DEFORMATION ANALYSIS OF A HIGH CONCRETE GRAVITY DAM

Abstract

The safety evaluation of a high concrete dam renders it necessary for design engineers to provide reliable control measures. In order to monitor the behaviour of dams, a large number of instruments are usually provided, which include stressmeters, strainmeters, plumb lines, uplift pressure pipes, resistance thermometers and joint meters for the measurement of stresses, strains, deflections, pore water pressure, temperature changes and joint movements respectively. Measurement of dam deformations is also made by Geodetic methods as this provides the only means of determining absolute deformations. The measurement of transverse deflections furnishes the most reliable data regarding the strucctural behaviour of a dam. In order to check the reliability of the instruments and to-interpret the measured deformation data, an analytical assessment of the dam deflections is necessary. The theoretical analysis of the dam can be carried out treating the dam as one dimensional structure such as beam analysis or two dimensional structure such as finite element analysis. However, for an accurate determination of the stresses, a finite element analysis is necessary. In this dissertation, a review of the factors influencing the dam deformations is presented. Instruments used to monitor the structural behaviour of dams, have also been briefly' discussed. A few case histories of the structural behaviour of some important dams has been included. Deformation analysis of three instrumented blocks of a 225.6m high concrete gravity dam has been carried out. Field data as actually measured has been utilised. For the purpose of comparison of deflections obtained analytically with those obtained from instrumental measurements, those loads have been considered to which the dam is subjected after the installation of the instruments. The actual sequence of installation of plumblines in the various blocks has been taken into account. It.is found that temperature deflections play a very significant role in the overall deformation behaviour of the dam. A comparison of the measured deflections has been made with those obtained analytically, and a good comparison has been obtained. The instrumental. measurements can be reliably used for assessing the performance of the dam in future, ' Evaluation of deflections for higher reservoir water level indicates that the deflections are dependent on ambient temperature conditions during the period. Large deflections are observed for lower reservoir water level, basically due to lower ambient temperature conditions. A comparison with measured deflections during the period has shown close agreement with the calculated deflections.