Fracture Distribution and Deformation Modulus on Serpentinite

―A Case Study in the Maruo District, Ube City, Yamaguchi Prefecture, SW Japan―

Abstract

Mode of occurrence and distribution of fractures are described on a boring core drilled in non-weathered serpentinite, exposed at the Ube coastal area, Yamaguchi Prefecture. The fracture tends to form a zone, named the fracture zone, composed of several fractures on the borehole fracture column. In the case of the Ube serpentinite body, a fracture zone includes 5～20 fractures and the mean fracture spacing is around 20～40 ㎜. The deformation modulus obtained by pressure meter test in the borehole ranges 30～500MPa, however, the re-calculated value of deformation modulus corresponding to the most fracture zone concentrates within 30 to 40MPa. This value is ca. 1/10 of the non-fractured part, which gives the mean deformation modulus of fracture zones （weakened parts） of serpentinite.