A Study on Mechanical Backgrounds of Sheeting Joints in a V-shaped Valley

Yoshiaki FUJII	Division of Structural and Geotechnical Engineering, Graduate School of Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628
Yoji ISHIJIMA	Division of Structural and Geotechnical Engineering, Graduate School of Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628
Natsuo HORIBA	Technical Research Institute, Nishimatsu Construction Co. Ltd., 2570-4, Shimoturuma, Yamato, Kanagwa 242-0001
Tsutomu INABA	Technical Research Institute, Nishimatsu Construction Co. Ltd., 2570-4, Shimoturuma, Yamato, Kanagwa 242-0001

J. of MMIJ, Vol.114, No.12, pp.869-874 (1998)

There are a considerable number of sheeting joints at a V-shaped valley in Japan, which is a construction site for a P-Dam. Sheeting joints could cause water leakage and reduce the strength of rock mass as a dam foundation. The mechanical backgrounds of sheeting joints were therefore investigated. In-situ stress measurement by the stress relief method revealed that maximum horizontal stress, which is almost perpendicular to the P-River, is about 12 MPa. This result coincides with results obtained by the Deformation Rate Analysis method. It was also clarified that the temperature in rock mass shows large day-variation as deep as 30 cm, and that a significant temperature gradient appears under direct sunlight. Through numerical analyses, it was determined that an inclined crack near a free surface can grow much longer than that in an infinite medium. From these points of view, it was considered that the sheeting joints are exfoliation as a result of crack propagation near the free surface under horizontal stress concentrated by the geometry of the V-shaped valley and periodically-acting horizontal thermal stress.

KEY WORDS: Sheeting Joints, V-shaped Valley, Exfoliation, Thermal Stress

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