Search

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]

To evaluate the feasibility of mixing saline underground water (SUW) in the preparation of cemented fine tailings backfill (CFTB), the compressive strength, pore fluid pH, slag hydration degree, hydration phase composition/structure, and pore morphology of CFTB have been tested. The binder used was a one-part alkali-activated slag composed of ground-granulated blast furnace slag (67.8% by weight) as precursor and desulfurized gypsum (25.9% by weight) and hydrated lime (6.3% by weight) as composite activator. The results showed that using SUW instead of deionized water as mixing medium had both negative and positive effects on the strength development of CFTB, depending on the curing time. At the very early ages (1–3 days), mixing SUW resulted in a decrease of the pore solution pH, which is due to the reaction of positive ions in SUW with OH− ions and the decrease of slag hydration rate, leading to a lower strength of CFTB. The positive effects were observed at the later ages (7–28 days). The higher later-age strength of SUW-mixed CFTB is attributed to two factors: (1) a smaller amount of ettringite (AFt) was generated at the very early ages, which reduced the encapsulation-hindering effect on the slag decomposition; and (2) SUW increased the slag hydration rate, promoting the condensation of calcium silicate hydrates, which results in increased formation of a calcium silicate aluminate hydrate [C-(A)-S-H] phase with rigid three-dimensional structure. These findings can provide important information for the use of SUW in CFTB in coastal and arid regions. [ABSTRACT FROM AUTHOR]

• The pressurizing rate model considering the physical properties of CO 2 is proposed. • A novel breakdown pressure model considering fluid infiltration effect is proposed. • The low viscosity and pressurization rate of CO 2 decreases breakdown pressure. • Influence of the pore pressure distribution on breakdown pressure is analyzed. • The pressurization rate affects breakdown pressure at different injection rates. Precisely predicting the breakdown pressure of rock fractured by supercritical CO 2 (SC-CO 2) is one of the major challenges for optimize in-situ fracturing schemes. However, the influence of the infiltration effect caused by the unique properties of SC-CO 2 on the fracture mechanism remains unclear, which may lead to inaccurate prediction of breakdown pressure. In this work, a pressurization rate model considering the physical properties changes of SC-CO 2 is proposed to describe the relationship between the pressurization rate and the injection pressure of the fracturing fluid in a wellbore. Ultimately, combined with the pressurization rate model and the point stress criterion, a breakdown pressure model is established by considering the changes in the in-situ stress of wellbore surrounding rock, the fluid injection pressure inside the wellbore, and the pore pressure distribution. The results show that for permeable reservoirs, the breakdown pressure increases as the viscosity and injection rate of fracturing fluid increase, but it decreases with increasing rock permeability. The low viscosity and pressurization rate of SC-CO 2 effectively increase the stress generated by the infiltration effect, which is negatively correlated with the breakdown pressure. In addition, the unique pressurization rate of SC-CO 2 is the key factor for the abnormal breakdown pressure at different injection rates. [ABSTRACT FROM AUTHOR]

During underground mining excavation, dynamic disturbances (e.g., blasting) may accelerate rock creeping and induce unstable failure. It is crucial to properly quantify the impact of dynamic disturbances on creeping behavior to understand the long-term effects of underground excavation on rock media. A damage-based creep model was established in this study and implemented in Fast Lagrangian Analysis of Continua in 3D (FLAC3D) to quantify the damage and unstable failure of creeping rock triggered by dynamic disturbance. This model reveals the mechanical behavior of rock under creep-impact loading. It was verified by calculating the viscoelastic deformation around circular excavation, by reproducing the damage process under static loading, and by simulating the rock damage and failure under creep-impact loading. The model was then used to examine the mining-induced creep deformation around an operational shaft in Xincheng Gold Mine, China, where both the mining-induced creep of the country rock mass and dynamic disturbance of blast-induced vibration were considered. Numerical simulation indicated that the dynamic disturbance could accelerate the damage of rock under creep stress, which may be an important factor to trigger the accelerating creep of rock, even though the unstable failure of rock lagged behind the dynamic disturbance. The case study on the shaft stability analysis indicated that the dynamic disturbance could accelerate the time-dependent deformation of the shaft, the first dynamic disturbance induced much more shaft deformation, while in long-term creep (e.g., 5 years), the effect of blasting vibration was not significant. The trend and magnitude of shaft deformation agreed with the in situ measurements, which indicates that the numerical simulation could be used to predict the long-term shaft deformation in future. [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]

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]

Heavy metal ions have attracted considerable concern for their high toxicity and potential malign effects on the water environment, and adsorption has been regarded as one of the most versatile and effective techniques towards water treatment. In view of this, hierarchical porous carnation-like Ca4B10O19·7H2O microspheres self-assembled by two-dimensional (2D) quasi-hexagonal nanoplates are successfully synthesized for the first time as far as we know, by a facile and surfactant ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) assisted hydrothermal approach using CaCl2·2H2O, NaOH and H3BO3 as the raw materials. The as-obtained carnation-like Ca4B10O19·7H2O microspheres exhibit a uniform morphology, ca. 89% of which have a diameter within the range of 8.0–11.0 μm. A probable EDTA-2Na assisted self-assembly formation mechanism has also been proposed based on systematic control experiments. Meanwhile, the carnation-like Ca4B10O19·7H2O microspheres demonstrate a transparent characteristic from the ultraviolet to the visible region, a hierarchical porous structure (specific surface area: 32.79 m2 g−1, pore volume: 0.151 cm3 g−1, average pore diameter: 3.704 nm) and satisfactory thermal stability. In addition, the carnation-like microspheres are confirmed as great satisfactory adsorbents for heavy metal ion (Pb2+) removal with an adsorption capacity qm of 256.4 mg g−1, which may also be employed as excellent adsorbent candidates for other heavy metal or organic dye removal in water treatment as well as catalyst carriers in heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

