Dry Quartz Research Articles

A Simplified Calibration Procedure for DEM Simulations of Granular Material Flow

The discrete element method (DEM) has emerged as an essential computational tool in geotechnical engineering for the simulation of granular materials, offering significant advantages over traditional continuum-based methods such as the finite element method (FEM) and the finite difference method (FDM). The DEM’s ability to model particle-level interactions, including contact forces, rotations, and particle breakage, allows for a more precise understanding of granular media behavior under various loading conditions. However, accurate DEM simulations require meticulous calibration of input parameters, such as particle density, stiffness, and friction, to effectively replicate real-world behavior. This study proposes a simplified calibration procedure, intended to be conducted prior to any granular material flow DEM modeling, based on three fundamental physical tests: bulk density, surface friction, and angle of repose. The ability of these tests, conducted on dry quartz sand, to accurately determine DEM micromechanical parameters, was validated through numerical simulation of cylinder tests with varying height-to-radius ratios. The results demonstrated that this calibration approach effectively reduced computational complexity while maintaining high accuracy, with validation errors of 0% to 12%. This research underscores the efficacy of simplified DEM calibration methods in enhancing the predictive reliability of simulations, particularly for sand modeling in geotechnical applications.

3D rock physics template-based probabilistic estimation of tight sandstone reservoir properties

Quantitative prediction of reservoir properties (e.g., gas saturation, porosity, and shale content) of tight reservoirs is of great significance for resource evaluation and well placements. However, the complex pore structures, poor pore connectivity, and uneven fluid distribution of tight sandstone reservoirs make the correlation between reservoir parameters and elastic properties more complicated and thus pose a major challenge in seismic reservoir characterization. We have developed a partially connected double porosity model to calculate elastic properties by considering the pore structure and connectivity to analyze these factors' influences on the elastic behaviors of tight sandstone reservoirs. The modeling results suggest that the bulk modulus is likely to be affected by the pore connectivity coefficient, while the shear modulus is sensitive to the volumetric fraction of stiff pores. By comparing the model predictions with the acoustic measurements of the dry and saturated quartz sandstone samples, the volumetric fraction of stiff pores and the pore connectivity coefficient can be determined. Based on the calibrated model, we have constructed a 3D rock physics template that accounts for the reservoir properties’ impacts on the P-wave impedance, S-wave impedance, and density. The template combined with Bayesian inverse theory is used to quantify gas saturation, porosity, clay content, and their corresponding uncertainties from elastic parameters. The application of well-log and seismic data demonstrates that our 3D rock physics template-based probabilistic inversion approach performs well in predicting the spatial distribution of high-quality tight sandstone reservoirs in southwestern China.

Chiral Lewis Acid-Catalyzed Norrish Type II Cyclization to Synthesize α-Oxazolidinones via Enantioselective Protonation

Chiral Lewis Acid-Catalyzed Norrish Type II Cyclization to Synthesize α-Oxazolidinones via Enantioselective Protonation

Bayesian calibration of GPU–based DEM meso-mechanics Part I: Parallelization of RVEs

Calibration of Discrete Element Method (DEM) parameters is essential for modeling geotechnical applications. This task can, however, be extremely tedious or sometimes even impossible to undertake. This is largely due to two issues namely: (1) a large sample size of DEM simulations and number of sampling iterations are necessary to accurately infer the probability distribution of a model over a large parameter space and (2) DEM is computationally intractable compared to other numerical methods. In the scope of reducing the number of sampling iterations, automatic calibration techniques are available to extract and make use of the hidden contact mesostructure correlations through adaptive sampling. Coincidentally, to improve computational speed, significant advances toward Graphics Processor Unit (GPU) based DEM algorithms have been achieved over the past years on particle parallelism. Nevertheless, the problem remains that DEM simulations are serialized during the calibration processes. While the companion paper addresses parameter calibration, this study presents a novel algorithm to parallelize independent simulations within a sample set. The selected system is the Representative Volume Element (RVE) which is widely used in geotechnics for solving soil response in the static regime. The algorithm includes the following key features: (1) simulation level parallelism of non-interacting RVEs through highly efficient hierarchical memory groups and access patterns (2) a low latency and memory-efficient implementation of deformable periodic boundary conditions (PBC) which uses lookup tables and bitmasks (3) modified Uniform Grid and Bounding Volume Hierarchy (BVH) contact detection algorithms which partitions the RVE index into the hashing keys. The drained DEM triaxial compression is used to validate the algorithm on dry graded quartz. Three performance degrading factors for the calibration processes are considered: (1) the number of particles per RVE (2) calibration sample size and (3) sequential launch time per calibration step. This algorithm shows a factor of about 9.8 times speedup when parallelizing 100 DEM RVEs in one batch.

