Experimental Investigations of a Tunnel Lining Segment Strengthened by In Situ Spraying Mortar

Abstract

After long-term operation, tunnel lining segments encounter various problems. Aiming at these problems, in this paper, we present a method of strengthening tunnel lining segments by in situ spraying mortar. An experimental study of the in situ spraying mortar was carried out to determine the compressive strength, flexural strength and interface properties (splitting tensile strength and shear strength) between concrete and H-70 mortar. The experimental results show that the mechanical properties of H-70 mortar are less dependent on the curing humidity than ordinary concrete under standard curing conditions, the 7-day compressive strength of H-70 is 55 MPa, which is 61% of the 28-day compressive strength. This shows that H-70 has high early strength and is very suitable for rapid reinforcement. The interface roughness has a significant effect on the splitting tensile strength, and it can be increased by chiseling to improve the bearing capacity of the strengthened structure. A full-scale loading experiment was carried out on the segment strengthened by in situ spraying mortar. The loading process, failure mode and ultimate bearing capacity of the strengthened structure were analyzed by full-scale loading experiment. The research shows that the ultimate bearing capacity of the tunnel segment strengthened by in situ spraying mortar increased significantly. The ultimate bearing capacity of the strengthened structure is 10% higher than that of the unstrengthened structure. The advantages and disadvantages of in the situ spraying-mortar strengthening method are analyzed in comparison with the internal-tension steel-ring strengthening method.