The dynamical models related to development of the joint system (commonly called “Sheeting”) with horizontal or slightly inclined trend, found frequently in the weathered granitic rocks, have been considered in detail concerning the cases of the primarily horizontal topography and of the sloping ground produced after dissection. As a result it has become evident that (1) removal of the stress ascrived to the load lying over the land surface in surely one of the important factors, (2) possibility of the dynamical heterogeneity resulted from development of the timy-scaled sheeting in the weathered part of the granitic rocks in deducible from inspection of some data of the measurement referred, and (3) in consequence scruting of disposition of the sheeting is considerably useful as a indicator for classifying the strength of the basement rocks.
In this paper we describe an experimental study of the joint shear strength of granite. The specimens used were chosen from fresh rocks (0.9% in porosity) to weathered rocks (5.6% in porosity). The area of shearing plane was about 24-46 cm2. Two kinds of joint planes were prepared, the one was “rough surface” split by Brazilian tensil test, the other was “smooth surface” sawcut with a diamond blade. The result obtained with a series of direct shear tests may be summarized as follows:(1) the shear strength on both surfaces can be expressed by Coulomb's friction law within applied normal stress range shown in Figs. 3 (a)-(e), (2) friction angles of rough and smooth surfaces were measured about 35°(30°-40°), 25°(23°-28°), respectively, (3) there is no effect of weathering of rock on shearing strength as shown in Fig. 6, and (4) the amount of shearing strein to peak or maximum strength was mainly influenced by the magnitude of normal stress, shown in Figs. 4, (a), (b).
Serious disaster occurred due to the Izu-hanto-oki earthquake of May 9, 1974. Investigation-team of 10 engineers was delegated from Public Works Research Institute, Ministry of Construction, to observe the damage and obtain the new information about the earthquake. The magnitude was 6.8, the epicenter was 5km west from Iro-zaki, 20km beneath the surface. Actural fault was found at Iro-zaki, whose horizontal displacement was 30cm, vertical was 20cm, and strike was N70°W, dip was 80°S. Along this fault, buildings were damaged by displacement, besides ground vibration. A great number of slope-failure and land-slide was occurred, and most of damage due to the earthquake was caused by that, and this fact is the characteristic of the Izu-hanto-oki earthquake. Another type of damage was caused by the settlement of loose fine sand layer, and that was observed in Iruma district.