The stress state in backfilled mine stopes is an important issue to assess the behavior of the interaction between the backfill and the surroundings or barricades. Most previous arching analyses have considered only the vertical backfilled stopes in both 3D and 2D conditions, and the 3D stress distribution that results from the arching effect in inclined mine stopes remains unclear. In this paper, based on the limit equilibrium theory, a 3D stress solution that is applicable to vertical and inclined backfilled stopes is proposed to further examine the arching effect. The solution is validated against an available centrifuge model by changing the inclination of the model. The proposed analytical solution is consistent with the numerical simulations, and it is suggested that neglecting the wall inclination causes one to underestimate the arching phenomenon. In other words, the vertical stresses at the bottom of the stope can decrease when the wall inclination is considered. Hence, when the stope is assumed in plain strain conditions, both the vertical and horizontal stresses exerted on the barricades are overestimated. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) nanostructured metal borates have drawn considerable attention owing to their versatile applications in a multitude of fields, but it is still a great challenge to achieve a high aspect ratio in these materials via a facile and feasible route. Herein, ultralong Ca2B2O5·H2O nanowires with a length of 110–230 μm and ultrahigh aspect ratio of 240–750 are successfully synthesized for the first time via a facile water-bath pretreated eco-friendly hydrothermal technique in the absence of any additives, using low cost CaCl2, H3BO3 and NaOH as the raw materials. The formation mechanism of the ultralong nanowires is studied in detail by varying the process parameters (water-bath and hydrothermal temperature, duration time, etc.). The water-bath treatment plays a key role in the formation of thin hexagonal Ca(OH)2 nanoplates, favoring subsequent conversion to ultralong nanowires with a high aspect ratio. The as-obtained Ca2B2O5·H2O:5.0%RE3+ (rare earth, RE = Eu, Tb) nanophosphors exhibit strong photoluminescence emission and excitation performance, with corresponding Commission Internationale de l'Eclairage (CIE) values determined as (0.635, 0.364) and (0.320, 0.597) within the red and green regions, respectively. This not only suggests that the ultralong Ca2B2O5·H2O nanowires are promising structure- and function-integrated photoluminescent host candidates, but also provides a novel and facile route for the formation of high aspect ratio 1D nanostructures of other metal borates. [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]

Abstract As a simple supporting structure, rockbolts are responsible for maintaining the integrity and stability as well as controlling the deformation, displacement, and crack development in the surrounding rock mass. Knowledge of rockbolt load-transfer behaviors constitutes valuable information, as the rockbolt functionality is affected by load-transfer processes. A series of pullout tests was conducted on a rockbolt with a long embedment length (1500 mm). The critical rockbolt embedment length at which yielding or necking occurs together with the friction coefficient at the residual axial stress was analyzed numerically. Additionally, the failure modes of rockbolt-grouted systems and the effects of several parameters, including the rockbolt diameter (18, 20, and 25 mm) and cement mortar strength, were assessed. The rockbolt strain and energy absorption during the pullout process were also investigated. The identified rockbolt failure modes, which are dependent on the cement mortar strength and rockbolt diameter, include pullout accompanied by partial concrete splitting failure parallel to the rockbolt. Under the same cement mortar strength, the maximum load increases and the rockbolt displacement at the maximum load decreases as the rockbolt diameter increases. When diameter is held constant, the maximum load and corresponding displacement increase as the cement mortar strength increases, but the residual load is irregular. The energy absorbed by the rockbolt in the pullout test is related to the cement mortar strength and failure mode. With an increasing embedment length, the failure process is converted from a completely damaged interface with little simultaneous damage to the cement mortar at the free end to the expansion of the cracks at the loaded and free ends toward each other. The interface is completely damaged when the cracks at both ends become connected. [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]

Abstract The reliable prediction of excavation responses for squeezing rock remains a challenging issue in rock engineering. This paper presents a numerical procedure for a strain-softening rock mass around highly deformed circular opening based on the finite strain theory, so the overall elasto-plastic analysis is a Lagrangian method which focuses on the motion of each material point and is well suited for the problems involving large deformation. The influence of axial in-situ stress is considered by introducing the initial axial stress into the elastic constitutive equations, and the axial plastic flow is realized by redefining the plastic internal variable and considering different stress distributions in the plastic zone. Thus, the numerical procedure enables prediction of the rock deformation and squeezing potential in a more rational and rigorous manner. The capability of the method for estimating the small strain and squeezing deformation is verified by being compared with the existing analytical results and the field measuring data. Negligence of the axial in-situ stress or the axial plastic flow underestimates the rock deformation, and the induced deviation essentially depends on the post-peak constitutive relation and the rock heterogeneity after rock yields. The higher level of the material homogeneity in the plastic zone, the lower effects of the axial in-situ stress on the rock responses. The stress distribution and strain-softening behavior of surrounding rock can be significantly affected by the axial in-situ stress and the critical plastic internal variable η *. Tunnel instability is independent of large deformation for the high η * but is closely associated with the squeezing problem when η * is small. As η * decreases, both of the plastic radius and wall convergence increase initially and remain constant afterwards. Lastly, the paper investigates the rock responses and ground-support interaction when the small strain theory is applied on the squeezing rock. [ABSTRACT FROM AUTHOR]

Highlights • The FBGs were used to measure CTB temperature and internal strain evolution. • In the liquid stage, the binder content had no effect on settlement behavior. • CTB internal strain was influenced by combined chemical and thermal effects. • No significant change occurred in settlement and strain in the hardened stage. Abstract The philosophy of the use of backfill is to return much of tailings waste to underground voids and increase working place stability to safely extract more minerals. The key issue for the safe and efficient design of cemented tailings backfill (CTB) structure is its mechanical properties and interaction with the surrounding rock. As a cemented material, CTB's strength is a function of hydration degree. As hydration is an exothermic reaction and results in net volume reduction, thermal expansion and chemical shrinkage occur simultaneously in the mixture. Each CTB component plays a significant role during this process and the most important factor is the binder content, because it influences the amount of cement hydration products that provide binding phases between tailing particles. In this paper, a number of fiber Bragg gratings (FBGs) were directly embedded into the 7-day cured CTB specimens to measure their temperature and internal strain evolution, with settlement development measured by Linear Variable Differential Transformer (LVDT). The experimental results showed that binder content had a significant effect on CTB temperature and internal strain evolution. Furthermore, the evolution of internal strain and settlement was an indicator of the transformation in different stages (such as fluid, skeleton formation and hardening) during the hydration process. [ABSTRACT FROM AUTHOR]

