A method to predict rockburst using temporal trend test and its application

Rockbursts have become a significant hazard in underground mining,underscoring the need for a robust early warning model to ensure safety management.This study presents a novel approach for rockburst prediction,integrating the Mann-Kendall trend test(MKT)and multi-indices fusion to enable real-time and quantitative assessment of rockburst hazards.The methodology employed in this study involves the development of a comprehensive precursory index library for rockbursts.The MKT is then applied to analyze the real-time trend of each index,with adherence to rockburst characterization laws serving as the warning criterion.By employing a confusion matrix,the warning effectiveness of each index is assessed,enabling index preference determination.Ultimately,the integrated rockburst hazard index Q is derived through data fusion.The results demonstrate that the proposed model achieves a warning effectiveness of 0.563 for Q,surpassing the performance of any individual index.Moreover,the model’s adaptability and scalability are enhanced through periodic updates driven by actual field monitoring data,making it suitable for complex underground working environments.By providing an efficient and accurate basis for decision-making,the proposed model holds great potential for the prevention and control of rockbursts.It offers a valuable tool for enhancing safety measures in underground mining operations.

Energy evolution and structural health monitoring of coal under different failure modes:An experimental study

Structural instability in underground engineering,especially in coal-rock structures,poses significant safety risks.Thus,the development of an accurate monitoring method for the health of coal-rock bodies is crucial.The focus of this work is on understanding energy evolution patterns in coal-rock bodies under complex conditions by using shear,splitting,and uniaxial compression tests.We examine the changes in energy parameters during various loading stages and the effects of various failure modes,resulting in an innovative energy dissipation-based health evaluation technique for coal.Key results show that coal bodies go through transitions between strain hardening and softening mechanisms during loading,indicated by fluctuations in elastic energy and dissipation energy density.For tensile failure,the energy profile of coal shows a pattern of “high dissipation and low accumulation” before peak stress.On the other hand,shear failure is described by “high accumulation and low dissipation” in energy trends.Different failure modes correlate with an accelerated increase in the dissipation energy before destabilization,and a significant positive correlation is present between the energy dissipation rate and the stress state of the coal samples.A novel mathematical and statistical approach is developed,establishing a dissipation energy anomaly index,W,which categorizes the structural health of coal into different danger levels.This method provides a quantitative standard for early warning systems and is adaptable for monitoring structural health in complex underground engineering environments,contributing to the development of structural health monitoring technology.

A new scientific explanation to rock fracture-induced electromagnetic radiation process

The electromagnetic radiation(EMR)monitoring and early warning technology has experienced decades of successful applications for worldwide coal and rock dynamic disasters,yet a fundamental model unifying physical mechanism and generation process for EMR is still lacking.The effective revealing of EMR's mechanism is crucial for dynamic disaster control and management.With this motive,a multi-scale experimental study was conducted in the earlier stage.At the micro-scale,the charge's existence and non-uniform distribution on rock's micro-surface were confirmed by atomic force microscope(AFM),and deduced the relationship with load changes.At the meso-scale,the time sequence synchronization and frequency domain consistency of EMR and micro-vibration(MV)in the rock fracture under load have been confirmed.Therefore,it is inferred that the vibration of the crack surface acts as the power source of rock fracture-induced EMR,and the original charge on the crack surface and the charge generated by the new crack surface are the electrical basis of EMR.Based on the above two experimental findings,this paper proposes a new mechanism of rock fracture-induced EMR defined as the electricity-vibration coupling mechanism,stating that,the vibrating charged crack generates the EMR.Subsequently,a generation model was constructed based on vibrating charged crack clusters to elucidate this mechanism.The experimental results demonstrated that the EMR waveform calculated by the model and measured by antenna exhibited good correspondence,thereby verifying the effectiveness of the constructed EMR model.The proposal of this new mechanism and the model further clarified the EMR's mechanism induced by rock fracture.Moreover,the inter-relationship among crack propagation,vibration,and EMR was developed by this model,which could be immensely beneficial in EMR-based identification and prediction of dynamic disasters in complex mining environments worldwide.

