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The displacement response of landslides to external influencing factors varies according to different creep stages. However, most traditional models ignored this variation and yielded low prediction accuracy especially for mutational displacements of acceleration deformation. To overcome this drawback, this study utilized the spatio-temporal association between the similar landslide cases with sufficient monitoring data and target case to replace the correlation between landslide displacement and external influencing factors to improve the prediction capacity for the mutational displacements. In order to reduce the prediction error caused by the difference between landslide cases, weights were assigned for similar cases according to the similarity of geological and hydrological conditions between cases in realizing the final weighted average prediction for target case. The model barely needs the long-time monitoring of external influencing factors, and it can not only enrich the data through historical landslide cases, but also reduce monitoring cost for target case. The findings of this study demonstrated the presence of a novel perspective for prediction, which may reduce prediction errors caused by any significant deviations in landslide from its previous deformation behavior. Application in engineering, as well as comparing prediction results from different models, may highlight the advantages of the proposed method. [ABSTRACT FROM AUTHOR]

Rockburst prevention is an urgent task in deep-rock engineering, as support systems alone are often insufficient for resisting high geostresses. Cutting slots in surrounding rock can directly reduce the circumferential stress of a tunnel, but it also destroys rock integrity and reduces rock mass strength, which leads to a contra-indication for using this method to prevent rockbursts. How to balance these two aspects and truly reduce the risk of rockburst is the topic of this study. Rockburst prevention experiments were implemented on both intact and slotted granite rock samples using the “slotting before loading” mode. Considerations included the loading force and deformation by the testing machine, sample surface displacement fields, acoustic emission signals, and fragment ejection energy. These were recorded during experiments and the influencing factors and precursory characteristics of a rockburst analyzed, with the stress-release effects of different slotting schemes also evaluated. The experimental results demonstrated that cutting slots on granite samples under eccentric loading conditions leads to direct damage, regardless of the depth, width, and number of slots implemented. And then, numerical simulation of rockburst experiments were performed based on an improved particle-flow program (PFC2D), in which a weakening mechanism was introduced, resulting in the macro compression-tension ratio (up to 25.8/1) approaching real granite. On this basis, numerical slotting tests were conducted and it revealed that cutting slots could lead to sudden tensile failure or fragment ejection under high eccentric stress. These findings were further validated through a physical experiment. Cutting slots in a tunnel model indicated that the energy released by two slots was 37.7% higher than one slot and triple slots 114.4% higher than one slot under a uniform geostress field of 25 MPa, revealing that the energy released by slotting did not increase linearly with slot number. However, the released energy almost increased linearly with increased slotting depth within a certain range and the lateral stress coefficient had an important influence on energy release. Both physical and numerical tests showed that the cutting-slot method could release strain energy and reduce stress, but appropriate support schemes must be matched with existing conditions when using this method to prevent rockbursts or the process might trigger early rockbursts and run counter to the goal of preventing rockbursts. [ABSTRACT FROM AUTHOR]

Seeking high performance adsorbents for highly efficient treatment of wastewater containing organic dyes has become increasingly imperative worldwide. Herein, with a specific surface area (SSA) of 2,745.4 m2·g−1, trace N-doped porous biochar nanospheres (NPBs) are derived for the first time from affluent waste corn roots, via a hydrothermal conversion followed by a mild calcined activation by K2CO3 (KC) in the presence of low virulent melamine. Melamine acts as N source and synergistic activator for significant promotion in SSA, pore volume, and surface defects. The obtained NPBs (CHC-0.5N-4KC-900) are confirmed as superior adsorbents for removal of organic dyes rhodamine B (RhB, qm = 1,630.7 mg·g−1) and Congo red (CR, qm = 1,766.2 mg·g−1) as well as their mixtures, within not only a low (< 50 mg·L−1) but also a high (> 50, esp. 250–1500 mg·L−1) concentration range. The values for qm are far beyond commercially activated carbon (AC) as well as most reported biomass derived carbons, undoubtedly revealing the NPBs as great promising candidate adsorbents for disposal of real industrial wastewater. In addition, the adsorption of RhB is fitted by Langmuir, Freundlich, Temkin, and Dubinin—Radushkevich isotherm models. The kinetic analysis indicates that the adsorption before equilibrium conforms to the pseudo-second-order model, and the hydrogen bonding, electrostatic attraction, and esp. π−π interaction have contributed to the superior adsorption performance of the NPBs. [ABSTRACT FROM AUTHOR]

