Subjects -> MINES AND MINING INDUSTRY (Total: 81 journals)
 Showing 1 - 42 of 42 Journals sorted alphabetically American Mineralogist       (Followers: 16) Applied Earth Science : Transactions of the Institutions of Mining and Metallurgy       (Followers: 4) Archives of Mining Sciences       (Followers: 3) AusiMM Bulletin       (Followers: 1) BHM Berg- und Hüttenmännische Monatshefte       (Followers: 2) Canadian Mineralogist       (Followers: 7) Clay Minerals       (Followers: 9) Clays and Clay Minerals       (Followers: 5) Coal Science and Technology       (Followers: 3) Contributions to Mineralogy and Petrology       (Followers: 14) Environmental Geochemistry and Health       (Followers: 2) European Journal of Mineralogy       (Followers: 14) Exploration and Mining Geology       (Followers: 3) Extractive Industries and Society       (Followers: 2) Gems & Gemology       (Followers: 2) Geology of Ore Deposits       (Followers: 5) Geomaterials       (Followers: 3) Geotechnical and Geological Engineering       (Followers: 9) Ghana Mining Journal       (Followers: 3) Gold Bulletin       (Followers: 2) Inside Mining International Journal of Coal Geology       (Followers: 4) International Journal of Coal Preparation and Utilization       (Followers: 2) International Journal of Coal Science & Technology       (Followers: 1) International Journal of Hospitality & Tourism Administration       (Followers: 15) International Journal of Mineral Processing       (Followers: 8) International Journal of Minerals, Metallurgy, and Materials       (Followers: 11) International Journal of Mining and Geo-Engineering       (Followers: 4) International Journal of Mining and Mineral Engineering       (Followers: 8) International Journal of Mining Engineering and Mineral Processing       (Followers: 6) International Journal of Mining Science and Technology       (Followers: 4) International Journal of Mining, Reclamation and Environment       (Followers: 6) International Journal of Rock Mechanics and Mining Sciences       (Followers: 9) Journal of Analytical and Numerical Methods in Mining Engineering Journal of Applied Geophysics       (Followers: 17) Journal of Central South University       (Followers: 1) Journal of China Coal Society Journal of China University of Mining and Technology       (Followers: 1) Journal of Convention & Event Tourism       (Followers: 6) Journal of Geology and Mining Research       (Followers: 10) Journal of Human Resources in Hospitality & Tourism       (Followers: 9) Journal of Materials Research and Technology       (Followers: 2) Journal of Metamorphic Geology       (Followers: 17) Journal of Mining Institute Journal of Mining Science       (Followers: 5) Journal of Quality Assurance in Hospitality & Tourism       (Followers: 6) Journal of Sustainable Mining       (Followers: 3) Journal of the Southern African Institute of Mining and Metallurgy       (Followers: 6) Lithology and Mineral Resources       (Followers: 4) Lithos       (Followers: 12) Mine Water and the Environment       (Followers: 5) Mineral Economics       (Followers: 2) Mineral Processing and Extractive Metallurgy : Transactions of the Institutions of Mining and Metallurgy       (Followers: 14) Mineral Processing and Extractive Metallurgy Review       (Followers: 5) Mineralium Deposita       (Followers: 5) Mineralogia       (Followers: 2) Mineralogical Magazine       (Followers: 1) Mineralogy and Petrology       (Followers: 5) Minerals       (Followers: 2) Minerals & Energy - Raw Materials Report       (Followers: 1) Minerals Engineering       (Followers: 14) Mining Engineering       (Followers: 7) Mining Journal       (Followers: 4) Mining Report       (Followers: 3) Mining Technology : Transactions of the Institutions of Mining and Metallurgy       (Followers: 4) Mining, Metallurgy & Exploration Natural Resources & Engineering Natural Resources Research       (Followers: 4) Neues Jahrbuch für Mineralogie - Abhandlungen       (Followers: 1) Physics and Chemistry of Minerals       (Followers: 4) Podzemni Radovi Rangeland Journal       (Followers: 4) Réalités industrielles Rem : Revista Escola de Minas Resources Policy       (Followers: 4) Reviews in Mineralogy and Geochemistry       (Followers: 5) Revista del Instituto de Investigación de la Facultad de Ingeniería Geológica, Minera, Metalurgica y Geográfica Rock Mechanics and Rock Engineering       (Followers: 9) Rocks & Minerals       (Followers: 5) Rudarsko-geološko-naftni Zbornik Transactions of Nonferrous Metals Society of China       (Followers: 9)
Similar Journals
 Rock Mechanics and Rock EngineeringJournal Prestige (SJR): 2.328 Citation Impact (citeScore): 3Number of Followers: 9      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1434-453X - ISSN (Online) 0723-2632 Published by Springer-Verlag  [2626 journals]
• Study on Crack Evolution Mechanism of Roadside Backfill Body in Gob-Side
Entry Retaining Based on UDEC Trigon Model
• Abstract: Abstract Gob-side entry retaining is a non-chain pillar mining technology in which reasonable roadside support is important for efficient roadway maintenance and goaf isolation in coal mines. A UDEC Trigon model is adopted in this paper to study the mechanism of crack expansion and evolution at various distances from the working face. This is done to optimize parameters for the roadside backfill body (RBB) by combining emergence, development and aggregation of micro-cracks with macroscopic mechanical responses. Results of the model show that cracks first appear in the top and bottom corner of the roadway in the lane-side RBB. Damage to the RBB is mainly caused by tensile cracks, which can be divided into main and secondary crack-development and yield-bearing zones. A reasonable aspect ratio of the RBB can greatly increase the area of the yield-bearing zone and reduce the damage degree, while reducing the number of penetrating cracks and preventing generation of seepage channels. The application of this model for gob-side entry retaining in the intake airway of the N2105 working face in the Yuwu coal mine indicates that deformation of the surrounding rocks can be effectively controlled.
PubDate: 2019-03-21
DOI: 10.1007/s00603-019-01789-6

