Abstract ▼ AI-Helper

Tunnel faces are subjected to many problems regarding stability during construction, but there has been little research with respect to the stability of the tunnel support and the surrounding ground. When a tunnel is excavated below the groundwater level, the groundwater flows into the excavated sur...

Tunnel faces are subjected to many problems regarding stability during construction, but there has been little research with respect to the stability of the tunnel support and the surrounding ground. When a tunnel is excavated below the groundwater level, the groundwater flows into the excavated surface of the tunnel and seepage forces act on the tunnel face. In this thesis, seepage forces arising from the groundwater flow into a tunnel were studied. First, the effect of seepage forces on the tunnel face stability was studied. The steady-state groundwater flow equation was solved by the finite element method and the seepage forces acting on the tunnel face were calculated and implemented into the upper bound solution. To verify the results of numerical analysis and limit analysis, a model test was performed. Second, the effect of tunnel advance rate on the tunnel face stability was studied. In this part, a finite element program to analyze the groundwater flow around a tunnel with the consideration of tunnel advance rate was developed. Using the program, the effect of the tunnel advance rate on the tunnel face stability was studied. From the results of the numerical analyses and the limit analysis, the ratio of the average seepage pressure to the hydrostatic pressure, named the seepage pressure ratio, was about 22% for the drainage type and about 28% for the water-proof type, which were also supported by experimental results. From the study on the effect of the excavation advance rate on the hydraulic head around the tunnel, it was concluded that the excavation advance rate must be taken into consideration as an additional parameter in tunnel design except for the extreme case of highly permeable ground or very slow excavation.

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