Crack initiation, propagation, and coalescence are important for the understanding of rock mass behavior. In this paper, we use an improved numerical manifold method (NMM) that can stimulate the initiation, propagation, and coalescence of many cracks simultaneously to model the continuous–discontinuous deformation of granite under uniaxial and confined compression. This new simulation method couples subcritical crack growth (SCG) theory and the Mohr–Coulomb strength criterion with tension cut-off to consider the propagation of virtual and real cracks, respectively, and uses a statistical Weibull distribution to study the influence of elastic modulus inhomogeneity on crack propagation and rock failure. The mechanical behavior and failure modes of the models are in good agreement with experimental data. Increasing elastic modulus inhomogeneity decreases strength and the strain required for macroscopic failure. The stress corrosion index (n) and crack growth constant (C) also have a strong influence on uniaxial compressive strength. Indeed, higher values of C and n result in faster virtual crack speeds, a lower uniaxial compressive strength, and a lower axial strain upon failure. Confining pressure also exerts an influence on crack propagation, compressive strength, and failure mode. Our study shows that the improved NMM code combined with the virtual crack model is therefore an effective and reliable method to simulate crack initiation, propagation, and coalescence in granite under uniaxial and confined compression. Highlights: A virtual crack approach combined with subcritical crack growth theory is implemented in numerical manifold method to simulate the initiation of multi-cracks. The Mohr–Coulomb criterion with tension cut-off coupled with subcritical crack growth theory is incorporated into numerical manifold method to simulate the propagation of micro-and macro-cracks. Three types of crack intersection are identified in numerical manifold method to allow the model to accurately simulate the propagation and coalescence of multi-cracks and large displacement. [ABSTRACT FROM AUTHOR]

Dagushan Iron Mine is a large-scale open-pit mine. In this mine, the belt conveyors residing in the rock slope are employed for ore haulage. However, after the − 210 m bench was excavated, many fractures occurred in one of the roadways placing the belt conveyors. In this paper, this engineering case was introduced in detail and the fracturing mechanism was investigated numerically. A numerical model containing complex stratigraphy and geological conditions was built for fracturing mechanism analysis. The strain-softening constitutive model was adopted to describe the post-failure behavior of rock mass. The model was validated with field monitoring data and spot observations, and then used to analyze the interactions between the roadway and rock slope induced by bench excavation. The deformation and stress evolutions in the rock slope and the fracturing process of concrete lining were further clarified for this roadway-landslide system. The numerical results show that the − 210 m bench excavation activated the F14 and F15 faults (with activity initiating low and extending upwards) and generated large shear bands, forming an isolated potential sliding strip. The large displacement of the potential sliding strip acting on the roadway led to the fracturing of the concrete lining. The rock masses around the roadway have also been damaged severely. The control measures of slope cutting were suggested for future production and evaluated using the numerical model. It was found that the suggested control measures could manage the convergent deformation of the roadway to within the appropriate limit and ensure that the belt conveyor can be used for ore haulage until nearly the end of production. The suggested control measures are feasible and practical, and provide a reference for addressing similar engineering problems. Highlights: This paper reports an engineering case of the Dagushan open-pit mine in detail, which is about the fracturing of the concrete lining of the belt conveyor roadway induced by slope excavation. To investigate the fracturing mechanism, a numerical model containing complex stratigraphy and geological conditions was built and basically verified by the field monitoring data and spot observations. The numerical studies show that the -210m bench excavation activated faults from down to up to form an isolated possibly-sliding strip and the large displacement of the possibly-sliding strip acting on the roadway leading to the fracturing of the roadway concrete lining. Based on the requirement of the normal operation of the belt conveyors, control measures of slope cutting were suggested for future production and evaluated using the numerical model. The suggested control measures can ensure the belt conveyor serves the ore haulage until the whole production ends. [ABSTRACT FROM AUTHOR]

