Minimal required boundary conditions for the thermal spallation process of granitic rocks

Kant, Michael A.; Rohr, Philipp Rudolf von

doi:10.1016/j.ijrmms.2015.12.009

Cited by 32 publications

(16 citation statements)

References 18 publications

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“…The Grimsel Test Site (GTS) is an underground rock laboratory located in the Aare massif of the Swiss Central Alps close to the Grimsel Pass [ Braeuer et al , ]. In this underground laboratory a wide range of research projects such as geological disposal of radioactive waste, in situ stress analysis, and geothermal stimulation experiments are conducted [ Doetsch et al , ; Ziegler et al , ; Kurosawa et al , ; Kant and Rudolf von Rohr , ]. In order to support these experiments with modeling and analysis efforts at elevated temperatures, the thermal properties of the formation have to be known for a large temperature range [ Kant and Rudolf von Rohr , ].…”

Section: Introductionmentioning

confidence: 99%

Thermal properties of Central Aare granite for temperatures up to 500°C: Irreversible changes due to thermal crack formation

Kant

Ammann

Rossi

et al. 2017

Geophysical Research Letters

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Thermal diffusivity, heat capacity, and thermal conductivity of Central Aare granite are reported in the temperature range from 25°C to 500°C. Each rock sample underwent three consecutive heating and cooling cycles. Significant irreversible changes in the properties due to thermal crack formation could be observed. After the first thermal cycle, both thermal diffusivity and conductivity dropped to about 75% of the initial value at room temperature, whereas the heat capacity did not show an irreversible decay. For subsequent thermal cycles, no further permanent changes of the investigated properties could be observed. From the conducted measurements, accurate correlations are derived, offering a platform for precise high‐temperature experiments and other research on Central Aare granite and similar granitic rocks. The report shows that the assumption of constant thermal properties leads to significant inaccuracies at elevated temperatures, especially if thermal cycles are present.

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Section: Introductionmentioning

confidence: 99%

Thermal properties of Central Aare granite for temperatures up to 500°C: Irreversible changes due to thermal crack formation

Kant

Ammann

Rossi

et al. 2017

Geophysical Research Letters

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“…If this limit is exceeded, the crack will propagate through the solid toward the closest stress drain which could be another crack or the surface of the half‐space. If the crack reaches the surface of the domain, a so‐called spall is formed, which will lead to the characteristic disintegration of the surface [ Kant and Rudolf von Rohr , ; Preston and White , ]. A dimensionless number called Spallability is introduced to describe this critical condition where crack formation is initiated.…”

Section: Derivation Of the Spalling Criterionmentioning

confidence: 99%

“…Both effects originate from the effect that Young's modulus and fracture toughness will significantly decrease at the brittle‐ductile transition or the melting temperature [ Heuze , ]. Therefore, the lowest melting temperature of all minerals present in the rock structure determines the upper temperature limit where spallation can appear [ Kant and Rudolf von Rohr , ; Rauenzahn and Tester , ]. Additionally, weak mineral components (as, e.g., in matrix supported rocks) or global fractures embedded in the rock structure will impede spalling of rocks, as the rock can expand into these components, preventing sufficiently high thermal stresses from being created.…”

Section: Sensitivity Analysis and Characteristics Of The Derived Spalmentioning

confidence: 99%

“…The spallation experiments were conducted with the setup and measurement procedure described by Kant and Rudolf von Rohr []. In this setup rock samples are rapidly exposed to a methane‐air flame jet with a temperature of about 1400°C.…”

Section: Preliminary Validation With Central Aare Granitementioning

confidence: 99%

“…Eventually, this spall will detach from the surface and expose the newly created surface [ Preston and White , ; Germanovich , ; Rauenzahn and Tester , ] (see Figure ). A possible application field of the spallation effect are thermal contactless drilling technologies [ Kant and Rudolf von Rohr , ; Hillson and Tester , ; Timoshkin et al , ; Kocis et al , ; Bybee , ], where hot fluid jets, laser beams, or plasma jets are used as the required heat source. These technologies recently came into renewed research focus, as they have the potential to significantly reduce the drilling costs [ Tester et al , ; Augustine , ; Kant et al , ] and many known problems have been overcome (e.g., ignition and drilling in an aqueous environment) [ Stathopoulos , ; Teodoriu and Cheuffa , ; Ndeda et al , ].…”

Section: Introductionmentioning

confidence: 99%

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A theory on thermal spalling of rocks with a focus on thermal spallation drilling

et al. 2017

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Thermal cracking of rocks is an intensively studied topic in different research areas and for various engineering problems. In this context, we present a modeling approach which describes thermal spalling of rocks with a focus on thermal spallation drilling. This drilling technology uses high thermal loads to locally destruct the surface of the rock formation. With the presented model, the operating conditions which are required to initiate spalling of rocks can be estimated. Additionally, a Spallability number is introduced allowing a categorization of rocks according to their ability to spall. The presented model is based on linear fracture mechanics and the stress intensity concept. It evaluates if a crack with a certain geometry embedded in a rock with specific properties propagates during exposure to different heat loads and external pressures. Thereby, rapid heat transfer processes are coupled with induced thermal stresses and fracture mechanics in rocks.

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Numerical modelling of heat shock‐assisted rock fracture

Pressacco

Saksala

2019

Num Anal Meth Geomechanics

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SummaryThis paper presents a numerical investigation on the effects of thermal shock as a pretreatment of rock prior to comminution. More specifically, the effect of heat shock‐induced cracks on the uniaxial compressive strength of rock is numerically studied. The chosen constitutive model of rock employs a (strong) embedded discontinuity finite element formulation to describe cracks. The thermomechanical problem that governs the heat shock pretreatment of rocks is considered as an uncoupled problem because of a highly dominating role of the external heat influx. Two solution methods of the global problem are presented: an explicit‐explicit dynamic scheme and an implicit‐implicit quasi‐static scheme. The model performance is tested in simulations on heterogeneous numerical rock samples subjected first to a heat shock pretreatment and then to a mechanical compression test. According to the results, the compressive strength of intact granite rock having the axial splitting failure mode can be substantially reduced by heat shock pretreatment.

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Minimal required boundary conditions for the thermal spallation process of granitic rocks

Cited by 32 publications

References 18 publications

Thermal properties of Central Aare granite for temperatures up to 500°C: Irreversible changes due to thermal crack formation

Thermal properties of Central Aare granite for temperatures up to 500°C: Irreversible changes due to thermal crack formation

A theory on thermal spalling of rocks with a focus on thermal spallation drilling

Numerical modelling of heat shock‐assisted rock fracture

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