Deformation behaviour of a concrete gravity dam based on monitoring data and numerical simulation

Abstract

Deformation behaviour is a key index for evaluating the health state of concrete dam structures in long-term service. Under regular loading conditions, dam’s deformation behaviour can be preliminary depicted using monitoring data. Physically well-founded numerical simulation of the dam’s deformation behaviour provides an efficient approach to comprehend the effects of different external loads. In this work, an advanced numerical model based on monitoring data and thermal-structural coupled analysis is developed for a concrete gravity dam, the Rappbode Dam, to gain insight into the current deformation behaviour of the dam under usual and unusual load conditions. Firstly, a graphical visualisation of the monitoring data, including air temperature, water temperature, water level in the reservoir, uplift water pressure at the dam base, temperature interior the dam body and horizontal displacements, is presented to illustrate ambient loading conditions and structural responses of deformation behaviour. Secondly, based on mesh accuracy analysis which considers the different element types and mesh densities, a functional finite element model of the dam-foundation system is generated with appropriate mesh, enabling the thermal analysis of time-varying temperature distributions and structural analysis of deformation behaviour. Thirdly, based on the thermal analysis, a transient heat transfer model is calibrated to describe the thermal transfer process from the ambient environment to the dam and to present the time-varying temperature distribution within the dam body. The initial condition in the transient thermal analysis is investigated to acquire a rational primary temperature distribution in the dam. The thermal properties of the dam’s concrete are back analysed based on the concrete temperature from thermometers. The time-dependent air temperature and water temperatures are considered to specify boundary conditions. Lastly, in structural analysis, by investigating the displacement response under the loads of temperature distribution within the dam body, the hydrostatic pressure, uplift pressure and self-weight, mechanical material parameters are back analysed based on the measurements. Hence, material parameters of the dam’s concrete are updated to the present operational phase, therewith an advanced numerical model of the dam is developed. In terms of recorded usual loading conditions, computed results are aligned with measured results of displacements. With the aid of the advanced numerical model of the dam, the thermal effect due to time-varying temperature distribution, structural effect due to water-level variation and simultaneous effect are investigated under usual and unusual loading conditions. The results show that thermal displacements at different points are in phase with each other despite the phase shift in temperatures from each other. Hydrostatic pressure is more significant than uplift water pressure in determining the structural displacement. The thermal effect dominates the displacement at the dam crown, while the effect due to water level begins to dominate with the decrease of elevation. The results from an example of an unusual load case indicate enlarged ranges of displacement variations and warn of areas with possible cracks in the dam.