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The technical challenges associated with deep underground space activities have become increasingly significant. Among these challenges, one major concern is the assessment of rockburst risks and the instability of rock masses. Extensive research has been conducted by numerous scholars to mitigate the risks and prevent occurrences of rockburst through various assessment methods. Rockburst incidents commonly occur during the excavation of hard rock in underground environments, posing severe threats to personnel safety, equipment integrity, and operational continuity. Thus, it is crucial to systematically document real cases of rockburst, allowing for a comprehensive understanding of the underlying mechanisms and triggering conditions. This understanding will contribute to the advancement of rockburst prediction and prevention methods. Proper selection of an appropriate rockburst assessment method is a fundamental aspect in underground operations. However, there is a limited number of studies that summarize and compare different prediction and prevention methods of rockburst. This paper aims to address this gap by analyzing global trends using CiteSpace software since 1990. It discusses rockburst classification and characteristics, comprehensively reviews research findings related to rockburst prediction, including empirical, simulation, mathematical modeling, and microseismic monitoring methods. Additionally, the paper presents a compilation of current rockburst prevention measures. Notably, the paper emphasizes the significance of control strategies, which provide key insights into the effective utilization of stored energy within rock. Finally, the paper concludes by suggesting six directions for implementing intelligent management techniques to mitigate hazards during underground operations and reduce the probability of rockburst incidents. [ABSTRACT FROM AUTHOR]

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The present paper focuses on the manufacturing of micro-groove heat pipes on hydrostatic thrust bearings of heavy machinery. Special multitooth tools were designed for plough-extrusion forming heat pipes on flat copper. Experimental results were conducted to determine whether the plough-extrusion forming could achieve better performance than traditional wire electrical discharge. Furthermore, the processing using multi-tooth tool with 10 mm length, 55 tooth number, 0.25 mm tooth depth and 0.22 tooth top width was found to achieve the best performance among the six optional tools. The 50 mm/min forming speed was determined to acquire the best surface quality of the microgroove structure. Through heat transfer testing, the theoretical model for a micro-groove heat pipe made by plough-extrusion forming was also verified. [ABSTRACT FROM AUTHOR]

Failure characteristics of rocks under polyaxial compression have been the subject of extensive laboratory testing, although a limited amount of literature is published on the numerical simulation of rock failure under such conditions. The current study was conducted by using a commercially available finite-difference program, FLAC3D, to model the hard rock strength and fracturing under polyaxial compression. The Mogi-Coulomb criterion, where the relevant parameters can be obtained from conventional triaxial tests, was simulated in the software for realistic reflection of the effects of intermediate principal stress on hard rock fracture characteristics. According to the elastoplastic mechanics, the incremental iterative calculation format of the Mogi-Coulomb strain-softening failure criterion was implemented in the program, and the results were compiled into a dynamically linked library (DLL) based on the program interface of secondary development provided by FLAC3D. The numerical results of the calculated peak strength were analyzed and compared with previous experimental data for verification of the effectiveness and accuracy of the simulation models. Laboratory tests with consideration of various intermediate principal stresses were also conducted to investigate the hard rock failure modes under polyaxial compression states. The comparison of experimental results with numerical results using bothMogi-Coulomb and Mohr-Coulomb strain-softening models further explained the validity of the former method. The results showed that proper numerical modeling can be considered for simulating hard rock fracturing under polyaxial compression states for complex stress conditions in future studies. [ABSTRACT FROM AUTHOR]

Underhand cut-and-fill stoping is an efficient, sustainable mining method that is particularly applicable to complicated mining conditions in which both the peripheral rocks and the orebody are extremely unstable. Considering the mining conditions of the shallow, steeply dipping, narrow orebody in the Canzhuang gold mine in Shandong Province, China, a new method of underhand cut-and-fill without sublevel stoping that does not use the conventional sublevel, access to stope, and decline is proposed. Additionally, a novel auxiliary ventilation mode is applied to achieve high-efficiency ventilation. The restrained-beam mechanical model is established for the overlying backfill in single drift to ensure stability of the test stope. The plane problem is transformed into a three-dimensional problem when deducing the theoretical evenly distributed load of the overlying backfill. The optimal bearing layer thickness of the overlying backfill is calculated. During a 2-year field industrial test, the ore dilution ratio reduced from 14 to 4%and the ore recovery ratio increased from 75 to 92%, which improved the economic efficiency significantly and satisfied safe-production requirements. The description of the new mining method might provide theoretical and practical guidance for mining in similar settings. [ABSTRACT FROM AUTHOR]