• Review of the Validity of the Use of Artificial Specimens for
Characterizing the Mechanical Properties of Rocks
• Abstract: Abstract The field of rock mechanics is concerned with the response of rocks to the forces acting on them, characterizing this behaviour in specific environments and under varying loading conditions. This review discusses the suitability of current mechanical testing methods for inhomogeneous rock bodies, with a specific focus on the use of artificial samples in place of real rocks in these tests. The use of artificial materials such as cement, resins, and sand-based mixtures is reviewed, as is the manufacture of three-dimensionally printed samples. The benefits and drawbacks of using such specimens in mechanical tests, and the validity of their simulation of real rock are discussed. There is evidence that 3D-printed samples have the advantage of overcoming the problems of specimen reproducibility and also make possible the ability to test the response of specific defects to loading. There is thus great potential for the use of 3D printing in this field. However, the review concludes that further post-processing and careful thought about the materials used must be carried out to ensure that printed samples are of adequate strength and brittleness to accurately simulate real rocks.
PubDate: 2019-03-20
DOI: 10.1007/s00603-019-01787-8

• The Microwave-Induced Fracturing of Hard Rock
• Abstract: Abstract A new, high-efficiency technology for fracturing and breaking rocks is required. Due to various advantages including high efficiency, energy-saving, and having no secondary pollution, the technology of microwave-induced fracturing of hard rock has been considered as a potential method for rock fracturing and breaking. Aiming at the realisation of two engineering applications: microwave-assisted mechanical rock breaking and stress release from rock masses in deep underground engineering works to prevent geological disasters caused by high-stress concentrations such as rockbursts, a novel (open-type) microwave-induced fracturing apparatus (OMWFA) for fracturing hard rocks was developed. On this basis, the two modes of microwave-induced subsurface fracturing and microwave-induced borehole fracturing of hard rocks were proposed. Due to removal of the restraint of the microwave cavity, OMWFA can be used to fracture large-size rock samples and engineering-scale rock masses. Using the apparatus, the fracturing effects of the two fracturing modes on different dimensions of cuboidal basalt samples were investigated. By combining the microwave-induced fracturing apparatus with a press machine to explore the influence of unidirectional stress on the fracturing effect of microwave treatment on basalt. Moreover, field tests were carried out on rock masses encountered in underground engineering works at Baihetan Hydropower Station in Sichuan Province, China, and the fracturing effects were evaluated by applying a digital borehole televiewer and conducting acoustic wave testing. The results show that the apparatus had favourable fracturing effects on the subsurface and borehole samples of basalt. When no stress was applied, the cracks radially expanded from the approximate centre of the radiant surface and unidirectional stress promoted fracturing. The number and depth of cracks increased with prolonged microwave exposure. After microwave treatment, the P-wave velocity of the samples declined, and the longer the microwave exposure, the more significant the reduction in P-wave velocity was. The results of field test reveal that borehole fracturing can exhibit a favourable effect around boreholes. The sound velocity around the borehole and between the boreholes both declined to some extent. Microwave-induced hard rock fracturing offers guiding significance to those exploring and developing new rock breaking and tunnelling methods, and generally enhances construction safety in deep underground engineering works.
PubDate: 2019-03-20
DOI: 10.1007/s00603-019-01790-z

