Abstract
There are several landslide areas along the axial trace of the Yamanaka anticline which is composed of the Miocene to Pleistocene formations. Landslides are well developed in the hinge of the anticline, but not in the limb, even though the strata are of the same horizon. Especially large landslide areas are situated where the anticlinal axis is curved or warped. It suggests that folding has influence on the development of landslides.
Mudstone and sandy mudstone of the Pliocene formations, collected from the hinge and the limb, are deformed and fractured under condition of triaxial compression at the strain rate of 1×10-4/sec. Rocks from the hinge have lower strength, smaller Young's modulus and higher ductility than those from the limb. Longitudinal strain under the hydrostatic pressures of 1, 000kg/cm2 is greater in the rocks from the hinge. Namely the rocks of the hinge can be strained more easily than those of the limb. It also shows that the rocks of the hinge is weaker to deformation and/or failure including landslide formation. It may be attributed to their textures disturbed by the tectonic flow in folding.
There are different kinds of fractures in the different parts of the anticline. Transversal extension fractures or gashes are well developed in the hinge. As weathering is accelerated by ground-water permeation through these fractures, landslides are well developed in the hinge of the anticline.
