Effects of thermal and seepage actions on seismic response of roller compacted concrete dams

Abstract

Roller compacted concrete (RCC) dams have been developed for their rapid construction and low cost. However, some issues associated with the analysis and design of RCC dams are related to the seismically induced damages and possible failure of the dam, seepage due to the weakness of roller compacted layers and thermal stresses due to massive concreting. Large seismic events, in addition to the thermal and seepage effects, can cause the cracking and nonlinear behaviour where these cracks may expand further under the water pressure inside them to affect the stability of the structure. Therefore, developing a suitable constitutive material model and a reliable computational procedure for the safety evaluation and prediction of cracking risk of these structures has been a challenging and demanding task. This research aims to present a new comprehensive numerical procedure to evaluate the seismically induced cracking of RCC dams under the effects of thermal and seepage actions. It takes into account the coupling effect of water pressure and the crack formation during an earthquake. In addition, more relevant features of the behaviour of concrete such as ageing, temperature, confining pressure and adiabatic temperature effects have been considered in the analysis. A purposeful comprehensive numerical system consists of several individual features and in combination. The system includes a combination of field problems (thermal and seepage fields), continuum mechanics (stress analysis), seismic hazard assessment and safety evaluation. The combination uses finite elements to introduce compatible units capable of analysing infrastructure, such as RCC dams, to evaluate and predict level of safety in terms of crack pattern development. The method, which is based on a principle of birth and death process, is capable of simulating and assessing safety of RCC dams during the construction and the operation phase. The constitutive material model for concrete is based on the combination of damage mechanics and plasticity. The mathematical models for mechanical behaviour of materials are given in the form of constitutive equations. The proposed constitutive models have been reformulated and presented in convenient forms for RCC materials. Ageing, temperature and confining pressure effects were taken into account and implemented in the proposed constitutive models. All the developments and analyses are performed using coded subprograms written in FORTRAN and developed in finite element program ABAQUS. Then, the validity of the proposed computational procedures and models has been confirmed by analysing and comparing the results obtained based on available experimental and analytical evidences. After the verification process, the material nonlinearity and proposed models are applied to analyse and evaluate the related dam safety against the cracking of an existing full-size dam. Finally, conclusions are drawn and recommendations are made based on the present research. Based on the conclusions, it is revealed that the numerical procedure developed in this study for the seismic evaluation of RCC gravity dams under thermal and seepage actions provides a general framework for the analysis and design of these critical structures. The results of the evaluation indicate that different response patterns result when considering and neglecting THM (thermos-hydro-mechnical) model in seismic analysis, suggesting the significance of incorporating the thermal and seepage fields into the seismic assessment and design of concrete gravity dams.

Date of Award	2017
Original language	English