Investigation on inspection scheduling for the maintenance of tunnel with different degradation modes

Abstract Inspection scheduling is an important task in the maintenance of tunnels, which will obviously affect the lifetime maintenance cost and risk. Traditional periodic inspection with fixed inspection interval has low efficiency in the early age or high risk in the later age of tunnel. This study aims at developing a novel non-periodic inspection policy and investigating the adaptability of several inspection scheduling functions with different degradation modes. Three classical degradation modes (namely, accelerated, decelerated and stationary) are categorized to describe the potential trends of degradation, and they are modeled by non-stationary Gamma process in a unified form. The effects of three types of inspection scheduling functions on the tunnel maintenance are compared in the view of the expectation of lifetime maintenance cost. The results of the numerical analysis show that inspection schedule function f 2 ( x ) (in the form of a convex curve) always yields the lowest maintenance cost, regardless of the degradation mode of tunnel. The results indicate that the inspection scheduling function in the type of a convex function is the best and shortening the inspection interval is an effective measure to reduce maintenance cost and risk. The proposed method and the obtained results are helpful for practitioners to make more effective inspection scheduling and to reduce both risk and cost associated with the maintenance of tunnels.