Research on the performance and reinforcement effect of shotcrete in small-section tunnels in plateau areas

Shotcrete has become an important part of the geotechnical engineering support system by virtue of its superior compatibility with surrounding rock, rapid load-bearing capacity, and structural integrity. The reinforcement effect of shotcrete significantly impacts the stability and safety of geotechnical engineering projects. This study investigated the effects of a novel nanocellulose-based shotcrete admixture on the early-age strength and durability of shotcrete, and conducted model tests to evaluate the supporting effectiveness of shotcrete on jointed rock masses. The test results demonstrated that under the strong disturbance conditions during specimen preparation, the shotcrete still achieved an early-age compressive strength of 8.46 MPa and bond strength of 0.87 MPa at 8 h. The material exhibited a saturated water absorption of 1.56% and softening coefficient of 88%. After 150 days of erosion, it maintained 83.06% resistance against sodium sulfate solution erosion. These findings confirm that the developed material satisfies both the early-age performance requirements and long-term serviceability criteria for tunnel support shotcrete applications. Shotcrete substantially improves tunnel support performance by simultaneously enhancing the bearing capacity of the shotcrete-surrounding rock system and preventing brittle failure in both the rock mass and sprayed layer. More importantly, through its ability to improve deformation coordination within the support system, the shotcrete further enables more effective stress redistribution. As a direct result of these combined mechanisms, this integrated performance leads to outstanding control of tunnel structural deformation, ultimately demonstrating significant effectiveness in maintaining long-term tunnel stability.