Theoretical solution approach and mechanical behaviors of prestressed reinforced concrete lining with un‐bonded annular anchors

The combined bearing characteristics of the lining and surrounding rock pose challenges in the design of new prestress annular anchor linings for pressure tunnels. By analyzing the interaction characteristics of the prestress annular anchor linings and surrounding rock, this study presents the phenomena, underlying mechanisms, and identification criteria of loading‐unloading yield state transitions and principal stress‐order reversals in the surrounding rock under high internal water pressure conditions. A radial equivalent load expression for the circumferential tensile force of the annular anchors is introduced to unify the load types for prestress, internal water pressure, and surrounding rock pressure. Accordingly, the load‐sharing coefficient of the surrounding rock is defined, and a mathematical model of the combined bearing behavior of the prestress annular anchors lining and surrounding rock is established based on the theory of multi‐layer thick‐walled cylinders, and the calculation example is verified and analyzed. The results show that under high internal water pressure conditions, the surrounding rock undergoes loading‐induced yielding. The mathematical model determines that the radial stress of the surrounding rock as the first principal stress is reasonable. The main factors affecting the load sharing of the surrounding rock are the modulus of elasticity of the surrounding rock, Poisson's ratio, and the diameter of the tunnel. After backfill grouting with the annular anchor linings, the surrounding rock is able to share the internal water pressure load. Therefore, it is inappropriate not to consider the surrounding rock bearing capacity in the tunnel design. Moreover, the design value of the annular anchor lining prestress can be reduced to increase structural safety.