In-situ Primary Stress Detection Based on Seismic Tomography Measurements and Numerical Back-analysis for an Underground Radwaste Repository

In order to understand how the in-situ primary stress state has evolved with subsidence and uplift in a granitic rock mass for anticipated of a radioactive waste repository in Hungary, the authors investigated the applicability of seismic tomography as an interpretive tool. Very high P wave velocity (Vp) values were obtained during the tomographic scanning of the study area of the repository, and these were compared with existing findings of in-situ and laboratory seismic measurements.Apart from seismic tomographic survey, dynamic FEM numerical modelling, empirical calculations of residual stresses, laboratory measurements of compression wave (ultrasonic) velocities on intact rock cores, in-situ primary stress measurements as well as site geological model were integrated to evaluate the use of seismic tomography for identifying possible in-situ stress increases around the excavation.A detailed calibration modelling was carried out based on the site seismic tomography measurements and during the large-scale modelling. It was observed that the increasing Vp is directly related to simulated increasing directional loadings on the rock mass. Using a measured wave raypath it was possible to check the different in-situ stress parametrizations which resulted in the best approximation to the measured Vp values.It was concluded that the rock mass under investigation to extend the repository must have higher in-situ stress values than the area of the constructed deposition chambers nearby. The results of this research indicated that seismic tomography is a useful tool for determining relative stress around and within the vicinity of underground excavation

Rock Mechanical Laboratory Testing of Thebes Limestone Formation (Member I), Valley of the Kings, Luxor, Egypt

The Thebes Limestone Formation of Lower Eocene age is one of the most extensive rock units in Egypt. It is of importance to the apogee of the ancient Egyptian civilization, particularly in Luxor (South-Central Egypt), where the rock formation hosts the Theban Necropolis, a group of funerary chambers and temples from the New Kingdom Egyptian era (3500-3000 BP). In this work, we investigated the petrophysical and rock mechanical properties (e.g., rock strength, critical crack stress thresholds) through laboratory tests on eleven rock blocks collected from one area within the Theban Necropolis known as the Valley of the Kings (KV). The blocks belong to Member I of the Thebes Limestone Formation, including six blocks of marly limestone, three blocks of micritic limestone, one block of argillaceous limestone from the Upper Esna Shale Formation, and one block of silicified limestone of unknown origin. Special attention was given to the orientation of bedding planes in the samples: tests were conducted in parallel (PA) and perpendicular (PE) configurations with respect to bedding planes. We found that the marly limestone had an average unconfined compressive strength (UCS) of 30 MPa and 39 MPa for the PA and PE tests, respectively. Similarly, the micritic limestone tests showed an average UCS of 24 MPa for the PA orientation and 58 MPa for the PE orientation. The critical crack thresholds were the first ever reported for Member I, as measured with strain gauge readings. The average crack initiation (CI) stress thresholds for the marly limestone (PA: 14 MPa) and the micritic limestone (PA: 11 MPa; PE: 24 MPa) fall within the typical ratio of CI to UCS (0.36-0.52). The micritic limestone had an average Young's modulus (E) of 19.5 GPa and 10.3 GPa for PA and PE, respectively. The Poisson's ratios were 0.2 for PA and 0.1 for PE on average. Both marly and micritic limestone can be characterised by a transverse isotropic strength behaviour with respect to bedding planes. The failure strength for intact anisotropic rocks depends on the orientation of the applied force, which must be considered when assessing the stability of tombs and cliffs in the KV and will be used to understand and improve the preservation of this UNESCO World Heritage site

Diverse silver(I) coordination chemistry with cyclic selenourea ligands

The coordination chemistry of two selenourea ligands (SeIMes and SeIPr) towards silver(I) triflate and silver(I) nitrate was investigated. Two aggregation modes were observed in the solid state, strongly influenced by the size of the aromatic substituents on the ligand. With mesityl groups, selenium-bridged bimetallic motifs [AgX(SeIMes)]2 were obtained, while for the bulkier diisopropylphenyl groups ion-separated species of formulae [Ag(SeIPr)2]+[X]− were obtained. Recrystallization of [Ag(NO3)(SeIMes)]2 from hot methanol resulted in the formation of a unique coordination polymer featuring three silver environments. Characterization of the complexes by NMR spectroscopy and mass spectrometry suggested all complexes adopt the ionic aggregation mode in methanol solution.Natural Sciences and Engineering Research Council of Canada (Discovery Development Grant (DDG-2017-00041))https://pubs.rsc.org/en/content/articlelanding/2018/DT/C7DT04243D#!divAbstrac

The three stages of stress relaxation - Observations for the time-dependent behaviour of brittle rocks based on laboratory testing

Underground openings can experience time-dependent deformations and stress changes. Studying time-dependent rock behaviour is commonly done with static load (creep) tests in the laboratory which typically exhibit three distinct stages of behaviour. In this study relaxation tests were conducted to examine if three stages also exist under constant strain boundary conditions and to understand how the relaxation behaviour changes as the driving stress to strength ratio is increased. Tests were conducted on two types of limestone. At different load levels similar stress-time responses were measured indicating three distinct stages of stress relaxation. The first stage of stress relaxation (RI) where the stress relaxes with a decreasing rate is followed by the second stage (RII) in which the stress decrease approaches a constant rate and in the third stage (RIII) no further stress relaxation takes place. In the first stage 55% to 95% of the total stress relaxation takes place. The test results are compared with literature data to understand the influence of the stiffness on the magnitude and time to reach the maximum stress relaxation. Relaxation tests could be used to derive numerical model inputs to describe the time-dependent behaviour in a manner similar to static load tests

