Abstract
The Rebun tunnel passes through a thick section of Pliocene agglomerate with a layer of altered tuff breccia and the Obira tunnel passes through a zone of Miocene decomposed mudstone. In these rocks the altered tuff breccia and the decomposed mudstone were so swelling that the support or the lining of these tunnels were squeezed.
The authors measured the rate of swelling and the swelling force of these rocks and analysed clay minerals in these rocks by X-ray diffraction method. The relation between the clay mineral and the swelling, and the amount of water absorption, the rate of swelling and swelling force are discussed.
