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A case study on the efficacy of different roof bolting schemes in Lhoist North America’s Crab Orchard Mine

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International Journal of Mining Science and Technology 2020年第1期30卷 99-104页

作者： Reece Kurre gabriel walton Stantec Consulting Services Inc. Walnut CreekCA 94597USA Department of Geology and Geological Engineering Colorado School of MinesGoldenCO 80401USA

Roof bolting has long been used in underground mines across the world to provide ground support.Modern roof bolts are cheap and easy to install with the use of specialized machines as a part of the production cycle. Lhoist North America’s Crab Orchard Mine is an underground room and pillar limestone mine that uses mechanically anchored roof bolts for ground support. The mine currently employs two different roof bolting patterns: a standard 1.5 × 1.5 m pattern, and another 0.8 × 0.8 m pattern for use in areas with particularly hazardous roof conditions. The purpose of this study is to evaluate the relative effectiveness of each bolting pattern. A series of numerical models were created using Roc Science’s RS2. The models were based on a symmetrical section of the mine at its deepest point, and were modeled using generalized Hoek-Brown failure criterion along with a discrete fracture network. A series of sensitivity analyses were performed on the models by varying parameters such as joint friction angle, crack persistence, joint randomization, and tensile strength of the limestone. Based on the results of the original models and sensitivity analyses, it appeared that the standard bolting pattern provided sufficient roof support capacity under almost all the expected conditions at the mine, since safety factors below the design value of 1.5 were only found for individual bolts in a few of the worst test cases considered.These results can help improve the mine’s productivity and reduce operating costs without compromising safety.

关键词： Numerical modeling Mining Roof bolting Roof stability Analysis RocScience’s RS2 Underground stone

Numerical analyses of pillar behavior with variation in yield criterion,dilatancy, rock heterogeneity and length to width ratio

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Journal of Rock Mechanics and Geotechnical Engineering 2019年第1期11卷 46-60页

作者： Sankhaneel Sinha gabriel walton Colorado School of Mines

With recent advances in numerical modeling, design of underground structures increasingly relies on numerical modeling-based analysis approaches. While modeling tools like the discrete element method(DEM) and the combined finite-discrete element method(FDEM) are useful for investigating small-scale damage processes, continuum models remain the primary practical tool for most field-scale problems.The results obtained from such models are significantly dependent on the selection of an appropriate yield criterion and dilation angle. Towards improving its capabilities in handling mining-related problems, the authors have previously developed a new yield criterion(called progressive S-shaped criterion). The focus of the current study is to demonstrate its use in modeling rock pillars through a comparative analysis against four other yield criteria. In addition to the progressive S-shaped criterion,only one out of the four other criteria predicted a trend in strength consistent with an empirical pillar strength database compiled from the literature. Given the closely-knit relationship between yield criteria and dilation angle in controlling the overall damage process, a separate comparison was conducted using a mobilized dilation model, a zero degree dilation angle and a constant non-zero dilation angle. This study also investigates the impact of meso-scale heterogeneity in mechanical properties on the overall model response by assigning probability distributions to the input parameters. The comparisons revealed that an isotropic model using a combination of progressive S-shaped criterion and mobilized dilation angle model is sufficient in capturing the behaviors of rock pillars. Subsequently, the pillar model was used to assess the effect of L/W(length/width) ratio on the peak strength.

关键词： Rock pillars Progressive S-shaped criterion Numerical modeling

Modeling behaviors of a coal pillar rib using the progressive S-shaped yield criterion

