Enhancing the anchorage force and deformability of the anchor bolt is key to controlling surrounding rock stability in soft rock tunnels. Based on the previously proposed interface-shear-stress-dispersing (ISSD) bolt, this study proposes an ISSD-yield bolt to more effectively address progressive anchorage interface damage. Based on the theoretical derivation and field pull-out tests, the anchorage mechanical behavior of the ISSD-yield bolt is obtained: (1) The ISSD-yield bolt comprises compressible layers in front of each anchor to accommodate anchor deformation. During the pull-out process, the compressible layers in front of the anchors are successively compressed to fully leverage the overall bonding strength of the grout-rock interface, thus increasing the load-bearing capacity and deformability of the bolt. The result of the field pull-out test verifies that the anchorage force and the deformation capacity of the ISSD-yield bolt improve by 1.4 times and 2.4 times, respectively. (2) Mechanical analysis of the ISSD-yield bolt yields an optimal method for determining the required number of anchors ( N b ) and compressible layer thickness ( d ). With the increase in the bonding strength and the decrease in the shear stiffness of the grout-rock interface, N b decreases, and d increases gradually. Under the anchor length of 4 m to 6 m, N b should be set to 2 to 6, and d should be set to 1 cm to 10 cm. The ISSD-yield bolt provides a feasible option for the support of soft rock tunnels with large deformation and poor bonding strength of the grout-rock interface.
Shu et al. (Fri,) studied this question.