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The homogeneous model of seepage flow through jointed rock was described in Section 5.3.2. is based on the assumption that a rock mass may be regarded as a homogeneous medium through which seepage water flows. Thus the permeability of individual discontinuities is converted into one for the entire rock mass and the rock’s generally anisotropic permeability is described by a permeability tensor [K].

The importance of seepage flow through a rock mass for the planning and construction of dams, slopes and openings has already been mentioned in Section 5.1. It has also been mentioned that the consideration of steady state problems is sufficient to cover most cases in rock engineering. Two conceptual models were formulated in Section 5.3 to provide the basis for the analytical treatment of seepage flow. Both employ friction factor equations for flow through discontinuities. It was demonstrated that the losses arising at the intersections between discontinuities of differing families could usually be neglected and that the piezometric head in each discontinuity immediately adjacent to the intersection could be assumed to be equal (5.60). The so-called discrete model was developed both from this assumption and the application of the continuity condition at the intersections (5.61), the model treating seepage flow as a sequence of flow processes through a grid of discontinuities (Section 5.3.1). A method of analysis for the investigation of two-dimensional (Section 9.2) and three-dimensional (Section 9.3) problems will now be developed on the basis of this model.

Seepage flow represents a highly significant factor in rock engineering and, particularly, in dam construction. To design sealing and drainage measures for the bedrock economically, a good knowledge of the rock mass’ permeability is essential. In the case of concrete arch dams, the forces exerted by the seepage flow on the rock mass play an important role since the resulting deformation of the abutment may lead to additional loading of the dams Similar circumstances are to be found in rock slopes. Here, forces caused by seepage flow in the slope may exercise a strong influence on stability, should drainage measures be inadequate. It must also be borne in mind that openings below the water table in a rock mass act, at least during construction, as a form of a drainage and may lead to a lowering of the water table.

It is most important that the interaction between structure and bedrock be taken into account in structural analyses of concrete dams since it critically influences the loading of the dam and the rock mass, particularly near to the bearing surface. The nature of the interaction between dam and bedrock in the various loading cases that may arise is therefore explained first to indicate the influences which have to be taken into account in the structural analyses. Prominence is given to the consideration of stresses, deformations and seepage flow in the rock mass. The loading of the dam is not considered in detail since it does not fall within the scope of this book.