In this study, a one-part alkali-activated slag (AAS) composed of ground-granulated blast furnace slag, desulfurized gypsum, and hydrated lime is proposed as alternative to cement for the production of cemented fine tailings backfill (CFTB), which is an environmentally friendly binder consisting of 93.72 wt.% industrial solid waste. Results show that AAS with 67.83 wt.% slag, 25.92 wt.% desulfurized gypsum, and 6.25 wt.% hydrated lime yields the highest strength, which is 1.7–3.2 times that of ordinary Portland cement (OPC). Aside from calcium silicate hydrate gel, appreciable quantity of ettringite characterized by interlocking needles structure and high bound water is also produced during the AAS hydration process. In addition, the hydration heat of the AAS binder is 48% less than that of OPC. Moreover, CFTB made of AAS provides better workability than that of CFTB with OPC up to 20 h. The findings of this study will contribute to the production of more cost-effective, durable, and environmental-friendly cemented fine tailings backfill. [ABSTRACT FROM AUTHOR]

The flywheel's stored energy is usually increased by increasing the thickness of the flywheel rotor due to the limit of radius and speed. However, the flywheel rotor is mostly simplified to a lumped mass point without considering the thickness of the flywheel rotor. This paper proposes a modeling method that considers the thickness of the flywheel rotor. The dynamic characteristics based on the lumped parameter model (LPM), the modeling method proposed in this paper (LFM method) and the finite element method (FEM) are calculated. The first two natural frequencies of the flywheel rotor under different thicknesses are compared with the results of the FEM. The results show that when the rotor thickness is small, the natural frequency results of the LPM are consistent with those calculated using the FEM. However, with the increase of rotor thickness, the error of the results calculated by the LPM increases gradually. The natural frequency results calculated by the LFM are consistent with those calculated by the FEM. The error of the LFM results is small, which verifies the effectiveness of the LFM method. [ABSTRACT FROM AUTHOR]

Towards bottlenecks demonstrated by typical Fenton-like catalysts in advanced oxidation processes (AOPs) for wastewater treatment, novel hierarchical porous Mn 2 + Mn 6 3 + SiO 12 (Mn7SiO12, MSO-12) microspheres (specific surface area: 434.90 m2·g−1, pore volume: 0.78 cm3·g−1) were rationally designed and achieved via a simple one-pot hydrothermal method (150 °C and 12.0 h) without any pre-prepared templates or organic solvents, by using abundant MnCl2·4H2O and Na2SiO3·9H2O as the basic raw materials. The MSO-12 microspheres are confirmed as high-efficiency Fenton-like catalysts for degradation of organic dyes (methylene blue (MeB), Rhodamine B (RhB), and methyl blue (MB)) in the presence of H2O2, with impressively high specific consumption amount of MeB (R = 12.35 mg·g−1min−1) and extremely low leaching of Mn (Mnloss% = 0.27%). Simultaneously, the synergetic effect of adsorption and degradation on the superior removal of MeB is uncovered. The excellent recycling performances, especially the satisfactory removal of MeB from the actual water bodies (e.g., tap water and river water), as well as potential applications for degradation of RhB and MB enable the MSO-12 microspheres as a novel promising competitive candidate Fenton-like catalyst. [ABSTRACT FROM AUTHOR]

This paper presents a modified relationship between small and large strain convergence by applying a small (residual) dilation angle, which behaves accurately for rock mass with the strain-softening behavior and complex dilatancy model. The modified relationship extends its applicability to a more general two- and three-dimensional excavation problems than previous study, irrespective of the constitutive behavior and rock dilatancy. On this basis, the longitudinal displacement profile (LDP) considering finite-strain is proposed, which can be corrected simply from the small strain analysis or obtained according to the actual parameters related to large deformation. The capability of the finite-strain LDP for estimating large convergences during tunnel advancement is verified by several comparisons with the existing numerical simulation and theoretical analysis results. The developed finite-strain LDP is promising to improve the convergence − confinement method when it applied to the rock-support interaction analysis in problems involving large deformation. The applicability of the displacement-release coefficient obtained from the small strain analysis for quantifying the stress relief to squeezing ground conditions is also investigated. [ABSTRACT FROM AUTHOR]