Mining-induced voids provide essential channels for heat and mass transfer in disturbed strata. A group of dynamic distribution models of voidage was proposed to investigate the heterogeneous distribution and dynamic change of longwall mining-induced voids in overlying strata of a coalbed. It indicated that the voidage distribution has an evident periodicity and heterogeneity due to the periodical and inconsistent fractured subsidence of each key stratum with different thicknesses, strengths, and loads. Disturbed by longwall mining, the degree of difficulty of development increases successively from the pores and from the bed-separation fissures to the fractured fissures. In the caved zone, the porosity distribution along the coalbed strike and dip always presents a U-type appearance. In the fractured zone, the distribution shape of the transverse voidage alters from a narrow inverted U-type to a wide M-type, but the longitudinal voidage distribution always presents as an M-type fromthe narrow to the wide with time. The voids successively open and then gradually close from deep to shallow strata, and along mining operations they advance direction and present an arch-type distribution called the void-rich arch. The peak voidage near the mining face periodically extends forward with the advance of the mining operations and is slightly higher than near the starting line. The models and results might be applied to guide coalbed methane extraction, water influx prevention, coal fire prevention and control, and so on. [ABSTRACT FROM AUTHOR]

Ground settlements above a tunnel as a result of tunnel construction can be predicted with the help of input variables that have direct physical significance. Several empirical and artificial intelligence methods for estimating ground settlements have been established by researchers. However, these methods have some limitations because the large number of influential factors involved makes tunnel-ground interaction complicated. In this work, a random forest (RF) was developed and employed to predict ground settlements above tunnels. To achieve this goal, tunnel geometry, geological properties, and construction parameters were investigated as input variables to utilize in the RF modeling, resulting in the maximum surface settlement value (Smax) and trough width (i) as the ground surface settlement index. To demonstrate the applicability of the RF model, two data sets associated with different features, which were obtained from a detailed investigation of different tunnel projects published in literature, were utilized for model development and were applied to check the performance capacity of the developed model. A fivefold cross-validation procedure was then applied to identify the optimal parameter values during modeling, and an external testing set was employed to validate the prediction performance of the model. Two performance measures, R2 and RMS error, were employed. The relative importance of different parameters in the prediction of ground settlements was also investigated. Findings demonstrate that the RF method provides promising results and offers an alternative means in predicting ground settlements induced by tunneling. [ABSTRACT FROM AUTHOR]

Mineral reserve estimation and mining design depend on a precise modeling of the mineralized deposit. A multi-step interpolation algorithm, including 1D biharmonic spline estimator for interpolating floor altitudes, 2D nearest neighbor, linear, natural neighbor, cubic, biharmonic spline, inverse distance weighted, simple kriging and ordinary kriging interpolations for grade distribution on the two vertical sections at roadways and 3D linear interpolation for grade distribution between sections, was proposed to build a 3D grade distribution model of the mineralized seam in a longwall mining panel with a U-shaped layout having two roadways at both sides. Compared to field data from exploratory boreholes, this multi-step interpolation using a natural neighbor method shows an optimal stability and a minimal difference between interpolation and field data. Using this method, the 97,576 m3 of bauxite, in which the mass fraction of Al2O3 (Wa) and the mass ratio of Al2O3 to SiO2 (Wa/s) are 61.68% and 27.72, respectively, was delimited from the 189,260 m3 mineralized deposit in the 1102 longwall mining panel in the Wachangping mine, Southwest China. The mean absolute errors, the root mean squared errors and the relative standard deviations of errors between interpolated data and exploratory grade data at six boreholes are 2.544, 2.674 and 32.37% of Wa; and 1.761, 1.974, and 67.37% of Wa/s, respectively. The proposed method can be used for characterizing the grade distribution in a mineralized seam between two roadways at both sides of a longwall mining panel. [ABSTRACT FROM AUTHOR]