• Effect of Abrasive Feed Rate on Rock Cutting Performance of Abrasive
Waterjet
• Abstract: Abstract Rock cutting with an abrasive waterjet system has been attempted in mining and construction fields. In abrasive waterjet cutting, the overall operating cost depends on the cost of the consumed abrasive. For this reason, it is important to identify an optimum abrasive feed rate for cost and performance efficiency. In this study, the concept of the abrasive/water ratio in volume (i.e., mixing rate of the abrasive and water amount) was introduced to explore the optimum feed rate for the cutting performance according to the water flow rate. Rock cutting tests were performed on intact granite specimens at different abrasive/water ratios. The test results were analyzed based on the effect of the abrasive feed rate in a constant water flow rate condition and on the effect of the water flow rate in a constant abrasive feed rate condition, respectively. In addition, the ratio of the abrasive particle size to the abrasive–water mixture flow space (i.e., mixing tube size) was considered and analyzed to determine the optimum abrasive/water ratio. Under the conditions given in this study, the optimum abrasive/water ratio ranges from 0.08 to 0.20 and tends to increase with an increase in the average particle size, particle size uniformity of the abrasive, and mixing tube size. In the performance analysis of rock cutting, a higher water flow rate causes a better cutting efficiency; meanwhile, the optimum abrasive feed rate achieves the maximum cutting performance. These findings can help to estimate the amount of abrasive required for efficient rock cutting.
PubDate: 2019-03-18
DOI: 10.1007/s00603-019-01784-x

• Very Slow Creep Tests on Salt Samples
• Abstract: Abstract The objective of this paper is to assess the creep law of natural salt in a small deviatoric stress range. In this range, creep is suspected to be much faster than what is predicted by most constitutive laws used in the cavern and mining industries. Five 2-year, multistage creep tests were performed with creep-testing devices set in a gallery of the Altaussee mine in Austria to take advantage of the very stable temperature and humidity conditions in this salt mine. Each stage was 8-month long. Dead loads were applied, and vertical displacements were measured through gages that had a resolution of 12.5 nm. Loading steps were 0.2, 0.4, and 0.6 MPa, which are much smaller than the loads that are usually applied during creep tests (5–20 MPa). Five salt samples were used: two samples were cored from the Avery Island salt mine in Louisiana, United States; two samples were cored from the Gorleben salt mine in Germany; and one sample was cored from a deep borehole at Hauterives in Drôme, France. During these tests, transient creep is relatively long (6–10 months). Measured steady-state strain rates ( $$\dot {\varepsilon }$$  = 10−13–10−12 s−1) are much faster (by 7–8 orders of magnitude) than those extrapolated from relatively high-stress tests (σ = 5–20 MPa). When compared to n = 5 within the high-stress domain for Gorleben and Avery Island salts, a power-law stress exponent within the low-stress domain appears to be close to n = 1. These results suggest that the pressure solution may be the dominant deformation mechanism in the steady-state regime reached by the tested samples and will have important consequences for the computation of caverns or mines behavior. This project was funded by the Solution-Mining Research Institute.
PubDate: 2019-03-15
DOI: 10.1007/s00603-019-01778-9

