Research on the Strengthening Mechanism of Layered Soft Rock Tunnel with Foot Locking Anchor Rods

In order to reveal the displacement and mechanical changes during the construction process of carbonaceous slate tunnels, the effectiveness of strengthening support measures is proposed and verified. Based on a certain highway tunnel project, through on-site experimental testing and numerical simulation, the settlement and peripheral convergence deformation curves of the arch crown of section YK11+460 were analyzed, revealing the surrounding rock pressure, steel arch frame, and concrete strain laws of section YK11+460. Proposed the strengthening support measures of "three step foot locking anchor rod+steel arch frame longitudinal connection". Research has shown that based on numerical simulation, the recommended angle for setting the locking anchor rod is 35°, and the appropriate setting length is 3.5 m. After adopting reinforced support measures to stabilize the structure, the surrounding rock pressure at the arch position decreased from 0.83 to 0.74 MPa, and the strain of the steel arch frame decreased from 4029 to 2719 με, Concrete deformation decreased from 2346 to 1773 με, The cumulative deformation of the arch crown at section ZK10+360 is 13.6 mm, and the cumulative convergence values of the upper, middle, and lower steps are 6.1, 5.4, and 3.9 mm, respectively. After adopting reinforced support technology measures, the stress level of the initial support arch after excavation of the upper platform is slightly higher than that of conventional construction techniques. After the construction of the inverted arch, the arch crown, arch waist, and side walls are in a unified stress state. The arch frame is connected longitudinally as a whole, enhancing the stability of the surrounding rock, reducing the loosening pressure of the surrounding rock, and improving the stress state of the initial support structure.