bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of anisotropic creep on the convergence of deep drifts in Callovo-Oxfordian claystone
Authors: Jung Sophie , Vu Minh Ngoc , Ghabezloo Siavash , Pouya Amade
Published: January 2023

The long term behavior of the lining support in deep drifts is a crucial issue for nuclear waste underground repository project. In order to demonstrate the feasibility of the project, the French Radioactive Waste Management Agency (Andra) has built an Underground Research Laboratory (URL) at Bure. The underground structure is composed of a network of galleries whose drilling generates stress redistribution, damage and fracture in the surrounding medium. The damage and fracturing of this excavation damage zone have a direct effect on the displacement field and on the interaction between the formation and the lining support. The design of the support system request, in order to be as efficient as possible, a precise knowledge of the stress and displacement fields around the drift. For viscoplastic rock formation, the stress field around the drift and its effect on the support system must be determined for at least a couple hundred years. This is why we have studied the long term behavior of drifts using an elasto-viscoplastic constitutive law. The laboratory test data and field observations have shown that the Callovo-Oxfordian claystone has a slightly anisotropic behaviour for its elasticity, failure criterion and also creep properties. This anisotropy is largely increased by the presence of the fractures, which we take into account with transverse isotropic models. Homogenization techniques are used to establish a macroscopic expression of the viscous deformation depending on the behavior of the rock matrix and of the fractures. The macroscopic viscous deformation depends on the orientation and density of fractures, which is why based on investigation campaign, we divide the fractured zone, in our numerical models, into zones with fractures of different density and orientation to describe the behavior of the fractured zone as closely to the reality as possible. The model is then applied to the simulation of the convergences of GCS drift. The so called GCS drift belong to the network of monitored drift of the URL and was excavated in the direction of the major principal horizontal stress.
Evaluation of progressive damage of discontinuity asperities due to shearing by means photogrammetric survey
Authors: Carriero M T , Ferrero A M , Migliazza M R , Umili G
Published: January 2023

It is well known that the mechanical behaviour of rock discontinuities strongly influences the stability of slopes and fractured rock walls. With this end, particular attention must be paid to the analysis of the roughness of natural discontinuities, which represents a peculiar geometric feature strongly influencing their shear strength. The paper describes an experimental procedure carried out at laboratory scale on natural rock discontinuities to measure the shear strength and the roughness of their surfaces to analyse the progressive damage of the asperities during shearing process. The direct shear tests along discontinuities were coupled to photogrammetric surveys of the surfaces carried out before the tests (natural surfaces), after the first cycle and at the end of the last cycle. This allowed the reconstruction of the digital surface models of the intact and degraded surfaces. Through analytical procedures, the data obtained were processed to obtain geometric descriptors and adequately estimate the Joint Roughness Coefficient (JRC), analysing several profiles extracted along the direction in which the mechanical tests were conducted. The comparison between the experimental results and the roughness surface direct measure showed that discontinuities, even at the small scale, have an inhomogeneous roughness and that discontinuity degree of damage is a progressive process influenced by the state of confinement applied during the tests.
Toppling of a rock block resting on a rough surface
Authors: Alejano L R , Gui J Y , González-Fernández M A , Pérez-Rey I , Muñiz M
Published: January 2023

The main aim of this study is trying to contribute to a better understanding of the role of surface roughness basal planes on toppling-related instability phenomena. In this way, the authors focus on the stability against toppling of a single block resting on a regular rough surface. To do that they have first artificially created sample rock blocks with a regular rough base and tested them against toppling in a tilt-test machine. The authors have also developed analytical formulations to theoretically estimate toppling instability under these circumstances and have carried out simple numerical DEM models to reproduce the corresponding tests. The comparison between obtained analytical and numerical results and the physical model response indicated good representativeness of both numerical and analytical approaches. Geometry characteristics of the saw cut artificially created blocks did affect results, so the numerical and analytical models were adapted by including an equivalent curvature radius in the corner of the cut block around which the overturning phenomenon takes place to account for this geometrical effect. Further research will extend these results to the case of blocks with natural irregular rough surfaces.
Identifying the “unidentifiable” contributors to large-scale instability experienced at a UG2 mine along the Western Limb of the Bushveld Complex
Authors: Plessis M du , Liebenberg S
Published: January 2023