Statistical damage constitutive models (SDCMs) have been widely employed to describe the mechanical response of strainsoftening rock, especially in brittle failure under moderate confining pressure. The residual strength, referring to the strength of strainsoftening rock in the postpeak region, has not been accurately considered in present works. In this study, an extended definition of damage was proposed based on the fact that the intact material gradually evolves into another damaged material, and these two parts are mixed together to carry external loads. Accordingly, a modified damage mechanical model was established. Then, the evolution equation of the damage variable was formulated based on the well-known Weibull distribution. Furthermore, a modified SDCM reflecting strain-softening and residual strength behavior for rocks loaded in conventional triaxial compression (CTC) was developed. The model parameters were estimated based on the extremum method. Finally, validation indicated that the calculated results from the modified SDCM had good agreement with the experimental observation and were much better than the calculated results from other models. Issues related to the lateral deformation of this model were also examined. [ABSTRACT FROM AUTHOR]

Rockburst prediction is of crucial importance to the design and construction of many underground projects. Insufficient knowledge, lack of characterizing information, and noisy data restrain rock mechanics engineers from achieving optimal prediction results. In this paper, a data set of 246 rockburst events was examined for rockburst classification using supervised learning (SL) methods. The data set was analyzed with 8 potentially relevant indicators. Eleven algorithms from 10 categories of SL algorithms were evaluated for their ability to learn rockburst, including linear discriminant analysis (LDA), quadratic discriminant analysis (QDA), partial least-squares discriminant analysis (PLSDA), naïve Bayes (NB), k-nearest neighbor (KNN), multilayer perceptron neural network (MLPNN), classification tree (CT), support vector machine (SVM), random forest (RF), and gradient-boosting machine (GBM). The data set was randomly split into two parts: training (70%) and test (30%). A 10-fold cross-validation (CV) method was applied during modeling, and an external testing set was employed to validate the prediction performance of the SL models. Two accuracy measures for multiclass problems were employed: classification rate and Cohen's Kappa. The accuracy analysis, together with Cohen's kappa and a nonparametric statistical test for the rockburst data set, revealed that the best models for the prediction of rockburst were GBM and RF when compared with other learning algorithms. [ABSTRACT FROM AUTHOR]

With the weight and volume increasing of the heavy/large equipment parts, the heavy CNC vertical lathe has become the ideal processing equipment for these parts. The main factor which affects the machining quality and efficiency of heavy CNC vertical lathe is the mechanical properties of the hydrostatic thrust bearing. This article do the research based on the large size circular ring oil pad's lubrication performance of the hydrostatic thrust bearing in the heavy/large equipment, establishing the lubrication performance distribution mathematical model of the velocity field, flow field, pressure field, etc., analysing the bearing behaviour of the large size circular ring oil pad. The results show that when the rotational speed of the hydrostatic thrust bearing is higher than a certain speed , the oil flow which is generated by the centrifugal force will be greater than that generated by the pressure difference. The friction heat is not easy to transfer out in the above situation, which restrains the bearing rotating speed of the hydrostatic thrust bearing. The paper author proposes that the temperature rise can be controlled by increasing the oil pressure or adding the cooling system which makes the oil in the oil-returning groove inflow to the resistive oil edge after cooling to the oil-returning groove in the third and fourth quadrant junction. The research provides powerful theoretical foundation for practical application of the large size circular ring oil pad hydrostatic thrust bearing, its structure design and operating reliability, realizing the lubrication performance prediction of the large size hydrostatic thrust bearing. [ABSTRACT FROM AUTHOR]

This paper presents an efficient closed-form solution (ECS) for acoustic emission(AE) source location in three-dimensional structures using time difference of arrival (TDOA) measurements from N receivers, N ≥ 6. The nonlinear location equations of TDOAare simplified to linear equations. The unique analytical solution ofAE sources for unknown velocity system is obtained by solving the linear equations. The proposed ECS method successfully solved the problems of location errors resulting from measured deviations of velocity as well as the existence and multiplicity of solutions induced by calculations of square roots in existed close-form methods. [ABSTRACT FROM AUTHOR]

This paper presents a three-dimensional analytical solution for acoustic emission source location using time difference of arrival (TDOA) measurements from N receivers, N ⩾ 5. The nonlinear location equations for TDOA are simplified to linear equations, and the direct analytical solution is obtained by solving the linear equations. There are not calculations of square roots in solution equations. The method solved the problems of the existence and multiplicity of solutions induced by the calculations of square roots in existed close-form methods. Simulations are included to study the algorithms' performance and compare with the existing technique. [ABSTRACT FROM AUTHOR]