An Experimental Investigation on the Creep Behavior of Deep Brittle Rock Materials.

The stability of deep rock engineering, especially during the excavation, is inextricably linked to the time-dependent mechanical properties of brittle rock. Therefore, the uniaxial creep test in a multilevel loading path is carried out, accompanying the real-time DIC (digital image correlation) and AE (acoustic emission) technologies. For the quartz sandstone, the lateral strain is more sensitive to increasing stress levels, and the lateral ductility is more significant during the creep process. The saturated quartz sandstone shows a certain bearing capacity before the volumetric dilation predominance. The softening effect of moisture causes a nearly invariable Poisson’s ratio during the middle stress stages, as well as the more notable increasing trend of a steady creep rate with an increasing stress level, reflected by the larger slope and the intercept in the fitting relations. The main shear pattern and the combination of the shear and splitting failures are separately shown by the dry and saturated quartz sandstone. For the granite, both compression and extension exist in the creep deformation, and the failure may first occur in the prominent deformation area with a cracking noise. The AE hits present a similar time-dependent behavior to the strain of rock, and the attenuation trend happens in both the AE amplitude and energy before the rock enters the unsteady phase. The incomplete specimen of granite exhibits a lower strength and a larger deformation, owing to the more remarkable damage accumulation reflected by the spatial distribution of the AE event points.

Calculation of the Fourier criterion in predicting the thermal regime of thawed and frozen dispersed rocks

The purpose of this work was to determine the range of changes in the Fourier criterion (number) when predicting the thermal regime of dispersed rocks in thawed and frozen state. And, also an assessment of the possibility of averaging the thermophysical characteristics of rocks to obtain universal values of Fourier numbers. To achieve this goal, an assessment of the influence of the thermophysical properties of dispersed rocks on the range of changes in the values of the Fourier number used in thermal calculations of technical objects of the cryolithozone is made. The calculation formulas took into account the functional dependence of the coefficient of thermal conductivity, density and specific heat capacity of rocks on humidity (iciness) in the thawed and frozen state. As an example, a mixture of quartz sandstone with water in a thawed and frozen state is considered when the ice content changes from zero (dry quartz sandstone) to full moisture saturation. It is established that the range and nature of the change in Fourier numbers for thawed and frozen dispersed rocks, depending on their humidity (iciness), differs significantly, not only quantitatively, but also qualitatively: for thawed dispersed rocks, the Fourier number decreases with increasing humidity, and for frozen rocks increases. The possibility of averaging the thermophysical characteristics of rocks to obtain universal values of Fourier numbers has been evaluated. It is shown that the use of universal Fourier numbers leads to a significant error for both thawed and frozen rocks and their use in thermal calculations with annual temperature fluctuations is impractical.

Strength of Dry and Wet Quartz in the Low-Temperature Plasticity Regime: Insights From Nanoindentation.

At low‐temperature and high‐stress conditions, quartz deformation is controlled by the kinetics of dislocation glide, that is, low‐temperature plasticity (LTP). To investigate the relationship between intracrystalline H2O content and the yield strength of quartz LTP, we have integrated spherical and Berkovich nanoindentation tests at room temperature on natural quartz with electron backscatter diffraction and secondary‐ion mass spectrometry measurements of intracrystalline H2O content. Dry (<20 wt ppm H2O) and wet (20–100 wt ppm H2O) crystals exhibit comparable indentation hardness. Quartz yield strength, which is proportional to indentation hardness, seems to be unaffected by the intracrystalline H2O content when deformed under room temperature, high‐stress conditions. Pre‐indentation intracrystalline microstructure may have provided a high density of dislocation sources, influencing the first increments of low‐temperature plastic strains. Our results have implications for fault strength at the frictional‐viscous transition and during transient deformation by LTP, such as seismogenic loading and post‐seismic creep.

