Shear Structure of Sliding Surface and Landslide Process of Noda Landslide developed in the Triassic Stratum Area, Okayama Prefecture, Japan

Abstract

Shear structure, clay minerals and carbonaceous materials in the Noda landslide area are studied mainly by X-ray diffractometry (XRD). The Noda landslide area is located in the central Chugoku, Japan and is underlain by the Triasic sedimentary rocks of Nariwa group. The sliding surfaces were confirmed in excarvated wall of drainege well. The specimens were obtained from the boring core and oriented block samples were obtained from drainege well. Carbonaceous materials were extracted from coaly mudstone. Various kind of deformation textures are confirmed through examinations of polished surfaces of oriented block samples. The obtained textures are well correlated with those of experimemtally established shear textures such as D shear, P shear and Riedel shear respectively.
Illite, chlorite, smectite, vermiculite and kaolin minerals are recognized in the samples. The amount of smectite increases with closing to the sliding surface. It is considered that smectite, vermiculite and kaolin minerals were formed through the weathering process whereas illite which occurred commonly with chlorite were representative constituent of the host sedimentary rocks.
The value of d (002) of carbonaceous materials is in the range of 3.40Å to 3.57Å It is to be noted that the d (002) value near the sliding surface is smaller than those of the others indicating that the crystalization degree of the carbonaceous materials near the sliding surface is relatively high.
Based mainly on clay minerals, carbonaceous materials and examination of deformation textures, occurrence mechanism of the lamdslide will be discussed.