Application of a Rapid Non-Core Drilling Exploration Ahead of the Tunnel Face using Water-Powered Hammer Drilling on Hydrothermally Altered Zones in Granodiorite
Generally speaking, in order to survey the geological conditions existing ahead of the face, tunnel excavation must be discontinued temporarily, and therefore it is necessary to bore over a long distance in as short a time as possible. To overcome these requirements, we have developed an exploration system with a water-powered hammer of down-the-hole drilling type, which is capable of surveying the geological conditions existing ahead of the face by rapid non-core boring. This technique was applied to construction of the Nonobori Tunnel on the Shin-Meishin Expressway. With the ground geology composed mainly of hard granodiorite, this report explains a project of using a forward exploration boring starting from the face extending about 150 meters in length, where we were able to successfully identify in advance conditions of the zone altered hydrothermally.