The geology intersected by a mining excavation dictate the rockmass condition and stability of the excavation. The general geologic structure of the UG2 Reef horizon with regard to rock type, jointing and potential parting planes are well understood. Mining layouts and support applications are applied to control the anticipated rockmass behaviour. Case studies conducted at several instability sites have, however, revealed that in most cases the rockmass behaviour is controlled by the geologic structure which may appear as intact joints visible from scanline or borehole core mapping. The significance of these structures within the hangingwall is mostly not visible in a 3-dimensional space. The prominent structure is related to deformation processes which crosscut the strata and ramp to areas with strength competent contrasts (i.e. stringers or alteration layers). As a result large-scale instabilities may occur. The extent of these structures are only realised following large-scale instability. At the study site a combination of visual observations, scanline and borehole mapping, ground penetrating radar and high definition 3-dimentional laser scans were used to interrogate the geologic structure intersected along the hangingwall of a stope contributing to the instability experienced. The intent was to identify the precursors of these “unidentifiable” structures present in the unexposed hangingwall. The paper discusses the findings of the investigation conducted.
Experimental study on fracture processes of granite cylinders with different decoupling conditions
Authors: Chi L Y , Zhang Z-X , Yang J , Qiao Y
Published: January 2023

Fracture processes of granite cylinders (a diameter of 240mm and a length of 300mm) subjected to blast loading were investigated using data from three-dimensional digital image correlation (DIC) method on images captured with two high-speed cameras. The five cylinders had a centric decoupled charge (PETN) of approximately 3 g or 4 g. The centric borehole with diameter 10mm or 20mm was drilled in each cylinder, and the charge diameter was around 6 mm/7 mm. Two decoupling ratios were applied, and each specimen has a decoupled charge with water or air. A partial cylindrical surface was captured by the high-speed cameras. Both the decoupling ratio and the filled-in medium influence the fracture pattern and initiation on the surface. The specimens with the air-decoupled charge produces gas ejection 440 μs-460 μs after detonation, while the specimen with the water-decoupled charge presents gas ejection at 960 μs. Displacement fields determined from the 3D DIC analysis were used to obtain strain fields on the observed surface. It is found that the initial strain on the surface was seen approximately 40 μs after the detonator initiation. The air-filled gap yields the vertical strain concentration zone in priority, while the water-filled gap produces horizontal concentration zone. The strain concentration corresponded well with the locations and direction of the developed cracks. The experimental findings of this investigation indicate that the decoupling ratio and decoupled materials have a great impact on rock fracturing.
A weakening-healing law to simulate stick-slip behavior of rock joint and the associated seismicity
Authors: Bai Qinsheng , Konietzky Heinz
Published: January 2023

The variation of frictional strength of asperities is one of the fundamental mechanisms that govern earthquake cycles. The rate - and - state friction (RSF) law has been widely employed to explain earthquake phenomena. In RSF, the frictional strength of fault depends upon the current slipping velocity and the conditions on the slipping surface (i.e., the state), which depends partly on the prior sliding history. In this study, we proposed a simplified weakening-healing law to describe the slip behavior of individual asperity. In the weakening-healing law, the friction strength linearly decreases to the residual value with shear displacement when slip occurs, and immediately recovers to its original value once slip terminates. In the numerical model, a power-law distribution is used to introduce asperity heterogeneity (e.g., size, frictional strength, and stiffness) on a rock joint. A displacement-based moment tensor method is used to calculate the seismic moment during fault slipping. The simulated b-value (magnitude-frequency distribution) and its evolution during stick-slip phases are compared with published experiments. Slip nucleation, growth, coalescence, and the associated spatial-temporal behavior of the simulated seismicity are delineated. Although this preliminary study focuses on simplified conditions (small-scale smooth rock joint sheared under constant normal pressure and shear rate), our method successfully duplicates laboratory observed stick-slip behavior, b-value evolution, slip nucleation process, etc., providing a promising way to mimic more realistic natural earthquake phenomena.
Validation of a Continuum-based Weak Zone Joint Model for Simulating Anisotropic Rock Mass Strength
Authors: Ziebarth R A , Corkum A G , Kinakin D , Stilwell I
Published: January 2023

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.
A new experimental device developed to study the creeping behavior of a rock joint under shear stress
Authors: Jung Sophie , Ghabezloo Siavash , Bornert Michel , Pouya Amade , Lebihain Mathias , Archez Julien , Lemaire Marine , Chabot Baptiste , Vu Minh Ngoc
Published: January 2023

In the context of nuclear waste management project Cigeo, the behavior of the fractured Callovo Oxfordian claystone (COx) is studied for its time dependent effect on the long term convergences of the drifts. We present an experimental setup designed to investigate the viscous behavior of a fracture. While few experimental setup already exist with the purpose of studying the time dependent deformation of a rock joint, all of them measure the displacement in the direction of the sheared discontinuities in one point of the sample with devices such as a linear variable displacement transducers (lvdt). The information provided by this sensor comes to measuring the average displacement of the fracture slip. Depending on the configuration of the experimental device, the lvdt sometimes also measures the deformation of the rock medium which cannot always be considered as a rigid body. Which is why we propose in this paper to set a camera up in order to use Digital Image Correlation to get an information of the slip along the fracture.
Experimental investigation of the effect of thermal cycling on the thermomechanical properties of three rock varieties for high temperature thermal energy storage
Authors: Fränzer S , Jeskulke J , Neumann K M , Schumski S , Thomas S L , Duda M , Witte L C , Brajer C , Backers T
Published: January 2023