• Simulation of Fracture Coalescence in Granite via the Combined
Finite–Discrete Element Method
• Abstract: Abstract Fracture coalescence is a critical phenomenon for creating large, inter-connected fractures from smaller cracks, affecting fracture network flow and seismic energy release potential. In this paper, simulations are performed to model fracture coalescence processes in granite specimens with pre-existing flaws. These simulations utilize an in-house implementation of the combined finite–discrete element method (FDEM) known as the hybrid optimization software suite (HOSS). The pre-existing flaws within the specimens follow two geometric patterns: (1) a single-flaw oriented at different angles with respect to the loading direction, and (2) two flaws, where the primary flaw is oriented perpendicular to the loading direction and the secondary flaw is oriented at different angles. The simulations provide insight into the evolution of tensile and shear fracture behavior as a function of time. The single-flaw simulations accurately reproduce experimentally measured peak stresses as a function of flaw inclination angle. Both the single- and double-flaw simulations exhibit a linear increase in strength with increasing flaw angle while the double-flaw specimens are systematically weaker than the single-flaw specimens.
PubDate: 2019-03-14
DOI: 10.1007/s00603-019-01773-0

• Probabilistic Characterization of Rock Mass from Limited Laboratory Tests
and Field Data: Associated Reliability Analysis and Its Interpretation
• Abstract: Abstract Probabilistic methods are the most efficient methods to account for different types of uncertainties encountered in the estimated rock properties required for the stability analysis of rock slopes and tunnels. These methods require estimation of various parameters of probability distributions like mean, standard deviation (SD) and distributions types of rock properties, which requires large amount of data from laboratory and field investigations. However, in rock mechanics, the data available on rock properties for a project are often limited since the extents of projects are usually large and the test data are minimal due to cost constraints. Due to the unavailability of adequate test data, parameters (mean and SD) of probability distributions of rock properties themselves contain uncertainties. Since traditional reliability analysis uses these uncertain parameters (mean and SD) of probability distributions of rock properties, they may give incorrect estimation of the reliability of rock slope stability. This paper presents a method to overcome this limitation of traditional reliability analysis and outlines a new approach of rock mass characterization for the cases with limited data. This approach uses Sobol’s global sensitivity analysis and bootstrap method coupled with augmented radial basis function based response surface. This method is capable of handling the uncertainties in the parameters (mean and SD) of probability distributions of rock properties and can include their effect in the stability estimates of rock slopes. The proposed method is more practical and efficient, since it considers uncertainty in the statistical parameters of most commonly and easily available rock properties, i.e. uniaxial compressive strength and Geological Strength Index. Further, computational effort involved in the reliability analysis of rock slopes of large dimensions is comparatively smaller in this method. Present study also demonstrates this method through reliability analysis of a large rock slope of an open pit gold mine in Karnataka region of India. Results are compared with the results from traditional reliability analysis to highlight the advantages of the proposed method. It is observed that uncertainties in probability distribution type and its parameters (mean and SD) of rock properties have considerable effect on the estimated reliability index of the rock slope and hence traditional reliability methods based on the parameters of probability distributions estimated using limited data can make incorrect estimation of rock slope stability. Further, stability of the rock slope determined from proposed approach based on bootstrap method is represented by confidence interval of reliability index instead of a fixed value of reliability index as in traditional methods, providing more realistic estimates of rock slope stability.
PubDate: 2019-03-14
DOI: 10.1007/s00603-019-01780-1

• A Laboratory Study of Shear Behaviour of Rockbolts Under Dynamic Loading
Based on the Drop Test Using a Double Shear System
PubDate: 2019-03-14
DOI: 10.1007/s00603-019-01776-x

• ISRM Suggested Method for In Situ Acoustic Emission Monitoring of the
Fracturing Process in Rock Masses
• Abstract: Abstract The purpose of this ISRM Suggested Method is to describe a methodology for in situ acoustic emission monitoring of the rock mass fracturing processes occurring as a result of excavations for tunnels, large caverns in the fields of civil, rock slopes and mining engineering, etc. In this Suggested Method, the equipment that is required for an acoustic emission monitoring system is described; the procedures are outlined and illustrated, together with the methods for data acquisition and processing for improving the monitoring results. There is an explanation of the methods for presenting and interpreting the results, and recommendations are supported by several examples.
PubDate: 2019-03-13
DOI: 10.1007/s00603-019-01774-z

