Study on Construction Risk Assessment of Tunnel Reconstruction and Expansion Works

To study the construction risks in the in-situ reconstruction and expansion of existing tunnels, by taking the Heiyu tunnel reconstruction and expansion project in Zichuan District, Zibo, Shandong Province as an example,an overall construction safety risk assessment table for tunnel reconstruction and expansion is established, the overall risk is evaluated as a very high risk with Ⅳ level. By conducting a general survey of hazard sources using the combined checklist method and expert investigation method, six major hazard sources are identified, and a special assessment of major risks is conducted. Taking the risk of collapse as an example, and in combination with the construction difficulty and supporting method of the tunnel reconstruction and expansion works, the index system method is used to assess the risk sources of the collapse, taking multiple factors into consideration such as advanced pipe-roof support, reinforcement of the existing tunnel portal, surrounding rock classification at the intersection of old and new tunnels, and support method at the intersection of old and new tunnels. Besides, risk mitigation measures in relation to supporting, blasting, reinforcement and other construction measures are developed to prevent tunnel collapse accidents.