Synthetic Rock Research Articles

Damage Evolution and Integrity Assessment of Jointed Rock Mass Based on Synthetic Rock Mass Approach

The integrity coefficient Kv of bed rock is one of the important approaches to evaluate the stability of engineering rock mass, but this parameter is difficult in frequent field tests. The integrity coefficient is the quantitative index for evaluating the complete deformation of rock mass, while the damage variable represents the level of damage of the jointed rock mass, and both have similar physical meanings and represent the degree of deterioration of surrounding rock. Damage variables and damage constitutive models were constructed based on Weibull distribution damage model and Synthetic Rock Mass (SRM) model. The relationship between damage variables and numerical calculation and damage constitutive curves of different weathered granite rocks in Hongtuzhang tunnel was calculated. A new method for evaluating integrity coefficient of rock mass is proposed.

Developing synthetic sandstones using geopolymer binder for constraining coupled processes in porous rocks

There is a current need for developing improved synthetic porous materials for better constraining the dynamic and coupled processes relevant to the geotechnical use of underground reservoirs. In this study, a low temperature preparation method for making synthetic rocks is presented that uses a geopolymer binder cured at 80 °C based on alkali-activated metakaolin. For the synthesised sandstone, the key rock properties permeability, porosity, compressive strength, and mineralogical composition, are determined and compared against two natural reservoir rocks. In addition, the homogeneity of the material is analysed structurally by micro-computed tomography and high-resolution scanning electron microscopy, and chemically by energy dispersive X-ray spectroscopy. It is shown that simple, homogenous sandstone analogues can be prepared that show permeability-porosity values in the range of porous reservoir rocks. The advance in using geopolymer binders to prepare synthetic sandstones containing thermally sensitive minerals provides materials that can be easily adapted to specific experimental needs. The use of such material in flow-through experiments is expected to help bridge the gap between experimental observations and numerical simulations, leading to a more systematic understanding of the physio-chemical behaviour of porous reservoir rocks.

Sensitivity of seismic attenuation and dispersion to dynamic elastic interactions of connected fractures: Quasi-static finite element modeling study

Prediction of seismic attenuation and dispersion that are inherently sensitive to hydraulic and elastic properties of the medium of interest in the presence of mesoscopic fractures and pores, is of great interest in the characterization of fractured formations. This has been very difficult, however, considering that stress interactions between fractures and pores, related to their spatial distributions, tend to play a crucial role on affecting overall dynamic elastic properties that are largely unexplored. We thus choose to quantitatively investigate frequency-dependent P-wave characteristics in fractured porous rocks at the scale of a representative sample using a numerical scale-up procedure via performing finite element modelling. Based on 2-D numerical quasi-static experiments, effects of fracture and fluid properties on energy dissipation in response to wave-induced fluid flow at the mesoscopic scale are quantified via solving Biot's equations of consolidation. We show that numerical results are sensitive to some key characteristics of probed synthetic rocks containing unconnected and connected fractures, demonstrating that connectivity, aperture and inclination of fractures as well as fracture infills exhibit strong impacts on the two manifestations of WIFF mechanisms in the connected scenario, and on resulting total wave attenuation and phase velocity. This, in turn, illustrates the importance of these two WIFF mechanisms in fractured rocks and thus, a deeper understanding of them may eventually allow for a better characterization of fracture systems using seismic methods. Moreover, this presented work combines rock physics predictions with seismic numerical simulations in frequency domain to illustrate the sensitivity of seismic signatures on the monitoring of an idealized geologic CO2 sequestration in fractured reservoirs. The simulation demonstrates that these two WIFF mechanisms can strongly modify seismic records and hence, indicating that incorporating the two energy dissipation mechanisms in the geophysical interpretation can potentially improving the monitoring and surveying of fluid variations in fractured formations.

Synthetic salt rock prepared by molten salt crystallization and its physical and mechanical properties

Physical simulation is an important research method for salt cavern energy storage construction technology. However, its progress is constrained by lack of effective model salt. Exploratory experiments were conducted to prepare salt rock by molten salt crystallization. A well-made synthetic salt rock was obtained from repeated adjustment of staged cooling conditions and controlled crystal growth procedures. Samples were taken for microscopic, physical, and mechanical tests, and compared with natural salt rock. SEM, CT and p-wave velocity results show that synthetic salt rock achieved crystallization. Its crystal structure, grain size and intercrystalline relationship are consistent with those of natural salt rock. Its density distribution is uniform and compaction is good. X-ray results prove a high crystallinity and stable mineral composition. Porosity of synthetic specimens ranges from 2.3% to 5.9%, permeability is in the range of E−13 to E−16 m2. Uniaxial compression stress-strain curves, strengths, deformation modulus and poisson's ratios are close to those of natural salt rock. It has obvious ductility and damage occurs after dilation deformation. We initially illustrate energy storage and heat storage-transfer principles of molten salt. The mechanism of layered growth in molten salt crystallization is revealed. The findings provide new insight on salt rock preparation, crystallography, molten salt and salt cavern study.