In order to reveal the load transfer mechanism during cascading pillar failure, compressive tests on treble-pillar specimens were conducted under soft and stiff loading conditions, where the stiffness of the test machine was adjusted with a disc spring group. Experimental results showed that the load transfer behavior of treble-pillar specimen could only be reproduced under soft loading condition when the rapid elastic rebound is achievable with disc spring group. The load transfer behavior of treble-pillar specimen is governed by energy storage characteristics of test machine and the mechanical properties of three rock specimens. In this respect, the failure behavior of treble-pillar specimen under soft loading condition was summarized into the following three failure modes: successive failure mode, compound failure mode and domino failure mode. Additionally, a theoretical model was proposed to further explain the physical mechanism of load transfer behavior, where the theoretical results of load transfer and elastic rebound of disc spring group were in good agreement with the experimental results. Finally, it was concluded that the elastic deformation of near-field surrounding rockmass (or the soft loading condition) was the necessary condition for load transfer of multiple pillars; and the rapid elastic rebound of near-field surrounding rockmass was the physical essence of load transfer behavior. This study may contribute to understanding the load transfer mechanism among pillars and to optimizing the design of room-and-pillar stopes during underground mining. Highlights: The soft loading condition of test machine is realized by adjusting the stiffness of disc spring group. The experiments on treble-pillar specimens are conducted to reveal the load transfer mechanism during cascading pillar failure. Three failure modes of treble-pillar specimen are successive failure, compound failure and domino failure. [ABSTRACT FROM AUTHOR]

The axial loading in rockbolts changes due to stress redistribution and rheology in the country rock mass. Such a change may lead to debonding at rockbolt to grout interface or rupture of the rockbolt. In this study, based on laboratory experiments, ultrasonic guided wave propagation in fully grouted rockbolt under different pull-out loads was investigated in order to examine the resultant debonding of rockbolt. The signals obtained from the ultrasonic monitoring during the pull-out test were processed using wavelet multi-scale analysis and frequency spectrum analysis, the signal amplitude and the amplitude ratio (Q) of low frequency to high frequency were defined to quantify the debonding of rockbolt. In addition to the laboratory test, numerical simulation on the effect of the embedment lengths on ultrasonic guided wave propagation in rockbolt was conducted by using a damage-based model, and the debonding between rockbolt and cement mortar was numerically examined. It was confirmed that the ultrasonic guided wave propagation in rockbolt was very sensitive to the debonding because of pull-out load, therefore, the critical bond length could be calculated based on the propagation of guided wave in the grouted rockbolt. In time domain, the signal amplitude in rockbolt increased with pull-out load from 0 to 100 kN until the completely debonding, thus quantifying the debonding under the different pull-out loads. In the frequency domain, as the Q value increased, the debonding length of rockbolt decreased exponentially. The numerical results confirmed that the guided wave propagation in the fully grouted rockbolt was effective in detecting and quantifying the debonding of rockbolt under pull-out load. [ABSTRACT FROM AUTHOR]

The stability graph is an empirical approach to predicting stope performance based on the geometric dimensions of stopes and the geotechnical conditions of the surrounding rock mass. Stability graph is commonly used to design and estimate the stability of open-stope mines and underground openings. Most engineers calculate the rock stress factor by the stability graph method considering the maximum principal stress at the center of the critical face and the uniaxial compressive strength of the intact rock, whereas the spatial multidimensional stress state, compressive strength of the rock mass, and tensile strength of the rock mass are not taken into account. In this study, the maximum and the minimum principal stresses dominating the rock stress factor are introduced into the stability graph. The rock stress factor (A) is modified by the Mohr-Coulomb criterion with tensile cutoff. The modified stability graph method was validated by adopting Cavity Monitoring System (CMS) laser technology, and it was then successfully applied in a case study at the Alhada Lead-Zinc Mine in Inner Mongolia. Compared with Mitri's method, the proposed stability graph expands the scope of the narrow vein stope design dimensions. The modified rock stress factor in the stability graph provides a technical basis for the subsequent recovery of residual orebodies. [ABSTRACT FROM AUTHOR]

The application of cable bolts tends to increase in both underground mining operations and civil tunnel excavations have given its outstanding performance to support the excavation surface and hence minimise the hazards and risk of failure in the field. Understanding the mechanical behaviour of cable bolts under axial loading subjected to different field environment from analytical perspective is essential and economic for selecting the most appropriate cable bolt for a specific scenario and also the ground support system design. This study develops a novel analytical model coupling the crack propagation in the grout annulus to capture the load–displacement performance of cable bolts under axial loading. The majority of the input parameters associated with mechanic properties of the cable bolt and grout are readily determinable by laboratory tests. Additionally, the model simulates the ongoing varying conditions of the confinement to the grouted cable bolt during the pull-out test based on the proposed crack propagation equation, leading to a more realistic reflection of the field conditions. Finally, the capability of the proposed model to simulate the performance of cable bolts under axial loading is demonstrated by validating against experimental results in the literature. [ABSTRACT FROM AUTHOR]