During underground hard-rock mining, the drilling and blasting method currently remains the most economical excavation method, and the rock may experience a multistrain-rate spectrum under quasi-static, dynamic, and rheological loading conditions and their combination as well. The study on the damage mechanism of rock under multistrain-rate condition that induced by mining excavation is the fundamental issue for predicting the mining-induced hazards such as rockburst. In this study, the state of the art of rock damage and failure under different strain rates is reviewed first. Then, the numerical model for rock failure under multiple strain rates is formulated when the rock damage is taken as the main thread. Meanwhile, we summarize our work in this area over the past ten years, and the constitutive law for the damage and failure of rock under multistrain rates is presented. Finally, several numerical examples, i.e., rock damage and failure under combined static and dynamic load, rock damage and failure triggered by dynamic stress redistribution due to excavation, rock damage and failure induced by blasting, and rock damage and failure due to the combination of dynamic disturbance and rheological load, are presented. Based on these numerical simulations, the associated rock damage mechanism and failure behaviors under differently combined multiple strain rates are clarified, which may provide a theoretical basis for clarifying the rock failure mechanism during rockbursts and rock blasting. Also, further studies on the damage and failure of rock under multiple strain rates are suggested. [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]

Relative to water-based fluids, non-aqueous fracturing fluids have the potential to increase production, reduce water requirements, and to minimize environmental impacts. Since the viscosity of supercritical CO 2 is one-tenth that of water, its density is close to that of water, and is capable of promoting sorptive rejection of methane, it is an attractive substitute for water in the extraction of shale gas and coalbed methane. The following defines a geomechanical model accommodating the interaction of fluid flow, adsorption-induced swelling stress, solid deformation and damage to quantify rock-gas interactions during supercritical CO 2 fracturing for shale gas production. The architecture of the shale is accommodated that includes both pore- and micro-crack-based porosity. According to the microcrack model representing shales with low porosity, both analytical and numerical results show that the effective stress coefficient is much smaller than unity. We analyze the potential advantages of fracturing using supercritical CO 2 including enhanced fracturing and fracture propagation, increased desorption of methane adsorbed in organic-rich portions of the shale and the potential for partial carbon sequestration. Rock-gas interactions include both the linear poroelastic response and the chemo-mechanical interaction due to sorption. Simulation results demonstrate that supercritical CO 2 fracturing indeed has a lower fracture initiation pressure and a significantly lower breakdown pressure, as observed in experiments, and that fractures with greater complexity than those developed with liquid CO 2 and water fracturing result. With increasing dynamic viscosity of the fracturing fluids, the predicted breakdown pressure also increases, consistent with experimental observations. [ABSTRACT FROM AUTHOR]

Mining of ore body in the vicinity of a shaft has a significant influence on its stability. The in situ monitoring and numerical simulation are employed to analyze the effect of shaft pillar extraction at Xincheng Gold Mine. The XI# ore body is recently found around and beneath the shaft, and mining in this area may be detrimental to the shaft. Firstly, on the base of geological survey and in situ displacement monitoring, mechanical parameters of rock mass are obtained and the displacement around the shaft is measured. Secondly, the sensitivities of five main factors that may affect the shaft displacement are analyzed by means of orthogonal experiment according to the numerical simulation with FLAC3D. Finally, a numerical model is established according to the in situ condition; in order to forecast the shaft displacement induced by mining activities of XI# orebody, the Mining Priority Index (MPI) is put forward and used to select the optimal mining sequence. Based on the comparison between the numerical results with the monitoring data, it is determined that the ore within 100 m from the shaft is not suggested to be extracted until the last period of the shaft life. [ABSTRACT FROM AUTHOR]

During the injection of CO 2 into coalbed for geologic sequestration, CO 2 is likely both adsorbed and dissolved in coals, and swells them slightly. When coal is swollen due to the adsorption and dissolution, the induced strain is relieved as the coal structure rearranges to a lower free energy state, causing coal damage and resulting in permeability change. This adsorption- and dissolution- induced coal damage is usually ignored in the permeability model, even though this kind of damage has been observed and detected in the past CO 2 injection experiments. In a previous study we generated a sequence of coal permeability profiles from the “V” shape as observed in experiments through a newly dual-permeability model. Based on this work, in this paper, the dual-permeability model is extended to take the coal damage induced by gas adsorption and dissolution into account according to the principle of damage mechanics, and this model is used to examine the permeability evolution during the injections of different gases, including CO 2 , CH 4 and N 2 , into coal specimen. Numerical simulation indicates that the model predicts well the permeability increase during the high injected gas pressure. In addition, since the highest gas adsorption into coal occurs for CO 2 , the coal permeability during CO 2 injection decreases most pronounced, in contrast, the permeability reduction during N 2 injection is the smallest. Also, it is confirmed that the adsorption-induced coal damage is dominated by tensile damage of coal during the injection of CO 2 . [ABSTRACT FROM AUTHOR]

• Chloride salts' effects on strength, hydration and microstructure of CTB were studied. • The influence of chloride salts is highly dependent on their cation type. • NaCl slightly weakens CTB's strength due to the C-(A)-S-H decalcification. • CaCl 2 promotes slag hydration and thus improves the CTB's microstructure and strength. • MgCl 2 inhibits slag dissolution due to the reaction between Mg2+ and OH–, markedly lowering CTB's strength. For mines located in saline areas, the use of mine water containing chloride salts to prepare cemented tailings backfill (CTB) for mined-out area treatment can realize the resource utilization of mine water and save a large amount of precious freshwater. However, the hydration behavior of binder and strength properties of CTB in the presence of chloride salts is still not well understood. This research investigates the effects of NaCl, CaCl 2 and MgCl 2 with different Cl- concentrations (0.50, 0.77 and 1.0 mol/L) on strength of CTB prepared with one-part alkali-activated slag binder. It analyzes the hydration process of binder and the microstructure of CTB. The results indicated that the decalcification of C-A-S-H (replaced by sodium to create N(C)-A-S-H at high Na+ concentrations) leads to numerous 0.01–0.1 μm micropores within the hardened backfill, increasing porosity while decreasing strength by 3.2–25.0%. Calcium ion (Ca2+) contributes to the formation of dense internal structures and high-strength backfill. Magnesium ion (Mg2+) reduces alkalinity by consuming Ca(OH) 2 , seriously impacts slag decomposition, but accelerates the dissolution of desulfurized gypsum. The study's findings will help the application of chloride-containing mixing water in mines situated in saline regions. [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]

