The contribution is focused on investigation of strains in a rock specimen during uniaxial compression test. Three components of strain occur in cylindrical shape specimen: axial, radial and volumetric. Determination of the strains is possible by using of local sensors. Strain gauges fixed on specimen surface were used in this study. Axial and radial components of strain were measured directly, and volumetric strain was calculated. Two types of rock were tested, syenite and sandstone, to illustrate variability of strain behaviour of rocks. Strain measurement is necessary for determination of Young's modulus and Poisson's ratio. Moreover, early states of failure can be identified by volumetric strain which is considerably sensitive to failure states.
This contribution brings overview of mechanical properties of greywacke with focus on fracture mechanics parameters. Investigated rock type is clastic sediment, relatively widespread in Moravia region. The rock type is significantly utilized in construction industry. For purposes of this study, Kobeřice quarry was selected as sampling locality. Mechanical properties were investigated by deformation controlled 3-point bending test. Chevron notch was created on specimens in order to study fracture mechanics parameters. Moreover, deformation controlled uniaxial compression tests were carried out, as well. Specimens were equipped with strain gauges; thus, elastic modulus and the Poisson’s ratio could be determined. Splitting tensile test was employed in order to determine tensile strength. Mean value of fracture toughness KIC was determined to 1.85 MPa·m0.5. Mean value of uniaxial compressive strength was observed at level of 211 MPa and tensile strength reached 19.4 MPa. Hence, the tested greywacke was considered as high strength rock. Brittle type of failure occurred during the tests. The obtained results were compared with values reported for clastic sediments from several localities in the Czech Republic. Moravian greywacke reached significantly high strength in comparison to other clastic sedimentary rocks and can be considered as valuable raw material for purposes of construction industry.
The paper brings description of the mechanical properties of greywacke sampled in Kobeřice quarry (Lower Carboniferous Culm Basin, Drahany Uplands, Bohemian Massif). Anisotropy of mechanical properties was identified from series of laboratory tests of oriented samples using following procedures:(1) indirect tensile testing, (2) uniaxial compressive testing and (3) triaxial compressive testing. Parameters of Mohr-Coulomb and Hoek-Brown failure criteria were determined by evaluation of the obtained laboratory data. The tested greywacke performed relatively high uniaxial compressive strength, roughly 200 MPa. Better fitting by Mohr-Coulomb criterion was identified than by Hoek-Brown one within the investigated interval of confining stresses (0-15 MPa). In addition, Schmidt hammer test was carried out with comparison of several correlation relationships to uniaxial compressive strength which were compared with directly obtained value from laboratory tests.
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