• Focal Mechanism of Mining-Induced Seismicity in Fault Zones: A Case Study
of Yongshaba Mine in China
• Abstract: Abstract It is essential to investigate focal mechanisms of induced seismicity for understanding the rock fracturing, the failure mode, and the hazard evolution in underground mines. But the conventional methods using empiricism to infer the source mechanisms usually lead to ambiguous results for individual events. An optimized moment tensor inversion method using full waveforms was employed to quantitatively determine the rock fracturing orientation and the type of rupture process. Source parameters including the scalar moment, the moment magnitude, the full moment tensor, and the fault plane solutions were resolved of a seismic sequence in fault zones. Results show that the shear failure events in the fault F1 vicinities have similar focal mechanisms and suggest that the fault F1 is a reverse fault. The resolved strikes and dips are basically constant with the orientation of the fault. The events in the fault F2 vicinities are mainly dominated by shear-tensional failure. But the shear events experienced shear rupture and crack opening simultaneously, resulting in slippages not along the actual fault plane. There are more events in the fault F3 area which are characterized by complicated focal mechanisms. Three of the non-shear events are dominated by compressional failure and related to rock collapse, while the other non-shear events are dominated by tensional failure and related to crack opening. The shear dominated events experienced dual effects of shear failure and compression failure. The resolved fault plane solutions cannot reflect the actual geometry of the fault. It is proved that the moment tensor inversion is able to quantitatively analyze the focal mechanism of mining-induced seismicity in fault zones and it provides beneficial understandings of mining-induced fault slips.
PubDate: 2019-03-12
DOI: 10.1007/s00603-019-01761-4

• Numerical Investigation of the Stress Distribution in Backfilled Stopes
Considering Creep Behaviour of Rock Mass
• Abstract: Abstract Evaluating the interaction between backfilled stopes and the surrounding rock mass is a vital issue during secure backfill application and stope stability analysis. With the increase of rock mass complexity and mining depth, weak rock masses and high in situ stresses are increasingly encountered, emphasising the consideration of the creep behaviour of the rock mass (CBRM). In this paper, a modelling framework was proposed by considering the CBRM and the time-dependent characteristics of backfill (e.g., increasing stiffness and cohesion with time). A generic study was present to investigate the effect of the CBRM on the stress distribution in the backfilled stope. In the generic study, a reference case was investigated in detail followed by an extensive parametric study. Furthermore, the proposed modelling framework was applied to an engineering instance, namely, the Baixiangshan Iron Mine, to verify its robustness. The generic study shows that the horizontal stress was much larger than the vertical stress in the backfilled stope at day 21 and the stress was transferred from the rock mass to the backfill (‘squeeze-induced stress effect’). The horizontal displacement of rock mass was responsible for the long-term stress development in the backfilled stope. Backfill parameters and backfill delay had a strong influence on the stope stress development while the influence of backfill gap was mainly around the upper part of the backfilled stope. The engineering application in Baixiangshan Iron Mine indicates that the proposed modelling framework can be well adopted to analyse the continuous increase in stress and displacement during backfill operations.
PubDate: 2019-03-12
DOI: 10.1007/s00603-019-01781-0