The 3D reconstruction of rock joint surfaces is crucial for quantifying rock joints. Through the uniform discretization of 2D and 3D rock joints, it was determined that both the climbing angles along the shear direction and the projection lengths of the consecutive ascending/descending segments follow normal distributions. This statistical distribution of climbing angles and projection lengths provides an important reference for rock joint reconstruction, although hypothesis testing indicated that some joint profiles/surfaces do not follow normal distributions. A normal distribution-based method and a bubbling method were used to reconstruct the 2D joint profiles. The bubbling method demonstrated good applicability for the generation of 3D rock joint surfaces, especially because it included surfaces with different roughness in two orthogonal directions. Therefore, ten typical 3D rock joint surfaces were reconstructed using the bubbling method, where both the size of asperities (waviness or unevenness) and the joint roughness coefficient values were quantified. To reconstruct a joint surface with a certain roughness coefficient, scaling the elevation of a generated surface was demonstrated as an effective supplementary approach. • Rock joints were statistically analyzed via normal distributions owing to a uniform discretization operation. • The normal distribution-based method and the bubbling method were both suitable for reconstructing 2D joint profiles. • The bubbling method could generate 3D joint surfaces with different roughness in two orthogonal directions. • Rock joints with different joint roughness coefficients were reconstructed by scaling their elevation coordinates. [ABSTRACT FROM AUTHOR]

[Display omitted] • A plastic-damage method considering inelastic behavior is developed to predict GRC. • Damage-induced inelastic response is significant for strain-softening rock mass. • The preliminary critical support pressure for the residual failure zone is given. During opening construction, the accumulated wall displacement and the developing excavation damaged zone are the results of stress redistribution and inelastic behavior induced by both the microcracking damage and the irreversible plastic deformation. The current approach to predict ground response to excavation disturbance is usually based on the Convergence-Confinement Method, which fails to consider the rock damage and the plastic-damage coupled mechanism, resulting in inaccurate estimation of rock deformation, particularly in the case of the weak rock with high deformability. This study establishes a plastic-damage theoretical approach for a circular opening by a kinematic decomposition of strains into an elastic, plastic and damage parts within the framework of finite strain using a hypoelastic–plastic theory, in order to investigate the inelastic behavior-induced excavation response. In this regard, the damage model provides the effective stress to the plasticity model defining the yield criterion, in combination with the strength-stiffness degradation and damage evolution. The numerical implementation is given and two examples are considered for validation. Extensive works are then carried out to clarify some issues, including the capacity of the model to characterize the inelastic behavior, the role of rock damage and confining stress dependence on ground response, and the preliminary critical support pressure for the residual failure zone. [ABSTRACT FROM AUTHOR]

Abstract: The rational integration of conductive nanocarbon scaffolds and insulative sulfur is an efficient method to build composite cathodes for high-energy-density lithium–sulfur batteries. The full demonstration of the high-energy-density electrodes is a key issue towards full utilization of sulfur in a lithium–sulfur cell. Herein, carbon nanotubes (CNTs) that possess robust mechanical properties, excellent electrical conductivities, and hierarchical porous structures were employed to fabricate carbon/sulfur composite cathode. A family of electrodes with areal sulfur loading densities ranging from 0.32 to 4.77mgcm−2 were fabricated to reveal the relationship between sulfur loading density and their electrochemical behavior. At a low sulfur loading amount of 0.32mgcm−2, a high sulfur utilization of 77% can be achieved for the initial discharge capacity of 1288mAhgS −1, while the specific capacity based on the whole electrode was quite low as 84mAhgC/S+binder+Al −1 at 0.2C. Moderate increase in the areal sulfur loading to 2.02mgcm−2 greatly improved the initial discharge capacity based on the whole electrode (280mAhgC/S+binder+Al −1) without the sacrifice of sulfur utilization. When sulfur loading amount further increased to 3.77mgcm−2, a high initial areal discharge capacity of 3.21mAhcm−2 (864mAhgS −1) was achieved on the composite cathode. [Copyright &y& Elsevier]

Supercritical carbon dioxide (SC–CO 2) is a promising fracturing fluid with unique properties, making it well-suited for unconventional reservoir stimulation. Laboratory experiments are essential for determining hydraulic parameters prior to field trials. The fracturing apparatus thus plays a primary and indispensable role in evaluating SC-CO 2 fracturing potential. In this review article, a simple overview of water-based and waterless fracturing fluids is first provided from the perspective of their application effects and limitations. It is concluded that, compared with hydraulic fracturing, CO 2 fracturing shows tremendous potential, the research of which has the need to conduct laboratory experiments with new or improved fracturing apparatuses. Second, many multifunctional apparatuses have been designed to investigate the SC-CO 2 fracturing of reservoir rocks. In this regard, the currently developed SC-CO 2 fracturing apparatuses are reviewed with respect to their function units and related existing shortcomings. Different apparatuses correspond to various test schemes and results, among which the influences of the apparatus design on the experimental results are discussed. In particular, some remarks are made regarding the control of the initial injected CO 2 phase and the temperature–pressure measurement of CO 2 during fracturing. Third, inspired by the literature review, a self-designed experimental apparatus is developed to conduct SC-CO 2 fracturing tests. In particular, an integrated structure for the temperature–pressure measurement associated with CO 2 injection is proposed. Moreover, a triaxial core holder is customized to assist in measuring specimen strains and acoustic emission (AE) signals while ensuring the sealing performance of loading and injection systems. Ultimately, the challenges faced in industrial applications, such as fracturing equipment, CO 2 –rock interactions, and CO 2 phase control, have impeded the field-scale application of SC-CO 2 fracturing for shale gas development. Hereby, future apparatus design concepts are given for comprehensive investigations of SC-CO 2 fracturing mechanism. • State-of-the-art and limitation of water-based and waterless fracturing fluids are reviewed. • Current development of SC-CO 2 fracturing apparatuses with respect to function units is briefly introduced. • A self-designed experimental apparatus is customized to maintain the super-critical state of CO 2 during CO 2 injection. • Obstacles remaining for field-scale SC-CO 2 fracturing are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Toward the efficient and cost effective synthesis of three-dimensional hierarchical architectures at mild condition and their potential applications in environmental protection, the materials chemistry for green synthesis of strontium carbonate (SrCO3) superstructures and their application as adsorbents for methylene blue solution and heavy metal ions were explored. Uniform hierarchical mesoporous SrCO3 microspheres with a narrow diameter distribution were synthesized via a mild hydrothermal treatment (110°C, 6.0h) of the slurry derived from the room temperature coprecipitation of SrCl2 and Na2CO3 solution, in the presence of ethylenediaminetetraacetic acid (EDTA). The as-synthesized mesoporous SrCO3 microspheres had a specific surface area of 56.3m2 g−1 and a narrow pore size distribution concentrating on 2–20nm, with an average pore diameter of 9.45nm. The introduction of EDTA in due case with tuned pH value was favorable for the formation of SrCO3 microspheres, whereas the mild hydrothermal treatment promoted the morphology uniformity of the mesoporous microspheres with narrow diameter distribution. The adsorption evaluation indicated that the present mesoporous SrCO3 microspheres exhibited excellent adsorption performance for deionized (DI) water containing methylene blue, or heavy metal ions such as Fe3+ and Pb2+, revealing the as-synthesized uniform hierarchical mesoporous SrCO3 microspheres as potential adsorbents with wide applications in environmental protection. [Copyright &y& Elsevier]

