Anisotropy of mechanical properties of greywacke

Havlíčková, Dagmar; Závacký, Martin; Krmíček, Lukáš

doi:10.35180/gse-2019-0005

Cited by 3 publications

(1 citation statement)

References 8 publications

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“…The strength of a rock derived from a uniaxial compression test (e.g., [44]) 70 to 134 [45] Average ≈ 200 (range 41-209) [46] 2.33 to 151.6 [47] MPa…”

Section: Uniaxial Compressive Strengthmentioning

confidence: 99%

Use of Mohr Diagrams to Predict Fracturing in a Potential Geothermal Reservoir

2021

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Inferences have to be made about likely structures and their effects on fluid flow in a geothermal reservoir at the pre-drilling stage. Simple mechanical modelling, using reasonable ranges of values for rock properties, stresses and fluid pressures, is used here to predict the range of possible structures that are likely to exist in the sub-surface and that may be generated during stimulation of a potential geothermal reservoir. In particular, Mohr diagrams are used to show under what fluid pressures and stresses different types and orientations of fractures are likely to be reactivated or generated. The approach enables the effects of parameters to be modelled individually, and for the types and orientations of fractures to be considered. This modelling is useful for helping geoscientists consider, model, and predict the ranges of mechanical properties of rock, stresses, fluid pressures, and the resultant fractures that are likely to occur in the sub-surface. Here, the modelling is applied to folded and thrusted greywackes and slates, which are planned to be developed as an Enhanced Geothermal System beneath Göttingen.

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“…The strength of a rock derived from a uniaxial compression test (e.g., [44]) 70 to 134 [45] Average ≈ 200 (range 41-209) [46] 2.33 to 151.6 [47] MPa…”

Section: Uniaxial Compressive Strengthmentioning

confidence: 99%

Use of Mohr Diagrams to Predict Fracturing in a Potential Geothermal Reservoir

2021

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Schmidt Rebound Hardness Dependence on the Core-Size: A Correction Model Presented and Tested on Greywacke

Brabec,

Krmíček

2024

Journal of Testing and Evaluation

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We determined the effect of the core sample dimensions on the measured values of the Schmidt rebound hardness and proposed a way to correct it to obtain unaffected value. The effect was previously investigated on cubes, where a clear dependence of the rebound hardness on the cube edge was proved. For cylindrical bodies, however, the problem is more complex. In order to determine and verify our model, a set of cylindrical samples was made from greywacke. After applying the correction, an improvement in the mean rebound hardness of the whole set was achieved from 80 to 98.8 % of the unaffected mean rebound value.

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Experimental Pilot Thermomechanical Study of Lower Carboniferous Greywacke: Temperature Effect on the Rock Mass Properties Investigated up to 1,200°C

Brabec,

Krmíček,

Sokolář

et al. 2024

Journal of Testing and Evaluation

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Greywacke, i.e., a non- to anchi-metamorphosed immature sandstone that contains more than 15 % clay minerals, occurs in most orogenic belts, with depositional ages ranging from Precambrian to recent. Our study focuses on thermomechanical rock properties of greywacke sampled in Kobeřice quarry (Lower Carboniferous Culm Basin, Drahany Upland, Bohemian Massif). Both relatively fine-grained and coarse-grained (with higher abundance of lithic fragments and small pebbles) intact rock core samples were tested. The experiment was divided into two sets. The first set made of the coarse-grained greywacke gave insight into the changes of properties across the whole temperature range, up to 1,200°C. The second set of samples was used to study the behavior of the fine-grained greywacke in the lower temperature range, up to 400°C. The lower temperature analysis showed an unexpected phenomenon at 200°C to 300°C, manifested by decrease in the strength coupled with higher values of deformation characteristics. These trends reverted at 400°C. The described phenomenon may have been caused by changes in water content combined with clay minerals composition alternation. Alternatively, it could be also related to the rock “paleotemperature memory.” On the wider temperature range, the greywacke holds relatively well to the lower temperatures, with the strengths decreasing slowly after 400°C and more rapidly after 800°C. At 1,200°C, partial melting at grain boundaries accompanied by formation of larger pores in the sample center was observed. Results of thermomechanical studies can be crucial during the design of underground constructions or for assessment of the fire damage on a rock-based constructions.

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Anisotropy of mechanical properties of greywacke

Cited by 3 publications

References 8 publications

Use of Mohr Diagrams to Predict Fracturing in a Potential Geothermal Reservoir

Use of Mohr Diagrams to Predict Fracturing in a Potential Geothermal Reservoir

Schmidt Rebound Hardness Dependence on the Core-Size: A Correction Model Presented and Tested on Greywacke

Experimental Pilot Thermomechanical Study of Lower Carboniferous Greywacke: Temperature Effect on the Rock Mass Properties Investigated up to 1,200°C

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