Evaluation of Fractured Neogene Mudstone for Tunnel Excavation

Abstract

The KITANOMINE tunnel (length : 2,928m) is a long bored tunnel. The north part of the tunnel is surrounded by squeezing mudstone, which became heavily fractured and then changed to clay as the tunnel advanced. The deterioration was so severe that the tunnel convergence and the crown settlement reached a non-negligible level. For safe and reasonable tunnel excavation, accurate evaluation of the ground conditions became more important. This report presents various kinds of new survey, measurement and devised boring method.