Abstract: Micro/nanostructured nickel borate (Ni3(BO3)2) has been widely explored as advanced materials for energy conversion and non linear optical applications, fabricating one-dimensional micro-/nanostructures of Ni3(BO3)2 has thus become increasingly necessary. In this contribution, pure phase of rod-like micron Ni3(BO3)2 particles were synthesized via a facile flux NaCl and surfactant poly(oxyethylene)9 nonylphenol ether (NP-9) assisted thermal conversion route at 750–800°C for 2.0h. The introduction of NaCl and NP-9 was favorable for the formation of the Ni3(BO3)2 particles with rod-like morphology and smaller size, respectively. When calcined at 750°C in the presence of 8.0mL of NP-9 and with the molar ratio of Ni:B:Na=3:8:3, high aspect ratio rod-like micron Ni3(BO3)2 particles were obtained. The FT-IR and UV–vis properties of the as-synthesized Ni3(BO3)2 particles were also presented. The as-synthesized Ni3(BO3)2 rod-like particles further enlarged the metal borate family, with corresponding potential applications in the areas of nanocomposites, catalysis, energy conversion and storage, etc. [Copyright &y& Elsevier]

Abstract: Uniform high crystallinity short belt-like Ca2B2O5·H2O nanostructures (nanobelts) were facilely synthesized through a room temperature coprecipitation of CaCl2, H3BO3, and NaOH solutions, followed by a mild hydrothermal treatment (180°C, 12.0h). By a preferential growth parallel to the (100) planes, Ca2B2O5·H2O nanobelts with a length of 1–5μm, a width of 100–400nm, and a thickness of 55–90nm were obtained. The calcination of the nanobelts at 500°C for 2.0h led to short Ca2B2O5 nanobelts with well preserved 1D morphology. Calcination at 800°C led to a mixture of Ca2B2O5 and Ca3B2O6. The products were with belt-like and quasi-polyhedron morphology, while they turned into pore-free micro-rod like and polyhedron morphology when the calcination was taken in the presence of NaCl. NaCl assisted high temperature calcination at 900°C promoted the formation of Ca3B2O6 in the products. When dispersed in deionized water or absolute ethanol, the Ca2B2O5·H2O nanobelts and Ca2B2O5 nanobelts showed good transparency from the ultraviolet to the visible region. The as-synthesized Ca2B2O5·H2O and Ca2B2O5 nanobelts can be employed as novel metal borate nanomaterials for further potential applications in the area of glass fibers, antiwear additive, ceramic coatings, and so on. [Copyright &y& Elsevier]

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]

Abstract: Uniform orthorhombic Li3B5O8(OH)2 micro-rods were hydrothermally synthesized at 150–210°C for 6.0–24.0h, using LiOH·H2O and H3BO3 as the reactants. The resulting Li3B5O8(OH)2 micro-rods had a length of 20–60μm, an aspect ratio of 6–14, and a high crystallinity. The presence of hexadecyl trimethyl ammonium bromide was favorable for the oriented growth of the Li3B5O8(OH)2 micro-rods. The orthorhombic Li3B5O8(OH)2 was decomposed into Li2B4O7 and α-LiBO2. Pore-free high crystallinity Li2B4O7 with quasi polyhedron morphology can be obtained by NaCl assisted calcination. This enlarged the controllable synthesis of the alkali borates, especially enriched the study on the lithium borates which can be potentially used as a perspective superionic conductor and electrode of lithium ion batteries. [Copyright &y& Elsevier]

Abstract: Uniform monodisperse porous silk-worm pod-like hematite (α-Fe2O3) superstructures were efficiently obtained via a facile hydrothermal route. This was realized via the co-precipitation of FeCl3 and NaOH solutions at room temperature in the presence of H3BO3, followed by a mild hydrothermal treatment (150°C, 12.0h). The UV–vis band is mainly located in the far-UV region, with one intense broadband from 260 to 290nm. The porous pod-like superstructures exhibit special magnetic properties with a remnant magnetization of 0.22emug−1 and a high coercivity of 3315.5Oe at room temperature, indicating the as-obtained porous pod-like superstructures of a promising candidate for gas sensors, lithium ion battery, photocatalysis, and water treatment. [Copyright &y& Elsevier]

Abstract: Mass production of one-dimensional (1D) nanomaterials has emerged as one of the most significant challenges in powder technology. In this contribution, MgBO2(OH) nanowhiskers were hydrothermally produced at a kilogram scale in a 150L stainless steel autoclave at 200°C for 12.0h by using MgCl2·6H2O, H3BO3 and NaOH as the raw materials. The subsequent thermal conversion of the MgBO2(OH) nanowhiskers at 700°C for 6h led to 3.75kg of high crystallinity monoclinic Mg2B2O5 nanorods, with a length of 0.47–1.3µm, a diameter of 55–160nm, and an aspect ratio of 3–15. After the nanorods have been surface modified with the silane coupling agent KH-550, the reinforcing and toughening effects of the Mg2B2O5 nanorods on the biaxially oriented polypropylene resins (BOPP-D1) were evaluated. The filling of the Mg2B2O5 nanorods into the resins resulted in the increase in the tensile strength, the impact strength, and the melt flow index of the BOPP-D1 composites. The appropriate ratio of coupling agent to fillers (Mg2B2O5 nanorods) and the ratio of fillers to resins were determined within the range of 0.6–1.2wt.% and 8–15wt.%, respectively. The optimal ratio of fillers to resins was ca. 10wt.%. The present mass production of MgBO2(OH) nanowhiskers and Mg2B2O5 nanorods is believed to be helpful for enlarging and propelling the applications of the 1D magnesium borate nanostructures in the near future. [ABSTRACT FROM AUTHOR]

