Modeling Joint Strength and Friction in Dry and Saturated Granite Under Near-Field Explosive Loads
Abstract
Recently, a suite of experiments has been designed to extend our current understanding of P and S wave propagation from chemical explosive 'sources' into jointed granite (Climax Stock). The near-source data from the first of the Source Physics Experiments (SPE) performed at the Nevada National Security Site showed significant shear wave generation and anisotropic wave propagation roughly corresponding to joint orientation. Common approaches to explain this behavior have relied on numerical calculations to reproduce experimental data by scaling or `fitting' material models that derive from small samples of intact material with limited success. Here the joint density and orientation in the rock are well characterized and are used to explain the observed anisotropy of wave propagation. The mechanics of the joint response including friction and saturation together with the intact material model, calibrated for the laboratory-scale granite samples collected from the test site, generate waveforms very similar to those observed in the experiment. Incorporation of the discrete nature of the rock mass in the simulations is imperative to understand the experimental data and to build a predictive capability. Evaluation of the overall strength of geologic materials requires careful attention to the joints or cracks within the bulk material. Thus, we also investigate the shear behavior of single granite joints under different normal loads to simulate experiments typically used for rock characterization. The main goal of this investigation is to provide a meaningful set of parameters for multi-scale contact physics implemented in codes that can handle contact. Both dry and saturated joints are considered. Here we show that explicit incorporation of the joints the simulation of the experiments is imperative to reproduce the observed directional variations in the recorded data. The experimental records show that displacements are much higher than expected, which is attributed to water saturated joints determined from the two and three-dimensional simulations by decreasing the effective friction angle. Lowering the friction angle in the simulations also increased the resulting anisotropic wave motion that traveled more readily along paths of joint persistency. Simulation results will be compared to experimental measurements of both radial and non-radial motions from all available SPE experiments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.S43A2216H
- Keywords:
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- 7290 SEISMOLOGY / Computational seismology