Rockbursts and mud

It has been observed that the presence of water or mud on the floor of a mining tunnel seems to reduce tunnel failure associated with remote seismic events. We examine two mechanisms that could explain this phenomenon. The investigations suggest that lubrication effects due to the presence of water within cracks could well affect the occurrence of spalling, and the results obtained suggest that coating the tunnel walls with moisture containing semi-liquid pastes may be effective for tunnel wall stabilization

Experimental study on the failure characteristic and mechanism of granite time-delayed rockburst under true triaxial condition

A series of tests for time-delayed rockburst of granite under true triaxial condition was designed and carried out. By using the true triaxial rockburst test system, an acoustic emission (AE) system, a high-speed camera system, and a digital image motion analysis software, the time-delayed rockburst development process was monitored and studied. Four stages were found in the failure of granite time-delayed rockburst, i.e. grains ejection, slab breaks and ejects, first fragments ejection and second fragments ejection. There is a “V” shear crack generated in the time-delayed rockburst sample, and several tensile cracks in the lower part of the rock sample cross through the “V” shear crack. The longer the duration (the time elapsed between the moments the AE hits rises rapidly and the rockburst occurs), the smaller the depth of the rockburst pit. The time-delayed rockburst debris are mainly composed of blocks and fragments. The longer the duration, the smaller the total debris mass, the percentage of ejected debris and the ejection kinetic energy. The fractal dimension of the debris is positively correlated with the duration. The longer the duration, the higher the degree of fragmentation. The cracks generated are tensile-shear composite cracks. In the loading stage, it is dominated by shear cracks. However, in the time-lag stage, it is dominated by tensile cracks. With the increase of the duration, the proportion of tensile cracks increased and the proportion of shear cracks decreased. The research results will have a certain reference value for the warning and risk mitigation of time-delayed rockbursts

Experimental and Numerical Analysis of Rock Burst Tendency and Crack Development Characteristics of Tianhu Granite

Rock burst is a serious nonlinear dynamic geological hazard in underground engineering construction. In this paper, a true triaxial unloading rock burst experiment and numerical simulation are carried out on Tianhu granite to investigate the rock burst tendency and crack development characteristics of surrounding rock after excavation. The experiment and numerical simulation process monitored the rock burst stress path to determine the rock burst stress. According to the evolution law of the frequency and amplitude of rock burst acoustic emission monitoring, the shape characteristics of rock burst fragments are analyzed. The rock burst numerical simulation analysis is carried out by the PFC software, and the temporal and spatial evolution law of cracks is obtained. The research results show that the laboratory experiment and numerical simulation of Tianhu granite have rock burst strengths of 163.4 MPa and 161 MPa, respectively, and the average rock burst stress ratio is 8.38, that is, the Tianhu granite has a low rock burst tendency. During the rock burst, the development of tensile cracks will produce flaky debris, and the development of shear cracks will produce lumpy debris. Rock burst will happen when the crack growth rate to be exceeded the unloading crack growth rate; therefore, it can be used as a precursor signal for the occurrence of rock burst

Analysis of rock burst in critical section of second part of Karaj-Tehran Water Supply Tunnel

Practical Applications and Case Studie

Barrett v. Hecla Min. Co. Clerk\u27s Record v. 2 Dckt. 43639

https://digitalcommons.law.uidaho.edu/idaho_supreme_court_record_briefs/7115/thumbnail.jp

Rock-burst occurrence prediction based on optimized naïve bayes models

Rock-burst is a common failure in hard rock related projects in civil and mining construction and therefore, proper classification and prediction of this phenomenon is of interest. This research presents the development of optimized naïve Bayes models, in predicting rock-burst failures in underground projects. The naïve Bayes models were optimized using four weight optimization techniques including forward, backward, particle swarm optimization, and evolutionary. An evolutionary random forest model was developed to identify the most significant input parameters. The maximum tangential stress, elastic energy index, and uniaxial tensile stress were then selected by the feature selection technique (i.e., evolutionary random forest) to develop the optimized naïve Bayes models. The performance of the models was assessed using various criteria as well as a simple ranking system. The results of this research showed that particle swarm optimization was the most effective technique in improving the accuracy of the naïve Bayes model for rock-burst prediction (cumulative ranking = 21), while the backward technique was the worst weight optimization technique (cumulative ranking = 11). All the optimized naïve Bayes models identified the maximum tangential stress as the most significant parameter in predicting rock-burst failures. The results of this research demonstrate that particle swarm optimization technique may improve the accuracy of naïve Bayes algorithms in predicting rock-burst occurrence. © 2013 IEEE

Experimental and numerical modelling investigations into coal mine rockbursts and gas outbursts

