Check of the reliability of concrete dams during their construction and operation

Abstract

Large concrete dams are complex hydraulic structures subjected to various static and dynamic effects which are designed to operate for 100 and more years. Despite the considerable progress made in construction techniques, perfection of its technology, improvement of the quality of construction materials used, and an increase of the general level of knowledge and technical designs, it is impossible to provide absolute reliability of concrete dams. Failures of dams, including concrete ones, occur.Although concrete dams do not rank first in the number of failures percentagewise, nevertheless during the past three decades a number of major failures have occurred on large dams [1]. The mean annual frequency of failures as of 1979 for large dams according to the data of the International Committee on Large Dams (ICOLD) was (0.5-2)" 10 -'4, and for earth dams (Z5-5) 9 10 -4.The basis for ensuring the normal operation of concrete dams is the fulfillment of the building codes during their design and construction. Correspondence of the behavior of the dam to the design is assessed during their construction and operation on the basis of the results of observations obtained by means of monitoring and measuring instruments (MMI), with which concrete dams of the I-III classes are equipped. Observations on concrete dams by means of MMI are carried out not only to obtain information for assessing the state of the dams during its construction and operation but also to check the design assumptions in the behavior of the dam, to perfect calculation methods, and to accumulate and generalize the observation data for their use when developing standards.The rather considerable experience of conducting on-site observations has made it possible to work out the optimal schemes of the distribution of MMI in concrete dams. On the basis of generalizing observation results, a number of standards on methods of conducting on-site observations and investigations have been developed [2, 3, 4].In the past 20 years the research department of the All-Union Planning, Surveying, and Scientific-Research Institute (Gidroproekt) has carried out on-site observations and investigations on gravity dams (Toktogul, Kurpsai, Tashkumyr, Boguchany hydrostations), buttress dam (dam of the Andizhan reservoir), arch dams (Mansour Eddahbi, Kasseb), etc.On all types of concrete dams (gravity, arch, buttress) observations were carried out of the horizontal and vertical movements of the dam and foundation, stresses in the concrete, temperature of the concrete, water in the reservoir, and foundation rocks, deformations of the joints between blocks, between columns, and between sections and along the concrete--rock contact, uplift pressure under the base of the dam, seepage discharges, as well as seismometric observations (accelerations, displacements). In recent years observations of the moisture content of the concrete of the upstream zones of the clams were included as part of the observations. To measure the parameters of the stress-strain state and seepage regime in...