Development and Application of High-Performance Grouting Materials for Anchoring Pipe in Soft Rock Tunnel

A high-performance grouting material is proposed to enhance the support effect of anchoring pipes in soft rock mass tunnels in this paper. Through mix proportion and strength tests, the initial setting time, compressive strength, and flowability of the grouting material were determined. Furthermore, based on grouting and pulling tests, the recommended parameters of the anchoring pipe were proposed. The results show that pure cement paste is an ideal grouting material for on-site application, demonstrating excellent anchoring, fluidity, high strength, and rapid hardening. Under optimal conditions of water-cement ratio at 0.46 and retarder proportion at 0.4‰, the initial settling time and the compressive strength of the grouting material are approximately 45 minutes and 28.5 MPa within 4 hours, respectively. The anchoring force of an anchoring pipe with a length of 6 m and a diameter of 76 mm can reach 448.9 kN within the same period. A field test involving anchoring pipes and pure cement paste was conducted during tunnel construction, resulting in a substantial reduction of maximum settlement and convergence of the tunnel by 57.53% and 40.48%, respectively. These results demonstrate the effectiveness of the proposed material and anchoring pipe in controlling deformation in soft rock tunnels.