2006 Volume 47 Issue 2 Pages 77-87
This paper describes a rock mass characterization of the Izumi Group for the tunnel construction of the expressway in the Shikoku region. The Izumi Group is mainly composed of interbeded sandstone and shale of Late Cretaceous in age. The tunnel grounds in the Izumi Group are geologically classified into the four types judging from the geological history of both rock mass slide and hydrothermal alteration. This classification is confirmed by the conversion data during tunneling. The first N-type of tunnel was constructed in undisturbed interbedded sandstones and shales. The second S-type was constructed in rock mass slides. The third H-type was constructed in hydrothermally alterated rock masses. The fourth HS-type was constructed in the ground with the complex history of both the rock mass slide and the hydrothermal alteration. Those four types of tunnel show distinct characteristics of conversion during tunneling respectively. Especially, it is clear that the large displacement tends to appear in H-type and HS-type tunnel ground. The X-ray diffraction analysis suggests that the smectite bearing clay veins originated from hydrothermal alteration have caused a large conversion during tunneling. Therefore, it is very important to confirm the presence of the swelling clay mineral (smectite etc.) before and during tunnel construction.