During underground mining, rock deformation may be time-dependent and is reflected in rheological behavior. These changes may be also accelerated by dynamic disturbances, such as rock blasting, which can trigger mining-induced hazards such as rockburst and a falling roof. A combined double-rock sample was analyzed to clarify the rockburst mechanism resulting from interaction between roof and pillar. In this work, a double-rock sample was subjected to a combined creep and dynamic loading condition. Based on the results, an ideal mechanical model was developed to describe the interaction between double rock samples loaded in series to simulate interaction between the pillar and roof. To test the model, a double-rock sample composed of granite and sandstone was loaded in series under creep and dynamic loading and the effect of dynamic disturbance on the creep process was quantified. Under the same creep stress, a higher impact dynamic disturbance resulted in shorter failure time. Under the same dynamic disturbance, the specimen failed faster with increased strain energy of rebound of the granite sample under increasing creep stress. The energy dissipation rate and energy transfer efficiency are defined to quantify the energy dissipation of double-rock sample and energy transfer between strong and weak sample. Based on the quantification of energy transfer efficient, it confirms that the ratio of stiffness of the double-rock sample should be a indicator for the energy transfer between strong and weak samples. The granite sample had higher uniaxial compressive strength, so it did not fail during the loading process. For the plaster-granite sample, the granite released most energy to accelerate the unstable failure of plaster. The granite-granite sample failed simultaneously and released most strain energy violently. The results can provide a reference to evaluate the delayed rockburst of rock subjected to creep stress. [ABSTRACT FROM AUTHOR]

Uniaxial compressive tests were performed on Y-jointed granite specimens to explore how intersecting rough joints affect the strength, failure mode, and precursory damage characteristics of the jointed rock mass. The mechanical properties, joint dip angles, and joint roughness of the specimens were measured prior to the tests, then the loading stress, surface displacement fields, acoustic emission (AE) signals, and failure modes were recorded during the loading process. As the uniaxial compressive strength (σ c) of the specimens increased, three different failure modes appeared: shear failure along the persistent joint with rock wedge falling, compressive failure with rock wedge ejection, and overall crushing accompanied with rock fragment splashing, the σ c thresholds of the three failure modes are about 50 MPa and 90 MPa, respectively. The deformability of the specimens weakened gradually as σ c increased. AE events spread from the joint surface to the interior of the rock block until final failure. For specimens that failed in shear mode, multiple sudden stress drops along with sharp displacement increases occurred during the tests but no entire failure occurred. Other specimens tended to present one eventual unstable failure. When the peak shear strength of the non-persistent joint was higher than or near to that of the persistent joint, the σ c of a given Y-jointed specimen was mainly determined by the persistent joint. Otherwise, it was simultaneously controlled by the two joints. Both the joint dip angle and joint roughness were found to significantly influence the σ c of the specimens. Each stress drop was accompanied by significant AE signal variations, though the AE indicators are difficult to effectively utilize for early warning of specimen failure. • The effects of joint dip angle and joint roughness on the strength of Y-jointed granite specimens were investigated. • Three different failure modes emerged as the peak compressive strength of the Y-jointed specimens increased. • Shear failure is not the main failure mode in the jointed rock mass under high geo-stress. • Unlike the damage location, the early warning time for specimen failure differs substantially in different cases. [ABSTRACT FROM AUTHOR]

Abstract: Preservation of one-dimensional (1D) morphology and improvement of crystallinity in the thermal conversion route to magnesium borate (Mg2B2O5) nanowhiskers at a relatively low temperature as 650–700°C (200–350°C lower than that of the literature) based on the hydrothermal synthesis of magnesium borate hydroxide (MgBO2(OH)) nanowhiskers were investigated; the results indicated that thermal conversion at appropriate temperature with a slow heating rate was favorable for the morphology preservation and crystallinity improvement. A specific heating procedure was developed according to the recrystallization phenomenon existing in the thermal conversion of the MgBO2(OH) nanowhiskers to produce Mg2B2O5 nanowhiskers with uniform morphology, improved crystallinity and fewer pores, in which Mg2B2O5 nanowhiskers (15.0–45.0nm in diameter, 0.2–2.0μm in length) were synthesized by heating MgBO2(OH) nanowhiskers (1.0°Cmin−1) to 650°C for 2.0h of isothermal condition first to preserve the 1D morphology, and thereafter to 700°C (1.0°Cmin−1) for another 2.0h of isothermal state to recrystallize. The designed specific heating procedure to reduce the mesopores and deformation could also benefit synthesis of other 1D anhydrous nanostructures via the wet chemistry-based thermal conversion route. [Copyright &y& Elsevier]

The dynamic disturbance is one of the major reasons to trigger rock block sliding along the discontinuities of roof rock mass during the mining excavation. A self-developed test machine was used in this study to investigate the sliding instability of an isosceles trapezoid rock block triggered by dynamic disturbance. The sliding displacement, strain, and impact energy were monitored during the hammer impact under different lateral clamping load conditions. The experimental results show that the typical vertical displacement of key blocks can be divided into three modes post-disturbance depending on the clamping load and impact energy. Two distinct instability processes were observed once the key block began to lose stability and fall: Immediate falling and delayed falling. The difference between them involves the instantaneous slide distance and pendulum-type wave propagating on the sliding interface. The critical impact energy causing the key block to fall shows a nearly logarithmical increment with the gradually ascending lateral clamping load. Based on the energy analysis, an analytical solution to key block sliding displacement under dynamic disturbance is proposed, which accounts for the influence of clamping load, disturbance energy, interface friction coefficient, and key block incline angle. By comparison with the experimental results, the theoretical calculation is shown to effectively estimate the sliding distance of the key block under dynamic disturbance. This work may provide some sound guidance for the real-time assessment of key rock block stability via displacement monitoring. [ABSTRACT FROM AUTHOR]