The AE energy radiated from rock microfractures is widely used to understand the rock failure process. However, the radiation energy of AE sources is usually inaccurately quantified because of imprecise knowledge of the radiation pattern associated with the tensile angle. Based on theoretical calculations, we quantify the radiation energy of the AE source more accurately by considering the influence of the tensile angle on the radiation pattern and then analyze the radiation energy evolution during the rock failure process. The energy radiation pattern and average energy radiation pattern coefficients of the P and S waves change significantly with the tensile angle. During the failure process of the granitic gneiss specimen, the radiation energy release of the rock specimen is characterized by a sudden intermittent increase in the time domain. The sudden increase is mainly due to the occurrence of large-energy AE sources rather than many low-energy AE sources in a short time. The main microfracture mechanism at the low stress level is shear compression; as the stress increases the main microfracture mechanism changes to shear. When the specimen is at failure, the shear microfractures account for > 70%. [ABSTRACT FROM AUTHOR]

Numerical simulation is a commonly used method for investigating rock failure. However, the numerical model is usually insufficient to predict real rock damage and failure because of rock microstructural heterogeneity. In fact, rock damage can be quantified using acoustic emission (AE) data. The aim of this study is to simulate and predict the failure of Brazilian and uniaxial compression specimens using AE data recorded during experiments. An AE data-driven model, in which cracks are assumed to be tensile in nature, is developed. AE data recorded from the test start up to a fraction of the peak stress (e.g., 20%, 40%, and 60%) are input into the data-driven model to predict the evolution of failure pattern beyond that stress level up to failure. First, we quantified stress-induced rock damage with AE data based on the tensile model. The results indicate that most of damage source radii are less than one millimeter, and the corresponding damage degree is close to one. Then, the inversed damage is input as the initial conditions for the numerical simulation to predict the future damage and failure of rock. With the increase of damage elements driven by AE data, the inversed damage zone develops from diffuse to localized, and the dominant factor for rock failure transits from microstructural heterogeneity into stress-induced rock damage. The damage and failure pattern of rock is well predicted when sufficient AE data are taken into account as known conditions. [ABSTRACT FROM AUTHOR]

Dynamic disturbance such as blasting may significantly affect the creep of rock. Quantification of the influence of dynamic disturbance on the creep behavior of rock is a prerequisite to the understanding of the long-term behavior of rock around excavations. In this study, a new creep-impact test machine that is capable of testing the rock failure behavior under combined creep loading and dynamic disturbance was introduced. We performed creep experiments on sandstone while a dynamic disturbance was applied. Axial strain, volumetric strain and acoustic emission (AE) events were measured. The results from the creep-impact experiment show that the rock creep was greatly affected by the dynamic disturbance. Dynamic disturbance may introduce further damage on rock and shorten the time-to-failure of creeping rock specimens. Combination of creep stress and dynamic disturbance resulted in two failure conditions: failure along with accelerating creep and failure during dynamic disturbance. If the dynamic disturbance was not followed by failure, the axial strain consisted of an instantaneous response as the dynamic disturbance was applied, followed by a primary phase of decelerating creep and a steady-state creep phase. This pattern was repeated after the next dynamic disturbance until the last dynamic disturbance that led to the failure. The creep resulted from micro-fracturing in the rock, which can be characterized by the cumulative AE energy if the AE events were monitored during the creep-impact test of rock. The creep behavior was more sensitive to dynamic disturbance under higher creep stress. Under the same creep stress, a dynamic disturbance with higher impact energy resulted in a higher axial strain rate, absolute volumetric strain rate and AE energy rate. Dynamic disturbance not only increased the axial strain rate but also promoted the dilatancy of the rock specimens. The failure of the rock specimens was mostly in the shear mode, and this failure pattern was merely affected by the dynamic disturbance, even though the specimens became more fragmented under the higher creep stress and higher impact energy. [ABSTRACT FROM AUTHOR]

