ダムグラウチングによる岩盤改良の評価方法に関する考察

Abstract

The purpose of consolidation grouting for dam foundation is to improve the permeability and mechanical properties of rock masses. For permeability, the grouting effect is usually confirmed by the permeability test at check holes. But for the change of mechanical properties, it has been difficult of confirmation. So, the mechanical improvement of foundation by grouting, like the changes of elasticity and strength, has not been considered in dam foundation design. In this study, an in situ experiment has been made in order to examine the grouting effect on mechanical properties of rock masses. The testing yard where the experiment was performed was 10m square, and 13 boreholes for grouting, divided into four (4) stages, were laid out. These boreholes had the length of 7m each, and the injection material was cement mixed with water. The experiments mainly consisted of elastic wave prediction and borehole expansion tests. As the results, the followings were obtained.(1) The change of distribution of elastic wave velocity by grouting represents the uniformity of rock masses.(2) Grouting can improve the deformability of rock masses.(3) For more deformable rock masses before grouting, the more mechanical improvement is achieved.(4) The reological model can be used to explain the grouting effect. By this model, the experiment results of poor rock. masses, which have lower mechanical properties, can be well expressed.