INFLUENCE OF COMPOUND DAM DESIGN ON ITS STRESS-STRAIN STATE

Subject: the dam of compound design in which the water pressure is borne mutually by a concrete gravity dam and a higher rockfill dam with reinforced concrete facing. Research objectives: 1) study the stress-strain state (SSS) of a compound dam, identify the effect of three main factors on the dam SSS. The first factor is the height of the concrete structure. The second factor is the height of the contact zone (conjugation) between the earth fill and the concrete structure. The third factor is deformability of riprap; 2) based on these studies, give recommendations for selection of the compound dam design. Materials and methods: SSS studies were conducted by numerical analysis using the finite element method (FEM). Nonlinear character of soils deformability and contacts of concrete structure with soils, foundation and reinforced concrete facing was taken into consideration. Sequence of the dam erection and loading was taken into account. Riprap’s modulus of deformation varied from 70 to 270 МPа. Results: results of the analysis showed that the concrete structure as a part of the compound dam withstands hydrostatic load almost independently, practically without transferring it to the earth fill. We have found out that the most sensitive part of the compound dam design is conjugation of the earth fill with the concrete structure. This zone is characterized by failures of the soil strength. The consequence of these failures are considerable displacements in the joint between the facing and the concrete structure as well as bending deformations of the lower part of the facing. Bending of the facing causes considerable tensile stresses. Conclusions: the results of studies permitted us to formulate the following recommendations: 1) it is not desirable to select the height of contact zone between the earth fill and the concrete structure more than 60-75 % of the concrete structure height because it leads to increase of loads borne by the concrete structure and may result in failure of strength of its contact with foundation; 2) it is not recommended to choose the height of contact between the earth fill and the concrete structure less than 30 % of the height of the latter as it results in increase of bending deformations of reinforced concrete facing; 3) for reliability of the compound dam, it is necessary to choose riprap’s modulus of deformation not lower than 200 МPа.