When translating digital roughness profiles of a closed rock joint along the shear direction, the overlapping translational areas can reasonably represent the main potential contact areas in shear tests. By translating Barton's ten typical roughness profiles, a series of statistical parameters, including the overlapping areas (S*), overlapping number (N*), cumulative overlapping projection length (Lsum∗), and the weighted cumulative overlapping projection length (Ssum∗), were utilized to quantify the 2D joint roughness. Based on the dimensional analysis, these parameters were combined to estimate the joint roughness coefficient. The correlation coefficient results show that the parameter combinations of S∗/L and N∗-1 or Ssum∗/STotal allow good estimation of the joint roughness coefficient of Barton's 2D roughness profiles. A conceptual joint model was used to extend the 2D translational overlapping statistical parameters to a 3D condition, revealing the suitability of the 3D translational overlapping volume parameter V∗/SL and the hourglass parameter to estimate the joint roughness coefficient of common rock joints. However, the overlapping number parameter N*−1 becomes unreliable and lacks practical significance for common rock joints because there are so many meaningless weak links among the overlapping volumes. Shear tests were conducted on 25 sandstone joints to verify the applicability of V∗/SL and Vsum∗/VTotal to estimate the joint roughness coefficient. The results indicated that these two parameters show good agreement with the experimentally back-calculated values, allowing the establishment of a new joint roughness coefficient fitting formula. [ABSTRACT FROM AUTHOR]

Rocks with microdefects exhibit viscoelastic behavior during stress wave propagation. The viscosity coefficient of the wave can be used to characterize the attenuation as the wave propagates in rock. In this study, a long artificial bar with a readily adjustable viscosity coefficient was fabricated to investigate stress wave attenuation. The viscoelastic behavior of the artificial bar under dynamic loading was investigated, and the initial viscoelastic coefficient was obtained based on the amplitude attenuation of the incident harmonic wave. A one-dimensional wave propagation program was compiled to reproduce the time history of the stress wave measured during the experiments, and the program was well fitted to the Kelvin-Voigt model. The attenuation and dispersion of the stress wave in long artificial viscoelastic bars were quantified to accurately determine the viscoelastic coefficient. Finally, the method used to determine the viscoelastic coefficient of a long artificial bar based on the experiments and numerical simulations was extended to determine the viscoelastic coefficient of a short rock bar. This study provides a new method of determining the viscosity coefficient of rock. [ABSTRACT FROM AUTHOR]

Abstract: Cu-doped three-dimensionally ordered macroporous (3DOM) SiO2 was prepared by a colloidal templating method and used as the support of heteropoly acid for the selective oxidation of methacrolein (MAL) to methacrylic acid (MAA). The doping effects of Cu on the structures, physico-chemical properties and catalytic performances of the catalysts were investigated. Results showed that Cu was well distributed in the SiO2 framework with the mole ratio of Cu/Si = 5%, and the specific surface area was much higher than that of the pure 3DOM SiO2. After supported with H4PMo11VO40 (HPVA), the specific surface areas of the as-synthesized catalysts significantly decreased, from 239 to 64 m2 g−1 for HPVA/3DOM (5%Cu)–SiO2 and from 141 to 32 m2 g−1 for HPVA/3DOM SiO2, respectively, because of the blockage of the micropores. The supported HPVA retained Keggin-type primary structure and its reducibility was obviously improved due to the existence of Cu in the supports, which thereby resulted in the great enhancement of the catalytic property. The conversion of MAL and the selectivity to MAA were respectively 36 and 47% on HPVA/3DOM SiO2. Comparatively, the conversion of MAL reached 63% with 82% MAA selectivity on HPVA/3DOM (5%Cu)–SiO2.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Conventional water-based fracturing treatments may not work well for many shale gas reservoirs. This is due to the fact that shale gas formations are much more sensitive to water because of the significant capillary effects and the potentially high contents of swelling clay, each of which may result in the impairment of productivity. As an alternative to water-based fluids, gaseous stimulants not only avoid this potential impairment in productivity, but also conserve water as a resource and may sequester greenhouse gases underground. However, experimental observations have shown that different fracturing fluids yield variations in the induced fracture. During the hydraulic fracturing process, fracturing fluids will penetrate into the borehole wall, and the evolution of the fracture(s) then results from the coupled phenomena of fluid flow, solid deformation and damage. To represent this, coupled models of rock damage mechanics and fluid flow for both slightly compressible fluids and CO are presented. We investigate the fracturing processes driven by pressurization of three kinds of fluids: water, viscous oil and supercritical CO. Simulation results indicate that SC-CO-based fracturing indeed has a lower breakdown pressure, as observed in experiments, and may develop fractures with greater complexity than those developed with water-based and oil-based fracturing. We explore the relation between the breakdown pressure to both the dynamic viscosity and the interfacial tension of the fracturing fluids. Modeling demonstrates an increase in the breakdown pressure with an increase both in the dynamic viscosity and in the interfacial tension, consistent with experimental observations. [ABSTRACT FROM AUTHOR]

