Calculation of Height of Lift and Placing Frequency in Concrete Dam Using Finite Element Analysis

Abstract

Construction of Dam requires concrete to be poured in large volume. The large volume of concrete placed in a concrete dam is subjected to high risk of thermal cracking due to internal heat generated by cement hydration. The thermal cracking decreases the durability of such massive structure. To tackle the problem, during the construction phase appropriate height of lift and the duration between two subsequent lifts is necessary. For lift calculation the thermal heat distribution was analyzed by three dimensional finite element model. The finite element software ABAQUS version 6.13 was used to study the thermal behavior of concrete in steady state and transient state for varying lift height. The study focuses on the thermal distribution in a lift height ranging 1.5 meters to 5 meters for a concrete block (5m x 5m). The temperature in each lift size is analyzed and appropriate lift height is decided. The maximum height of pour in one lift depends on the thermal gradient and the time required for the heat generated in the core to dissipate. The time required for placing the lift and the laying of next lift represents placing frequency in a dam structure. The placing frequency of next lift is decided on the basis of the heat dissipation rate of concrete. If the second lift is delayed, the lower is temperature attained by concrete but the time of construction also increases and thus the costs also go hand in hand. The properties of concrete used in dam model were taken from Indian Standard temperature control of mass concrete for dams IS 14591:1999.The density, thermal conductivity and specific heat were the main thermal properties taken into consideration for the model. The Placing temperature, the most important parameter for the temperature profile generated, was also used as input. The efficiency of a dam construction project lies with durability, the effectiveness of construction technique used and the time of construction, thus affecting the economy of the project.