The discrimination of seismic event and nuclear explosion is a complex and nonlinear system. The nonlinear methodologies including Random Forests (RF), Support Vector Machines (SVM), and Naïve Bayes Classifier (NBC) were applied to discriminant seismic events. Twenty earthquakes and twenty-seven explosions with nine ratios of the energies contained within predetermined "velocity windows" and calculated distance are used in discriminators. Based on the one out cross-validation, ROC curve, calculated accuracy of training and test samples, and discriminating performances of RF, SVM, and NBC were discussed and compared. The result of RF method clearly shows the best predictive power with a maximum area of 0.975 under the ROC among RF, SVM, and NBC. The discriminant accuracies of RF, SVM, and NBC for test samples are 92.86%, 85.71%, and 92.86%, respectively. It has been demonstrated that the presented RF model can not only identify seismic event automatically with high accuracy, but also can sort the discriminant indicators according to calculated values of weights. [ABSTRACT FROM AUTHOR]

To eliminate the location error of MS/AE (microseismic/acoustic emission) monitoring systems caused by the measurement deviations of the wave velocity, a MS/AE source location method using P-wave and S-wave arrivals for unknown velocity system (PSAFUVS) was developed. Arrival times of P-wave and S-wave were used to calculate and fit the MS/AE source location. The proposed method was validated by numerical experimentations. Results show that the proposed method without the need for a premeasured wave velocity has a reasonable and reliable precision. Effects of arrival errors on location accuracy were investigated, and it shows location errors enlarged rapidity with the increase of arrival errors. It is demonstrated the proposed method can not only locate the MS/AE source for unknown velocity system but also determine the real time PS waves velocities for each event in rockmass. [ABSTRACT FROM AUTHOR]

The relationships between geological features and rockmass behaviors under complex geological environments were investigated based on multiple intelligence classifiers. Random forest, support vector machine, bayes' classifier, fisher's classifier, logistic regression, and neural networks were used to establish models for evaluating the rockmass stability of slope. Samples of both circular failure mechanism and wedge failure mechanism were considered to establish and calibrate the comprehensive models. The classification performances of differentmodeling approaches were analyzed and compared by receiver operating characteristic (ROC) curves systematically. Results show that the proposed random forest model has the highest accuracy for evaluating slope stability of circular failure mechanism, while the support vector Machine model has the highest accuracy for evaluating slope stability of wedge failuremechanism. It is demonstrated that the established randomforest and the support vector machinemodels are effective and efficient approaches to evaluate the rockmass stability of slope. [ABSTRACT FROM AUTHOR]

Surface-parallel slabbing is a failure mode often observed in highly stressed hard rocks in underground excavations. This paper presents the results of experimental studies on slabbing failure of hard rock with different sample height-to-width ratios. The main purpose of this study was to find out the condition to create slabbing failure under uniaxial compression and to determine the slabbing strength of hard rock in the laboratory. Uniaxial compression tests were carried out using five groups of granite specimens. The mechanical parameters of the sample rock, Iddefjord granite from Norway, were measured on the cylindrical and Brazilian disc specimens. The transition of the failure mode was studied using rectangular prism specimens. The initiation and the propagation of slabbing fractures in specimens were identified by examining the relationship among the applied stress, strain and the acoustic emission. The stress thresholds identified were compared to those reported by other authors for crack initiation and brittle failure. It is observed that the macro failure mode will be transformed from shear to slabbing when the height/width ratio is reduced to 0.5 in the prism specimens under uniaxial compression. Micro σ-parallel fractures initiate when the lateral strain departs from its linearity. Slabbing fractures are approximately parallel to the loading direction. Labotatory tests show that the slabbing strength ( σ) of hard rock is about 60% of its uniaxial compression strength. It means that if the maximum tangential stress surrounding an underground excavation reaches about the slabbing threshold, slabbing fractures may take place on the boundary of the excavation. Therefore, the best way to stop or eliminate slabbing failure is to control the excavation boundary to avoid the big stress concentration, so that the maximum tangential stress could be under the slabbing threshold. [ABSTRACT FROM AUTHOR]