During the past years “rock batteries” have become increasingly relevant for the storage of renewable energy sources, such as wind and solar energy, because of their economic and ecological advantages with respect to previously more common materials for thermal energy storage (TES) such as salt. In rock-based TES systems, thermal energy is stored in packed-bed rock using air as heat transfer fluid. We investigated three different rock types with respect to changes in thermomechanical properties after different numbers of thermal cycles, Ruhr sandstone (Oberste quarry in Dortmund - Germany), basalt (commercial MTV basalt) and Calanca gneiss. Cylindrical samples were heated to 800°C within 11,5 h before temperature was kept constant for another 30 min and then decreased within 11,5 h. Samples were thermomechanically investigated before thermal treatment, and again after 1, 3, 7 and 15 cycles. Additionally, two samples of each rock type were subjected to a thermal cycle with a maximum temperature of 450°C and to 1000°C, respectively, at a heating/cooling rate corresponding to that of the samples heated to 800°C. Samples were characterised with respect to ultrasound wave velocity, bulk density, thermal conductivity, thermal diffusivity, uniaxial compressive strength, splitting tensile strength, mineral content (X-ray powder diffraction) and microstructure (thin section analysis). Samples of basalt could not withstand the standard heating rate. The samples crushed into small pieces also when heating rates were reduced and at a maximum heating temperature of 800°C. For sandstone and gneiss, the ultrasound wave velocity, bulk density, thermal conductivity, thermal diffusivity, uniaxial compressive strength and splitting tensile strength decreased systematically with increasing number of cycles, while the maximum reduction occurred after the first cycle and the relative reduction was similar between both rocks. Microstructural analysis indicated an increase in crack density and minor mineralogical changes upon heating. Both rocks, Ruhr sandstone and Calanca gneiss, appear suitable for TES, but Calanca gneiss is less suitable for temperatures above 800°C due to a significant reduction in bulk density and uniaxial compressive strength when heated to 1000°C. Also, its anisotropy and anisotropic response to heating can lead to preferred flow paths of the heat transfer fluid. Ruhr sandstone maintains a high uniaxial compressive strength of about 100 MPa even after 15 cycles while thermal capacity was only slightly reduced or even increased, and can be recommended for use in high temperature TES. This study is the outcome of a research-oriented teaching program at Ruhr-University Bochum within the Geoscience curriculum for students with focus on Engineering Geology. Student authors (Fränzer to Thomas) are listed in alphabetical order.
Data preparation for machine learning in rock engineering
Authors: Yang B , Nazari R , Elmo D , Stead D , Eberhardt E
Published: January 2023

Digitalization in rock engineering has resulted in significant technological advancements and the increasing use of machine learning techniques. As rock engineering transitions into becoming more data-driven, machine learning can help rock engineers improve the efficiency and utilization of large data sets in the design process. While machine learning is a powerful tool, the success of machine learning algorithms is intrinsically related to the quality and quantity of data available. It is commonly accepted that machine learning algorithms that are trained on poor quality data will result in poor and inaccurate (i.e. highly subjective) results. To limit the human factors that result from using data that represent qualitative assessments rather than objective measurements of physical properties, it is imperative to improve the data analysis and preparation/labelling process. Data preparation is especially important when applying machine learning to rock engineering problems due to the inductive and empirical nature of the design process as a result of the inherent variability of geological materials. Despite data preparation accounting for more than half of the machine learning process, there is limited research on data preparation for machine learning in rock engineering. This paper aims to fill this gap by providing a set of guidelines on the necessary data preparation steps for applying machine learning to rock engineering problems, thereby helping rock engineers improve the performance of their machine learning models.
Synergies between Heat- and Stress-Induced Spalling Theory Applied to Rock and Concrete in Tunnel Applications
Authors: Saha S , Serati M , Maluk C , Sahoo D R
Published: January 2023