The gas adsorption/desorption-induced coal deformation effect is a significant factor governing the evolution of coalbed permeability. Current theoretical investigations typically coal bulk and fracture deformation induced by gas are equivalent, neglecting the matrix-fracture interactions. Based on internal adsorption stress, this paper proposes Internal Differential Strain Coefficient (IDSC) to quantitatively characterize the relationship between coal bulk and fracture strain under equilibrium conditions. Coupling this coefficient constructs a binary gas permeability evolution model considering matrix-fracture interactions. Through numerical simulations of CO 2 -ECBM processes under various internal differential strain circumstances using this model, dynamic evolution patterns of diverse parameters are obtained. The research findings indicate that along the direction of CO 2 injection, matrix-fracture interactions exhibit a complex trend of initially increasing, then decreasing and then increasing, and the increase in internal differential strain levels results in a downward trend in permeability peak. Additionally, the evolutionary characteristics of CH 4 recovery and cumulative CO 2 storage rising with increasing internal differential strain levels were obtained on time scales using a fixed-point monitoring methodology. Inspired by the aforementioned laws, this paper discusses the macroscopic influence of burial depth on the effects of internal differential strain, providing new theoretical support for CO 2 sequestration injection methods in deep coal seams. • A coefficient capable of quantitatively analyzing the internal differential strain in the CO 2 -ECBM process is proposed. • Based on IDSC, a model describing the evolution of coal seam permeability in CO 2 -ECBM process is established. • Analyzed the influence of internal differential strain on the permeability of coal beds in the CO 2 -ECBM process. • Analyzed the influence of internal differential strain characteristics on CO 2 injection capacity. [ABSTRACT FROM AUTHOR]

Hierarchical porous urchin-like Cu 2−x Si 2 O 5 (OH) 3 ·xH 2 O and CuO/SiO 2 composite hollow microspheres are rationally designed and facilely achieved by a one-pot hydrothermal-thermal conversion, as competitive candidates for high efficiency catalytic reduction of 4-NP and satisfactory adsorbents for MeB removal. • Hierarchical porous Cu 2−x Si 2 O 5 (OH) 3 ·xH 2 O and CuO/SiO 2 microspheres are developed. • Etching formation mechanism assisted by intermediate SiO 2 nanospheres is illuminated. • Excellent catalytic reduction of 4-NP and satisfactory adsorption of MeB are achieved. • Synergic effect of in situ reduced Cu0 and hierarchical porous structures is revealed. • Superb recyclability in 10 cycles' reduction of 4-NP is demonstrated. Hierarchical porous urchin-like Cu 2−x Si 2 O 5 (OH) 3 ·xH 2 O hollow microspheres constructed by radially aligned one-dimensional (1D) nanotubes (NTs) are rationally designed and facilely fabricated via a one-pot hydrothermal method (120 °C, 12.0 h) using abundant CuCl 2 ·2H 2 O and Na 2 SiO 3 ·9H 2 O as the basic raw materials, in the absence of any pre-prepared templates, additives or organic solvents. A probable etching formation mechanism of the Cu 2−x Si 2 O 5 (OH) 3 ·xH 2 O hollow microspheres assisted by the intermediate SiO 2 nanospheres is proposed. The subsequent mild thermal conversion (750 °C, 2.0 h) results in CuO/SiO 2 composite hollow microspheres. Both of the hierarchical porous Cu 2−x Si 2 O 5 (OH) 3 ·xH 2 O and CuO/SiO 2 composite microspheres present highly catalytic activity to the reduction of the nitroarenes (e.g. 4-NP and 2-NP). Particularly, the hierarchical porous Cu 2−x Si 2 O 5 (OH) 3 ·xH 2 O hollow microspheres bearing high specific surface area (528.2 m2 g−1) and large pore volume (1.083 cm3 g−1) and in situ reduced highly dispersed metallic Cu0 demonstrate high activity for the 4-NP reduction, with an exceptional rate constant (K nor = 60.6 s−1 g−1) higher than that of many other previously reported results. The synergic effect of the in situ reduced Cu0 and hierarchical porous structures on the reduction of 4-NP has also been deliberately investigated. Moreover, the Cu 2−x Si 2 O 5 (OH) 3 ·xH 2 O and CuO/SiO 2 composite microspheres have also displayed excellent recycling catalytic performance during the tested 10 successive runs of reduction of 4-NP without significant degradation in its activity. Additionally, the Cu 2−x Si 2 O 5 (OH) 3 ·xH 2 O microspheres also exhibit excellent adsorption performance for removal of cationic dye methylene blue (MeB), with the maximum adsorption capacity q m of 242.5 mg g−1. The hierarchical porous Cu 2−x Si 2 O 5 (OH) 3 ·xH 2 O and CuO/SiO 2 composite microspheres thus demonstrate great potentials as low-cost, environmentally friendly and competitive candidates in future practical wastewater treatment. [ABSTRACT FROM AUTHOR]

This communication describes the design and synthesis of anti-sintering and -coke nickel phyllosilicate (PS) nanotubes (Ni/PSn) for hydrogen production via reforming reactions. The introduction of nickel particles in PS nanotubes could effectively maintain the Ni size and increase the resistance of metal particles for carbon deposition. [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]

• The hardening processes of backfill was characterized by ultrasonic P-wave. • Different binder contents, curing temperatures and silica fumes were experimented. • Addition of silica fume makes backfill structure enhanced, improving in strength. Cemented paste backfill (CPB) is broadly used for underground backfilling, improving the mechanical performance through the modification of its composition and, therefore, its microstructure and characteristics. In order to assess the applicability of ultrasonic waves to better comprehend relations among composition-microstructure-characteristics; an experimental program was realized using the magnitude and frequency spectrum of ultrasonic P-wave which is considered as an effective system for characterizing the hardening processes of cementitious materials. In this study, different binder contents (3, 5 and 7 wt%) and curing temperatures (20 and 35 °C) were tested for investigating CPB's hardening processes. Silica fume (0, 5 and 20 wt% of binder) was used as an additive in replace of binder to determine its effect on behavior of ultrasonic waves. Component (TG and DTG) and microanalysis (SEM) were adopted to improve the understanding of ultrasonic behavior. Results show that there is a positive relationship between the strength and magnitude of ultrasonic P-wave in CPB, except for the sample with 3 wt% binder. The magnitude and frequency spectrum of ultrasonic P-wave is more sensitive than P-wave velocity to reflect the variation in the backfill strength. Higher binder content can densify the microstructure of CPB with longer curing time and reduce the energy attenuation of ultrasonic P-wave, resulting higher magnitude obtained. The addition of silica fume makes CPB having a finer pore structure enhanced, thereby improving in the strength, P-wave velocity and magnitude. The energy attenuation of ultrasonic P-wave can be notably weakened at a curing temperature of 35 °C due to a dense network formed by both hydration products and tailings. The magnitude and frequency spectrum of ultrasonic P-wave can be capable of reflecting and characterizing the pore structure, hydration processes and water content in CPB comprehensively. Consequently, the proposed technique can be well used to illustrate the hardening processes of CPB and hence improve the understanding of its early-age behavior. [ABSTRACT FROM AUTHOR]