Research progress of monitoring, forecasting, and prevention of rockburst in underground coal mining in China

As one of the dynamic disasters of coal mines,rockburst seriously affects underground safe coal mining.Based on the laboratory test,field test,and theoretical analysis,this study proposed the principle of the rock burst induced by the combination of dynamic and static stresses and divided such rock burst into three types,including induced by primary dynamic stress,mainly induced by dynamic stress,and by dynamic stress in low critical stress state.The expressions of the static stress induced by coal mining and dynamic stress induced by mining tremors were obtained.Moreover,theories and technologies at home and abroad were summarized concerning the monitoring,forecasting,and preventing of rockburst.These mainly include the zoning and leveling forecasting method,electromagnetic radiation technology,elastic wave and seismic wave computed tomography technologies in aspect of rockburst monitoring,as well as the intensity weakening theory,the strong-soft-strong structure effect,the directional hydraulic fracturing technology,the roadway support system in regards of rockburst prevention.The prospect of rockburst development suggested that researches concerning the rockburst mechanism should be quantitatively developed around the roadway and coalface surrounding coal-rock mass.It should be focused on the rockburst mechanism and prevention technology of mining with over 1,000 km deep and mining in large tectonic zone.In addition,the monitoring and prevention of rockburst should be based on rockburst mechanism.

A dynamic ejection coal burst model for coalmine roadway collapse

In this study,we established a dynamic ejection coal burst model for a coalmine roadway subject to stress,and held that the stress concentration zone at the roadway side is the direct energy source of this ejection.The formation and development of such burst undergoes three stages:(1)instability and propagation of the cracks in the stress concentration zone,(2)emerging of a layered energy storage structure in the zone,and(3)ejection of coal mass or coal burst due to instability.Moreover,we figured out the initial strength of periodic cracks is parallel to the maximal dominant stress direction in the stress concentration zone and derived from the damage strain energy within the finite area of the zone based on the Griffith energy theory.In addition,we analyzed the formation process of the layered energy storage structure in the zone,simplified it as a simply supported restraint sheet,and calculated the minimum critical load and the internally accumulated elastic energy at the instable state.Furthermore,we established a criterion for occurrence of the coal burst based on the variational principle,and analyzed the coal mass ejection due to instability and coal burst induced by different intensity disturbances.At last,with the stratum conditions of Junde Coalmine as the model prototype,we numerically simulated the load displacement distribution of the stress concentration zone ahead of the working face disturbed by the main roof-fracture-induced dynamic load during the mining process as well as their varying characteristics,and qualitatively verified the above model.

AFM characterization of surface mechanical and electrical properties of some common rocks

The characterization of micro-surface mechanical and electrical properties of the natural rock materials remains inadequate,and their macroscopic performance can be better comprehended by investigating the surface properties.With this purpose,the present research focuses on characterizing the microsurface morphology,Derjaguin-Muller-Toporov(DMT)modulus,adhesion,and potential of granite,shale,and limestone by employing the atomic force microscope(AFM)as a pioneer attempt.The results show that the micro-surface morphology of the rock fluctuates within hundreds of nanometers,among which the granite micro-surface is comparatively the smoothest,followed by limestone.The morphology of the shale is the roughest,indicating that the regional difference of shale micro-surface is dominant.The distribution of the adhesion on rock micro-surface is uneven;the average adhesion of eight measuring areas for shale is 23.93 n N,accounting for three times of granite and limestone,while the surface DMT modulus of shale is relatively lower than granite and limestone.It is inferred from the obtained results that higher surface adhesion is helpful to the gas adsorption of shale,and the lower surface DMT(elastic)modulus is useful to the formation of fractures and pores.Thus,these two are the micromechanical basis of shale gas adsorption.Additionally,introducing a method to reduce the surface adhesion will benefit the exploration of unconventional resources such as shale gas.The micro-surface of the three types of rocks all shows electricity,with average potential ranging from tens of millivolts to hundreds of millivolts.Besides,the micro-surface potential of the rocks are heterogeneous,and both positive and negative points can be found.The existence and uneven distribution of micro-surface potential provide a robust physical basis for the electromagnetic radiation generated by rock fracture under loading.This study offers a new method for revealing the adsorption characteristics of unconventional gas reservoir rocks and the electromagnetic radiation mechanism of the rock fracture.

Inhibiting effect of tungstic compounds on glucose hydrogenation over Ru/C catalyst

The effect of acid component including various conventional acids and tungstic compounds on glucose hydrogenation over a series of binary catalyst system containing Ru/C catalyst was investigated. The results showed that HC1, H2SO4, H3BO3, H3PO4, and HNO3 had negligible effect, while all the tungstic compounds imposed inhibiting effects on the hydrogenation of glucose over Ru/C catalyst, and the suppressing effect followed the order of H2WO4〉HPW〉WO3〉AMT〉HSiW. This order is the same as the order of ethylene glycol （EG） yields in the one-pot conversion of glucose to EG, suggesting the important role of competition between glucose hydrogenation and retro-aldol condensation in controlling the selectivity of EG.