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第3期12卷 484-492页

作者： Sankhaneel Sinha gabriel walton Colorado School of Mines GoldenCO80401USA

Spalling of pillar ribs has been a major hazard in the mining industry for decades.In the absence of rib support guidelines,accidents have continued to occur in recent years.Developing effective support guidelines requires a complete understanding of complex pillar damage mechanisms.Continuum models represent a convenient tool for analyzing this problem,but the behavior of such models is dependent of the choice of the constitutive model.In this study,a recently proposed constitutive model was used to simulate the rib fracturing process in a longwall chain pillar at West Cliff mine.After calibration,the model was able to capture the rib displacement profiles for multiple locations of the longwall face and the stress evolution 4 m into the pillar.The rib bolts in the model were found to be yielding over 60% of their length under the headgate loading condition.The model also predicted a steady damage accumulation in the rib for certain face locations,which is consistent with the description of the rib at the site.Damage was localized along the upper part of the pillar and underscored the role that the dirt band played in controlling rib deterioration at the site.The ability of the numerical model to replicate field measurements provides confidence in the capabilities of the new constitutive model.Finally,the need of using multi-point calibration is highlighted by comparing the results of the calibrated model to an alternative model calibrated to a smaller amount of data.

关键词： S-shaped yield criterion Coal pillar Back-analysis Numerical modeling

Integration of three-dimensional continuum model and two-dimensional bonded block model for studying the damage process in a granite pillar at the Creighton Mine,Sudbury,Canada

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第2期13卷 275-288页

作者： Sankhaneel Sinha gabriel walton Geology and Geological Engineering Colorado School of MinesGoldenCO80401USA

Bonded blockmodel(BBM)has shownpotential in replicating rockmass behavior aswell as the rockesupport interactionmechanism,but their practical application is limited totwo dimensions due to the high associated computational demand.To allow for the use of BBM in simulating three-dimensional(3D)problems,this study proposes an integrated 3D continuumetwo-dimensional(2D)discontinuum approach,in context of rock pillars.A cross-section of a granite pillar was simulated using a BBM with a load path from a calibrated mine-scale FLAC^(3D)model.Pillar support as employed in the mine was also incorporated in different stages during the simulation.Themodel was calibrated by varying the input parameters until the displacements at six locations within the pillarmatchedthosemeasuredby amulti-point borehole extensometer(MPBX)inthe field.The calibratedmodel was subsequently used to understand how the support and load path influenced the damage evolution in the pillar.The shear component of the load pathwas found to have amajor effect on the severity and extent of the damaged regions.When the support density was increased in the model,the lateral displacements along the pillar walls were significantly suppressed in a somewhat unpredictable manner.Thiswas explained by the interaction between the supports and the damaged regions at the corners,which ultimately modified the stresses along the pillar periphery.The amount of displacement reduction obtained by increasing the support density illustrates the potential of BBMto be used as a support design tool.

关键词： Bonded block model(BBM) Rock pillars Supports Continuum-discontinuum integration

Understanding roof deformation mechanics and parametric sensitivities of coal mine entries using the discrete element method

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International Journal of Mining Science and Technology 2020年第1期30卷 123-129页

作者： Rami Abousleiman gabriel walton Sankhaneel Sinha Department of Geology and Geological Engineering Colorado School of MinesGoldenCO 80218USA

Although conventional coal mine designs are conservative regarding pillar strength,local failures such as roof-falls and pillar bursts still affect mine safety and operations.Previous studies have identified that discontinuous,layered roof materials have some self-supporting capacity.This research is a preliminary step towards understanding these mechanics in coal-measure rocks.Although others have considered broad conceptual models and simplified analogs for mine roof behavior,this study presents a unique numerical model that more completely represents in-situ roof conditions.The discrete element method(DEM)is utilized to conduct a parametric analysis considering a range of in-situ stress ratios,material properties,and joint networks to determine the parameters controlling the stability of single-entries modeled in two-dimensions.Model results are compared to empirical observations of roof-support effectiveness(ARBS)in the context of the coal mine roof rating(CMRR)system.Results such as immediate roof displacement,overall stability,and statistical relationships between model parameters and outcomes are presented herein.Potential practical applications of this line of research include:(1)roof-support optimization for a range of coal-measure rocks,(2)establishment of a relationship between roof stability and pillar stress,and(3)determination of which parameters are most critical to roof stability and therefore require concentrated evaluation.