Fire-induced and stress-driven catastrophic failures in rock and concrete are commonly known as spalling (or rockburst in its severe form) that have jeopardised the safety of personnel, seriously damaged rock structures, and shut down operations for months or even permanently in certain circumstances. Particularly in Australia, spalling and rockburst in deep excavations results in a heavy toll on mine safety and have become a constraint to the economic viability of several Australian deep mines since the early 1950s. The prevailing industry approach is to treat such unwanted failures and associated microseismic events as a result of insufficient energy absorption by the spalling-prone rock/concrete at the post-peak stage. However, this approach does not allow efficient handling of heat- or stress-induced failures as it requires an in-depth understanding of their mechanics. Prediction of these events based on the available failure criteria does not help either due to the numerous criteria involved and the difficulty in determining their parameters at the excavation scale. A proper understanding of the fracture growth in such failures is needed to understand the behaviour of rock or concrete structures resulting in a sudden release of energy at deep excavations. This paper investigates the similarities and differences between heat-induced concrete spalling and stress-driven rockburst and further examines the effect(s) of material, geometrical, geological properties, and the applied deviatoric stresses on these failure modes.
Some thoughts on rock slope stability issues in Mars
Authors: Aydan Ömer
Published: January 2023

In this study, the author outlines rock slope stability issues in Mars through the images provided by Mars Rovers of NASA and investigates the rock slope stability issues with the consideration of the various conditions such as layering, discontinuous nature of rock mass, overhanging, impact, vibrations as well as precarious rock blocks. Rock slope failures in Mars are categorized with references to those on Earth and the fundamental mechanisms are summarized. It is shown that. the methods developed for rock slopes can be utilized with due considerations of environmental and gravitational differences using the principles of Rock Mechanics. The outcomes of these investigations are presented and discussed in this contribution.
Probabilistic characterization of correlation between two rock properties: a data-driven approach
Authors: Aladejare A E , Akeju V O
Published: January 2023

Rock parameters are required during the design and stability analysis of mining and geotechnical structures. There is a correlation between some rock properties, especially those obtained from the same experimental set-up, and the proper estimation of such correlation is important for reliable mining engineering analysis. However, a limited quantity of rock property data often available for most mining project sites makes it difficult to estimate a reliable correlation between two rock properties. To overcome this challenge, a data-driven approach that is based on Bayesian framework is presented in this study. The approach utilizes limited data pairs of rock parameters from a site and characterizes the site-specific joint probability distribution of two correlated rock properties, without the use of an empirical model. Real data of rock properties obtained from uniaxial compression tests on migmatites at the Sanandaj-Sirjan zone in Iran is used to illustrate the approach. The results from the approach show that the marginal statistics, marginal and joint probability distributions, and correlation coefficient from the proposed approach are consistent with those of the measured data from the adopted site. This indicates that the approach is effective for characterizing the correlation between correlated rock properties and can be used when there is a need for such characterization at a site with limited data.
Application of DInSAR for monitoring slopes around a dam basin in Japan
Authors: Shoji Y. , Shigeoka Y. , Kikuchi T. , Shimizu N.
Published: January 2023

Monitoring the behavior of slopes around the sites of hydroelectric power plants and dam reservoirs is important from the viewpoints of their stable operation and a reduction in the risk to the local community. Since their facilities are widely located at dam sites, however, it is not easy to efficiently monitor the behavior of them. SAR can be a solution to the problem. On the other hand, there are still difficulties that must be overcome when applying DInSAR as an engineering tool for monitoring in practice, i.e., phase decorrelation, the accuracy and reliability of the results, etc. In particular, the dense vegetation that often covers mountainous areas can prevent the acquisition of precise measurement results. In this paper, DInSAR using ALOS-2 data is applied around a dam basin and the results are compared with the actual ground behavior to confirm the applicability of DInSAR. It is concluded that DInSAR using ALOS-2 data could be a useful tool for monitoring the slope stability of large dam basins, even those covered with dense vegetation.
Monitoring Fracture Saturation using Transportable Acoustic Sources and a Neural Network Differential Autoencoder
Authors: Nolte David D. , Pyrak-Nolte Laura J.
Published: January 2023

Acoustic signals from transportable acoustic sources were analysed using a Siamese twin neural network differential autoencoder (TDAE) to monitor changing fracture saturation within a laboratory testbed consisting of synthetic fractures. The small transportable acoustic sources, called “chattering dust” and introduced inside the fractures, generate hundreds to thousands of acoustic wavepackets that propagate across other fractures in the system. A 4-class study was performed using the TDAE by physically cycling among four different saturation conditions of the fractures. Accurate classification of all four fracture saturation conditions was achieved using mode-pooling. This work demonstrates that the twin neural network differential autoencoder, which is ideally suited to identify subtle differences among classes, can extract information about the conditions of fractures from complex and variable wavefields consisting of overlapping coda wave signals.
Micromechanical characterisation of overburden shales in the Horn River Basin through nanoindentation
Authors: Charlton T S , Rouainia M , Aplin A C , Fisher Q J , Bowen L
Published: January 2023

