RESEARCH INTO RATIONAL ROCK MASS CLASSIFICATION DURING SURVEY AND DESIGN USING SCORING POINTS FOR TUNNEL CONSTRUCTION

Abstract

In recent years, more than 300 km of tunnel has been constructed by the new Austrian tunneling method (NATM) every year, with an annual construction cost of more than a trillion yen. However, the support patterns used during construction are frequently heavier than the designed support patterns, thus increasing the cost. Therefore, a major issue for those engaged in tunnel site investigation and design is the classification of the rock mass such that there is little divergence from the support patterns when the tunnel is constructed. Beginning in 2001, the authors introduced a scoring method for evaluating the geological information from preliminary surveys, with the objective of minimizing the deviation between support patterns in design and support patterns in construction. The scoring method is a method for evaluating the geological information from preliminary surveys in accordance with the same criteria used for evaluation of cutting faces during tunnel construction. As a result, rock masses such as granite, volcanic rocks, and accretionary complexes can now be evaluated with high accuracy during design. Borehole surveys and geophysical investigations recently have been kept to a minimum as clients attempt to reduce costs. Therefore, research was carried out on methods for high-accuracy rock mass classification that use to the maximum extent scoring points obtained from topographical analysis, surface reconnaissance, and borehole cores.