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Settlement behaviors investigation for underwater tunnel considering the impacts of fractured medium and water pressure

Abstract Settlement behavior plays an important role for the stability of underwater tunnel due to the different responses of fractured surrounding rock to external load. In contrast to the traditional analysis method based on continuum mechanics, the presented numerical model using improved hybrid finite element was performed to study the settlement behaviors of structure, and structural health monitoring system (SHMS) was introduced for field verification. The Nanjing Yangtze River tunnel, a typical underwater shield tunnel was selected as a case study for numerical simulation and real-time monitoring. First, an improved numerical model was developed on the basic of our previous research, which considers the impact of natural geological fractures on structure stability. Then, numerical investigation was applied to study the displacement of settlement under different boundary conditions. The differences between intact and fractured surrounding rock were discussed, which denote the response of fractured surrounding rock is significantly larger. To verify the numerical results, SHMS was employed in this project to monitor its mechanical behaviors. On the basis of the mass monitoring data, the analytical method was introduced to investigate the response of tunnel settlement to water pressure, which agreed well with the results obtained from the model of fractured surrounding rock.