The testing of shear strength and deformability characteristics of the contact between the limestone and concrete was carried out for the purpose of foundation of the high arch dam, using the test of constant normal load. Nine blocks with contact surface of 707×707mm were tested in the underground testing adits.The results of the peak and residual strength of the contact are presented through the Mohr-Coulomb linear and nonlinear strength criteria. It is shown that at the determination of residual strength, the application of normal stress reducing procedure is more adequate than normal stress increasing procedure. The deformability of the contact zone is described by the shear stiffness and dilation angle. The analysis of shearing results shows that the concrete to limestone contact behaves in accordance with the constant peak displacement model.
The contact between concrete structures and the rock mass (concrete-to-rock contact) represents a discontinuity between two distinct media, and can therefore be regarded as a specific case of the rock mass discontinuity. The strength and deformability of the concrete-to-rock contact is a significant element in every study of interaction between the concrete structure and the rock mass (piles, dams, retaining walls, tunnels). This contact is modelled in the way that is similar to the modelling of discontinuities in the rock mass.A great attention is paid to the behaviour of discontinuities since the times the discontinuitieswere first recognized as a factor of dominant significance for the strength and deformability of the rock mass.Test methods and empirical procedures developed for testing discontinuities in the rock mass can also be applied to the contact (discontinuity) between concrete and rock. Two procedures, the use of which depends on the way in which normal stress is applied, are used in the laboratory and field testing of shearing behaviour of discontinuities. In case of structures where the displacement perpendicular to discontinuity is not limited (dams, slopes), the decision is normally made to use the test procedure in which the normal stress is not changed during the testing (CNL – constant normal load). If normal displacements are limited (piles, tunnels), the testing is conducted at constant normal stiffness (CNS). The CNL method is applied for the testing presented in this paper. The behaviour of discontinuities in the rock mass, and hence the behaviour at the concrete to rock contact, is normally defined based on laboratory testingwhich is for economic reasons usually conducted on small samples. The tests normally conducted in laboratory are the direct or triaxial shear tests, and the samples are either natural or artificially created discontinuities. Artificial materials (such as mortar, gypsum, etc.) are often used instead of the rock. Big sample testing is rarely conducted in laboratory, and this practice is even more rare in field conditions. In fact, big samples for laboratory testing are difficult to extract, transport, protect against change in humidity, etc. The field testing of such samples is extremely costly as the tests are usually conducted in underground galleries of appropriate dimensions.