Reconciliation of contrasting theories for fracture spacing in layered rocks

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Title: Reconciliation of contrasting theories for fracture spacing in layered rocks
Authors: Schöpfer, Martin P. J.
Arslan, Arzu
Walsh, John J.
Childs, Conrad
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Date: Apr-2011
Online since: 2011-07-19T16:19:17Z
Abstract: Natural and man-made brittle layers embedded in a weaker matrix and subjected to layer-parallel extension typically develop an array of opening-mode fractures with a remarkably regular spacing. This spacing often scales with layer thickness, and it decreases as extension increases until fracture saturation is reached. Existing analytical one-dimensional (1-D) 'full-slip' models, which assume that interfacial slip occurs over the entire length of the fracture-bound blocks, predict that the ratio of fracture spacing to layer thickness at saturation is proportional to the ratio of layer tensile to interface shear strength (T/s). Using 2-D discontinuum mechanical models run for conditions appropriate to layered rocks, we show that fracture spacing at saturation decreases linearly with decreasing T/s ratio, as predicted by 1-D models. At low T/s ratios (ca. <3.0), however, interfacial slip is suppressed and the heterogeneous 2-D stress distribution within fracture-bound blocks controls further fracture nucleation, as predicted by an existing 2-D 'fracture infill criterion'. The applicability of the two theories is hence T/s ratio dependent. Our models illustrate that fracture spacing in systems permitting interfacial slip is not necessarily an indicator of fracture system maturity. Fracture spacing is expected to decrease with increasing overburden pressure and decreasing layer tensile strength.
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Funding Details: Science Foundation Ireland
Type of material: Journal Article
Publisher: Elsevier
Journal: Journal of Structural Geology
Volume: 33
Issue: 4
Start page: 551
End page: 565
Copyright (published version): 2011 Elsevier Ltd.
Keywords: Fracture spacingRock jointsShear lag modelDistinct element method
Subject LCSH: Fracture mechanics
Rock mechanics
Joints (Geology)
Shear (Mechanics)
DOI: 10.1016/j.jsg.2011.01.008
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Language: en
Status of Item: Peer reviewed
Appears in Collections:Earth Sciences Research Collection

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