Laboratory-Scale Investigation on Shear Behavior of Non-Persistent Joints and Joint Infill Using Lattice-Spring-Based Synthetic Rock Mass Model

Discontinuities mainly control the mechanical behavior of rock mass and cause a significant reduction in the rock mass strength. Joint persistency and joint infill conditions are considered the most significant joint parameters that control the mechanical response of rock mass. In this study, numerical and statistical analyses were performed on pre-cracked specimens with two flaws to investigate the effect of joint persistence parameters on shear strength. In addition, an extensive study was conducted to explore the effect of infilled mineral strength, infill thickness, and infill wall roughness on shear strength. The Lattice-Spring-Based Synthetic Rock Mass (LS-SRM) approach was utilized to perform the numerical models. The results showed that the tensile crack propagation is limited at higher normal stresses as tensile damage is largely suppressed. The increases in rock bridge angle slightly increased the shear strength and caused a change in the failure mechanisms of the rock bridge from tensile to shearing. The results of the models with infilled minerals revealed that infilled minerals mainly controlled the shear strength of specimens when the infill thickness was 4.0 mm or greater. The infill wall roughness had no apparent effect on the shear strength. In contrast, it governed the failure mechanisms; cracks initiated at the asperity of the rough filling wall and propagated through the hosted rock mass.

Validation of a Continuum-based Weak Zone Joint Model for Simulating Anisotropic Rock Mass Strength

In recent decades, the approach to estimating rock mass strength and its anisotropic behaviour more accurately has been a growing topic of interest in the rock mechanics community. To evaluate jointed rock mass behaviour more accurately, sophisticated modelling techniques such as Synthetic Rock Mass (SRM) models are becoming increasingly popular. Still, these methods are computationally intensive and require detailed site characterization data that are often unavailable during the initial stages of project development and are not always the most practical option. This study developed an alternative continuum-based SRM-like model where thin contiguous regions of weak continuum material with equivalent joint properties are in place of explicit interface joint elements. The finite-difference program FLAC used these weak zone joints (WZJ) to generate a jointed rock mass continuum model (JRCM). The JRCM concept was applied to systematic sets of persistent joints, a single non-persistent joint, and two intersecting joints to validate the practicality of using WZJ. Results found that the concept produced reasonable anisotropic rock mass strength estimates for most cases, with some limitations. The model captured the anisotropic behaviour while reducing time requirements to develop and recalibrate a conventional SRM. The JRCM concept demonstrates a practical alternative to estimating anisotropic rock mass strength for specific projects where the quantity or quality of data is limited. Furthermore, the reduced run times could allow multiple iterations to perform a probabilistic assessment of the rock mass strength.

Urban endoliths: incidental microbial communities occurring inside concrete

Concrete is now a prevalent type of synthetic rock, and its production and usage have major environmental implications. Yet, assessments of ordinary concrete have rarely considered that concrete itself is potential habitat for a globally important microbial guild, the endolithic microbes, which live inside rocks and other mineralized substrates. We sought evidence that many common concrete structures harbor endolithic microbial communities and that these communities vary widely depending on the conditions imposed by the concrete. In Summer 2022, we obtained samples from various concrete structures found throughout Lubbock, Texas, USA and subjected the internal (non-surface) portions of each sample to controlled microbial life detection tests including culture tests, DNA quantifications, DNA amplification tests, and ATP assays. The great preponderance of positive life detection results from our concrete samples suggests that most modern concrete hosts cryptic endolith communities composed of bacteria, sometimes co-occurring with fungi and/or archaea. Moreover, many of these microbes are viable, culturable, and identifiable via genetic analysis. Endolith signatures varied widely across concrete samples; some samples only yielded trace evidence of possibly dormant microbes while other samples contained much more microbial biomass and diversity, on par with some low-biomass soils. Pre-cast masonry units and fragments of poured concrete found underwater generally had the most endolith signatures, suggesting that concrete forms and environmental positioning affect endolithy. Endolith biosignatures were generally greater in less dense and less alkaline concrete samples. So, concrete endolith communities may be as ubiquitous and diverse as the concrete structures they inhabit. We propose further research of concrete endoliths to help clarify the role of modern concrete in our rapidly urbanizing biosphere.

