The effect of discontinuities on friction, wave propagation, and fluid flow
Abstract
Research was conducted to study several physical phenomena related to discontinuities such as joints and fractures in rocks. These phenomena include the precursory change of shear-wave amplitude during frictional sliding, the existence of interface waves between two non-welded solids, and the flow of fluid through a single fracture with non-uniform apertures. First, a series of experiments were conducted using shear waves to detect sudden movements along a discontinuity between two granite blocks. Second, a parametric study was undertaken to analyze the existence of interface waves between two elastic solids for a range of material properties and interface conditions. Finally, the relationship between the volume of flow and the distribution of apertures using a numerical simulator in a fracture was studied. Three major findings resulted from this research. First, a precursory decrease in shear-wave amplitude is observed to occur prior to slip along interfaces between granite blocks because of changes in the condition of interface. Second, the existence of interface waves along a fracture is initially related to the material properties and fracture stiffness. Third, the volume of flow through a fracture depends on the spatial distribution of the void spaces. Predicting frictional movement along joints, faults or fractures is applicable to engineering projects that involve rock slope and tunnel stability, as well as research in the area of fault stability. The observed precursory change in shear-wave amplitude had a duration of 0.1 second to 10 seconds prior to slip. An area for future research is to determine if this precursor to slip would increase in duration as the length scale increases. The parametric study on the existence of interface waves indicates that these waves could be used as an additional probe for detecting shear movement along interfaces. Finally, fluid flow through a fracture depends strongly on the spatial correlations in aperture distribution. To apply the simulation to natural fractures, it will require the comparison of the flow simulation results with experimental measurements to ascertain the validity of simulation.
Degree
Ph.D.
Advisors
Lovell, Purdue University.
Subject Area
Civil engineering
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