During the excavation of underground opening, the rock may experience a complex loading path that includes the highly confined compression before excavation, unloading of confining stress and further disturbance of dynamic loading after excavation. By using Rock Failure Process Analysis for Dynamics (RFPA-Dynamics), the failure of rock sequentially subjected to this complex loading path is numerically simulated, in order to examine the rock failure mechanism induced by excavation. The RFPA-Dynamics is firstly used to reproduce the failure of rock under confined compression, followed by unloading of confining pressure, and it is validated against with the existing experimental observation. Then, the failure characteristics of rock specimen sequentially subjected to the quasi-static triaxial loading, unloading of confining pressure and dynamic disturbance are numerically simulated, where the effect of magnitude of axial loading and confining pressure, and duration and amplitude of the dynamic disturbance on the final failure patterns of rock are examined. The numerical results indicate that the arc-shaped spalling damage zone is prone to develop with the increase in the axial pressure and lateral pressure coefficient. As for the effect of dynamic disturbance, the contribution of duration and amplitude of dynamic disturbance on the energy input are similar, where the area of damage zone increases with the energy input into the rock specimen. In this regard, the area of the damage zone is influenced by both the magnitude of in situ stress and waveform of dynamic disturbance. This study denotes that it is of great significance to trace the complex loading path induced by excavation in order to capture the rock failure mechanism induced by underground excavation. [ABSTRACT FROM AUTHOR]

In order to smooth ore production during the transition from open pit to underground mining at Yanqianshan Iron Mine, China, it is necessary to select an appropriate mining method to operate simultaneously open-pit mining and underground mining for inner-slope (hanging-wall) ore-body. Based on practical geologic setting of the hanging-wall ore-body, a comprehensive evaluation model for selecting the underground mining method to extract handing-wall ore-body was proposed, which is constituted by 3 sub-systems of safety factors, production factors and technical-economic factors. This evaluation model could be analyzed by the mutation progression method, which based on catastrophe theory and fuzzy mathematics. In addition, the FLAC is employed to simulate the mining process of hanging-wall ore-body, and finally the optimal mining scheme is determined. By using mutation progression analysis and numerical modeling, some useful conclusions for hanging-wall ore-body mining have been drawn, which will be beneficial to mining safety during transitional period from open-pit to underground mining. [ABSTRACT FROM AUTHOR]

Time-dependent rheological deformation of rocks affects the stability of underground stopes or constructions. It may also be altered by dynamic disturbances, such as rock blasting. To study such effects, a new stress relaxation-disturbance testing machine was invented, capable of loading conditions for stress relaxation and dynamic disturbance. Effects of testing machine stiffness on rock deformation behavior were examined to confirm that rocks had undergone stress relaxation. Stress relaxation tests on specimens under uniaxial compression were carried out over 6 or more days. Under single-stage stress relaxation, axial stress relaxed within 5-7 days, stabilizing at constant strain. During two-stage stress relaxation, larger stress decay was observed under the higher strain level. A dynamic disturbance from a pendulum hammer was applied to specimens under stress relaxation to evaluate their response. In these tests, stress decline and strain increase were related to residual strain induced by the dynamic disturbance. The strain variation in specimens was found to be within 1.5 % of values before the disturbance. Finally, a damage-based constitutive model for rocks subjected to stress relaxation and dynamic disturbance is proposed. It reproduces the stress relaxation behavior of rock observed in our experiments. The model was used to quantify stress relaxation of rocks and the effects of dynamic disturbance on this process. The larger stress decay of rocks under higher strain is likely related to damage in the rock. Clearly, increases in strain and decreases in stress induced by dynamic loading, coupled with rock damage, are over-estimated in our numerical simulations. [ABSTRACT FROM AUTHOR]