As a stress wave propagates in rock, the amplitude of the stress wave will attenuate, and the waveform will dissipate, which can be equivalently characterized by the stress wave propagation in a viscoelastic material. The stress wave propagation may induce rock damage when the stress is greater than the rock strength. In this study, viscoelastic wave propagation in rock and the damage and failure process of rock induced by viscoelastic wave propagation, which are usually examined separately in existing theoretical and numerical models, were investigated under a unified framework. Based on viscoelastic damage theory and the theory of stress wave propagation in a one-dimensional viscoelastic bar, theoretical equations for spalling fracture of a viscoelastic bar were obtained. Then, the numerical model implemented by the one-dimensional wave propagation program was validated by reproducing the dynamic spalling of green sandstone bar; after that step, the program was employed to study the behavior of viscoelastic bar spalling. Based on the numerical simulation, the condition, position and time of the dynamic spalling induced by quarter sine wave propagation in the viscoelastic bar were examined, and the influence of the amplitude and frequency of the quarter sine wave and the viscosity coefficient and length of the viscoelastic bar on the spalling were quantified. [ABSTRACT FROM AUTHOR]

• The lower cured temperature is (<0 °C), the higher backfill strength is. • The binder content effects are greatly limited in the frozen environment. • The frozen backfill shows ductile or slight strain-softening deformation behavior. • The frozen CTB shows higher void ratio and water content. Mining activities have become increasingly common in cold or permafrost regions. However, there is limited information regarding the behavior of cemented tailings backfill (CTB) cured under freezing conditions. This paper was aimed to assess the coupled effects of temperature and binder content on the mechanical and physical properties of frozen CTB. Thus, CTB mixtures with various binder contents (3, 5, and 7%) were tested at different curing times and temperatures (20, 0, −5, and −15 °C). The results indicated that, due to ice formation and hydration reaction inhibition at freezing temperatures, frozen CTB simultaneously presented higher strength and poorer structure, compared with CTB cured at normal temperatures (>0°C). The deformation behavior of frozen CTB showed ductile or slight strain-softening behavior that was dependent on the temperature and curing time. Moreover, binder content effects were greatly limited by freezing temperatures and the binder content had little effect on the properties of CTBs cured at −15 °C. However, when the temperature increased to −5°C, the higher binder content resulted in an increase in unfrozen water content, which led to lower strength. The present results demonstrated that the coupled effects of temperature and binder content on frozen CTBs were important factors for considering the design of cost-effective and safe CTB structures in cold regions. [ABSTRACT FROM AUTHOR]

Rock is a typical porous and heterogeneous geological medium, and water imbibition has a great influence on its mechanical properties. The degree of water imbibition in rock heavily depends on the internal fissures of rock and the soaking time. Here, sandstone specimens were soaked in a red ink solution for different amounts of time, and then cross sections were photographed to obtain RGB images of the water distribution in the rock. Next, the correlation between the water distribution in the rock specimens and the RGB values of the images was established to characterize the water distribution in the sandstone specimens. Finally, the water imbibition in rock was quantified with the diffusion equation, which was applied to determine the diffusivity of rock when the quantitated water distribution was matched to the observed wetted ring in the laboratory. This study quantifies the evolution of unsaturated moisture distribution in sandstone with soaking time and the variation of uniaxial compression strength as it is affected by the water distribution. The results from this study can be used as the scientific bases to study the rock weakening mechanism in a water environment. [ABSTRACT FROM AUTHOR]

When underground openings are excavated in weak rocks under a high overburden, large deformation and squeezing problems may take place. This paper generalizes the finite strain theoretical solution of Vrakas and Anagnostou (2014) for the ground squeezing response to elastic-brittle-plastic deformed rocks subjected to both the in-plane hydrostatic stress and the arbitrary axial in-situ stress. The ground behavior is analyzed based on the motion of material points in deformed configuration, thus the geometric non-linearity of rock mass is considered. Three different types of the plastic region can develop which depends on the magnitude of the axial in-situ stress, and the effects of axial in-situ stress and axial plastic flow on the squeezing response of rock mass are clarified in the case of large deformation. Comparisons among the large strain formula, the small strain theory and the numerical simulation results are made by using some examples, and the applicability of small strain method and some simplified models neglecting the axial in-situ stress is investigated. Finally, an engineering application in the severe squeezing Yacambú-Quibor tunnel in Venezuela is introduced to show the validity of the present large strain method in practical engineering. It is therefore very helpful from a practical standpoint for the preliminary design of cavities in squeezing rock mass, where the large deformation may exist and the classical small strain elasto-plastic analyses are inappropriate. [ABSTRACT FROM AUTHOR]

• Internal strain of sulphated CPB that related to strength development can be considered as a hydration process indicator. • Sulpahte concentration and curing temperature can significantly affect the evolution of internal strain in CPB. • Final internal strain is an important indicator for the barricades stability as well as mining cycle. Cement hydration is a volume reduction reaction which can result in negative pore water pressure while strengthening the structural stiffness of cemented paste backfill (CPB). Both sulphate and temperature significantly affect the hydration process and thus influence the internal volume change and mechanical properties of CPB. The expansive hydration products produced in sulphated CPB may create an increase in volume which subsequently weakens the CPB. This paper presents an experimental study conducted to evaluate the coupled effects of sulphate and curing temperature on the internal strain evolution of early aged CPB. CPB samples of various initial sulphate concentrations (0, 5000 and 25,000 ppm) were prepared and cured at various temperature (20 °C and 35 °C) at early ages (≤7 days). Mechanical tests were conducted on the samples as internal strain was monitored by Fiber Bragg Grating (FBG) sensors. The results indicate that the FBG sensor is sufficiently sensitive to detect the internal strain development of sulphated CPB mixtures during the hydration process. At sulphate concentration of 25,000 ppm, the expansive strain occurred at curing temperature of 35 °C due to the internal expansive force of the expansive materials. The final internal strain value corresponds closely to the strength of the sulphated CPB. As the internal strain of sulphated CPB decreased, the uniaxial compressive strength and tensile strength showed similar trends throughout the experiment. When expansive strain emerged after the initial thermal strain stage, however, there was a higher ratio of uniaxial compressive strength to tensile strength. This phenomenon merits careful consideration in the stability analysis of exposed CPB in underground mines. [ABSTRACT FROM AUTHOR]