Study on rock mass classification method based on geological investigation in NATM

摘要

In order to construct mountain tunnels rationally and safely, observational construction method has been employed. The necessity for such observation relating to the behavior of tunnel and surrounding ground means that there are so many uncertainties in the tunnel construction process. Uncertainties are inaccuracy in the geological survey before construction start, many assumptions in the design of tunnel supports, difference between design and constructed result and so on. Especially rock mass classification is important, because a design of tunnel supports and tunneling method is carried out based on the pre- investigated result under the condition of budget and construction period. However the item in pre-investigation might be limited. And rock mass class selected in the design is often different from that of actual condition. In this paper, rock mass classification result based on the advancing boring from tunnel face is compared with actually constructed rock mass class. Authors also discussed about rock mass classification process with geological engineers who have had many experiences in pre-investigation and advancing boring. As a result, it was suggested that rock mass classification table given in the standard cannot exactly provide a good result. So rock mass classification process should be examined in detail and a new scheme to have more reliable classification results should be discussed.