As jointed rocks consist of joints embedded within intact rock blocks, the presence and geometrical fabric of joints have a great influence on the mechanical behavior of rock. With consideration of the actual spatial shape of joints, a numerical model is proposed to investigate the fracture evolution mechanism of jointed rocks. In the proposed model, computerized tomography (CT) scanning is first used to capture the microstructure of a jointed sandstone specimen, which is artificially fabricated by loading the intact sample until the residual strength, and then digital image processing (DIP) techniques are applied to characterize the geometrical fabric of joints from the CT images. A simple vectorization method is used to convert the microstructure based on a cross-sectional image into a layer of 3-D vectorized microstructure and the overall 3-D model of the jointed sandstone including the real spatial shape of the joints is established by stacking the layers in a specific sequence. The 3-D model is then integrated into a well-established code [three-dimensional Rock Failure Process Analysis, (RFPA3D)]. Using the proposed model, a uniaxial compression test of the jointed sandstone is simulated. The results show that the presence of joints can produce tensile stress zones surrounding them, which result in the fracture of jointed rocks under a relatively small external load. In addition, the spatial shape of the joints has a great influence on the fracture process of jointed rocks. [ABSTRACT FROM AUTHOR]

Shirengou iron mine in Hebei Province, China is now under transition from open pit to underground mining. During this process, the unstable failure risk of crown pillar is growing as a result of underground mining, fault activation and water seepage. To monitor the stability of the crown pillar, a microseismic monitoring system was equipped in 2006. Based on temporal and spatial distribution of microseismic events and deformation mechanism, it was found that it is the propagation of the buried fault F15 that causes the failure of the crown pillar, resulting in increased water seeping into the underground drifts. By analyzing the temporal changes in multiple microseismic parameters during the fracture process of the crown pillar, it was found that several distinct abnormalities in the microseismic data such as a rapid decrease in the b value, a sharp increase in energy release, an abnormal increase in apparent stress and a low dominant frequency, could be judged as the signal of an increasing risk. Therefore, the microseismic monitoring has been proven to be a suitable method for understanding damage and fracture process of the crown pillar during the transition from open pit to underground mining. [ABSTRACT FROM AUTHOR]

Hollow or porous hematite (α-FeO) nanoarchitectures have emerged as promising crystals in the advanced materials research. In this contribution, hierarchical mesoporous α-FeO nanoarchitectures with a pod-like shape were synthesized via a room-temperature coprecipitation of FeCl and NaOH solutions, followed by a mild hydrothermal treatment (120°C to 210°C, 12.0 h). A formation mechanism based on the hydrothermal evolution was proposed. β-FeOOH fibrils were assembled by the reaction-limited aggregation first, subsequent and in situ conversion led to compact pod-like α-FeO nanoarchitectures, and finally high-temperature, long-time hydrothermal treatment caused loose pod-like α-FeO nanoarchitectures via the Ostwald ripening. The as-synthesized α-FeO nanoarchitectures exhibit good absorbance within visible regions and also exhibit an improved performance for Li-ion storage with good rate performance, which can be attributed to the porous nature of FeO nanoarchitectures. This provides a facile, environmentally benign, and low-cost synthesis strategy for α-FeO crystal growth, indicating the as-prepared α-FeO nanoarchitectures as potential advanced functional materials for energy storage, gas sensors, photoelectrochemical water splitting, and water treatment. [ABSTRACT FROM AUTHOR]

Water outbursts from the floor during underground mining, and those from the surrounding rock mass of tunnels, involve the basic principle of hydraulic fracturing. Based on the hydraulic-fracturing mechanism, considered to be dependent on the coupling between seepage and damage, it is deemed that the variation of the pore-fluid pressure coefficient must be taken into account during this coupled process, in order to correctly establish the crack propagation mechanism during hydraulic fracturing. The coupled seepage-damage model is validated using numerical simulations of hydraulic fracturing around one hole and three holes; the model may also enable scientific and reasonable explanation of the dominance of hydraulic gradient on the crack propagation path in permeable rock. Finally, the water outburst from the floor at a coal mining site in Hebei Province, China, is numerically simulated, and the coupled seepage and damage mechanism during the mining-induced rock failure is clarified. The numerical simulation implies that the seepage-damage is the main mechanism for controlling the water outburst. Therefore this mechanism should be considered in the numerical simulation to understand the essence of water outburst induced in mines. [ABSTRACT FROM AUTHOR]