SYNERGY PRINCIPLE OF COMPLEX SUPPORTING STRUCTURAL SYSTEMS IN TUNNELS

A composite supporting system consists of multiple supporting structures with different construction sequences of time and space. To clarify the internal coordination of the composite supporting structure, a circle model of the composite supporting system consisting of preliminary reinforcement, initial supports, secondary lining ring retainers is established. On the basis, by solving the problem of concentric composite rings, the internal force and deformation expression of the arbitrary circle model are given. The deformation evolvement of the surrounding rock is divided into three stages, namely advanced deformation stage, sharp deformation stage and slow deformation stage. Based on this, the key point of each stage is defined. The characteristic curves of the composite support system with different supporting strength, supporting stiffness and supporting time are qualitatively given. The internal coordination bearing model is established. It is concluded that the mutual enhancement in supporting stiffness of the "advanced supporting shell" and "rock mass in front of the tunnel face" can improve the overall stability of the advanced support. By studying the replacement relationship in space positions of the core of rock mass and the follow-up support retainer layer, from the viewpoint of the rigidity demand, it is revealed that it is necessary to improve the bearing capacity of surrounding rock, or there will be a certain deformation to make it possible to reach the new equilibrium state again.