Innovated Monitoring System of Ground Water Information Ahead of Tunnel Face

Abstract

Prediction of geological and hydraulic conditions ahead of tunnel face is very important because misjudgment of the ground conditions may lead to a tremendous disaster and a delay in schedule planning. However, due to the long and linear nature of tunnel, pre-geological investigation is sometimes insufficient. Especially, as to the groundwater, installation of observation wells is quite difficult due to huge overburden. In order to solve this problem, the authors have developed a new system of monitoring groundwater information in combination with several types of pilot boring ahead of the tunnel face. The horizontal pilot boring for the tunnel was categorized into three types by drilling length; extra-long boring, moderate-length boring and short boring. Also the authors have developed new devices to measure water inflow information by each three drilling system. These devices have different concept and structure depending on the purpose of measurement. By applying these systems at appropriate construction stages in turn, hydraulic information can be obtained quantitatively. Three types of the device were respectively tested in a tunnel site and were verified their good performance. In the future, the system that combines three different techniques will be applied to the estimation of the groundwater conditions ahead of tunnel face and judgement of the appropriate countermeasures that could lead to safety tunnel excavations.