Range of change in Fourier numbers in thermal calculations of automobile roads in the cryolithic zone

An assessment of influence of thermal physical properties of dispersed rocks on the range of change in the values of Fourier numbers, used in thermal calculations of soil foundations of the automobile roads in the cryolithic zone, was carried out. The formulas applied in the calculation have considered the functional dependence of the thermal conductivity coefficient and the total heat capacity on the moisture (ice) content in the thawed and frozen state. A mixture of quartz sandstone with water in thawed state and ice in frozen state, with moisture (ice) content changing zero (dry quartz sandstone) to full moisture saturation, was used as an example. It was determined that the range and type of Fourier numbers for thawed and frozen dispersed rocks differs significantly, both quantitatively and qualitatively, depending on their moisture (ice) content. For thawed rocks, the Fourier number decreases as moisture content rises. For frozen rocks, it increases. It was demonstrated that in calculation of Fourier numbers for dispersed rocks it is important to properly apply the calculation models. In particular, if the model of material structure is not changed the reflect the respective contents of the binder and the filler components, above a particular concentration of the respective components, the calculation error in Fourier numbers can exceed 30%. An assessment of the possibility of averaging the thermal physical characteristics of the rocks to obtain the universal Fourier numbers was done. It was concluded that the use of universal Fourier numbers causes a significant error for both thawed and frozen rocks. Their use in thermal calculations over the yearly temperature changes is not expedient. It is correct to separate the thermal calculations into three components: calculation in the thawed state, calculation in the frozen state and calculation in the phase transition period of freezing and thawing, with corresponding calculation of Fourier numbers for every period and the aggregate state of the moisture in the dispersed rocks.

New granular rock-analogue materials for simulation of multi-scale fault and fracture processes

AbstractIn this study, we present a new granular rock-analogue material (GRAM) with a dynamic scaling suitable for the simulation of fault and fracture processes in analogue experiments. Dynamically scaled experiments allow the direct comparison of geometrical, kinematical and mechanical processes between model and nature. The geometrical scaling factor defines the model resolution, which depends on the density and cohesive strength ratios of model material and natural rocks. Granular materials such as quartz sands are ideal for the simulation of upper crustal deformation processes as a result of similar nonlinear deformation behaviour of granular flow and brittle rock deformation. We compared the geometrical scaling factor of common analogue materials applied in tectonic models, and identified a gap in model resolution corresponding to the outcrop and structural scale (1–100 m). The proposed GRAM is composed of quartz sand and hemihydrate powder and is suitable to form cohesive aggregates capable of deforming by tensile and shear failure under variable stress conditions. Based on dynamical shear tests, GRAM is characterized by a similar stress–strain curve as dry quartz sand, has a cohesive strength of 7.88 kPa and an average density of 1.36 g cm−3. The derived geometrical scaling factor is 1 cm in model = 10.65 m in nature. For a large-scale test, GRAM material was applied in strike-slip analogue experiments. Early results demonstrate the potential of GRAM to simulate fault and fracture processes, and their interaction in fault zones and damage zones during different stages of fault evolution in dynamically scaled analogue experiments.