关键词： Numerical modeling Discrete element method Coal mine roof rating Analysis of roof bolt systems Sensitivity analysis Strain softening ubiquitous joints Discrete fracture network

Investigation of factors influencing roof stability at a Western U.S.longwall coal mine

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International Journal of Mining Science and Technology 2019年第1期29卷 139-143页

作者： Meriel Young gabriel walton Elizabeth Holley Department.Geology&Geol.Engineering Colorado School of Mines Department Mining Engineering Colorado School of Mines

The coal mine roof rating(CMRR) was developed to bridge the gap between geological variation in underground coal mines and engineering design. The CMRR accounts for the compressive strength of the immediate roof, the shear strength and intensity of any discontinuities present, and the moisture sensitivity of the immediate roof. The CMRR has been widely used and validated in Eastern US coal mines, but it has seen limited application in the Western US. This study focuses on roof behavior at a Western coal mine(Mine A). Mine A shows significant lateral geological variation, along with localized faulting and a laterally extensive sandstone channel network. The CMRR is not used to predict roof instability at the mine. It is, therefore, hypothesized that there are other factors that are correlated with roof instability in underground coal mines that could potentially also be considered in conjunction with the CMRR.This hypothesis was tested by collecting 30 CMRR measurements at Mine A. At each measurement location, a binary record of the roof condition(stable or unstable) was made, and other parameters such as depth of cover, presence of faulting, and sandstone channels were also recorded. ANOVA tests showed that the CMRR values and the roof conditions were not strongly correlated, indicating that the CMRR input criteria are not fully predictive of roof stability at this mine. The CMRR values showed statistically significant correlations(p less than 0.05) with faulting as well as with location at an intersection. For areas that had previously experienced roof fall but were currently stable, faulting was correlated with roof condition(p less than 0.05) only when the condition was classified as unstable.

关键词： Coal mine roof stability CMRR Western U.S.coal Case study

Investigation of the anisotropic confinement-dependent brittleness of a Utah coal

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International Journal of Coal Science & Technology 2021年第2期8卷 274-290页

作者： Bo-Hyun Kim gabriel walton Mark KLarson Steve Berry CDC/NIOSH 315 E.Montgomery Ave.SpokaneWAUSA Department of Geology and Geological Engineering Colorado School of MinesGoldenCOUSA Department of Geological Engineering Montana TechButteMTUSA

Changes of failure mechanism with increasing confinement,from extensional to shear-dominated failure,are widely observed in the rupture of intact specimens at the laboratory scale and in rock masses.In an analysis published in 2018,both unconfined and triaxial compressive tests were conducted to investigate the strength characteristics of 84 specimens of a Utah coal,including the spalling limits,the ratio of apparent unconfined compressive strength to unconfined compressive strength(UCS),the damage characteristics,and the post-yield dilatancy.These mechanical characteristics were found to be strongly anisotropic as a function of the orientation of the cleats relative to the loading direction,defined as the included angle.A total of four different included angles were used in the work performed in 2018.The authors found that the degree of anisotropic strength differed according to the included angle.However,the transition from extensional to shear failure at the given confinements was not clearly identified.In this study,a total of 20 specimens were additionally prepared from the same coal sample used in the previous study and then tested under both unconfined and triaxial compressive conditions.Because the authors already knew the most contrasting cases of the included angles from the previous work using the four included angles,they chose only two of the included angles(0°and 30°)for this study.For the triaxial compressive tests,a greater confining stress than the mean UCS was applied to the specimens in an attempt to identify the brittle-ductile transition of the coal.The new results have been compiled with the previous results in order to re-evaluate the confinement-dependency of the coal behavior.Additionally,the different confining stresses are used as analogs for different width-to-height(W/H)conditions of pillar strength.Although the W/H ratios of the specimens were not directly considered during testing,the equivalent W/H ratios of a pillar as a function of the confining stresses were estimated using an e

关键词： Utah coal Spalling limit AUCS/UCS ratio Damage characteristic Post-yield dilatancy Anisotropic

Validity of continuous-failure-state unloading triaxial tests as a means to estimate the residual strength of rocks