Experimental assessment of dynamic loading response of grouted non-persistent jointed rock

Grouting is a well-established engineering practice for stabilizing the jointed and/or fractured rock mass. This process may lead to the enhancement of the mechanical properties of fractured rocks. In the majority of the studies, the efficiency of grouting is determined under static loading conditions. Nonetheless, the grouted rock may be subjected to different dynamic loading from blasts or earthquakes. The present study explored the dynamic loading response, in terms of strength and fracture propagation, of a rock mass having a diagonal non-persistent joint (45° to the loading direction) subjected to impact loading to determine the efficiency of grout material. The focus of the study is to present a comparative assessment of different grout materials under dynamic loading. Split Hopkinson Pressure Bar (SHPB) was used to conduct the compressive impact tests on the synthetic rock mass with varying infill conditions (unfilled, cement-filled and epoxy-filled). The progressive fractures within the specimens were monitored by Photron fastcam analysis (PFA, a high-speed image analysis) and digital image correlation (DIC). The experiments highlighted that the strength of rock mass has an increasing trend with the dynamic strain rate. Epoxy resin provided a better strength enhancement than cement paste as the grout material. Due to the higher strength of epoxy resin than cement paste, the epoxy-grouted jointed rock demonstrates a similar response as the intact rock. In the case of both unfilled and cement-filled specimens, the nature of the primary crack was the coplanar shear crack. In contrast, with the injection of epoxy grout, the nature of the initial crack became the tensile or far-field tensile crack, which is often noticed in intact rocks.

ЛИРИЧЕСКИЙ ГЕРОЙ В РОК-ПОЭЗИИ

An issue of the subject in contemporary lyrics is widely discussed at the present time, being one of the most relevant in the research of contemporary poetry. One of the issues is the relevance of the term lyrical hero in relation to contemporary poetry, which, following the analyticism path, departs from the actual lyrical utterance. The article expresses an opinion that the idea of a lyrical hero remains relevant in the study of song poetry, in particular rock poetry of the 1980s – 1990s. Based on the classic article by Yu.N. Tynyanov «Block», in which an attempt is made for the first time to qualify the definition under discussion, the article analyzes the work of Russian rock poets, proves the presence of the lyrical hero in the lyrics of K. Kinchev and Yu. Shevchuk. Also, the conclusion is made about the lyrical hero specifics in classical Russian rock poetry. It is connected not only with intratext factors, such as the presence of the self-subject, the possibility for a rock poet of constructing a single plot of the hypertext, which includes biographical motives, but also extratext factors of the existence of a synthetic rock text, including the presence of the image of a lyrical hero in the socio-cultural sphere, the creation of a media image, the formation of a stage image.

The pre-launch on-ground characterization of Mars Multispectral Imager for Subsurface Studies (Ma_MISS) spectrometer for ExoMars rover mission: Spectral calibration.

The Ma_MISS spectrometer is integrated within the drilling system of the Rosalind Franklin ExoMars rover. This paper reports the on-ground calibration campaign performed on the spectrometer. Here, we focus on the spectral calibration of the instrument. The experimental setup used to carry out calibration is described, and the methods used for data processing and key parameters retrieval are explained. In particular, the spectral parameters such as (i) pixel central wavelengths, (ii) spectral response function, (iii) spectral resolution, (iv) sampling, and (v) range are determined. In a follow-up paper, the linearity and radiometric calibrations are described, while in De Sanctis etal. [Planet. Sci. J. 3, 142 (2022)], the validation of spectral measurements performed on synthetic and natural rock targets is presented.

Challenges associated with numerical back analysis in rock mechanics

Numerical back analysis is a valuable tool available to rock mechanics researchers and practitioners. Recent studies related to back analysis methods focused primarily on applications of increasingly sophisticated optimization algorithms (primarily machine learning algorithms) to rock mechanics problems. These methods have typically been applied to relatively simple problems; however, more complex back analyses continue to be conducted primarily through ad hoc manual trial-and-error processes. This paper provides a review of the basic concepts and recent developments in the field of numerical back analysis for rock mechanics, as well as some discussion of the relationship between back analysis and more broadly established frameworks for numerical modelling. The challenges of flexible constraints, non-uniqueness, material model limitations, and disparate data sources are considered, and representative case studies are presented to illustrate their impacts on back analyses. The role of back analysis (or “model calibration”) in bonded particle modelling (BPM), bonded block modelling (BBM), and synthetic rock mass (SRM) modelling is also considered, and suggestions are made for further studies on this topic.

