. Through physical experiments, numerical simulations, and field tests, the mechanical properties of sulphoaluminate cement-based backfill and grouted steel tube structures were analyzed. The results indicate that the sulphoaluminate cement-based slurry with a water-cement ratio of 0.4 exhibits remarkable early-strength characteristics, achieving compressive strengths of 30.85 and 31.26 MPa at 1 and 28 days, respectively. The support system attains the 28-day bearing capacity of traditional CFST within 24 h, effectively resolving the timeliness inadequacy of gob-side support. Increasing the steel tube wall thickness enhances the bearing capacity more significantly than material strength improvement, with notable stress concentration and bending deformation observed at the middle region during loading. These findings provide a theoretical basis for support parameter optimization. Field applications demonstrate that this technology ensures surrounding rock stability while offering advantages such as simplified construction and reduced labor costs. This study provides theoretical support for the development of gob-side entry retaining technology and offers practical guidance for its application in fully mechanized caving faces.