The paper presents a micromechanical characterisation of Fort Simpson shale, which overlies unconventional gas-producing lithologies in the Horn River Basin, NW Canada. The Fort Simpson formation is clay-rich and microseismic data recorded during hydraulic fracturing events in the underlying reservoir has shown the formation acts as a barrier to fracture development, with a notably anisotropic seismic response. Samples were prepared from core fragments and the composition and texture of the shale was characterised using X-ray diffraction, mercury injection porosimetry and scanning electron microscopy (SEM). Nanoindentation testing was used to obtain the mechanical response of the shale microstructure, at grain-scale. The indentation was conducted on a grid pattern and samples were oriented both parallel and perpendicular to the bedding plane to assess the inherent mechanical anisotropy. Chemical analysis of the grids was also undertaken through SEM/EDS (energy dispersive X-ray spectroscopy) and the coupled chemo-mechanical data was used to characterise the material phases of the shale through a statistical clustering procedure. The results show that Fort Simpson shale broadly consists of a soft clay phase, with strongly anisotropic elastic stiffness, and stiffer but effectively isotropic grains of quartz and feldspar. A simple upscaling scheme was also applied to link the grain-scale elastic stiffness to the field-scale microseismic data.
A Multimodel Bayesian Reliability Analysis for a Rock Slope to Counter Data Insufficiency
Authors: Kumar A , Tiwari G
Published: January 2023

Data insufficiency of input rock properties is a major issue to analyze the stability of slopes via traditional deterministic and reliability approaches. This data insufficiency in the properties arises due to complexities associated with in-situ and lab testing of rocks. The traditional Bayesian approach overcomes this issue by considering uncertainties in model parameters by combining available prior information neglecting the uncertainty associated with the distribution type/probability model. This study proposes a novel Bayesian multimodel inference approach to incorporate the uncertainties associated with probability models/distribution types along with model parameters for rock properties. The approach first identifies a set of candidate probability models and then employs the Bayesian framework to incorporate the parameter uncertainties for each model. The approach is demonstrated for a rock slope case with the potential of structurally controlled planar failure. It is concluded that the approach effectively treats the statistical uncertainties associated with probability model types and parameters with limited data and provides a more realistic stability assessment than the traditional Bayesian approach. Results show that the uncertainty in probability model parameters affects the stability of rock slope much more significantly than model types.
Design of falling rock preventive countermeasure based on three-dimensional simulation
Authors: Kitauchi H , Nishiyama S , Song J
Published: January 2023

To rationally design rockfall countermeasures, detailed rockfall behavior must be predicted using numerical simulations based on the conditions of slopes and rockfalls. In this study, we perform a rockfall simulation using discontinuous deformation analysis. This method is used to analyze the motion between blocks composed of polygons of arbitrary elastic bodies; furthermore, the energy conservation law and the uniqueness/convergence of the solution are guaranteed for the entire analysis target. Additionally, the rockfall shape is reproduced in detail. Both the rockfall shape and a parameter known as the velocity energy ratio, which indicates the decay of energy at the collision time of the rockfall, significantly affect the rockfall behavior. In this study, we model the actual slope shape from data measured via airborne laser and quantitatively evaluate the effect via simulations by changing the rockfall shape and velocity energy ratio. In this paper, we consider how to use the simulation for the design of rockfall countermeasures based on the results such as the change in the amount of jumping due to the difference in slope shape, geology, and rockfall shape.
The effectiveness of epoxy coating for preventing microbially induced corrosion of rock bolts
Authors: Chen H , Kimyon O , Chen R , Gunawan C , Ramandi H Lamei , Canbulat Ismet , Saydam S
Published: January 2023

In the past two decades, the corrosion failures of rock reinforcement bolts in underground coal mines have been increasingly reported. Preliminary studies have shown that these failures were predominantly related to pitting and stress corrosion cracking. The analyses in affected mines indicated microbially induced corrosion (MIC) as one of the primary corrosion causes. As such, there is an urgent demand from industries to develop methods to mitigate MIC-associated failures of rock bolts in underground coal mines. This study examined epoxy coating to determine its effectiveness in preventing biofilm formation on steel surfaces and, in turn, averting MIC. The corrosion-causing bacteria were isolated and enriched from groundwater samples collected from the affected mine sites. Coated and uncoated rock bolt samples were prepared from the bolts and incubated in media in the absence and presence of the corrosion-causing bacteria. Fluorescence microscopy imaging found no evidence of bacterial biomass growth on the surface of the epoxy-coated steel surfaces after 30 days, while the non-coated surfaces were colonised by biomass. The observations suggest the potential of epoxy coating for bolt MIC prevention. Future studies to assess the applicability of epoxy coating in the underground mine environment are recommended.
An issue in the current definition of the factor of safety for rock slopes and suggestions for improvement
Authors: Li Charlie C , Høien Are Håvard
Published: January 2023

