triaxial deformation
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Author(s):  
C. Geel ◽  
E.M. Bordy ◽  
S. Nolte

Abstract Permian black shales from the lower Ecca Group of the southern main Karoo Basin (MKB) have a total organic carbon (TOC) of up to ~5 wt% and have been considered primary targets for a potential shale gas exploration in South Africa. This study investigates the influence of shale composition, porosity, pressure (P) and temperatures (T) on their geomechanical properties such as compressive strength and elastic moduli. On average, these lower Ecca Group shales contain a high proportion, ~50 to 70 vol%, of mechanically strong minerals (e.g., quartz, feldspar, pyrite), ~30 to 50 vol% of weak minerals (e.g., clay minerals, organic matter) and ~0 to 50 vol% of intermediate minerals (e.g., carbonates), which have highly variable mechanical strength. Constant strain rate, triaxial deformation tests (at T ≤100°C; P ≤50 MPa) were performed using a Paterson-type high pressure instrument. Results showed that the Prince Albert Formation is the strongest and most brittle unit in the lower Ecca Group in the southern MKB followed by the Collingham and then the Whitehill Formation. Compressive strength and Young’s moduli (E) increase with increasing hard mineral content and decrease with increasing mechanically weak minerals and porosity. On comparison with some international shales, for which compositional and geomechanical data were measured using similar techniques, the lower Ecca Group shales are found to be geomechanically stronger and more brittle. This research provides the foundation for future geomechanical and petrophysical investigations of these Permian Ecca black shales and their assessment as potential unconventional hydrocarbon reservoirs in the MKB.


Author(s):  
Yoshiko Kanada-En'yo ◽  
Kazuyuki Ogata

Abstract The triaxial and hexadecapole deformations of the Kπ = 0+ and Kπ = 2+ bands of 24Mg have been investigated by the inelastic scatterings of various probes, including electrons, protons, and alpha(α) particles, for a prolonged time. However, it has been challenging to explain the unique properties of the scatterings observed for the 41+ state through reaction calculations. This paper investigates the structure and transition properties of the Kπ = 0+ and Kπ = 2+ bands of 24Mg employing the microscopic structure and reaction calculations via inelastic proton and α scattering. In particular, the E4 transitions to the 41+ and 42+ states are reexamined. The structure of 24Mg was calculated employing the variation after the parity and total angular momentum projections in the framework of the antisymmetrized molecular dynamics (AMD). The inelastic proton and α reactions were calculated by the microscopic coupled-channel (MCC) approach by folding the Melbourne g-matrix NN interaction with the AMD densities of 24Mg. Reasonable results were obtained on the properties of the structure, including the energy spectra and E2 and E4 transitions of the Kπ = 0+ and Kπ = 2+ bands owing to the enhanced collectivity of triaxial deformation. The MCC+AMD calculation successfully reproduced the angular distributions of the 41+ and 42+ cross sections of proton scattering at incident energies of Ep = 40–100MeV and α scattering at Eα = 100–400 MeV. This is the first microscopic calculation to describe the unique properties of the 01+ → 41+ transition. In the inelastic scattering to the 41+ state, the dominant two-step process of the 01+→ 21+→ 41+ transitions and the deconstructive interference in the weak one-step process were essential.


2021 ◽  
Author(s):  
Michael Heap ◽  
Tobias Baumann ◽  
Marina Rosas-Carbajal ◽  
Jean-Christophe Komorowski ◽  
H. Albert Gilg ◽  
...  

<p>Volcanoes are inherently unstable structures that spread and frequently experience mass wasting events (such as slope failure, rockfalls, and debris flows). Hydrothermal alteration, common to many volcanoes, is often invoked as a mechanism that contributes significantly to volcano instability. We present here a study that combines laboratory deformation experiments, geophysical data, and large-scale numerical modelling to better understand the influence of hydrothermal alteration on volcano stability. La Soufrière de Guadeloupe (France) is a hazardous andesitic volcano that hosts a large hydrothermal system and therefore represents an ideal natural laboratory for our study. Uniaxial and triaxial deformation experiments were performed on samples prepared from 17 variably-altered (alteration minerals include quartz, cristobalite, tridymite, hematite, pyrite, alunite, natro-alunite, gypsum, kaolinite, and talc) blocks collected from La Soufrière de Guadeloupe. Our uniaxial compressive strength experiments show that strength and Young’s modulus decrease as a function of increasing porosity and increasing alteration. Triaxial deformation experiments show that cohesion decreases as a function of increasing alteration, but that the angle of internal friction does not change systematically. We first combined recent muon tomography data with our laboratory data to create a 3D strength map of La Soufrière de Guadeloupe. The low-strength zone beneath the southern flank of the volcano exposed by our 3D strength map is coincident with the hydrothermal system. We then assigned laboratory-scale and upscaled mechanical properties (e.g., Young’s modulus, cohesion, and angle of internal friction) to zones identified by a recent electrical survey of the dome of La Soufrière de Guadeloupe. Numerical modelling (using the software LaMEM) was then performed on a cross-section of the volcano informed by the recent electrical data, and on a cross-section in which we artificially increased the size of the hydrothermally altered zone. Our modelling shows (1) the importance of using upscaled values in large-scale models and (2) that hydrothermal alteration significantly increases the surface velocity and strain rate of the volcanic slope. We therefore conclude, using models informed by experimental data, that hydrothermal alteration decreases volcano stability and thus expedites volcano spreading and increases the likelihood of mass wasting events and associated volcanic hazards. Hydrothermal alteration, and its evolution, should therefore be monitored at active volcanoes worldwide.</p>


2021 ◽  
Vol 103 (1) ◽  
Author(s):  
M. Rocchini ◽  
K. Hadyńska-Klȩk ◽  
A. Nannini ◽  
A. Goasduff ◽  
M. Zielińska ◽  
...  

2021 ◽  
Vol 70 (19) ◽  
pp. 192101-192101
Author(s):  
Shen Shui-Fa ◽  
◽  
Wang Hua-Lei ◽  
Meng Hai-Yan ◽  
Yan Yu-Peng ◽  
...  
Keyword(s):  

Tectonics ◽  
2020 ◽  
Vol 39 (11) ◽  
Author(s):  
Alexis Del Pilar‐Martínez ◽  
Angel F. Nieto‐Samaniego ◽  
Susana A. Alaniz‐Alvarez

2020 ◽  
Vol 8 (3) ◽  
pp. 40-46
Author(s):  
Mikhail Berlinov ◽  
Marina Belinova ◽  
A. Tvorogov ◽  
E. Petschkina

The problem of linearization of resolving equations for calculating operational reinforced concrete structures under three-axis deformation, taking into account corrosion damage, is considered. A method for accounting for corrosion damage based on a phenomenological approach for deformations under triaxial deformation is presented.


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