Assessment of Material Properties of Concrete Gravity Dams – An Indian Case Study
P N Ojha(1), Brijesh Singh(1), V V Arora(1), Pramod Narayan(2), Amit Trivedi(1) & Mantu Gupta(1)
Abstract: In India more than 5000 large dams have an average age of 40 years wherein assessment of dam health is an emerging requirement. Due to ageing, the materials are subjected to severe weather impacts that affect the strength and, ultimately, the operational performance of the dam. This paper presents the case study of a concrete gravity dam currently being investigated under the ongoing Dam Rehabilitation & Improvement Project (DRIP) of the Central Water Commission in India. The dam chosen is more than 50 years old. To study the unusual deflection of this dam detailed assessment of concrete and rock properties for conducting advanced Finite Element Analysis (FEA) of a gravity dam was needed. This study was undertaken through a multi-disciplinary approach which involves testing of the dam material, studying available instrument readings and developing a 3D numerical model of the dam, its foundation and reservoir to perform sequential thermal, static and linear dynamic analysis. It covers a complete material property investigation in order to carry out an accurate and reliable analysis. The complete investigations of mechanical properties included a field assessment, thermal properties, and expansion issues. Concrete core samples from the dam were used to determine mechanical properties, chemical properties, petrographic studies, surface morphology study of concrete samples using the Scanning Electron Microscopic (SEM) method, including detection of ettringite presence and fracture pattern, X-Ray diffraction analysis and Alkali Aggregate Reactivity. Testing on rock samples from the left and right bank on the downstream side of the dam for determining volumetric weight, Modulus of Elasticity, Poisson’s Ratio, Uni-axial Compressive Strength, Ultrasonic Pulse Velocity (UPV) (P-wave only) and permeability co-efficient of the rock mass (laboratory test only) are also presented in this paper. Based on the study, it is seen that the overall quality of concrete is sound and the experimental test results of compressive strength, modulus of elasticity, Poisson’s Ratio and split tensile strength are of a similar range to the designed values for these parameters. The test results of the resistivity test and humidity meter indicate that moisture content in the upstream side is higher than the downstream side. The impact of aggregate and other concrete constituents on the deterioration of concrete, which can have a significant impact on the durability and safety of the dam, are discussed. The chloride, sulphate, pH and other chemical parameters are within the permissible limits given in IS: 456-2000[7] for both concrete and water.
Keywords: Gravity dam, mechanical property, non-destructive test, ettringite, alkali silica reaction.
Vol XXXII Issue 1
Author Details: (1)National Council for Cement & Building Materials, Ballabgarh, Haryana, India; (2)Dam Safety Rehabilitation Directorate, Central Water Commission, Delhi, India.
DAM ENGINEERING 5
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