P N OJHA, BRIJESH SINGH, V V ARORA, PRAMOD NARAYAN, AMIT TRIVEDI & MANTU GUPTA
1. Introduction
Concrete gravity dams are large, complicated structures that are expected to withstand various usual loads and seismic effects without unacceptable levels of damage. However, due to aging, these dams are subjected to severe environmental conditions that affect their strength and, ultimately, their seismic performance. Therefore, in order to execute an accurate and reliable analysis for a concrete dam, it is necessary to estimate the properties of the concrete in the dam appropriately. In concrete dams the stresses caused by temperature changes can be larger than those from reservoir loading. The effects of temperature change depend on the thermal properties of the concrete[10,11,12].
The two most important chemical reactions which have the capability to cause swelling in concrete dams are Alkali Aggregate Reaction (AAR) and Ettringite Formation (EF)[3,4,9,17,18,19]. They lead to an expansion of the material, and induce general cracking and degradation of the mechanical properties. This implies problems in terms of serviceability, structural integrity[14,15,16] and durability since cracking favours the ingress of external species prone to initiate other degradations. To deal with the affected structures it is thus necessary to precisely understand the chemo-mechanical effects of each reaction. Ageing of a dam is a process which includes the dam structure together with grouting works, joints, etc. and the foundation. Therefore, in order to ensure expected operational performance, comprehensive safety reviews of such massive structures are warranted[21,22]. These reviews provide the basis to address various associated risks through required rehabilitation measures. The modelling and analysis of complicated structures like concrete dams needs thorough understanding of the structural behaviour in the static and dynamic loading, boundary conditions of the system, and the redistribution of the loads on the structural elements during failure mechanism. The actual properties of materials plays an important role in advanced FEM modelling of dams wherein the basic objective remains to obtain reliable model output regarding the realistic deformations, stresses, inclination etc. in order to address the problem through appropriate rehabilitation[27,28]. Also, it gives an overall view of the expected behaviour of the material at the construction stage and design life. These material properties are very sensitive in evaluating various engineering parameters required for bankable dam design.
In the present investigation, assessment of the concrete properties of a gravity dam in India aged over 50 years old is presented. The dam is a 225.55m high straight gravity concrete dam, built across the Sutlej River in a deep and narrow gorge of the Lower Siwalik Hills. The length and width of the dam at the top is 518.16m and 9.14m, respectively, with the width of the dam at the base being kept as 190.5m, and the width including apron and heel claystone plug as 402.33m. No major distress in the dam was observed and health monitoring investigation was undertaken. The interpretation of field and laboratory studies, including microstructure studies of the concrete in the dam, were evaluated in order to provide accurate and reliable finite element modelling for determining the reason behind unusual deflection of the dam.
6 DAM ENGINEERING Vol XXXII Issue 1
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