Fairly detailed experimental and theoretical studies have been made of the effect of a ledge-rock foundation, regarded as an isotropic body, on the stress state of a large concrete dam [1-6]. However, in nature, in most cases, owing to fissuration, stratification, and other causes, ledge rock is anisotropic (or quasianisotropic). We are thus faced with the problem of studying the effect of anisotropy of a foundation on the stress state and stability of a structure.

The experimental model investigations of a narrow-profile alternative for a gravity dam designed in conformity with the conditions at the Kurpsa hydroelectric development were carried out with the object of evaluating the strength and stability of this new type of dam which, under service conditions, permits tensile stresses to occur in its upstream face.An analysis of the investigation results makes it possible to judge the efficiency of the new design. The stability of this structure was evaluated for the limiting state where the c@rrying capacity of the dam is fully exhausted when only the horizontal component of the hydrostatic pressure on its upstream face is increased above the design value. This approach, although it is somewhat conditional, makes it possible, having regard to various factors, to establish the state of the structure when it is overloaded by the most dangerous horizontal forces, to determine the method of failure and the strength and stability factors of safety for the structure in the limiting state. In addition, it should be borne in mind that such a method enables the actual reserves of concrete gravity dams to be disclosed and the means for further improvement in their design to be substantiated.

: 12The determination of the deformative properties of a rock foundation is an important stage in the study of the conditions of the joint behavior of a structure and foundation. Under full-scale conditions these characteristics are determined by static tests and seismoacoustic investigations. However, the results of these investigations do not always reflect the real overall deformative properties of the foundation. The relation between the results of dynamic and static investigations of the deformability of a rock mass is not always constant, which hampers the use of these data and an evaluation of the possible behavior of a structure with consideration of the real engineeringgeologic structure of the foundation.Model investigations of the static behavior of dams with consideration of the foundation structure, its deformative and strength properties have been carried out for a number of years at the department of hydraulic structures of the V. V. Kuibyshev Moscow Institute of Civil Engineering. We undertook the problem of investigating the use of static and dynamic methods of investigating the deformative properties of a rock foundation on models. In the first stage of these investigations we made a plane model of a foundation having a block structure (Fig. 1). This model (200 x 70 X 7 era) was composed of individual blocks measuring 7 x 7 x 7 cm laid up dry. The blocks fitted into one another on all adjacent sides, which ensured virtually no opening of cracks between them (the coefficient of friction of block against block was 0.60-0.65). Rigid fastening was provided about the stand along the contour of the foundation (displacements were equal to zero). The blocks were made of gypsum plaster-sand mortar, having a block modulus of elasticity 40,000 kg/em 2.During the investigations we made the following studies: a) evaluation of the static modulus of deformation of the base as a function of the size of the plate and magnitude of the external load; b) evaluation of the dynamic modulus of elasticity for different directions of action of the forces and as a function of the elevation of the reference plane; c) effect of the external load on the value of the dynamic modulus of elasticity; d) determination of the relation between the modulus of deformation and dynamic modulus of elasticity.

This article presents the results of model investigations of the stress state of the powerhouse section of a dam from the effect of static operating loads and also of the strength and stability of the structure in the limit stage of its work. Maximum attention was devoted to determining the character of the distribution of stresses in the contact region of the upstream face of the dam and in zones of verticalcolumn and diagonal structural joints. The task of the investigations included also a determination of the effect of grouting of the vertical joint between the toe of the dam and powerhouse on the stress state of the structure and value of the safety factor.A section of a concrete gravity dam with a height of 87.2 m (Fig. i) with a slope of the downstream face of 1:0.7 (1), a par t of the foundation with a different modulus of deformation, and schematically a powerhouse (2) with a spiral casing, turbine shaft, and draft tube were modeled.The downstream face of the section was made in the form of two buttresses (3), between which is the penstock (4), and the joints (5) between the buttresses and penstock were made through (without modeling elastic packing).The joints between the foundation part of the section and buttresses (6) and also the joints in,he zone of thrust of the buttresses and penstock against the toe (7) were reproduced as grouted.A characteristic feature of the models was reproduction on them of toothed ungrouted (R b = 0) column joints (8) in the upper and lower zones of the buttresses, in the lower part these joints were vertical. The joint between the toe of the dam and powerhouse (9) was realized on the models in two variants. On model i this joint was through and on model 2 it was grouted, which provided in this case interaction of the dam and powerhouse.Models were made in a scale of 1:150 from plaster.In the zone of the upstream face of the dam the weakened rock of the zone (B) in the foundation was modeled with a modulus of deformation twofold less than the modulus of deformation of the main mass (see Fig. i).The loads from the dead weight of the dam and powerhouse, hydrostatic pressure on the upstream face of the sections, and the seepage pressure on the base of the structure were reproduced on the models.The dead weight was created by hydraulic jacks and was transmitted through flexible nylon threads to anchors placed in the models.The hydrostatic load was transmitted to the models through a system of rods, crossbeam, and distributing plates.Deformations on the models were measured by resistance strain gauges. The readings were recorded by an electronic static deformation meter with a scale division value equal to 2.57. i0 ~6 units of strain.The investigations were conducted in two stages. The calculated values of the loads on the model in the operating stage of work of the structure (first stage) were determined from the relationship of the elastic characteristics of thematerials of the prototype and model, in which case it was assumed: modulus of deformation of the concrete E c = 20,...