To evaluate the stability of a rock slope a common practice is to calculate the factor of safety by dividing the driving forces on the resisting. Hoek and Bray [1] proposed a formula for the calculation of the factor of safety FS for rock slopes reinforced by pre-tensioned bolts and anchors, so-called active support devices. The formulas have been used worldwide for active support of rock slopes in the past 40 years and are also incorporated in different rock slope stability software. The reinforcement force of the active support is in the formula considered a negative driving force. On the other hand, for passive support, referring to reinforcement by non-tensioned bolts and anchors, the reinforcement force is counted as an additional resisting force in the calculations. In this paper, the two definitions to the factor of safety are examined with the help of an example of simple block equilibrium, which demonstrates issues regarding the formula for active support. It is concluded that the reinforcement force should always be counted as a resisting force in the calculation of the factor of safety regardless it is active or passive support. Concepts of factors of safety for shear failure and collapse are proposed and verified with a calculation example.
Improving Rock Pillar Stability Guidelines Through Detailed Numerical Investigation
Authors: Dressel E J , Diederichs M S
Published: January 2023

Pillar stability guidelines have been presented by numerous authors in the past, based on a combination of empirical observations (mostly visual) from mining applications and simple numerical (elastic or simple continuum plasticity) models. In many cases, the resulting design limits for pillar dimensioning are presented as universal for all rockmass conditions and stress regimes. There have been numerous developments in the past decades in mechanistic classification (brittle spalling, effective continuum rockmass, structural control) and mechanism-appropriate modelling and design metrics. These new tools and paradigms for rockmass behaviour allow for a modelling-based revision of the empirical guidelines from the past century that still form the basis of many performance critical designs. This paper includes the consideration of rockmass deformation and yield (rockmass strength approach), brittle strength, and damage behaviour where appropriate. This paper presents correlations for residual GSI and the effects of Hoek-Brown dilation on pillar behaviour. The investigation includes generating 3D FEM synthetic pillar models with equivalent elastic and plastic continuum.
Clay–rock fracturing risk assessment under high gas pressures in repository systems
Authors: Mollaali Mostafa , Buchwald Jörg , Montoya Vanessa , Kolditz Olaf , Yoshioka Keita
Published: January 2023

At the interface between the steel canister and the bentonite in a nuclear waste repository, we expect generation of hydrogen gas because of corrosion processes. The pressurized gas might fracture the engineered or natural clay barrier system, enhancing radionuclide transport into the geosphere. To assess the long-term integrity of the clay host rock under various conditions and scenarios, we need a large number of numerical simulations. However, a simulation tool for complex fracture propagation is often prohibitively expensive to run many realizations. Here, we developed a risk analysis tool based on the Design of Experiments to overcome the computational challenges by generating a computationally inexpensive proxy fracture model using a set of critical factors known as heavy hitters. We provided parameters and their probability distributions that are subject to uncertainty, as well as an objective function that assesses the risk of fracturing due to high gas pressures. Through various scenarios, we found that the fracture toughness dominates the impact on the risk.
The relict landslide in bimsoils in downtown Genova, Italy: a new modeling approach
Authors: Napoli M L , Barbero M , Minuto D , Morandi L , Ullah H
Published: January 2023

Stability problems occurring in geological units with a block-in-matrix fabric are often analyzed with deterministic approaches and/or assuming block-in-matrix rocks/soils (bimrocks or bimsoils) to be homogeneous equivalent geomaterials. However, recent studies have demonstrated that since these formations are characterized by a great (dimensional, spatial and lithological) variability, reliable results can only be obtained if a stochastic approach accounting for different block arrangements and dimensions is used.

This paper extends and improves a previous study from Minuto and Morandi (2015) to evaluate the stability of a relict landslide in bimsoil located in downtown Genova (Italy), where a deterministic approach and the traditional limit equilibrium method were used. In this work, different slope models with elliptical blocks of variable eccentricity, size and positions are generated by means of a stochastic approach and are analyzed with the FEM code RS2. Moreover, since the slope can be considered to be a bimsoil, interfaces between the blocks and matrix are introduced in order to better simulate the lower strength at the block/matrix contacts. The numerical analyses of the slope reveal that shallow failure surfaces have a higher probability of occurrence as compared to the deep failure surfaces considered by Minuto and Morandi (2015). Furthermore, lower safety factors are obtained when a block-matrix interface strength smaller than that of the matrix (i.e., a bimsoil) is simulated.
Vertical Well Assisted Hydraulic Fracturing in Mudstone Interlayer of Terrestrial Ultra-heavy Oil Reservoir
Authors: Wang Qiqi , Chen Mian , Lin Botao , Huang Yong , Chen Sen
Published: January 2023

