Review of unloading tests of dynamic rock failure in compression

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Abstract

Dynamic rock failure at the walls of an opening, so-called rock burst or strain burst is one of the major types of rock failure capable of causing human and financial loss. Initially the rock at the place of the future excavation is in a polyaxial stress state. When excavating an opening, the rock elements at the excavation boundary are overloaded in the tangential (with respect to excavation wall) direction and unloaded in the radial direction. This situation can be reproduced by the modified true triaxial test in which only one surface of prismatic rock sample is unloaded. This paper reviews the tests under true triaxial unloading condition and the corresponding failure modes and types (static or dynamic). In these tests the violent (dynamic) ejection of rock fragments and arc-shape fractures near the free face are often observed. However these tests are affected by friction between the sample and the loading platens. We analyse the end friction effect and show that unlike the conventional end friction effect produced in uniaxial and biaxial loading tests, the true triaxial unloading test induces additional shear stress needed to prevent sliding of the rock sample from the loading platens. This additional shear stress is shown to considerably affect the geometry of fractures.

Original languageEnglish
JournalEngineering Fracture Mechanics
DOIs
Publication statusE-pub ahead of print - 31 Dec 2018

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Unloading
Compaction
Rocks
Excavation
Friction
Shear stress
Rock bursts
Failure modes
Geometry

Cite this

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title = "Review of unloading tests of dynamic rock failure in compression",
abstract = "Dynamic rock failure at the walls of an opening, so-called rock burst or strain burst is one of the major types of rock failure capable of causing human and financial loss. Initially the rock at the place of the future excavation is in a polyaxial stress state. When excavating an opening, the rock elements at the excavation boundary are overloaded in the tangential (with respect to excavation wall) direction and unloaded in the radial direction. This situation can be reproduced by the modified true triaxial test in which only one surface of prismatic rock sample is unloaded. This paper reviews the tests under true triaxial unloading condition and the corresponding failure modes and types (static or dynamic). In these tests the violent (dynamic) ejection of rock fragments and arc-shape fractures near the free face are often observed. However these tests are affected by friction between the sample and the loading platens. We analyse the end friction effect and show that unlike the conventional end friction effect produced in uniaxial and biaxial loading tests, the true triaxial unloading test induces additional shear stress needed to prevent sliding of the rock sample from the loading platens. This additional shear stress is shown to considerably affect the geometry of fractures.",
keywords = "End friction effect, Fracture growth, Fracture shape, Shear stress, True triaxial unloading test",
author = "Hongyu Wang and Arcady Dyskin and Phil Dight and Elena Pasternak and Ariel Hsieh",
year = "2018",
month = "12",
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doi = "10.1016/j.engfracmech.2018.12.022",
language = "English",
journal = "Engineering Fracture Mechanics",
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T1 - Review of unloading tests of dynamic rock failure in compression

AU - Wang, Hongyu

AU - Dyskin, Arcady

AU - Dight, Phil

AU - Pasternak, Elena

AU - Hsieh, Ariel

PY - 2018/12/31

Y1 - 2018/12/31

N2 - Dynamic rock failure at the walls of an opening, so-called rock burst or strain burst is one of the major types of rock failure capable of causing human and financial loss. Initially the rock at the place of the future excavation is in a polyaxial stress state. When excavating an opening, the rock elements at the excavation boundary are overloaded in the tangential (with respect to excavation wall) direction and unloaded in the radial direction. This situation can be reproduced by the modified true triaxial test in which only one surface of prismatic rock sample is unloaded. This paper reviews the tests under true triaxial unloading condition and the corresponding failure modes and types (static or dynamic). In these tests the violent (dynamic) ejection of rock fragments and arc-shape fractures near the free face are often observed. However these tests are affected by friction between the sample and the loading platens. We analyse the end friction effect and show that unlike the conventional end friction effect produced in uniaxial and biaxial loading tests, the true triaxial unloading test induces additional shear stress needed to prevent sliding of the rock sample from the loading platens. This additional shear stress is shown to considerably affect the geometry of fractures.

AB - Dynamic rock failure at the walls of an opening, so-called rock burst or strain burst is one of the major types of rock failure capable of causing human and financial loss. Initially the rock at the place of the future excavation is in a polyaxial stress state. When excavating an opening, the rock elements at the excavation boundary are overloaded in the tangential (with respect to excavation wall) direction and unloaded in the radial direction. This situation can be reproduced by the modified true triaxial test in which only one surface of prismatic rock sample is unloaded. This paper reviews the tests under true triaxial unloading condition and the corresponding failure modes and types (static or dynamic). In these tests the violent (dynamic) ejection of rock fragments and arc-shape fractures near the free face are often observed. However these tests are affected by friction between the sample and the loading platens. We analyse the end friction effect and show that unlike the conventional end friction effect produced in uniaxial and biaxial loading tests, the true triaxial unloading test induces additional shear stress needed to prevent sliding of the rock sample from the loading platens. This additional shear stress is shown to considerably affect the geometry of fractures.

KW - End friction effect

KW - Fracture growth

KW - Fracture shape

KW - Shear stress

KW - True triaxial unloading test

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