Improvement of traction capacity of industrial railway transport in the Arctic and on the continental shelf

The Russian Arctic is extremely rich in minerals (hydrocarbons, various minerals, precious metals, etc.). In modern conditions, it is of particular importance to develop vast territories located beyond the Arctic Circle, due to their special socio-economic, geopolitical and defense significance. The rapid development of the Yamal field needs a reliable and modern trunk railway. The project called the Northern Latitudinal Railway has been included in the Strategy for the Development of Railway Transport until 2030. At the temperatures below minus 20 °C, the use of ordinary sand to improve adhesion usually has low effect due to a significant increase in the hardness of ice and ice crust. It should be noted that given sand is present at the contact of ice-glazed rails and wheels, their metal–metal interaction is interrupted by of this sandwiched sand interlayer, which leads to a decrease in the traction characteristics of locomotives. To increase the adhesion coefficient in winter, the author has proposed an engineering solution protected by patent No. 2504492, which consists in the feed of pre-heated, for example, using an induction heater, dry quartz sand to the rail–wheel contact zone. This invention allows increasing the coefficient of adhesion and, consequently, the traction force of locomotives on average up to 10%. Currently, we are carrying out studies to solve the problem of removing ice deposits from the working surface of rails using innovative “sandless” methods that eliminate the need of using ordinary sand. The solution to the problem of removing ice from rails will contribute to the creation of a terrestrial year-round communication between Chukotka and the Barents Sea, which duplicates the Northern Sea Route.

Numerical modeling of post-collisional carbonated alkaline magmatism: Variscan style Orogeny (the Ivrea Zone as natural laboratory)

The Ivrea Zone of northwest Italy exposes a section of the lower crust and lithospheric mantle deformed during the Variscan Orogeny, where a series of carbonated alkaline pipes was emplaced over a time span of ca. 40 Ma, following a crustal underplating event at ca. 288 Ma. We use a coupled 2D petrological-thermomechanical approach to geodynamically model the processes that led to the Variscan continental collision and subsequent emplacement of the alkaline pipes with application to craton margin metasomatic events. The following criteria are assessed to develop a generic model: 1) closure of Rheic Ocean through subduction of oceanic crust and subduction-related metasomatism of the lithospheric mantle, 2) high-temperature metamorphism of the lower crust associated with continental collision, preceding the 3) emplacement of a crustal underplating event, and 4) partial melting of metasomatized lithospheric mantle domains during gravitational collapse of the orogen to source the alkaline pipes. Our model investigates the collision process by varying thermal ages of the intervening oceanic crust (40, 60, and 80 Ma) and by changing the rheological strength of the lower crust. We employ two ideal end-member cases, wet quartzite and plagioclase An75, an intermediate dry quartz case to represent a migmatized lower crust, and two polymineralic cases of felsic granulite and mafic granulite as possible representations to the Ivrea Zone specifically. We discuss the results through three scenarios controlled by the age of the oceanic crust and rheology of the lower crust that can reproduce tectonic scale features that are observed in the Ivrea Zone. Scenario 1: the wet quartzite 40 Ma model features widespread H2O and CO2 fluxes within the continental lithospheric mantle. The model displays little melt productivity due to the presence of an overthickened crust and the continental lithospheric mantle decouples and peels off beneath the lower crust of the colliding terrane. Scenario 2: the plagioclase An75 60 Ma model shows high-temperature metamorphism in the lower crust and reproduces the metasomatism of the continental lithospheric mantle that is a precursor to the genesis of the alkaline pipes. The model is permissive for the emplacement of the crustal underplating event, but the relative timings are misplaced. Scenario 3: the mafic granulite 80 Ma model recreates the tectonic relationships between lower crustal high-temperature metamorphism followed by initiation of the magmatic underplating event, and lastly by localized melting of metasomatized domains of the lithospheric mantle. This model can potentially explain two of the prevailing hypotheses for the formation of the alkaline pipes. Whereas all models reproduced different stages of the tectono-magmatic evolution of continental collision, only scenario 3 could sufficiently recreate the relative sequence of events observed in the Ivrea Zone. Scenarios 1 and 2 may provide precious information about the nature and timing of metasomatic processes in the lithospheric mantle, with implications for the enhanced prospectivity for a wide range of ore systems in specific domains along the margins of lithospheric blocks.

