The stability of gravity dam has ever been calculated as a two dimensional problem by Using representative section to a direction of the stream. In case of an example shown in this report, there are several fractured zone Within the foundation rock at the site of a gravity dam(37.5 meters of height). For example, between No.8 and No.5 of lack of the dam there are from 5 to 6 strips of fractured zone which have widths of about 5 meters and directions of parallel to the stream. In such a case, conventional approach can not take non-homogeneous rigidity of foundation rock. In this report, the distribution of fractured zone in foundation rock is represented by three dimensional finite elements. Stresses and displacements caused by water pressure on dam, earthquake and pore pressure, are calculated. From the beginning to the completion of the dam, mechanical behavior of the dam had been 0bserved. Based on the results of both calculation and Observation, the stability is considered.
Geological features of this site are shown as its plan in Figure 1 and its section in Figure 2. The foundation rock of this site consists of a kind of metamorphic rock of Hida and of a kind of mesozoic bedding rock of Tedori. These rocks are covered with quaternary terrace deposit and actual river deposit. Geological characteristics are as follows:
Among metamorphic rock of Hida, those existed in the neighbourhood of foundation of the dam are gneiss. These are distributed mainly from the side of right bank to the river bed. Gneiss has many open joints and generally crushed. It is certainly effected by the existence of fractured zone. Along these joints, there are chlorite, calsite and limonite. They are to a certain degree alternated.
Bedding rock of Tedori consists of conglomerate and interface of shale and sand-stone. At the site of the dam, mainly exists the interface of shale and sandstone and is distributed at right bank.
(Figure in full paper)
Shale has a property of mica and contains organic remains of plants and of limnetic shell-fishes. These organic remains can be seen in test adits at the site. Sand-stone is siliceous and of fine and coarse grannular. So far as the observation in test adits is concerned, in the interface shale exists predominantly. Even though there are calsite or limonite partly in joints, alternation is slightly developed and rocks are generally fresh and sound.
Metamorphic rock of Hida contacts with mesozoic bedding of Tedori by the interposition of fractured zone near at the river bed of left bank of the dam site.
Quaternary terrace deposit which covers foundation rocks, has the depth of from 3 to 7 meter. The deposit distributes in the area between the river Tedori and the side mountains and exists in strip shape along the river. Almost of the terrace has been cultivated as rice field. Actual river deposit mainly consists of gravels which have the diameter of 1 meters approximately.