Prophylactic Melatonin for Delirium in Intensive Care (Pro-MEDIC): Study protocol for a randomised controlled trial

Background: Delirium is an acute state of brain dysfunction characterised by fluctuating inattention and cognitive disturbances, usually due to illness. It occurs commonly in the intensive care unit (ICU), and it is associated with greater morbidity and mortality. It is likely that disturbances of sleep and of the day-night cycle play a significant role. Melatonin is a naturally occurring, safe and cheap hormone that can be administered to improve sleep. The main aim of this trial will be to determine whether prophylactic melatonin administered to critically ill adults, when compared with placebo, decreases the rate of delirium. Methods: This trial will be a multi-centre, randomised, placebo-controlled study conducted in closed ICUs in Australia. Our aim is to enrol 850 adult patients with an expected ICU length of stay (LOS) of 72h or more. Eligible patients for whom there is consent will be randomised to receive melatonin 4mg enterally or placebo in a 1:1 ratio according to a computer-generated randomisation list, stratified by site. The study drug will be indistinguishable from placebo. Patients, doctors, nurses, investigators and statisticians will be blinded. Melatonin or placebo will be administered once per day at 21:00 until ICU discharge or 14days after enrolment, whichever occurs first. Trained staff will assess patients twice daily to determine the presence or absence of delirium using the Confusion Assessment Method for the ICU score. Data will also be collected on demographics, the overall prevalence of delirium, duration and severity of delirium, sleep quality, participation in physiotherapy sessions, ICU and hospital LOS, morbidity and mortality, and healthcare costs. A subgroup of 100 patients will undergo polysomnographic testing to further evaluate the quality of sleep. Discussion: Delirium is a significant issue in ICU because of its frequency and associated poorer outcomes. This trial will be the largest evaluation of melatonin as a prophylactic agent to prevent delirium in the critically ill population. This study will also provide one of the largest series of polysomnographic testing done in ICU. Trial registration: Australian New Zealand Clinical Trial Registry (ANZCTR) number: ACTRN12616000436471. Registered on 20 December 2015

Predicting excavation damage zone depths in brittle rocks

During the construction of an underground excavation, damage occurs in the surrounding rock mass due in large part to stress changes. While the predicted damage extent impacts profile selection and support design, the depth of damage is a critical aspect for the design of permeability sensitive excavations, such as a deep geological repository (DGR) for nuclear waste. Review of literature regarding the depth of excavation damage zones (EDZs) indicates three zones are common and typically related to stress induced damage. Based on past developments related to brittle damage prediction using continuum modelling, the depth of the EDZs has been examined numerically. One method to capture stress induced damage in conventional engineering software is the damage initiation and spalling limit (DISL) approach. The variability of depths predicted using the DISL approach has been evaluated and guidelines are suggested for determining the depth of the EDZs around circular excavations in brittle rock masses. Of the inputs evaluated, it was found that the tensile strength produces the greatest variation in the depth of the EDZs. The results were evaluated statistically to determine the best fit relation between the model inputs and the depth of the EDZs. The best correlation and least variation were found for the outer EDZ and the highly damaged zone (HDZ) showed the greatest variation. Predictive equations for different EDZs have been suggested and the maximum numerical EDZ depths, represented by the 68% prediction interval, agreed well with the empirical evidence. This suggests that the numerical limits can be used for preliminary depth prediction of the EDZs in brittle rock for circular excavations

An Overview of Opportunities for Machine Learning Methods in Underground Rock Engineering Design

Machine learning methods for data processing are gaining momentum in many geoscience industries. This includes the mining industry, where machine learning is primarily being applied to autonomously driven vehicles such as haul trucks, and ore body and resource delineation. However, the development of machine learning applications in rock engineering literature is relatively recent, despite being widely used and generally accepted for decades in other risk assessment-type design areas, such as flood forecasting. Operating mines and underground infrastructure projects collect more instrumentation data than ever before, however, only a small fraction of the useful information is typically extracted for rock engineering design, and there is often insufficient time to investigate complex rock mass phenomena in detail. This paper presents a summary of current practice in rock engineering design, as well as a review of literature and methods at the intersection of machine learning and rock engineering. It identifies gaps, such as standards for architecture, input selection and performance metrics, and areas for future work. These gaps present an opportunity to define a framework for integrating machine learning into conventional rock engineering design methodologies to make them more rigorous and reliable in predicting probable underlying physical mechanics and phenomenon

Dynamic Nuclear Polarization of Metal-Doped Oxide Glasses: A Test of the Generality of Paramagnetic Metal Polarizing Agents

Nuclear magnetic resonance (NMR) spectroscopy can provide unique, atomic-level insights into the structure and dynamics of materials, but its applications are impeded by the intrinsically low sensitivity. Dynamic nuclear polarization (DNP) is poised to overcome this limitation, and indeed has revolutionized the study of surfaces; however, the current approaches are ill-suited for bulk solids. One potential pathway toward the hyperpolarization of bulk solids by DNP is through the inclusion of paramagnetic metal ions that can serve as polarizing agents. In this work, we compared the relative performance of two such dopants, Mn2+ and Gd3+, in three series of oxide glasses having chemical environments representative of those found in other crystalline and amorphous solids. In our studies, Gd3+ outperformed Mn2+, consistently providing more than one order of magnitude greater time savings. We attributed this difference mainly to the lack of hyperfine interaction to 55Mn.</p