SPECIFIC FEATURES OF NITROGEN METABOLISM DURING FERMENTATION OF MUST FROM WHITE GRAPE VARIETIES GROWN IN THE ODESSA REGION

For wine quality management, nitrogen metabolism should be considered as a key process in the system “grape – wine.” Nitrogen is one of the dominant elements a grapevine receives from the soil. It is important in many biological processes of the plant itself and of the microorganisms involved in fermentation. Nitrogen-containing compounds are nutrients necessary for yeast growth, in particular, for stable fermentation. This group of compounds directly and indirectly affects the aromatic and taste qualities of wine during its maturation and largely determines its stability. Nitrogen compounds are transferred to wine directly from grapes and yeast during fermentation. Since their role in the formation and maturation of wine is significant, it is highly important to regulate their metabolism in the fermenting must. On analysing literature references and summarising the information on the metabolism of nitric substances, a scheme has been developed reflecting how these substances influence the formation of the quality characteristics of grape wines. The paper presents the results of studying the metabolism of total nitrogen and amino nitrogen in grape must during its fermentation. The grape variety considered in the research was Sukholimansky White bred by the National Science Centre “Tairov Institute of Viticulture and Winemaking” and harvested in 2015–2017. It has been established that nitrogen metabolism during fermentation does not depend on the feedings added. However, the yeast race affects the physicochemical parameters, namely the content of volatile acids. It has been observed that during fermentation, the amine nitrogen concentration decreases by 90% and the total nitrogen concentration by 40–50%. Regarding the factors that effect on the quality characteristics of wines produced in the South of Ukraine, the physicochemical parameters of wine materials can be improved by using the active dry yeast Vitilevure Quartz and the nutritional supplements Actiferm 1 and Actiferm 2, in combination with aeration. This allows revealing fruity aromas, and achieving the right acidity and harmony of taste due to the presence of the descriptors (butter, apple, peach, apricot, and geranium) characteristic of the grape variety Sukholimansky White.

A unified soil thermal conductivity model based on artificial neural network

An accurate prediction of thermal conductivity (k) of unsaturated soils is a challenging problem in geothermal applications because k is affected by various factors such as soil fabric, water content, dry density, soil mineralogy and type. This study proposes a unified soil thermal conductivity model to consider these influence factors based on a screened artificial neural network (ANN) approach. Two hundred and fifty-seven (257) thermal conductivity measurements of unsaturated soils were first collected from the literature to compile a database. The ANN approach constrained with model complexity optimization and monotonicity control was then utilized to overcome the potential sample insufficiency problem in order to establish reliable correlations between k (represented by an empirical coefficient) and its influence factors including dry density (ρd), porosity (n), saturation degree (Sr), quartz content (mq), sand content (ms) and clay content (mc). Using this approach, some easy-to-use ANN-based contours for predicting k were developed to guide engineering practice. Results revealed that ANN-based predictions of k by the developed model matched experimental data with enhanced accuracy as compared with some benchmarking thermal conductivity models. The model can rationally consider the effects of multiple influence factors and their coupling effects on k in a quantitative and systematical way.

Forced and natural gas movement in dry sand – Barrel experiments and models

AbstractThe physical processes governing advective and diffusive gas movement and distribution in dry soils are, in general, well understood and quantified. In this study, we derived and applied analytical and numerical models to describe these processes under different conditions and scenarios and conducted gas flow experiments in 200‐L barrels packed with dry quartz sand in a temperature‐controlled laboratory. We used either pure N2 (0% O2) or atmospheric air (20.9% O2) injection or gas extraction from (or into) buried point sources (or sinks) to examine the effects of (a) source depth, (b) source discharge rate, and (c) injection cycle period on gas concentration and pressure distribution. We further quantified the contribution of diffusion from the atmospheric soil surface for the different scenarios, made possible by injecting N2 and tracking the complementary O2 concentration [i.e. the difference between atmospheric (20.9%) and the measured soil O2 concentration]. An analytical solution for steady air flow from a point source in a finite, cylindrical domain is presented. The main findings are that air injection, and air extraction, are efficient at aerating the soil volume above the buried gas source or sink. On the other hand, air injection increases the aeration's effectiveness, especially below the source. Shortening the cycle period of gas injection increases gas‐use efficiency (i.e., increases the injected gas concentration) in most of the soil domain. The measurements were in good agreement with the results computed by the models’ analytical and numerical solutions.

