Cause identification of damage in tunnel constructed in soil-rock mixture site and effect of suggested reinforcement measures

Abstract

A running tunnel in Chongqing, China was constructed in a soil-rock mixture (SRM) by the open-cut method. During the construction period, severe cracks occurred on the tunnel lining floor, which will significantly affect the tunnel’s long-term stability. In this study, the numerical investigation was performed to study the development trend of damage zones in the tunnel lining, identifying the causes of damage and further evaluating the effects of suggested reinforcement measures. Firstly, numerical modeling experiments were conducted to obtain the physical and mechanical parameters of SRM. Then, three 3-dimensional (3D) numerical simulation models were established. The settlement, tensile stress, and distribution of damage zones on the tunnel floor were highlighted. Results indicated that the maximum deformation occurs on the roof of the tunnel lining, and the minimum displacement is in the middle part of the tunnel floor. The maximum compressive stress is within the ultimate compressive strength. However, the tensile strength significantly exceeded the ultimate tensile strength, resulting in cracks in the tunnel lining. If no reinforcement measures are taken, about 66% of the tunnel floor will be tensioned to damage, significantly reducing the bearing capacity and long-term stability of tunnel lining. The stiffness difference between SRM and the bored piles is the reason for damage zones in tunnel lining. It is suggested that grouting reinforcement and steel fiber reinforced concrete should be taken on the tunnel floor to improve damage resistance. Finally, it is verified that the suggested reinforcement measures can effectively control uneven settlement and damage zones in the tunnel floor.