The phosphoenolpyruvate:glycose phosphotransferase system (PTS) participates in important functions in the bacterial cell, including the phosphorylation/uptake of PTS sugars. Enzyme I (El), the first protein of the PTS complex, accepts the phosphoryl group from phosphoenolpyruvate, which is then transferred through a chain of proteins to the sugar. In these studies, a mutant GFP, enhanced yellow fluorescent protein (YFP), was linked to the N terminus of El, giving V-El. V-El was active both in vitro (≥90% compared with El) and in vivo. Unexpectedly, the subcellular distribution of V-El varied significantly. Three types of fluorescence were observed: (i) diffuse (dispersed throughout the cell), (ii) punctate (concentrated in numerous discrete spots throughout the cell), and (ii:) polar (at one or both ends of the cell). Cells from dense colonies grown on agar plates with LB broth or synthetic (Neidhardt) medium showed primarily bipolar or punctate fluorescence. In liquid culture, under carefully defined carbon-limiting growth conditions [ribose (non-PTS), mannitol (PTS sugar), or DL-lactatei, cellular levels of enzymatically active V-El remain essentially constant for each carbon source, but fluorescence distribution depends on C source, cell density, growth phase, and apparently on "conditioned medium." Fluorescence was diffuse during exponential growth on LB or ribose/Neidhardt medium. On ribose they became punctate in the stationary phase, reverting to diffuse when more ribose was added. In LB, both V-El and a nonphosphorylatable mutant HIS9Q-V-El, showed a diffuse fluorescence during growth, but, shortly after the addition of isopropyl β-D-thiogalactopyranoside, V-El became bipolar; H189Q-V-El did not. The functions of El sequestration remain to be determined. [ABSTRACT FROM AUTHOR]

Two-component signal transduction systems also known as His-Asp phosphorelay systems, play essential roles in transferring information from the environment to the respective genomes of prokaryotes and some eukaryotes. There are at least 29 His kinase signal transduction systems in Escherichia coli. Researchers report that two marine Vibrios, Vibrio furnissii and Vibrio cholerue express a unique two-component signaling system that stringently regulates expression of many genes required for chitin catabolism.

Chitin, one of the most abundant organic substances in nature, is consumed by marine bacteria, such as Vibrio cholerae, via a multitude of tightly regulated genes (Li and Roseman 2004, Proc Natl Acad Sci USA. 101:627–631). One such gene, cod, is reported here. It encodes a chitin oligosaccharide deacetylase (COD), when cells are induced by chitobiose, (GlcNH2)2, or crude crab shells. COD was molecularly cloned (COD-6His), overproduced, and purified to apparent homogeneity. COD is secreted at all stages of growth by induced V. cholerae. The gene sequence predicts a 26 N-terminal amino acid signal peptide not found in the isolated protein. COD is very active with chitin oligosaccharides, is virtually inactive with GlcNAc, and slightly active with colloidal ([3H]-N-acetyl)-chitin. The oligosaccharides are converted almost quantitatively to products lacking one acetyl group. The latter were characterized by mass spectrometry (ESI-MS), and treatment with nitrous acid. COD catalyzes the following reactions (n = 2–6): (GlcNAc)n→ GlcNAc-GlcNH2-(GlcNAc)n−2 + Ac−. That is, COD hydrolyzes the N-acetyl groups attached to the penultimate GlcNAc residue. The gene bank sequence data show that cod is highly conserved in Vibrios and Photobacteria. One such gene encodes a deacetylase isolated from V. alginolytics (Ohishi et al. 1997, Biosci Biotech Biochem. 61:1113–1117; Ohishi et al. 2000, J Biosci Bioeng. 90:561–563), that is specific for (GlcNAc)2, but inactive with higher oligosaccharides. The COD enzymatic products, GlcNAc-GlcNH2-(GlcNAc)n, closely resemble those obtained by hydrolysis of the chitooligosaccharides with Nod B: GlcNH2-(GlcNAc)3-4. The latter are key intermediates in the biosynthesis of Nod factors, critically important in communications between the symbiotic nitrogen fixing bacteria and plants. Conceivably, the COD products play equally important roles in cellular communications that remain to be defined. [ABSTRACT FROM AUTHOR]