Rotation of the Stress Tensor in a Westerly Granite Sample During the Triaxial Compression Test

We simulated the spatiotemporal modelling of 3D stress and strain distributions during the triaxial compression laboratory test on a westerly granite sample using finite-difference numerical modelling implemented with FLAC3D software. The modelling was performed using a ubiquitous joint constitutive law with strain softening. The applied procedure is capable of reproducing the macroscopic stress and strain evolution in the sample during triaxial deformation until a failure process occurs. In addition, we calculated focal mechanisms of acoustic emission (AE) events and resolved local stress field orientations. This detailed stress information was compared with that from numerical modelling. The comparison was made based on the 3D rotation angle between the cardinal axes of the two stress tensors. To infer the differences in rotation, we applied ANOVA. We identified the two time levels as the plastic deformation phase and the after-failure phase. Additionally, we introduced the bin factor, which describes the location of the rotation scores in the rock sample. The p values of the test statistics F for the bin and phase effects are statistically significant. However, the interaction between them is insignificant. We can, therefore, conclude that there was a significant difference in the time between the rotation means in the particular bins, and we ran post hoc tests to obtain more information where the differences between the groups lie. The largest rotation of the stress field provided by the focal mechanisms of AE events from the numerically calculated stress field is observed in the edge bins, which do not frame the damage zone of the sample.

Study on the Mechanical Behavior and Acoustic Emission Properties of Granite under Triaxial Compression

To study the rock mechanical behaviors and damage process mechanism of granite samples under triaxial stress, conventional triaxial compression tests were carried out on an RMT-150B rock mechanics testing machine and acoustic emission detector. The test results show that the strength of the granite sample has a good linear relationship with the confining pressure, the cohesion force c of the granite samples is 29.37 MPa, and the internal friction angle is 54.23° by calculation based on the Mohr-Coulomb strength criterion. The larger the initial confining pressure of the rock sample is, the larger the crack initiation stress ( σ ci ) and dilatancy stress ( σ cd ) of the granite specimen are, the larger the energy values at the crack initiation point and dilatancy point are, and the larger the peak energy storage and energy release rate at the failure are. In the case of a small initial confining pressure, the AE ringdowning counts and the cumulative AE ringing counts increase to their maximum instantaneously at the peak stress point, and the damage of the sample develops rapidly. While the initial confining pressure is high, the AE ringing counts and the cumulative AE ringing counts of the granite specimens increase evenly, and the deformation damage of the granite specimens is slow. Before the crack initiation point, AE signals are mainly low-energy and low-frequency friction-type AE events, while after the dilatation point, AE signals of samples are mainly high-frequency and high-energy fracture-type AE events. The failure mode of granite samples judged by acoustic emission parameters according to the distribution of characteristic values of AE parameters RA and AF is consistent with the reality. The AE b value of the granite sample is large when the confining pressure is low, and there will be a sudden drop, the decrease time is late, and the decrease rate is large. Under the same stress level, the larger the confining pressure is, the larger the damage variable D is.

Revealing microstructural properties of shocked and tectonically deformed zircon from the Vredefort impact structure: Raman spectroscopy combined with SEM microanalyses

ABSTRACT Finite deformation patterns of accessory phases can indicate the tectonic regime and deformation history of the host rocks and geological units. In this study, tectonically deformed, seismically deformed, and shocked zircon grains from a granite sample from the core of the Vredefort impact structure were analyzed in situ, using a combination of Raman spectroscopy, backscatter electron (BSE) imaging, electron backscattered diffraction (EBSD) mapping, electron probe microanalyses (EPMA), energy-dispersive X-ray spectroscopy (EDS) qualitative chemical mapping, and cathodoluminescence (CL) imaging. We aimed to reveal the effects of marginal grain-size reduction, planar deformation bands (PDBs), and shock microtwins on the crystal structure and microchemistry of zircon. Deformation patterns such as PDBs, microtwins, and subgrains did not show any significant effect on zircon crystallinity/metamictization degree or on the CL signature. However, the ratio of Raman band intensities B1g (1008 cm–1) to Eg (356 cm–1) slightly decreased within domains with low misorientation. The ratio values were affected in shocked grains, particularly in twinned domains with high misorientation. B1g/Eg ratio mapping combined with metamictization degree mapping (full width at half maximum of B1g peak) suggest the presence of shock deformation features in zircon; however, due to the lower spatial resolution of the method, they must be used in combination with the EBSD technique. Additionally, we discovered anatase, quartz, goethite, calcite, and hematite micro-inclusions in the studied zircon grains, with quartz and anatase specifically being associated with strongly deformed domains of shocked zircon crystals.

