The Effect of and Case Research on High-Prestressed Active Support in Large-Section Tunnels

A large-section tunnel has a large excavation span and high construction difficulty and is prone to roof fall and collapse and other engineering disasters under complex geological conditions. Due to the influence of the size effect, it is difficult for surrounding rock to form an arch and form an effective load-bearing structure. A timely and proactive anchoring support system is required to fully utilize the self-bearing capacity of the surrounding rock. Therefore, this paper studies a case of high-prestressed active support based on a large cross-section tunnel in eastern China, clarifying that high-prestressed active support can effectively control rock stress, plastic zone distribution, and surrounding rock deformation. Based on a prestress conversion test, the support structure and application method that meet the high-prestress application requirements of the tunnel engineering site are clearly defined. An active support field test was carried out, and the influence of prestress on the supporting structure stress and the surrounding rock deformation was analyzed. The results show that compared with a no-prestress support scheme, active support with 100 kN high prestress increased the utilization rate of anchor rod strength by 35.29%, reduced the external load on the arch by 40.9%, and reduced the settlement of the arch crown by 34.9%. This indicates that high-prestressed active support can improve the self-bearing capacity and control effect of the surrounding rock.