Risk management for the new tunnelling construction using other tunnel records and helicopter borne survey in accretionary complex

摘要

In this survey, we assessed the convergence displacement and settlement displacement, as contained in the tunnel construction records, with lithofacies confirmed by boring cores. In addition, magnetic susceptibility of boring cores was measured, and a comparative study was conducted regarding its correlation with magnetic intensity distribution by helicopter magnetic survey in helicopter borne survey. Lithofacies of tunnel ground were classified into units from ⅰ to ⅳ. It was confirmed that the density of the fracture and shear zones tends to increase in the following order: ⅱ < ⅲ < ⅰ. Figures (a) and (b) describe the relationships among convergence displacement, settlement displacement and each unit. The final displacement (a) indicates that the convergence displacement and settlement displacement are 10 and 13 mm, respectively. Although this tunnel ground consists primarily of basalts, which has numerous cracks, it was confirmed that displacement was relatively low. In addition, when the proportions of convergence displacement and settlement displacement during the progress of tunnel face 1D and the final stage were compared in this tunnel ground as opposed to the initial values (b), no difference was discovered among units during the progress of tunnel face 1D. In the final stage, however, proportion to the initial value was small in Unit ⅰ and tended to be large in Units ⅱ and ⅲ. Since the density of fractures and shear zones is high in Unit ⅰ, it is possible that stress has already been released due to the development of cracks. In addition, when the helicopter borne survey method is applied to the geological survey of tunnel in this location, it is possible, to a certain extent, to evaluate the state of geological distribution based on relative differences in magnetic intensity distribution by concurrently using ground reconnaissance results since the intensity of the magnetic force in Unit ⅰ is larger than the intensity in Unit ⅱ.