Developing a Model for Analyzing Risks Affecting Machinery Tunnel Execution

Tunneling projects face several risks during the execution stage that affect the execution objectives (cost, time, quality, and safety). This study aimed to define the main execution activities of machinery tunnels with the associated risk factors and to develop a model for evaluating and analyzing the effects of the risk factors on the execution stage. The recognized activities of executing tunnels included the following: (A01) thrust and reception shaft installation; (A02) machine setup and break-in; (A03) machine progression and lining placing; and (A04) machine break-out and removal. Additionally, thirty-two risk factors associated with these activities were identified. Risk factor probability of occurrence and impacts on cost, time, quality, and safety were determined. Due to this risky and uncertain environment, the fuzzy logic method was applied for developing a model to analyze the effects of the risks on the tunneling process. The model was applied and verified using data collected in Egypt. Many correlations were determined among risk factors that affected tunneling execution objectives, resulting in close relationships with each other. The results emphasized many significant risk factors, such as "conflict between technical geological report and the ground nature", and "shaft wall damage during break-out". A03, which is related to machine progression and lining placing, was declared the riskiest activity group during tunneling execution. Further, safety was rated as the objective most affected by risks. The risk model presented in this study can be modified and applied to other cases, while the results and key risks can support the decision-makers who deal with tunneling construction.