Comparison of Hydraulic and Conventional Tensile Strength Tests

Molenda, Michael; Stöckhert, Ferdinand; Brenne, S.; Alber, Michael

doi:10.5772/56300

Cited by 11 publications

(15 citation statements)

References 6 publications

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“…However, successful application of the method remains strongly dependent on the precision of specimen preparation. This fact was investigated in [3]. and was also observed during the conducted tests (Figure 4).…”

Section: Discussionsupporting

confidence: 59%

“…A series of STT and MTT tests were carried out with 28 % higher value of tensile strength by STT. Thus, overestimation of tensile strength by the indirect method was indicated, as was stated in previous studies [3,8].…”

Section: Discussionsupporting

confidence: 55%

“…Eccentricity of drilling was found by investigation of the specimen after the test (Figure 4). Hence, distribution of load in the specimen was not uniform during the test and concentration of stress probably caused failure under the lower level of loading [3]. Therefore, only the results of tests 1 and 3 were considered as valid.…”

Section: Resultsmentioning

confidence: 99%

“…The splitting tensile tests were carried out with respect to testing standard requirements ČSN EN 12390-6. The modified tension test procedure was carried out according to suggestions and reported experience published in previous studies [3,8]. The tension annulus in the specimens was prepared with a thickness of 13 mm.…”

Section: Determination Of Sprayed Concrete Tensile Strengthmentioning

confidence: 99%

“…However, indirect methods may result in different values of tensile strength and they often overestimate parameter values [1]. Comprehensive comparative studies have been carried out also in the field of rock mechanics [2,3]. Thus, direct tensile testing is still important.…”

Section: Introductionmentioning

confidence: 99%

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A Comparison of Testing Methods for Determination of Sprayed Concrete Tensile Strength

Závacký¹

2019

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Sprayed concrete is important construction material in tunnelling. Primary lining is essential in NATM where the sprayed concrete can be loaded by tension due to bending moments. The tension is common reason of failure because concrete has a relatively low tensile strength. The tensile strength is usually determined by splitting tensile test in laboratory. However, the results can be distorted because the specimen is not loaded by pure tension in this case. The paper compares results of concrete tensile strength determined by two methods: indirect by the splitting tensile test and direct by the modified tensile test.

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Section: Discussionsupporting

confidence: 59%

Section: Discussionsupporting

confidence: 55%

Section: Resultsmentioning

confidence: 99%

Section: Determination Of Sprayed Concrete Tensile Strengthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Comparison of Testing Methods for Determination of Sprayed Concrete Tensile Strength

Závacký¹

2019

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The Role of Rock Matrix Permeability in Controlling Hydraulic Fracturing in Sandstones

et al. 2021

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A concomitant effect of a hydraulic fracturing experimenting is frequently fluid permeation into the rock matrix, with the injected fluid permeating through the porous rock matrix (leak-off) rather than contributing to the buildup of borehole pressure, thereby slowing down or impeding the hydro-fracturing process. Different parameters, such as low fluid viscosity, low injection rate and high rock permeability, contribute to fluid permeation. This effect is particularly prominent in highly permeable materials, therefore, making sleeve fracturing tests (where an internal jacket separates the injected fluid in the borehole from the porous rock matrix) necessary to generate hydraulic fractures. The side effect, however, is an increase in pressure breakdown, which results in higher volume of injected fluid and in higher seismic activity. To better understand this phenomenon, we report data from a new comparative study from a suite of micro-hydraulic fracturing experiments on highly permeable and on low-permeability rock samples. Experiments were conducted in both sleeve fracture and direct fluid fracture modes using two different injection rates. Consistent with previous studies, our results show that hydraulic fracturing occurred only with low permeation, either due to the intrinsic low permeability or due to the presence of an inner silicon rubber sleeve. In particular, due to the presence of quasi-impermeable inner sleeve or borehole skin in the sleeve fracturing experiment, fracturing occurs, with the breakdown pressure supporting the linear elastic approach considering poroelastic effects, therefore, with low stress drop and consequently low microseismicity. Rock matrix permeability also controls the presence of precursory Acoustic Emission activity, as this is linked to the infiltration of fluids and consequent expansion of the pore space. Finally, permeability is shown to mainly control fracturing speed, because the permeation of fluid into the newly created fracture via the highly permeable rock matrix slows down its full development. The application of these results to the field may help to reduce induced seismicity and to conduct well stimulation in a more efficient way.

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