Risk Evaluation and Leakage Mechanism on Runoff in Coal Mining Area—A Case Study in Jinjie Coal Mine of Tuwei River

According to the aims of the runoff protection in coal mining area, taking Jinjie coal mine as an example, the risk zonation and mechanism of runoff leakage were carried out based on the dimen-sionless multi-factor information fusion technique. Based on the analysis of field exploration and borehole data, four key factors affecting the runoff leakage from the roof were identified, which included the deposition features of aquifer in Sala Wusu Group, the distribution of overburden rock and soil mass, effective thickness of aquiclude layer and the height of water flow cracking zone. The evaluation criterion was whether the development height of the water flow cracking zone reaches or exceeds the bottom plate of the sandy phreatic aquifer and even penetrates the surface ground, which results in the complete or partial leakage of the phreatic water. According the evaluation criterion, the influence of coal mining disturbance on runoff leakage was divided into three zones: zone of seriously runoff leakage, zone of general runoff leakage and zone of slight runoff leakage. Furthermore, the influence mechanism of different zones in coal mining also been discussed preliminarily, which included drainage Sarawusu aquifer, groundwater leakage in Sarawusu aquifer, water level fluctuation in Sarawusu aquifer and so on. Finally, classification pattern diagram was drawn.

Impact of blast zone on mining processes in fractured rock mass

Generalization of the abundant experimental and theoretical research accomplished by Russian and foreign scientists in the 20th–21st centuries enables distinguishing between a few action zones of blasting, namely, crushing zone (fine grain crushing), radiating cracking zone, induced-fracture zone, shaking zone (residual stress after blasting), and blast-induced load zone. In the crushing zone, overgrinding takes place, which has an adverse influence on efficiency of processing of uranium, for instance, or granular quartz. The radiating cracking zone size in blasting in fractured rock masses governs the quality of drilling and blasting. The induced-fracture zone determines stability of rock mass and, consequently, safety of production processes both in surface and underground mines. In the shattering zone, fractured rock mass experiences residual stresses, which induces new fractures and rock falls, or dynamic events due to lithostatic pressure in rockburst-hazardous rock mass. This article aims at the experimental and theoretical determination of geometrics of blast-induced impact zones in different geological and geotechnical conditions with a view to developing appropriate actions toward abatement of the adverse effect exerted by these zones on geomechanical and technological processes in the course of mining. The theoretical formulas are given for the radii of the crushing, radiating cracking, induced fracturing and residual stress zones. Reliable applicability of the formulas in actual mining is proved by comparison of the calculations with the full-scale testing data. To mitigate the crushing zone impact, it is possible to charge the wellhead interval with a radial air gap, which decreases density of charging. Arrangements toward reduction of the zones of induced-fractures and residual stresses are proposed. Energy of the man-mane zone of residual stresses after blasting can be targeted at activation of raise driving with raise borer 2KV.

Analysis of internal cracks in high carbon casting bloom induced by soft reduction process and its improvement using numerical simulations and industrial experiments

To comprehensively investigate and improve the internal cracks in high carbon casting bloom induced by the soft reduction process, a three-dimensional mechanical model was developed to calculate the cracking zone, centre solid fraction and the strain states in as-cast bloom. In the present work, the specific relationship between cracking zone area, centre solid fraction and maximum equivalent strain in cracking zone has been established under a number of withdrawal machines. A two-stage sequential soft reduction method was carried out for high carbon bearing steel, which aims to provide theoretical basis for improving the internal quality and effectively decrease the risk of internal cracks. According to the experimental results, the internal cracks were effectively alleviated and center shrinkage cavities were nearly eliminated by optimum designed experiments. Along the bloom central part, the proportion of length where the segregation rate is between 0.95 and 1 has been increased from 16.7% to 91%, and the fluctuation of carbon distribution in the center line of as-cast bloom was decreased to obtain the high homogeneity of the internal structure. In addition, grade of banded carbide in the hot-rolled wire decreased accordingly from 2.5 to 1.67.

Investigation of the effect of carbon nanotubes on electrical properties of woven fiberglass/epoxy composite laminate

The effect of epoxy modified by 0.05 wt. % of CNTs on electrical properties of woven fiberglass/epoxy composite laminate was examined. The electrical resistance was measured using 4-point probe method and LCR-meter during cyclic tensile and fatigue test. Microstructural analysis using field emission scanning electron microscopy (FESEM) was carried out. Based on the experimental data, the increase in load is accompanied by growth in electrical resistance. The change in resistance after 20 cycles was up to 3 %. During fatigue test, the change in resistance was considerable and made up to 25 % in cracking zone of the sample and over 110 % at the failure mode.

Research on Low Velocity Impact Damage of Laminated Composite

Damage caused by low-velocity-impact in laminated composite will significantly reduce the strength of the structure. A new numerical model is proposed for the research on the impact induced damage of laminated composite. Multiple forms of damage within and between layers are considered in this model. The cohesive contact technology is used to simulate the bonding properties between layers. The model can describe the information of delamination more accurately and efficiently. Then, a study is carried out to investigate the relationship of delamination and matrix cracking caused by low-velocity-impact. The result reveals that the area and axis of the delamination zone is affected by the direction of the matrix cracking zone.

Application of Digital Image Correlation in Fatigue Crack Analysis

In the paper method of displacement analysis in the cracking zone based on digital image correlation and advanced multi-processor graphic cards procedures was presented. The basic assumption for the discussed displacement and strain measurement method under time variable loads was obtaining high measurement sensitivity by simultaneously minimizing the measurement time consumption. The developed digital procedures for correlation of images has been used for an example of displacement analysis in the crack propagation testing in airplane riveted joints.

Experimental Study on Cracking and Integrity Stability of Xiluodu Arch Dam

In this paper, by employing a three dimensional geomechanics model test whose scale is 1:250, the dam cracking process was observed, and integrity stability was analyzed and evaluated under overloading test. The experimental results show that: the stress and strain of the dam can basically meet the requirements of dam safety under normal water load, and the dam failure mode of the left abutment is different from that in the right side because of different types of dam figure and geological conditions. Firstly, the local slip fracture is formed on the foundation, then extends along the bottom of dam, and leads to instability and final failure. In overloading process, crack initiate from dam heel under twice normal water pressure, and form a small cracking zone, then yielding continuously and crack band appearing in downstream surface under 4.5th normal water pressure, and overall failure under 8.5th normal water pressure. The integrity stability is shown strong enough with experimental dam shape (XLD03 Figure) and the configuration of its foundation.