Mechanism exploration of brittle-plastic transformation of synthetic rocks in thermal environments

Mechanism exploration of brittle-plastic transformation of synthetic rocks in thermal environments

Classifying Facies in 3D Digital Rock Images Using Supervised and Unsupervised Approaches

Lithology is one of the critical parameters influencing drilling operations and reservoir production behavior. Well completion is another important area where facies type has a crucial influence on fracture propagation. Geological formations are highly heterogeneous systems that require extensive evaluation with sophisticated approaches. Classification of facies is a critical approach to characterizing different depositional systems. Image classification is implemented as a quick and easy method to detect different facies groups. Artificial intelligence (AI) algorithms are efficiently used to categorize geological formations in a large dataset. This study involves the classification of different facies with various supervised and unsupervised learning algorithms. The dataset for training and testing was retrieved from a digital rock database published in the data brief. The study showed that supervised algorithms provided more accurate results than unsupervised algorithms. In this study, the extreme gradient boosted tree regressor was found to be the best algorithm for facies classification for the synthetic digital rocks.

Application of microtomography and petrography techniques for the characterization of porosity of synthetic carbonatic rock minerals before and after acidification processes

The objective of this work is to physically characterize and analyze synthetic carbonate rocks through microtomography and petrography techniques, focusing on a comparative analysis before and after degradation with a reactive fluid. For this study, physical characterization analysis with computerized microtomography and petrography on the samples before and after the acidification procedure was performed. The petrographic analysis verified an increase in both intergranular and intragranular porosities after dissolution. The microtomography analysis quantified the maximum increase in porosity, from 11.8 to 41.3% in the two-dimensional analysis and 31.6–52% in the three-dimensional analysis of the porous structures. Furthermore, the pores were quantified according to their area, and data was obtained on the orientation of the pores, providing insight into the preferred paths of fluid flow. It was also observed that the microtomography technique was an effective tool for characterizing fractures in the samples before and after dissolution. Such analyses are crucial for the extraction and injection of fluids at high depths due to the mechanical and physical risks arising from the dissolution of minerals as well as changes in pressure, temperature, and saturation, all of which affect the stress state of the reservoir rock.

Staged multicluster hydraulic fracture propagation mechanism and its influencing factors in horizontal wells for CBM development

AbstractStaged multicluster fracturing (SMCF) is crucial for the low‐permeability coalbed methane (CBM) reservoirs development. To reveal the fracture propagation mechanism and characteristics in SMCF and select appropriate hydraulic fracturing parameters, this study considers CBM exploitation in the Shizhuang block, Qinshui Basin in China as the engineering background. Then, XSite hydraulic fracturing software based on the discrete lattice theory and synthetic rock mass method is used to construct a three‐dimensional model. The influence mechanisms of the cluster spacing (CS) and lateral pressure coefficient (LPC) on the fractures propagation characteristics were investigated. With an increase in the CS, the stress interference between fractures gradually weakens, and the fracture deflection also decreases. Both the stimulated reservoir area (SRA) and fracture aperture of a single cluster increase with an increase in CS, but the SRA and fracturing efficiency exhibit limited growth when the CS is greater than 15 m. The SRA decreases exponentially with an increase in LPC. When the LPC increases from 0.4 to 1.4, the SRA decreases by 74.2%. The LPC plays a decisive role in the fracture propagation direction. When the LPC reaches 1.4, the fractures propagate along the horizontal direction. With an increase in LPC, the fracturing fluid pressure increases linearly, and the fracturing efficiency decreases exponentially. The results of this study reveal the fracture propagation law of SMCF and can provide a reference for engineering applications. In the SMCF at the 3# coal seam of the Shizhuang block, the CS can be set to approximately 15 m, and the CS can be appropriately reduced when the LPC is large.

Triaxial compression behavior of large-scale jointed coal: a numerical study

Accurate estimation of the triaxial compression behavior of jointed coal is essential for coal mining. Few studies addressed the triaxial compression behavior of large-scale rock mass, especially with real joint geometry. We employed a numerical synthetic rock mass (SRM) method to study the triaxial compression behavior of jointed coal. Jointed-coal specimens were constructed based on in-situ joint measurements and microparameter calibration against laboratory experiments. A series of triaxial compression tests under different loading orientations and confining pressures were numerically performed to obtain joint and confining-pressure effects on the triaxial compression behavior and reveal the failure mechanism of jointed coal. Results suggest that the triaxial compression behavior of the jointed coal has strong joint and confining-pressure effects. Joints weaken the strength and elastic modulus, reduce the lateral deformation, and affect the geometries of the shear-rupture surface. An increase in the confining pressure causes the peak and residual strength increase significantly. With an increase in the confining pressure, the elastic modulus increases sharply at low confining pressure, the mechanical behavior transitions from brittleness to ductility, the failure mode transitions from shear-rupture surface to plastic flow, and the joint effect diminishes and even disappears. The jointed coal fails by means of a shear-rupture surface under triaxial compression loading with a confining pressure (which is not too high), and the geometries of the shear-rupture surface vary with the distribution of joints.