• Performance of a New Yielding Rock Bolt Under Pull and Shear Loading
Conditions
• Abstract: Abstract High stress in surrounding rock mass could cause serious stability problems such as larger squeezing deformation in soft rock and rock burst in hard rock. The support system applied in high in situ stress conditions should be able to carry high load and accommodate large deformation of rock mass. This paper presented a new yielding rock bolt, called tension and compression-coupled yielding rock bolt, which is promising to provide support for both squeezing and burst-prone rock mass encountered in mining or tunneling at depth. The new bolt mainly consists of a steel rod and two additional anchors. The steel rod is a round shape bar with varying surface conditions. The inner segment is processed into rough surface, while the middle segment of the rod has smooth surface. Two additional anchors were arranged on both ends of smooth segment. The bolt is fully encapsulated in a borehole with either cement or resin grout. The rough segment and the inner anchor are firmly fixed in the bottom of the borehole, while the smooth segment has no or very weak bonding to the grout, which can stretch to accommodate rock dilatation. First, direct quasi-static pull tests were performed to examine the load capacity of tension and compression-coupled anchor. The results showed that the coupling action of tension to the rough rod and compression on the inner additional anchor by grout in different positions can increase the ultimate bearing capacity of inner anchoring segment significantly. Second, the performance of the new bolt and the fully encapsulated rebar bolt was tested under fracture opening condition. Results showed that the load and strain concentration could result in premature failure of fully encapsulated rebar bolt. However, the smooth segment of TCC Yielding rock bolt can detach from the grout under pull loading and provide a larger deformation to accommodate rock dilations. Third, shear tests were performed to examine the deformation mechanism of the new rock bolt under fracture sliding condition. Results showed that the smooth section of the new bolt specimen can deform freely to accommodate the sliding of fracture. The maximum shear displacement of the new bolt specimen is much larger than the fully encapsulated rebar bolt specimen, which is promising a better ability to accommodate the large displacement sliding of fracture in engineering practice.
PubDate: 2019-03-11
DOI: 10.1007/s00603-019-01779-8

• Analysis of a Complex Flexural Toppling Failure of Large Underground
Caverns in Layered Rock Masses
• Abstract: Abstract Flexural toppling failure is one of the most common instabilities in large underground caverns and occurs when the steeply inclined rock layers form a small angle to the cavern axis. This study investigates a typical flexural toppling failure in the underground powerhouse at the Wudongde hydropower station, Southwest China, using in situ tests and numerical tools. The characteristics of flexural toppling failure in the large underground caverns were initially analysed by field observations and conventional testing methods, including the use of multipoint extensometers, acoustic wave tests and borehole television images. A high-resolution microseismic monitoring system was installed in the right main powerhouse to reveal new and important insights into the mechanisms of typical failures that occur in bedded rock masses. The fracturing processes of the rock mass associated with the flexural toppling failure were analysed based on microseismic monitoring data, and the development of flexural toppling failure was related to shear failure. Then, the discrete element method was used to further investigate the effect of geological planes on the formation of flexural toppling failure. Finally, the complex mechanism of flexural toppling failure was evaluated by incorporating field observations, in situ monitoring and numerical modelling. An effective method of preventing this type of failure in underground caverns was analysed. The results can improve our understanding of flexural toppling failure in the underground caverns of the Wudongde hydropower station, and the proposed method can be adopted to study similar large underground caverns.
PubDate: 2019-03-08
DOI: 10.1007/s00603-019-01760-5

• On the Strain Rate Sensitivity of Coarse-Grained Rock: A Mesoscopic
Numerical Study
• Abstract: Abstract A numerical study on the strain rate sensitivity of coarse-grained rock fracture under dynamic loading is presented. For this purpose, the embedded discontinuity finite element method is employed as a numerical tool. Moreover, a mesoscopic description of grain boundary-grain interior structure of rock is given. Thereby, the present approach is able to account for inter- and intragranular failure types of rock. The numerical simulations carried out here corroborate the conception that in direct tension the dynamic increase of tensile strength of rock is a real material property. Moreover, the simulations agree with the hypothesis that in uniaxial compression the dynamic increase of compressive strength is a structural effect due to lateral inertia. Finally, the numerical simulations of the dynamic Brazilian disc test suggest that structural effects also contribute to the dynamic increase in the apparent indirect tensile strength.
PubDate: 2019-03-07
DOI: 10.1007/s00603-019-01772-1

