Bridges outside fracture process zone: Their existence and effect

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Abstract

Bridges connecting opposite sides of the crack surface are normally found near the crack tip (e.g. in the hydraulic fracture); their extension and breakage are considered to constitute the mechanism of formation of the fracture process zone. Bridges however may be distributed all over the crack. It primarily relates to natural fractures in rocks and rock masses, which are usually non-persistent. This paper reports series of laboratory experiments showing the presence of distributed bridges in the hydraulic fractures induced in mortar and three different types of rock samples. This is confirmed by direct observations via X-ray micro-CT scans as well as by tensile tests of the samples which remain in one piece after hydraulic fracturing. A model of hydraulic fractures with bridge-produced constricted opening is proposed and the effect of bridges is investigated. It is shown that there exists a characteristic length associated with the combined action of bridges such that the effect of bridges is considerable only for the cracks whose dimensions exceed the characteristic length.

Original languageEnglish
JournalEngineering Fracture Mechanics
DOIs
Publication statusE-pub ahead of print - 28 Apr 2019

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Rocks
Hydraulics
Cracks
Hydraulic fracturing
Computerized tomography
Mortar
Crack tips
X rays
Experiments

Cite this

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title = "Bridges outside fracture process zone: Their existence and effect",
abstract = "Bridges connecting opposite sides of the crack surface are normally found near the crack tip (e.g. in the hydraulic fracture); their extension and breakage are considered to constitute the mechanism of formation of the fracture process zone. Bridges however may be distributed all over the crack. It primarily relates to natural fractures in rocks and rock masses, which are usually non-persistent. This paper reports series of laboratory experiments showing the presence of distributed bridges in the hydraulic fractures induced in mortar and three different types of rock samples. This is confirmed by direct observations via X-ray micro-CT scans as well as by tensile tests of the samples which remain in one piece after hydraulic fracturing. A model of hydraulic fractures with bridge-produced constricted opening is proposed and the effect of bridges is investigated. It is shown that there exists a characteristic length associated with the combined action of bridges such that the effect of bridges is considerable only for the cracks whose dimensions exceed the characteristic length.",
keywords = "Characteristic length, Constricted crack opening, Hydraulic fracture, Rock bridges, Winkler layer",
author = "Junxian He and Elena Pasternak and Arcady Dyskin",
year = "2019",
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doi = "10.1016/j.engfracmech.2019.04.027",
language = "English",
journal = "Engineering Fracture Mechanics",
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TY - JOUR

T1 - Bridges outside fracture process zone

T2 - Their existence and effect

AU - He, Junxian

AU - Pasternak, Elena

AU - Dyskin, Arcady

PY - 2019/4/28

Y1 - 2019/4/28

N2 - Bridges connecting opposite sides of the crack surface are normally found near the crack tip (e.g. in the hydraulic fracture); their extension and breakage are considered to constitute the mechanism of formation of the fracture process zone. Bridges however may be distributed all over the crack. It primarily relates to natural fractures in rocks and rock masses, which are usually non-persistent. This paper reports series of laboratory experiments showing the presence of distributed bridges in the hydraulic fractures induced in mortar and three different types of rock samples. This is confirmed by direct observations via X-ray micro-CT scans as well as by tensile tests of the samples which remain in one piece after hydraulic fracturing. A model of hydraulic fractures with bridge-produced constricted opening is proposed and the effect of bridges is investigated. It is shown that there exists a characteristic length associated with the combined action of bridges such that the effect of bridges is considerable only for the cracks whose dimensions exceed the characteristic length.

AB - Bridges connecting opposite sides of the crack surface are normally found near the crack tip (e.g. in the hydraulic fracture); their extension and breakage are considered to constitute the mechanism of formation of the fracture process zone. Bridges however may be distributed all over the crack. It primarily relates to natural fractures in rocks and rock masses, which are usually non-persistent. This paper reports series of laboratory experiments showing the presence of distributed bridges in the hydraulic fractures induced in mortar and three different types of rock samples. This is confirmed by direct observations via X-ray micro-CT scans as well as by tensile tests of the samples which remain in one piece after hydraulic fracturing. A model of hydraulic fractures with bridge-produced constricted opening is proposed and the effect of bridges is investigated. It is shown that there exists a characteristic length associated with the combined action of bridges such that the effect of bridges is considerable only for the cracks whose dimensions exceed the characteristic length.

KW - Characteristic length

KW - Constricted crack opening

KW - Hydraulic fracture

KW - Rock bridges

KW - Winkler layer

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