Upscaling the Mechanical Properties of a Fractured Rock Mass Using the Lattice-Spring-Based Synthetic Rock Mass (LS-SRM) Modeling Approach—Comparison of Discontinuum, Continuum and Empirical Approaches

A numerical characterization of a fractured rock mass and its mechanical behavior using a discontinuum approach was carried out utilizing lattice-spring-based synthetic rock mass (LS-SRM) models. First, LS-SRM models on a laboratory scale were created to reproduce standard rock mechanical tests on Triassic sandstone samples from a quarry in Germany. Subsequently, the intact rock properties were upscaled to an element volume representative for geotechnical applications, recalibrated and combined with a Discrete Fracture Network (DFN) model. The resulting fractured rock mass properties are compared to predictions from empirical relationships based on rock mass classification schemes and the DFN-Oda-Geomechanics approach. Modeling results reveal a significant reduction in the strength of the fractured rock mass compared to the intact rock, showing a high agreement with empirically calculated values. Results for the deformation modulus reveal a significant reduction induced by the fracture network and a good agreement compared to the results obtained by other approaches. It is shown that the LS-SRM allows analyzing the complex mechanical behavior during failure of rock masses, including crack initiation, propagation and coalescence. The resulting rock mass properties are key parameters for a wide range of geotechnical applications and can be used for large-scale numerical modeling as well.

A Novel 3D Printing Technology for Synthetic Hard Rock and the Fabrication of Jinping Marble

A Novel 3D Printing Technology for Synthetic Hard Rock and the Fabrication of Jinping Marble

Experimental investigation of the flow properties of layered coal-rock analogues

Coals are heterogeneous and the zones of interest for gas production (high fracture density) are often friable. 3D printed (3DP) rocks can create a repeatable analogue by minimizing specimen variability. This study investigates a series of 3DP coal seam gas packages under various flow conditions to determine the impact of fracture network and interburden rock on the dynamics of permeability. The 3DP coal analogue is treated with sodium silicate and carbon dioxide to reduce porosity and permeability. Seven cylindrical specimens are analysed including: the intact 3DP coal analogue, the intact interburden analogue, the unidirectionally and multi-directionally fractured coal analogues, and packages of coal-interburden-coal with different fracture systems. These specimens are subjected to isotropic triaxial flow tests to compare the properties of natural and synthetic rocks. The experimental results revealed that the pore compressibility of 3DP rock treated with sodium silicate is in the same range as coal. 3DP specimens with multi-directional fractures exhibited lower fracture compressibility than ones with unidirectional fractures. The results suggested that the flow properties of a single coal layer might differ from that of a composite coal-interburden rock. The experimental outcomes indicate that 3D printing is a valuable tool to investigate coal behaviour under depletion conditions.

Influence of Coal Cleats on Conical Pick Cutting Process Based on PFC

With the rising mining mechanized level, the conical pick is widely used in mining machines. The structure and mechanical properties of rocks and minerals are important factors affecting the cutting characteristics of the conical pick. In this paper, how the coal cleats affect the cutting process of shearers was researched, which will be of great significance to mining technology design. After analyzing the cutting process of conical pick and the test of coal mechanical properties, a group of coal cutting models of conical pick was established based on the empirical cutting parameters, various cleat spacing, simulation of mechanical performance of coal specimens, profile of conical pick, and SRM (synthetic rock mass) method in PFC (Particle Flow Code). Then, the simulations of the cutting process were carried out. The simulation results show that lump coal chips begin to form and fall off after the conical pick cuts to 50°; the cleats near the conical pick grow to be more obvious fractures; the mean and maximum fluctuations of cutting force increase with the increase of face and butt cleat spacing; the lower the density of cleat is, the more the cracks are formed during the cutting process; the face cleat spacing has greater influence on the service life of conical pick than the butt cleat spacing. This study more vividly reflects the influence of cleats on coal cutting process of the conical pick and plays a guiding role in design of mining technology.