It had been believed that the valley for an arch dam should be narrow and the side walls of the canyon should be rigid enough for the efficiency of the arch dam.
However, recent investigations indicate that the construction of arch dams in a wide valley is feasible. And we have 5everal reports showing that arch dams have been built successfully on deformable rock foundations.
But we have also learned from these reports that if we require to develop the principal advantage of on arch dam fully in such cases, a peculiar design of structural and geometrical feature of the darn should be chosen by taking the shape and the geological feature of the valley into account.
The authors have studied the design of the Osako arch darn projected to be constructed in a wide valley, by laboratry model tests. It is generally known that the arch dam stability in a wide valley mainly depends on the cantilever action and that applicatian of a horizontal joint is one of the effective works to decrease this action.
In this paper the authors investigate the effect of a horizontal joint on the stress distribution and its influence on the ultimate strength of the Osako arch darn.
The abstract of results obtained is as follows.
(1) Arch action is satisfactorily developed along the lower arch element by inserting the horizontal joint at EL. 338m.
(2) The maximum compressive stress on the intrados side would be at the abutment region of the middle height of the dam. This region coincide with the discontinuous part of the elastic property of the foundation rock. But it is observed that the maximum compressive stress region is lowered in height by inserting the horizontal joint. This is preferable for the stability of the both darn and foundation.
(3) Although the value of safety factor (K) of the dam with horizontal joint is slightly decreased compared with that without horizontal joint, we can conclude through the whole tests that the ultimate strenght of the Osako arch dam which has horizontal joint is large enough.