Numerical simulation of bimetallic casting cooling during the process of lost foam casting

The authors consider cooling process of a “gray cast iron–austenitic stainless steel” bimetallic casting in the lost foam casting conditions. They provide a mathematical model of coupled heat transfer between the molten gray cast iron, stainless steel, nonstick coating and dry quartz sand during the process of bimetallic casting cooling, taking into account phase transitions in gray cast iron and quartz sand. The article shares calculated data on casting crystallization time and a solid-phase fraction formed in gray cast iron with temperature field changes with time and cooling rates of the bimetallic casting. The data have been obtained for stainless steel thicknesses of 1.5 mm, 5 mm and 10 mm (volume ratio of 20:1, 6:1 and 3:1, respectively) and two pouring temperatures of 1350 °C and 1500 °C. The calculated values of the bimetallic casting solidification time are summarized as a polynomial. Formation of shrink holes near the left wall of the casting proves to be possible with a stainless steel thickness of 1.5 mm.

Disordering of 13C[sbnd]18O bonds in CO2 gas over a heated quartz surface at 50–1100 °C: Insights into the abundance of mass 47 (∆47) in CO2 gas at thermodynamic equilibrium

The clumped isotope composition or the ∆47 value of CO2 relates the abundance of 13C18O16O among all the CO2 isotopologues to the formation temperature of a carbonate mineral or the equilibration temperature of CO2 gas. The ∆47 data typically requires several standardization steps and one of which heavily relies on true or equilibrium Δ47 values from different temperatures. However, they have not yet been experimentally quantified and only theoretically predicted Δ47 values are available to the community (e.g., Wang et al. 2004). In this study, a series of CO2 gases were cleaned using a custom-designed automated CO2 cleaning system, baked in a pre-cleaned dry quartz tube and then measured for their ∆47 values (the CBM protocol) to examine ∆47 change kinetics of CO2 gas over a heated quartz surface between 50 and 1100 °C. In another test, a series of CO2 gases were baked first, cleaned subsequently, and finally measured for their ∆47 values (the BCM protocol) to evaluate the effect of the CO2 cleaning on the ∆47 value in a routine ∆47 measurement. Our experimental results showed that ∆47 value of the CO2 gas over a heated quartz surface attained thermodynamic equilibrium in 191, 7, 0.23 and 0.1 h at 50, 100, 491 and 1000 °C, respectively. We also reported the first experimentally determined equilibrium ∆47–T relation in CO2 gas between 50 and 1100 °C as follows (∆47 in ‰, T in °C; R2 = 0.99, P < 0.0001):Absolute∆47=0.9791±0.0029×e−0.0045TThe comparison between the two CO2 preparation protocols also revealed that the CO2 cleaning step after the baking in the BCM protocol could alter the original ∆47 signature of CO2 gas by 0.04 and 0.07‰ at 100 and 1000 °C, respectively, increasing the empirical transfer function (ETF) slope to >1. Therefore, the isotope scrambling effect reported in the literature (e.g., Dennis et al. 2011) might be resulted from CO2 cleaning process because isolating the CO2 cleaning effect (before the baking) yielded an ETF slope of 1, implying that instrumental or analytical artifacts that could affect the measured ∆47 were not significant. We suggest using a set of heated CO2 gases prepared by the BCM protocol from several different temperatures as an alternative for the conventional use of heated and water-equilibrated CO2 gases to construct an absolute reference frame and standardize Δ47.