• Hydraulic Fractures Induced by Water-/Carbon Dioxide-Based Fluids in Tight
Sandstones
• Abstract: Abstract To investigate the impact of fluid viscosity and rock heterogeneity on the characteristics (such as geometric complexity, roughness, and micro-morphology) of hydraulic fractures (HFs), laboratory triaxial fracturing experiments were conducted on homogeneous and layered tight sandstones using water- and carbon dioxide (CO2)-based fluids. The fractal dimension of HFs (Df) and the stimulated fracture area were quantitatively analyzed based on computerized tomography scanning and three-dimensional reconstruction methods. The surface roughness and micro-characteristics of HFs were then evaluated. Experimental results showed that CO2-based fracturing tended to create more HFs with a higher degree of geometric complexity (Df ranging 2.1113–2.2271) than that of HFs created by water-based fracturing (Df ranging 2.0952–2.1081) in a homogeneous tight sandstone. A complex HF network (Df = 2.4092) was generated in the layered tight sandstone using supercritical CO2 (SC-CO2) fracturing. The SC-CO2-induced fracture area in the layered tight sandstone was approximately three times larger than that of the homogeneous tight sandstone. Both the fluid viscosity and particle size of the host rock have a great effect on the roughness of the HF surface. CO2-based fracturing tends to generate curved HFs with uneven and cracked HF surfaces and massive microfractures, whereas water-based fracturing is more likely to induce straightforward HFs with smooth and clean HF surfaces and few microfractures. These induced microfractures enhance the micro-complexity of HFs, which may contribute to additional conductivity in the production stage. The obtained results provide a laboratory research basis for fracturing fluid selection and fracturing treatment design in tight sandstone reservoirs.
PubDate: 2019-03-07
DOI: 10.1007/s00603-019-01777-w

• An Experimental Investigation of the Effects of Grain Size and Pore
Network on the Durability of Vicenza Stone
• Abstract: Abstract The textural properties of a rock and the characteristics of its pore network are intrinsic variables to consider when investigating the resistance of rock to weathering. To establish the influence of these variables on the effectiveness and progression of weathering processes, two lithotypes of a limestone were analyzed with respect to their texture and porosity, and to their performance during artificial weathering experiments. The studied rock is Vicenza Stone, a bioclastic limestone with heterogeneous texture, variable grain size from fine to coarse, and high levels of open porosity (27–28%). Two sets of samples were obtained from a quarry, defining coarse-grained (CGV) and fine-grained (FGV) lithotypes of Vicenza Stone. Multiple techniques (optical microscopy, scanning electron microscopy, image analysis, mercury intrusion porosimetry, hygroscopicity, ultrasound, and water absorption) were used to characterize the texture and porosity of the limestone. The sample sets were subjected to freeze–thaw (UNI 11186:2008, Cultural heritage—Natural and artificial stone—Methodology for exposure to freeze-thawing cycles, 2008) and salt-crystallization (partial continuous immersion method with a Na2SO4-saturated saline solution) weathering experiments to investigate the processes and progression of mechanical and chemical weathering. Differences in freeze–thaw-induced micro-cracks and in the deposition of secondary micrite between the lithotypes show that the CGV has an overall higher susceptibility to freeze–thaw weathering than FGV. Salt-weathering processes induced micro-crack formation, material dissolution, and secondary precipitation, suggesting the simultaneous occurrence of mechanical stress and chemical dissolution–precipitation processes. FGV is more prone to salt-induced weathering than CGV, whereas CGV is susceptible to the wide thermal excursions of freeze–thaw weathering.
PubDate: 2019-03-07
DOI: 10.1007/s00603-019-01768-x

• An Innovative Acousto-optic-Sensing-Based Triaxial Testing System for
Rocks
• Abstract: Abstract The failure mechanisms of rocks as a result of hydro-mechanical coupling effects have not been fully understood due to the limited abilities of conventional triaxial test equipment in measuring both the internal and external damage of rocks simultaneously in real time. This study presents an innovative triaxial testing system for detecting the internal and external damage of rocks. The system consists of an innovatively designed built-in acoustic emission sensor, an optical measurement system and a fully transparent pressure chamber. This work shows that the developed system can capture the internal and external damage behaviour of rocks using triaxial tests. The results demonstrate that the developed built-in acoustic emission sensors can measure the internal damage of rock specimens in an aqueous environment during a load test, while the proposed configuration of the optical measurement system together with the developed imaging construction technique can capture the surface crack development of samples. In addition, the acoustic ring-down counts and event counts can be used to detect the internal damage of the rock specimens, and the ring-down counts reach a significantly high level when the maximum axial force is reached. Furthermore, damage to rock specimens due to triaxial loading first occurs internally, and damage then extends externally. The critical failure point of a specimen can be determined when large fluctuations in the crack fractal dimension and ring-down counts occur simultaneously.
PubDate: 2019-03-05
DOI: 10.1007/s00603-019-01764-1