Rockbursts and gas outbursts are a longstanding hazard in underground coal mining due to their sudden occurrences and high consequences. These hazards are becoming prominent due to the increase in mining depth, difficult mining conditions, and adverse gas pressure conditions. Several researchers have proposed different theories, mechanisms, and indices to determine the rockbursts and gas outbursts liability but most of them focus on only some aspects of the complex engineering system for the ease to represent them using partial differential equations. They have often ignored the dynamics of changing mining environment, coal seam heterogeneity and stochastic variations in the rock properties. Most of the indices proposed were empirical and their suitability to different mining conditions is largely debated. To overcome the limitations of previous theories, mechanisms and indices, a probabilistic risk assessment framework was developed in this research to mathematically represent the complex engineering phenomena of rockbursts and gas outbursts for a heterogeneous coal seam. An innovative object-based non-conditional simulation approach was used to distribute lithological heterogeneity occurring in the coal seam to respect their geological origin. The dynamically changing mining conditions during a longwall top coal caving mining (LTCC) was extracted from a coupled numerical model to provide statistically sufficient data for probabilistic analysis. The complex interdependencies among several parameters, their stochastic variations and uncertainty were realistically implemented in the GoldSim software, and 100,000 equally likely scenarios were simulated using the Monte Carlo method to determine the probability of rockbursts and gas outbursts. The results obtained from the probabilistic risk assessment analysis incorporate the variations occurring due to lithological heterogeneity and give a probability for the occurrence of rockbursts, coal and gas outbursts, and safe mining conditions. The framework realistically represents the complex mining environment, is resilient and results are reliable. The framework is generic and can be suitably modified to be used in different underground mining scenarios, overcoming the limitations of earlier empirical indices used.Open Acces

Proposing a novel comprehensive evaluation model for the coal burst liability in underground coal mines considering uncertainty factors

Coal burst is a severe hazard that can result in fatalities and damage of facilities in underground coal mines. To address this issue, a robust unascertained combination model is proposed to study the coal burst hazard based on an updated database. Four assessment indexes are used in the model, which are the dynamic failure duration (DT), elastic energy index (WET), impact energy index (KE) and uniaxial compressive strength (RC). Four membership functions, including linear (L), parabolic (P), S and Weibull (W) functions, are proposed to measure the uncertainty level of individual index. The corresponding weights are determined through information entropy (EN), analysis hierarchy process (AHP) and synthetic weights (CW). Simultaneously, the classification criteria, including unascertained cluster (UC) and credible identification principle (CIP), are analyzed. The combination algorithm, consisting of P function, CW and CIP (P-CW-CIP), is selected as the optimal classification model in function of theory analysis and to train the samples. Ultimately, the established ensemble model is further validated through test samples with 100% accuracy. The results reveal that the hybrid model has a great potential in the coal burst hazard evaluation in underground coal mines. © 202

A new in situ test for the assessment of the rock-burst alarm threshold during tunnelling

Rock-burst is one of the most serious risks associated with hard rock tunnelling and mining at high depths. Monitoring of acoustic emissions emitted by the rock-mass during excavation and their interpretation now permits the early assessment of failure events and makes the safe management of the construction works possible. A reliable set-up of the alarm threshold is thus fundamental for the correct implementation of the procedures planned to minimise rock-burst related risk. This paper focuses on a novel in situ test specifically developed to provide an experimental basis for a more accurate assessment of the alarm threshold during tunnelling, representative of the local geomechanical conditions. The test, thanks to the compression induced by two flat jacks at the tunnel side wall, produces an artificial failure process during which acoustic emissions are measured and correlated to the mechanical response of the rock-mass, without the typical limitations of scale that characterised the laboratory experiments. The new methodology, named the Mules method, was successfully tested during the excavation of some stretches of the Brenner Base Tunnel in the Brixner granite, affected by mild spalling episodes. The case-history is fully described in the paper to illustrate the practical application of the proposed approach

The Dangerous Condition of Ground during High Overburden Tunneling (A Case Study in Iran)

Knowledge of the ground condition and its hazards can play an important role in the selection of support and suitable excavation method in underground structures. Water transport tunnel is one of the most important structures with regard to the goal of excavation, special conditions and limitations considered in the design and execution of them. Beheshtabad Water Conveyance Tunnel with 64930 meters length, 6 meters final diameter is the largest water Conveyance tunnel in Iran. Because of high over burden and weak rock in the most of tunnel path, the probable hazardous of the ground condition such as squeezing and rock burst must be studied. Squeezing stands for large timedependent convergence during tunnel excavation. This phenomenon occurs in weak rocks and deep conditions. Besides, the height of overburden in some of the zone tunnel is about 1200 meters. The occurrence of this phenomenon is always together with the instantaneous release of strain energy stored in the rock materials, causing the harm to the personal equipment and the collapse of underground structures. The existence of high thickness overburden in some the zones of this project indicates the high potential of rock burst hazard. In this research, the length of the tunnel has been partitioned into sections using the interpreted geological, geophysical studies and borehole data. After evaluating rock burst and squeezing potential with alternative analytical and experimental methods for each section, the results of dierent methods were compared with each other. Results predict low to moderate squeezing potential and moderate to high rock burst potential for some panels of the tunnel