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.

At present it is planned to construct in the USSR high roundhead butress dams (Kirov, Andizhan, and others) under complex and diverse geological conditions. Among the various types of dam foundations, of definite interest are those consisting of two types of sedimentary rocks: rigid and strong (sandstones, limestones) and yielding (shales, marls).In this work we investigated the stress of a roundhead buttress dam on a foundation composed of two masses with different physicomechanical characteristics. The ratio of the moduli of elasticity of the material of the dam body and of the masses of the foundation was taken to be equal to E d : Er: E w = 1 : 1 : 0.2, here E d, E r, and E w are the moduli of elasticity, respeotively, of the dam body, relatively rigid mass, and relatively weak mass of the foundation. The plane dividing the mass of the foundation is taken to be vertical.The first series of experiments were carried out in accord with the I-IV schemes of the foundation structure, and in the second series we used schemes V-VII (Fig. 1). The investigations were carried out on brittle models in the elastic stage of their operation.The body of the dam model and the rigid foundation were made out of gypsum-sand mortar with a modulus of elasticity of 40,000 kgf/cm z at a weight ratio of the gypsum, sand, water of 1 : 0.5: 0.878. To model the weak foundation we used a mixture of cement (C), limestone (L), sand (S), rubber crumbs (R), and water (W) at their weight ratio of C : L: S : R : W = 1 : 6 : 7 : 2 : 4.2. The modulus of elasticity was 8,000 kgf/cm z. We reproduced on models a section of an 86-m-high roundhead buttress dam of a scale of 1:170 together withthe foundation* (Fig. 2). The dimensions of the model foundation were 4H in length and H in depth (H is the height of the model dam).A hydrostatic load was created by a system of hydraulic jacks and the buttresses' own weight by a system of pull rods. Deflections of the dam were measured on the model's surface by electrical resistance strain gauges with * Investigations were carried out at the department of Hydraulic Structures of the V. V. Kuibyshev Moscow Civil Engineering Institute applicable to the roundhead buttress dam of the Kirov Reservoir.