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第4期13卷 717-726页

作者： gabriel walton Steven Gaines Leandro R.Alejano Department of Geology and Engineering Geology Colorado School of MinesGoldenCO80401USA Natural Resources Canada CanmetMININGOttawaOntarioK1A 1M1Canada Department of Natural Resources and Environmental Engineering Universidad de VigoVigo36310Spain

The residual strength of rocks and rock masses is an important parameter to be constrained for analysis and design purposes in many rock engineering applications.A residual strength envelope in principal stress space is typically developed using residual strength data obtained from compression tests on many different specimens of the same rock type.In this study,we examined the potential for use of the continuous-failure-state testing concept as a means to constrain the residual strength envelope using a limited number of specimens.Specifically,cylindrical specimens of three rock types(granodiorite,diabase,and Stanstead granite)were unloaded at the residual state such that a full residual strength envelope for each individual specimen was obtained.Using a residual strength model that introduces a single new strength parameter(the residual strength index,or RSI),the results of the continuous-failurestate unloading tests were compared to conventionally obtained residual strength envelopes.Overall,the continuous-failure-state residual strength data were found to be consistent with the conventional residual strength data.However,it was identified that the primary factor limiting an accurate characterization of the residual strength for a given rock type is not the amount of data for a given specimen,but the variety of specimens available to characterize the inherent variability of the rock unit of interest.Accordingly,the use of continuous-failure-state testing for estimation of the residual strength of a rock unit is only recommended when the number of specimens available for testing is very limited(i.e.<5).

关键词： Residual strength Continuous-failure-state testing Compression testing Brittle rock mechanics

Fatty Acid Binding Protein-4 Silencing Attenuates Atherosclerosis Progression by Affecting Macrophage Apoptosis and Autophagy

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Journal of Biosciences and Medicines 2019年第7期7卷 99-109页

作者： Siqin Zhaorigetu Priyanka Prathipati Cristian Rodriguez-Aguayo Brian L. walton Anil K. Sood gabriel Berestein-Lopez Department of Pediatric Surgery Center for Advanced Heart Failure University of Texas Health Science Center at Houston Houston TX USA Department of Advanced Cardiopulmonary Therapies and Transplantation Center for Advanced Heart Failure University of Texas Health Science Center at Houston Houston TX USA Department of Experimental Therapeutics The University of Texas M.D. Anderson Cancer Center Houston TX USA The Center for RNA Interference and Non-Coding RNA The University of Texas M.D. Anderson Cancer Center Houston TX USA Department of Cancer Biology The University of Texas M.D. Anderson Cancer Center Houston TX USA Department of Gynecology Oncology & Reproductive Medicine The University of Texas M.D. Anderson Cancer Center Houston TX USA

Background: Atherosclerosis, which is the principal cause of heart attacks and strokes, is the leading cause of death in the United States. Various biological processes such as apoptosis and autophagy are involved in almost every stage of atherosclerosis, which could lead to plaque instability causing stroke and death. Fatty Acid Binding Protein 4 (FABP4) is an adipokine released by macrophages and is involved in multiple disease conditions including stroke. However, the association of FABP4 with macrophage apoptosis and autophagy in atherosclerosis has not been elucidated. We hypothesize that silencing FABP4 protein could be a novel therapeutic approach to attenuate macrophage apoptosis and autophagy thereby minimizing plaque instability in atherosclerosis. Methods: RAW264 mouse macrophage cells were transfected with siRNA control liposome quantum dots (QD), siFABP4 liposome QD at the concentration of 150 μg/ml total lipids, or TNF-α at 100 ng/ml. Western blot and reverse phase protein array (RPPA) analysis were completed. Results: Inhibiting the translation of FABP4 blocked the apoptotic pathway as evidenced from the increased expression of anti-apoptotic BCL-xL and BCL-2 along with reduced expression of BAX and activated Caspase 3 levels. Beclin-1 and LC3-II levels were also reduced with knocking down FABP4 indicating the attenuation of autophagy. Conclusion: Targeting FABP4 protects against macrophage processes associated with the progression of atherosclerosis.

关键词： Atherosclerosis Apoptosis Liposomes Macrophages FABP4