In this study, the effects of foundation replacement on improving the shear resistance of a soft rock foundation were considered by model tests. As a result, it was clarified that the shape and size of the foundation replacement affects the improvement of shear resistance of a soft rock foundation.
Recently, there have been an increasing number of cases of constructing concrete gravity dams on rock foundations under complicated geotechnical conditions. Generally, the safety of a concrete gravity dam is evaluated by the following three items:
Safety for turning over
Safety for sliding
Safety for allowable stress
When a concrete gravity dam is constructed on a soft rock foundation which has low shear strength, careful examination is required since the shear strength (б, f) of the rock foundation greatly affects the safety, as shown in Henny's equation. Generally, when safety for sliding cannot be satisfied, the safety for sliding is ensured by changing the shape of the dam body in order to increase the base length L and vertical load V. For example, increasing the gradient of the upstream face and downstream face of the dam body, constructing a fillet or a base mat on the dam body, as shown in fig. 1. In these cases, more careful consideration is necessary to ensure integrity and watertightness of the dam body. Another approach to ensuring the safety for sliding is to improve the shear strength (б, f) of the rock foundation, instead of changing the shape of the dam body. For example, weak parts (such as a fault) in the rock foundation have been removed and substituted by concrete in many dam sites. Expanding this approach, it is proposed by the new method that whole rock foundation is replaced by an artificial material, in cases where construction of a concrete gravity dam is difficult due to large deformability or weakness of a foundation rock. The part of a foundation replacement is designed not as a structure such as the dam body, but as part of the foundation rock. It is located just beneath the bottom of dam, and is a discontinuous body with cracks. Therefore, cooling works to prevent cracks caused by exothermic reaction during concrete placement of the dam body are unnecessary. However, grouting is required to prevent seepage, same as other rock foundations. At present, poor mixed concrete is being considered as an artificial material for foundation replacement. Although the construction method for the foundation replacement is simple and has major effects, the design method has not been clearly established. Especially, it is important for the design to clarify the effects of the shape and size of the foundation replacement on increasing the shear strength of the rock foundation. In this study, model tests were carried out, and the effects of the shape and size of the foundation replacement on increasing the shear strength of the rock foundation were considered.