Measurements of Radioactivity Concentrations in Granites and Sedimentary- Rocks and their Leaching Components in Egyptian Deserts

Concentrations of radionuclides in sediments and granite samples were determined by γ- ray spectrometer using High Pure Germanium Detector; HPGe, with a specially designed shield. Six different rock samples were collected from different sites: four samples of sediments from Um Bogma southwest Sinai, and two granite samples from Gabal Gattar, the northern part of the East- ern Desert of Egypt, where all samples were subject to investigation. Their samples were selected because the activity before being dissociated in sulfuric acid was less than after dissociation. The samples were dissolved in sulfuric acid with the same parameters of solid to liquid ratio; S/L, acid concentration, and leaching time. After the leaching process, the pregnant solution was separated from the residual, and the latter was dried. The two units, named the pregnant solutions and residu- als, were also measured radiometrically using the HPGe detector to determine the activity concen- trations (Bq/kg) of the different radionuclides of the six samples. The results showed that the rela- tion between the sum of activities of both pregnant solutions and residuals with the originals have different categories. In the sediment samples; the activity of solution+ residual was 72.37% from the original of siltstone, the activity of solution + residual was 90.02% from the original claystone sample, the activity of solution + residual was 92.6% from the original of shale, the activity of solu- tion + residual was 74.07% from the original claystone. In the granite samples, the activity of solu- tion + residual was 130.39% from the original of the first granite sample and 142.3% from the orig- inal of the second granite sample. This phenomenon varied in magnitude due to the different radio- nuclides in each sample. These variations depend mainly on the nature of the grain surfaces in the different rock types and their Pb content. As for leachability analysis, leaching experiments have been performed using sulfuric acid. The leaching efficiency (%) of uranium is estimated by the measurements of the HPGe detector. The result showed almost constant values for leachability. The non-frequent appearance of attenuation of gamma activities during leaching processes indicates that the acid solutions may have led to clean the grain surfaces and thus permit gamma activities of the inner grains to be measured. The treatment of the samples before measurements may have been needed.

Defining Stress Thresholds of Granite Failure Process Based on Acoustic Emission Activity Parameters

In order to study the crack closure stress threshold σcc of hard rock, crack initiation stress threshold σci, stress threshold σcs of crack interaction, and damage stress threshold σc d, uniaxial compression test was carried out on granite samples. Stress sensor and dynamic strain gauge are used to measure the load, longitudinal, and lateral deformation of rock in real time. The acoustic emission characteristic parameters of rock fracture process are obtained by using the acoustic emission system. According to the change rule of the AE event rate, cumulative energy, energy rate, duration, and amplitude in the whole process of granite sample fracture, the stress threshold (σcc, σci, σcs, and σc d) of each loading stage in the process of rock sample fracture is obtained. The relationship between the stress threshold (σcc, σci, σcs, and σc d) of each stage and the uniaxial compressive strength σUCS of rock samples in the whole process of fracture is analyzed, which shows that the deformation characteristics and crack evolution law of the rock are unified. The research results can provide some reference for further understanding of rock damage evolution mechanism in engineering field.

Characterization of Silica Exposure during Manufacturing of Artificial Stone Countertops

Artificial stone is increasing in popularity in construction applications, including commercial and residential countertops. Eco-friendliness, durability, and resistance to staining, make artificial stone attractive to consumers. Health concerns have arisen during manufacturing of artificial stone due to increased incidence of silicosis after relatively short exposure. Three artificial stone samples (A, B, and C) and one natural granite sample were subjected to cutting and grinding in a controlled environment. Gravimetric analysis, X-Ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy were employed to determine crystalline silica concentrations and particle morphology of bulk and respirable particles. Silica content of bulk dust from artificial samples A and B was 91%, sample C was <10%, while granite was 31%. Silica percent in the respirable fraction for samples A and B was 53% and 54%, respectively, while sample C was <5% and granite was 8%. Number concentrations for samples A and B were mainly in the nano-fraction, indicating potential for translocation of silica particles to other organs outside of the lungs. Respirable dust concentrations inside the chamber were well above Occupational Safety and Health Administration standards for all materials, indicating that confined-space exposures require ventilation to lower risks of acute silicosis regardless of the nature of the stone.

Quantitative Minerological Analysis of Some Granite Rocks of Deoghar Jharkhand

Crystalline minerals in granite rocks has been quantatively analysed by powder X-ray diffraction (XRD) and Scanning Electron Microscope supported with Energy Dispersed Spectroscopy (SEM-EDS). SEM microphotograph reveals that rock is dominated by brightly illuminated quartz imbedded in the matrix with mica and other minor minerals. The X-ray mineral composition data have been plotted with SEM-EDS mineral composition, data shows that the composition obtained by two technique are in consistent within the experimental limit and in good agreement. Further plot of chemical composition of constituent oxides of granite sample by XRD and SEM-EDS confirm the consistency of two technique and similarity with Jharkhand mean granite composition. Silica composition have been plotted with trace element Pb, Ba, Zr, Rb, and Alumina composition with Pb , Ba, Zr and Rb shows that these elements are randomly imbedded in the matrix with almost uniform composition. Al2O 3 composition have been plotted with Ba, Pb, and Zr shows almost constant composition in all the five samples. Based on XRD and SEM-EDS results, it was reveals that granite sample from the study areas are peraluminius rocks composed of mainly quartz, muscovite, kaolinite, chlorite and albite.