The widely developed impermeable interlayers hinder the migration of steam and condensate in a steam stimulation project, bringing the difficulty of developing the formation part overlying the interlayer. Hydraulic fracturing the interlayer through an existing neighboring observation (vertical) well can break through the interlayer without significantly increasing the budget. In this study, the laboratory test results of true triaxial hydraulic fracturing experiments and CT tests were analyzed to investigate the fracture propagation in the oil sand-mudstone multi-layer samples. A geological model was established to simulate the crack expansion using the finite element (FE) method by employing the cohesive element to represent fracture apertures. Furthermore, the geological model after the fracturing treatment was imported to a thermo-hydro-mechanical simulator to predict its mechanical and production behavior under steam circulation. It was found from laboratory experiments that the hydraulic fractures that initiated in the mudstone layer effectively propagated into the oil sand layer. The FE simulation shows that vertical fractures can be formed under field stress conditions. The fracture would extend into the overlying and underlying oil sand layers passing through the lithological interface. Accordingly, the fractures caused by hydraulic fracturing treatment can accelerate the diffusion of injected steam and the flow of crude oil after substantial viscosity reduction by steam heating. Future research is dedicated to generating a more complex fracture network in the mudstone interlayer so that the oil and steam flow paths can be strengthened considerably.
Blominmäki wastewater treatment plant’s sewage tunnels: Challenging connection of a vertical shaft to the existing operating offshore tunnel.
Authors: Konstantas Ioannis , Paajanen Janne , Salmelainen Juha , Yli-Kuivila Jukka
Published: January 2023

The sewage tunnels of the Blominmäki Wastewater Treatment Plant (WWTP) consist of approximately 20 kilometers of inlet and discharge tunnels, access tunnels and shafts. The most challenging and technically critical part of this project was the connection of the operating offshore tunnel of the old treatment plant with the Blominmäki discharge route, through a vertical shaft. Lack of information regarding the exact location, the shape and the geological conditions of the existing tunnel called for an accurate excavation design to avoid a potential tunnel collapse and rock blocking or massive waterflow during breakthrough. An additional complexity related to the continuous operation of the tunnel in question, as both non-stop flow of treated wastewater and cooling water of the nearby heat and powerplant, had a huge impact to the ways that all work phases were carried out. All parts involved, including the clients, the contractor and a variety of consultants cooperated in order that one of the most demanding shaft excavations in Finland be carried out successfully. This paper aims to present an overview of the related challenges, along with the detailed design, risk assessment and respective mitigation measures, information about problem solving and lessons learned during the execution.
The Allegory of the Rock Engineering Cave
Authors: Elmo D , Yang B , Shapka-Fels T , Tsai R
Published: January 2023

Geoscientists and engineers are part of a system that produces changes to the world we live in. As machines are expected to gradually replace humans in various technical tasks (e.g., data collection and data characterisation), it becomes crucial to apply critical thinking and to question the foundations of commonly accepted practices. The challenge is to accept that empirical methods are shaped by cognitive biases, which result from our mind interpreting data by a process of data simplification. Indeed, it is possible to draw an analogy between rock engineering methods and Plato’s Allegory of the Cave. The fire casting the shadows along the cave walls represents the process of quantification of qualitative assessments of commonly accepted data collection methods. The chains holding the engineers as prisoners in the cave are empirical methods accepted as industry standards despite important limitations. Engineering judgment alone will not allow engineers to break free of those chains, and to emerge from the confined spaces of the cave and see things for what they really are (i.e., introduce truly objective data collections methods that better reflect failure mechanisms). In this paper the authors use philosophical arguments to justify the need to “dequantify” the GSI classification system and to teach us that engineering design should always be driven by the important questions of how, why, and whether.
Investigation, numerical model, and monitoring for Follo line - a metro project in Oslo
Authors: Trinh Nghia Quoc
Published: January 2023

Just south of Oslo Central Station the new high-speed Follo Line railway tunnels pass beneath the existing Ekeberg road tunnels. This paper presents the construction methods, numerical model, and monitoring program used to assess the stability of the E6 road tunnels during the excavation of the Follo Line tunnels only a few metres below. The construction of the Follo Line was approved subject to three conditions: (1) There should be no negative effect on the stability of the Ekeberg tunnels, (2) The traffic flow in the Ekeberg tunnels must be maintained at all times and (3) Any risk of instability in the existing tunnels must be detected beforehand so that necessary precautionary action could be taken in good time. In order to deal with the challenges, SINTEF has carried out different investigations (including rock stress measurements), established a comprehensive numerical model, and a thorough monitoring program for analyses. The activities were combined in a so-called “rock mechanic tool”, and the tool has been used successfully in this project, operating smoothly to provide adequate information for excavation planning and decision making.
3D slope stability analysis of a limestone quarry expansion in Northern Italy
Authors: Martinelli D , Pasqualone G , Cardu M , Gonzalez M Linares
Published: January 2023

