Enlargement of concrete blocks of arch dams with allowance of the formation of radial thermal cracks

Abstract

1. Considerable acceleration of the construction of arch dams with the use of modern highly productive continuous concreting mechanisms is possible with enlargement of the blocks and allowance of the formation of thermal radial cracks in them. 2. A theoretical analysis and the results of on-site observations show that under the effect of the hydrostatic head of water, radial joints and cracks in compressed zones of an arch dam close and the dam in these zones works as a solid dam. Grouting of such cracks is not required according to the conditions of the operation and impermeability of the dam. 3. The 25-year experience of designing and constructing concrete and reinforced-concrete hydraulic structures with alowance of the formation of cracks of limited opening shows that with respect to the durability of concrete, cracks can be allowed also in arch dams. 4. Thermal cracking in concrete blocks of arch dams enlarged in plan (lengthened along the faces of the dam) should be controlled by making radial notches concentrating tensile stresses providing the formation of radial cracks at prescribed places. To prevent the formation of cracks in other directions, the probability of which is determined by thermal calculations, the usual methods of thermal regulation of the blocks should be used. 5. With the organized formation of thermal radial cracks, the size of the blocks along the faces of an arch dam is not limited by the condition ofcrack resistance; it is determined by the rate of concreting and organization of the works. The formation of radial cracks is allowed only in zones of the dam with a unique diagram of arch compressive stresses, the calculated value of which under the effect of the total hydrostatic load is not less than 4 MPa. 6. The technical and economic effect from concreting arch dams as enlarged blocks with allowance of the formation of thermal radial cracks consists in considerable acceleration of dam construction and reduction of material and labor expenditures on constructing formwork, preparation of the blocks, and grouting the joints.