Blasting is one of the major threats to the safety of dams. It may lead to excessive settlement, damage to soil fabric, failure of water-proof structures, and increase of pore pressure in the dam body, which may reduce the stability of the dams. As blast-induced failures of dams can cause severe destruction and a large number of fatalities, the response of embankment dams subjected to blasting and the possible failure process should be studied thoroughly. The primary objectives of this doctoral research are to develop and implement a constitutive model for soil under high strain-rate loading, to investigate the responses of a concrete-faced rockfill dam and a core rockfill dam to blast loading and to develop a simple numerical model for the piping failure of an embankment dam subjected...[ Read more ]

Blasting is one of the major threats to the safety of dams. It may lead to excessive settlement, damage to soil fabric, failure of water-proof structures, and increase of pore pressure in the dam body, which may reduce the stability of the dams. As blast-induced failures of dams can cause severe destruction and a large number of fatalities, the response of embankment dams subjected to blasting and the possible failure process should be studied thoroughly. The primary objectives of this doctoral research are to develop and implement a constitutive model for soil under high strain-rate loading, to investigate the responses of a concrete-faced rockfill dam and a core rockfill dam to blast loading and to develop a simple numerical model for the piping failure of an embankment dam subjected to blasting.

Sand under high strain-rate loadings such as blasting and impacts tends to exhibit higher shear strength and dilation tendency than that under low strain-rate loadings such as the loading in conventional laboratory triaxial tests. A rate-dependent bounding surface plasticity model is proposed in this doctoral research to simulate the stress-strain behavior of sand under high strain-rate loadings. In this model, the model surfaces, i.e. the critical surface, the dilation surface and the bounding surface, are first defined following the bounding surface framework. Then rate-dependent features are added to the elastic moduli and the model surfaces by incorporating explicitly the strain rate into the model formulations.

The proposed rate-dependent bounding surface model is implemented on a generic finite element platform, LS-DYNA, to simulate blasting and impact problems. The implementation follows an explicit modified Euler stress integration scheme. Procedures of stress updating and correction of yield surface drift are established for the rate-dependent bounding surface model. As an application example, drained triaxial tests on a crushed coral sand under different strain rates are simulated. Characteristics of soil behaviour under high strain rates are reproduced. Simulation results show that the strain rate influences not only the plastic behaviour of soil, but also the uniformity of stresses and strains in the soil specimens.

Finite element simulations are performed in this doctoral research to look into the response of a high-rise zoned concrete-faced rockfill dam to a near-field underwater explosion. In the simulations, the energy release and the expansion of the production gas in an explosion process are reproduced. The dam materials are modeled using the constitutive model proposed in this research. According to the simulation results, the maximum values of peak ground acceleration, peak ground velocity and peak displacement occur in the area nearest to the blast location. As the distance to the center of blasting increases, the peak particle velocity and acceleration, the predominant frequency and the band width of the Fourier spectra decrease. The concrete face slab may fail because of the large strains or the slippage along the dam surface, increasing the risk of seepage failure of the dam. Contact blasting on the concrete faced rockfill dam is also simulated using a simplified plasticity soil model. The formation of craters and the generation of waves in the reservoir are examined in particular. Extensive damage to the concrete face can result from the contact blasting.

The response of a high-rise core rockfill dam to upstream underwater explosion is also investigated. The propagation of blast waves in the dam body is reproduced and examined. The direction of wave propagation alters at the phreatic line in the clayey core because of the refraction of the waves propagating from the saturated zone to the dry materials. In the saturated part of the dam body, pore pressures of magnitude in megapascals are generated when the wave front arrives. A large part of the dam under the phreatic line experiences large peak and residual pore pressures, indicating a high risk of the liquefaction of the upstream filters.

Piping is one of the possible causes of failure of an embankment dam subjected to blast loading. A physically-based numerical model for analyzing the piping process initiated by concentrated leak erosion is developed. In this model, the evolution of piping is caused by wall surface erosion and collapses of soil due to loss of support. The variation of soil properties is also included in the model. The outflow hydrograph and piping characteristics (i.e. pipe geometry, time of formation, etc.) can be predicted using this new model, which helps assess the risk of dam-breaching floods.