Slope stability is a crucial aspect in case in quarrying, both in term of legal and technical restrictions. The availability of data regarding the rock mass characterization is not sufficient to guarantee a satisfactory stability analysis, which must be assessed by means of more accurate procedures. Limit equilibrium analyses have been used since many decades, as they can give satisfactory results for simple cases, such as planar or wedge blocks. Nevertheless, when dealing with more complex cases, such as opencast quarries and mines, where the slope geometry consists on several benches plunging in different directions, this simplified approach cannot give a satisfactory answer. In this scenario, numerical models can return a much more complete and accurate assessment of the overall stability. The paper describes a possible approach to evaluate the stability of the slopes of a limestone opencast quarry in Northern Italy. The country is experiencing a growing demand of limestone for the production of cement for the construction sector and this determined the need to expand the previous exploitations. Since the quarry experienced several expansion plans throughout the years, several site investigation campaigns have been carried out and the results were not always consistent with each other. Starting from the two most recent rock mass characterizations and by using 3D numerical models, the overall stability has been simulated by means of continuum and discontinuum analyses, to obtain a reproduction of the real episodes of instabilities that occurred in the past. The implementation of models with reliable data is essential to obtain results that are comparable with the reality: this would allow to proceed more effectively and safely with the exploitation of the future slopes.
Deployable extrusion bioprinting of compartmental tumoroids with cancer associated fibroblasts for immune cell interactions
Authors: Mazzaglia Corrado , Sheng Yaqi , Rodrigues Leonor Nunes , Lei Iek Man , Shields Jacqueline D , Huang Yan Yan Shery
Published: January 2023

Realizing the translational impacts of three-dimensional (3D) bioprinting for cancer research necessitates innovation in bioprinting workflows which integrate affordability, user-friendliness, and biological relevance. Herein, we demonstrate ‘BioArm’, a simple, yet highly effective extrusion bioprinting platform, which can be folded into a carry-on pack, and rapidly deployed between bio-facilities. BioArm enabled the reconstruction of compartmental tumoroids with cancer-associated fibroblasts (CAFs), forming the shell of each tumoroid. The 3D printed core–shell tumoroids showed de novo synthesized extracellular matrices, and enhanced cellular proliferation compared to the tumour alone 3D printed spheroid culture. Further, the in vivo phenotypes of CAFs normally lost after conventional 2D co-culture re-emerged in the bioprinted model. Embedding the 3D printed tumoroids in an immune cell-laden collagen matrix permitted tracking of the interaction between immune cells and tumoroids, and subsequent simulated immunotherapy treatments. Our deployable extrusion bioprinting workflow could significantly widen the accessibility of 3D bioprinting for replicating multi-compartmental architectures of tumour microenvironment, and for developing strategies in cancer drug testing in the future.
Sharp ring of light spotted around supermassive black hole
Authors: Johnston Hamish
Published: January 2023

A sharp ring of light created by photons racing around the back of a supermassive black hole has been spotted by researchers working on the Event Horizon Telescope (EHT).
Academics worked longer hours during COVID-19 pandemic
Authors: Hiscott Laura
Published: January 2023

A new international study has found that academics worked longer hours during the COVID-19 pandemic than before, and that longer working weeks have become part of a “new normal”.
Laser-fusion milestone ignites debate
Authors: Cartlidge Edwin
Published: January 2023

After failing to reproduce last year’s record-breaking fusion-energy shot, scientists at the US National Ignition Facility have gone back to the drawing board. Edwin Cartlidge discusses their next steps.
Beam me back
Authors: Cartwright Jon
Published: January 2023

The notion of capturing sunlight in space and beaming it to Earth has long been the stuff of science fiction. But as Jon Cartwright discovers, governments around the world are now taking “space-based solar power” seriously as a potential solution to our energy needs.
Turning a quantum advantage
Authors: Ball Philip
Published: January 2023

Vice-president of IBM Quantum Jay Gambetta talks to Philip Ball about the company’s many quantum advances over the last 20 years, as well as its recently announced five-year roadmap to “quantum advantage”.
Earth is ‘well-hidden’ from extraterrestrials
Authors: Randall Ian
Published: January 2023

The Earth’s location relative to the Sun and the galactic centre would make it difficult to spot using photometric microlensing techniques, as Ian Randall reports.
CERN slashes experiment time by 20% to save energy
Authors: Allen Michael
Published: January 2023

The CERN particle-physics lab near Geneva will reduce the planned operation of its accelerator complex by 20% next year in a response to the energy supply crisis.