Characteristics of electromagnetic vector field generated from rock fracturing

Rock fracturing is often accompanied by electromagnetic phenomenon.As a vector field,in addition to the intensity that is widely concerned,the generated electromagnetic field also has obvious direction-ality.To this end,a set of electromagnetic antennas capable of simultaneous three-axis measurement is used to monitor the electromagnetic vector field generated from rock fracturing based on Brazilian tests.The signal amplitude on each axis can represent the magnitude of actual magnetic flux density component on the three axes.The intensity and directional characteristics of electromagnetic signals received at different positions are studied using vector synthesis.The directionality of electromagnetic radiation measured using a three-axis electromagnetic antenna shows that the direction of the magnetic flux intensity generated by rock fracturing tends to be parallel to the crack surface,and the measured signal intensity is greater in a direction closer to the crack surface.

A multi-scale framework for life reduction assessment of turbine blade caused by microstructural degradation

The prolonged thermal exposure with centrifugal load results in microstructural degradation,which ultimately leads to a reduction in the fatigue and creep resistance of the turbine blades.The present work proposes a multi-scale framework to estimate the life reduction of turbine blades,which combines a microstructural degradation model,a two-phase constitutive model,and a microstructure-dependent fatigue and creep life reduction model.The framework with multi-scale models is validated by a Single Crystal(SC)Ni-based superalloy at the microstructural length-scale and is then applied to calculate the microstructural degradation and the fatigue and creep life reduction of turbine blades under two specific service conditions.The simulation results and quantitative analysis show that the microstructural degradation and fatigue and creep life reduction of the turbine blade are heavily influenced by the variations in the proportion of the intermediate state,namely,the maximum rotor speed status,in the two specific service conditions.The intermediate state accelerates the microstructural degradation and leads to a reduction of the life,especially the effective fatigue life reserve due to the higher temperature and rotational speed than that of the 93%maximum rotor speed status marked as the reference state.The proposed multi-scale framework provides a capable approach to analyze the reduction of the fatigue and creep life for turbine blade induced by microstructural degradation,which can assist to determine a reasonable Time Between Overhaul(TBO)of the engine.

An orientation-dependent creep life evaluation method for nickel-based single crystal superalloys

This paper aims to propose a creep life evaluation method considering the effect of crystallographic orientation.First,the maximum Schmid factor of{111}〈112〉and the corresponding lattice rotation angle were introduced to form an“orientation factor”.Then the equivalent stress was calculated by multiplying this factor and the nominal stress.Latterly,the Larson-Miller Parameter(LMP)method was adopted as the rupture life evaluation criteria,in which the input variable was the equivalent stress instead of the nominal stress.All the predictions showed high accuracy when the proposed method was applied to Mar-M247,SC7-14,CMSX-2,Alloy454,CMSX-4 and DD6.Finally,the applicable temperature ranges of the orientation-dependent method(using equivalent stress)and the traditional LMP method(using nominal stress)were discussed.The results show that only the Orientation-Dependent(OD)method is reliable at intermediate temperatures(760–850°C)because the orientation has significant effect on the stress rupture life,while the influence of orientation is considerably reduced at high temperatures.Both methods provide precise predictions in this situation,and the LMP method should be favored since it is much easier to implement.

An energy-based low-cycle fatigue life evaluation method considering anisotropy of single crystal superalloys

The crystal orientation significantly affects the low-cycle fatigue (LCF) propertiesof single crystal (SC) superalloys. However, the orientation-dependent LCF life model withprecise mechanisms and strong applicability is still lacking. This investigation aims at establishing an energy-based LCF life evaluation method that could consider the orientation effect. First,the influencing factors of anisotropy were identified through the literature review. Secondly, themultiaxial formula of the Ramberg-Osgood (ReO) equation was established to describe theanisotropic cyclic deformation characteristics. Furthermore, the strain energy density of SC superalloys was determined based on this equation, and the effective strain energy density wasintroduced to account for the effect of orientation. Finally, the energy-based method was validated by its application to several SC superalloys. Results showed that the crystallographicorientation with a lower Young’s modulus usually exhibits better LCF resistance. This phenomenon could be attributed to the different values of strain energy density dissipated in one cycle.The multiaxial ReO relationship could capture the anisotropic cyclic deformation response ofDD6. Compared with the classical methods, the energy-based model is favored by its precisemechanism and strong applicability. And it also exhibited better prediction accuracy. Most datapoints of different crystallographic orientations lay within the
3 error band.