Investigation of the opening of construction joints in an experimental section of the Andizhansk dam (Uzbek SSR)

Abstract

The solidity of mass-burgess dams depends to a considerable extent upon the state of the construction joints between the head and the buttremes. Open and ungrouted joints considerably weaken the static operation of the dam. During the construction period there is the possibility of gravitational deflection of the inclined section of the head until it rests on the buttress. As a result of such a deflection, tensile stresses develop in the water-retaining face of the head. For this reason, in the design and construction of mass-buttress dams considerable attention is paid to the technical and practical measures required for the proper grouting of these joints. To select these mea-sure% the required analyses are made to determine the value and characteristics of the inter-section joint openings in accordance with the actual dam construction conditions. Such analyses are highly complex since the magnitude of the joint opening is affected by many factors, This makes it necessary to introduce several simplifications which lower the reliability of the results obtained.During the summer of 1970, at the mass-buttress darn forming Andizhamk reservoir, investigations were conducted on the inter-section joint openings in a specially concreted experimental section. The investigations were intended to evaluate the effect of the structural temperature regimen on the joint openings and to verify in this manner a design procedure [1, 2] which is based on the hypothesis of plane sections and does not take into consideration the embedment of the blocks in the foundation or the foundation temperature, At the same time it was intended to verify the correctness of the assumption that in long thin-walled structures opening of the inter-section joints starts in the absence of compressive stresses in the joint plane and that opening of the joints along the width of the concrete blocks takes place uniformly. In addition, it was intended to investigate the effect of the comlzuctional characteristics of the joints upon the size of uhe openings.The experimental dam section consisted of a lower head and two adjacent buttresses. The adopted concreting rate was 6 m per month, with a height of I m for the first two blocks and 2 m for subsequent blocks.The contact between the buttresses and the head was H o u g h a plane joint in the left buttress and a stepped joint in the tight abutment. The composition adopted for the concrete mix, with a water-cement ratio of 0.55, is shown in Table 1.During the investigation the following physical quantifies were measured: mean temperatures of the concrete blocks, heat irradiation of the concrete during setting, opening of the conslzuction joints between the head and the adjacent buttresses, and compressive stresses in the plane of the joint.The mean temperatures of the blocks, which affected the construction-3oint openings between the sections, were measured by means of linear resistance thermometers installed along ~e measuring alignment.On the basis of a preliminary analysis of the nature of the temperat...