Improving a thermal conductivity model of unsaturated soils based on multivariate distribution analysis

Soil thermal conductivity (k) is a key parameter for the design of energy geo-structures, and it depends on many soil properties such as saturation degree, porosity, mineralogical composition, soil type and others. Capturing these diversified influencing factors in a soil thermal conductivity model is a challenging task for engineers due to the nonlinear dependencies. In this study, a multivariate distribution approach was utilized to improve an existing soil thermal conductivity model, Cote and Konrad model, by quantitatively considering the impacts of dry density (ρd), porosity (n), saturation degree (Sr), quartz content (mq), sand content (ms) and clay content (mc) on thermal conductivity of unsaturated soils. A large database containing these seven soil parameters was compiled from the literature to support the multivariate analysis. Simplified bivariate and multivariate correlations for improving the Cote and Konrad model were derived analytically and numerically to consider different influencing factors. By incorporating these simplified correlations, the predicted k values were more concentrated around the measured values with the coefficient of determination (R2) increased from 0.83 to 0.95. It is concluded that the developed correlations with the information of different soil properties provide an efficient, rational and simple way to predict soil thermal conductivity more accurately. Moreover, the quartz content is a more important factor than the porosity that shall be considered in the establishment of thermal conductivity models for unsaturated soils with high quartz content.

Sliding friction of shale rock on dry quartz sand particles

The sliding friction of rock, involving all kinds of particles at the contact surface, is relevant to many problems, ranging from those in artificial engineering to earthquake dynamics. In this work, the frictional performance of the shale rock–dry quartz sand contact was investigated using a self-developed testing device. The study showed that the coefficient of friction of the contact increases with nominal stress and that the corresponding friction force increases approximately linearly with nominal stress, which is directly related to the contact stress between each single sand particle and rock shale. An overall dynamic coefficient, γ, reflecting the response of friction force to nominal stress, first decreases and then increases with area ratio, which is determined by not only the contact stress but also the interparticle friction force. These have important repercussions for a preliminary understanding of the frictional properties of the shale rock–dry quartz sand contact in hydraulic fracturing and related industrial applications.

Effect of joint thickness on seismic response across a filled rock fracture

This study aims to investigate the influence of joint thickness on seismic response across a filled fracture with strong nonlinear deformability. To simulate seismic attenuation of thicker joints subject to high-amplitude stress waves, the split Hopkinson pressure bar is utilised to generate normally incident P wave and the dry quartz sand is used to simulate the filled joints. Three joint thicknesses – that is 5, 10 and 15 mm, are studied under identical incident waves. The stress–strain response of the filling materials is described by Barton–Bandis model having different loading–unloading behaviours. The initial stiffness and the maximum allowable closure of the joints changing with the joint thickness are studied. The thicker joints result in lower initial stiffness and cause lower seismic wave transmission across the fracture. The high-amplitude stress strengthens the nonlinearity of the filling materials and increases the stiffness. Besides, the seismic attenuation factor Q, derived from the energy dissipation, is lower than that computed by the transmission coefficient due to the frequency filtering.

TitaniQ deformed: Experimental deformation of out-of-equilibrium quartz porphyroclasts

The role of deformation on the equilibration of Ti concentrations in quartz was investigated by running experiments on out-of-equilibrium quartz crystals embedded as porphyroclasts within quartz aggregates. Quartz crystals were first grown from a hydrostatic fluid to set the initial Ti content; crystals grown at temperatures above (925 °C) and below (875 °C) the deformation temperature (900 °C) contain Ti contents ∼60 ppm higher or lower than the equilibrium solubility. These out-of-equilibrium quartz crystals were then deformed as porphyroclasts by embedding them in a matrix composed of either dry or wet quartz to induce two end-member deformation regimes, high-stress or low-stress, respectively. In high-stress experiments, quartz porphyroclasts contain deformation bands and undulose extinction, with some grains showing evidence for grain boundary bulging (BLG) recrystallization. In low-stress experiments, some grains deformed to high strains with minimal evidence for dynamic recrystallization, resulting in ribbon grains, whereas others recrystallized by dislocation creep processes, showing microstructural evidence for subgrain rotation (SGR) and grain boundary migration (GBM) recrystallization. By comparing quartz microstructures with patterns of Ti re-distribution in variably deformed and recrystallized porphyroclasts, we find that grains deformed to high strain with minimal recrystallization show little to no evidence for re-equilibration, whereas grains that recrystallized via grain boundary processes have equilibrated Ti contents that reflect the pressure-temperature conditions of deformation.