Seismic analysis of gravity dam-reservoir-foundation systems using scaled boundary finite element method

Abstract

A gravity dam is designed to retain water by using its self-weight to resist hydro-pressure of the reservoir. When an earthquake occurs, the energy emanated from the earthquake source may reach the dam site and cause the dam to vibrate. The earthquake action at the site is often the most critical loading case in the design of gravity dams. The estimation of the dynamic responses of gravity dams to earthquakes is necessary for achieving optimal upgrades and maintenance, and for improving our confidence in knowing that a dam will survive the impact of an earthquake of a specified magnitude.

This thesis develops an efficient approach to the seismic analysis of gravity dam-reservoir-foundation systems with an emphasis on the seismic input modelling and adaptive damage simulation of dams. The whole system is divided into a bounded domain including the dam body and adjacent parts of reservoir and foundation, and an unbounded domain of reservoir and an unbounded domain of foundation.

The dynamic properties of the unbounded domains are simulated by artificial boundaries formulated in the framework of Scaled Boundary Finite Element Method (SBFEM). The seismic waves are considered as plane waves in both two-dimensional and three-dimensional media. The seismic waves are inputted to the bounded domains by means of the Domain Reduction Method (DRM) through a single layer of elements adjacent to the interface between the bounded domain and the unbounded domain of foundation.

The fully automatic quadtree/octree mesh technique is employed to discretize the complex geometry of the bounded domain including the dam and geological features in the foundation. The scaled boundary finite element method is applied in the bounded domain and overcomes the issue of hanging node faced by standard finite elements.

The continuum damage mechanics is applied to model concrete and rocks as quasi-brittle materials. An h-adaptive strategy is developed for damage analysis to improve the computational efficiency. A progressive damage process is simulated through a series of optimal meshes. The proposed strategy simplifies the implementation of the adaptive analysis in automatic mesh refinement and data transfer.

As the final outcome of this thesis, an automatic and efficient SBFEM formulation for seismic analysis of gravity dam-reservoir-foundation interaction systems has been developed. Case studies of gravity dams are performed.