The nature of groundwater flow through joints in actual rock masses has not been known in detail. The purpose of this study is to understand the groundwater flow characteristics (especially actual velosity of flow) in jointed rock masses by field measurement. This paper presents the results of the in-situ test related to groundwater flow through joints.
Massive hard rocks, which are often used as a foundation for civil structures, have strong connection force on their constitutional particles and very low permeability on their rock materials. In such case, since water flows in various joints existing in massive rocks are greater than the flows passing through rock materials, it is considered seepage flows at massive hard rocks are the flows of which flow channels are existing mainly in joint systems. However, at the stage now, it is fact that fundamental knowledges on the actual flow conditions and flow characteristics in actual joints are not yet clarified. Currently, in general, various hydraulic models have been established based on a hypothesis that flows in joints flow like parallel plates, though, since actual flow conditions have not been confirmed yet, basic formula to be a logical basis of these hydraulic models is only a hypothetical one. In addition to that, it can be assumed to be difficult to explain actual local flow conditions, such as flows out of tunnels or of ground surface, through current models. Therefore, currently it seems to be difficult to grasp an accurate flow process in rocks, because actual flow situation in joints are still unclear, though, some engineering points related to this matter can be considered. For example, with regard to geological disposal problems of radioactive wastes, to grasp flow velocity and flow channels accurately relating to translation works of radioactive wastes is a very important theme to secure the safety of disposal site surroundings. Moreover, in order to carry out grouting works effectively by considering on critical velocity of flow as foundation works for rock improvement, it is also an important theme that to grasp actual flow velocity and flow channels. Corresponding to the current situation, authors carried out various field tests at a site where hard granites are distributed in order to clarify flow conditions and flow characteristics of seepage flows in an actual rock mass. This time we report the outline of the tests and their results and analyzed considerations.
The test site is a quarry where Ryoke granites are distributed. Since quarry works had been done, top soil and weathered zone have already been removed and hard fine non-weathered granites are outcropped. As shown in the figure, this site is surrounded by perpendicular surface in front and a cliff behind. The objected joint was positioned at this vertical surface in front, which includes a natural water flow to be tested this time. Further, since there are various puddles around the site, it can be assumed that this site is rich in water supplying.