• An Empirical UCS Model for Anisotropic Blocky Rock Masses
• Abstract: Abstract The Hoek–Brown (HB) failure criterion is one of the most widely used failure criteria in rock engineering. Based on the Geological Strength Index (GSI) system, a number of empirical models have been proposed in parallel with this criterion to estimate the strength and deformation properties of rock masses such as uniaxial compressive strength (UCS) and deformation modulus. However, the GSI system does not incorporate the effects of joint orientation β on the quality of a rock mass. This means that these empirical models cannot capture anisotropic rock mass strength caused by joint orientations. In this research, UDEC rock mass models, which are calibrated by laboratory data, are used to investigate the effects of joint orientation on rock mass strength in an unconfined state. The values of UCS obtained from the numerical simulation are then compared with those calculated from traditional empirical UCS models based on the GSI system. The comparison study shows that the value of UCS is significantly overestimated by the traditional empirical model when 10° < β < 45°, which will have serious safety implications for engineering designs. To rectify the problem, based on the analysis of numerical simulation results, an anisotropic weighting factor fβ is proposed to be used to refine the empirical UCS model. The modified UCS model is demonstrated to be capable of giving conservative but more accurate prediction of the rock mass strength for various joint orientations, which will result in more optimal and safer engineering designs.
PubDate: 2019-03-05
DOI: 10.1007/s00603-019-01771-2

• Rock Cutting Experiments with an Actuated Disc
• Abstract: Abstract This paper reports the results of actuated disc cutting (ADC) experiments, conducted with an instrumented tabletop ADC rig on a soft limestone. The experiments were designed to assess the predictions of an ADC model (Dehkhoda and Detournay in Rock Mech Rock Eng 50(2):465–483, 2016) and the validity of the assumptions on which the model is constructed, in particular the invariance of the specific energy on actuation. All the experiments were conducted at the same depth of cut, which was selected to ensure a brittle mode of failure, characterized by the formation of chips. By changing the disc size and actuation amplitude, as well as the actuation frequency and the cartridge velocity, the experiments covered a large enough range of the two numbers controlling the cutting response, to rigorously test the theoretical model and its assumptions. Analyses of the experimental data show in general good agreement with the theoretical predictions, in particular the decrease of the thrust force with increased actuation and the partitioning of the external power between actuation of the disc and translation of the cartridge. The experimental results do not show any significant dependence of the specific energy on actuation.
PubDate: 2019-03-05
DOI: 10.1007/s00603-019-01767-y

• Reverse Time Migration of Seismic Forward-Prospecting Data in Tunnels
Based on Beamforming Methods
• Abstract: Abstract For tunneling in complex geological conditions, effective and accurate advanced prospecting techniques are required to detect unexpected geological heterogeneities in front of the tunnel face. Reverse time migration (RTM) method is a promising method to image the geological changes based on seismic forward-prospecting data acquired in tunnels. However, conventional tunnel-based RTM images suffer interference of “trailing” artifacts. Beamforming method can obtain a focused wave front through the stack of wavefield, resulting in improved data quality and RTM results. In this study, we incorporate the beamforming method in RTM imaging procedure, and propose a “sweep and stack” mode RTM method as well as its calculation scheme. Three tunnel-based models with different kinds of geological interfaces are designed to generate synthetic seismic records. Wavefield extrapolation is achieved by an acoustic staggered-grid finite-difference algorithm and zero-lag cross-correlation imaging condition is applied to present RTM results. Analysis and comparison of conventional RTM results and “sweep and stack” mode record-side beamforming RTM results illustrate that, both methods can successfully identify the geological interface ahead of the tunnel face, while record-side beamforming RTM images present more concentrated energy arcs with higher amplitude, which is preferred for geology interpretations. Moreover, the synthetic test in a noisy environment demonstrates that record-side beamforming RTM has better anti-noise capability than the conventional RTM approach. A field test in a highway tunnel construction site is performed to show the good application effects of “sweep and stack” mode RTM in practical seismic detections.
PubDate: 2019-03-04
DOI: 10.1007/s00603-019-01763-2

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Heriot-Watt University
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