Mining Science and Technology (China)最新文献

Deep large span cut holes are difficult to stabilize. The 7801 cut hole in the Lu’an Wuyang Mine was used as this project’s background. The main factors affecting large span cut hole stability are analyzed. Pre-stressed bolting theory was used to design a roof control method for a large span roadway. By reducing the span and applying equal strength coordinated supports the rock could be stabilized. The control principles and methods are given herein along with the analysis. A double micro arch cross section roadway is defined and its use in solving the current problem is described. Beam arch theory was used to build a model of the double micro arch cross section roadway. A support reverse force model for the arch foot intersection was also derived. A support method based upon reducing the width of the large span in the cut hole is presented. These results show that the reduced span of the roadway roof plus the use of cable anchors and single supports gives an effective way to control the large span cut hole. On site monitoring showed that the reduced span support from the double micro arch cross section roadway design had a significant effect. The roadway surface displacement was small and harmful deformation of the cut hole was effectively controlled. This will ensure its long term stability.

The experimental tests for limestone specimens at 700 °C in uniaxial compression were carried out to investigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servo-controlled testing system considering the loading rate as a variable. The mechanical properties of limestone such as the stress–strain curve, variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the strain rates ranging from 1.1 × 10⁻⁵ to 1.1 × 10⁻¹ s⁻¹. (1) Sharp decreases were shown for the peak strength and elastic modulus of limestone from 1.1 × 10⁻⁵ to 1.1 × 10⁻⁴ s⁻¹ at 700 °C as well as a downward trend was shown from 1.1 × 10⁻⁴ to 1.1 × 10⁻¹ s⁻¹ with the rise of the strain rate. (2) The peak strain increased from 1.1 × 10⁻⁵ to 1.1 × 10⁻⁴ s⁻¹, however, there was no obvious changes shown for the peak strain of limestone from 1.1 × 10⁻⁴ to 1.1 × 10⁻¹ s⁻¹. These results can provide valuable references for the rock blasting effect and design of mine.

Severe production conditions in coal mines cause damage and failure problems with the oriented sliding boots of the mechanical shearer. Wear has been an especially vexing problem. Plasma cladding methods were used to study optimized sliding boot design. By cladding the substrate steel the surface may be made of a material more resistant to wear. The iron based alloy Cr₄MnTi was coated onto a modified 45 steel matrix material in these tests. The results show that the alloy cladding layer is high strength, has high hardness, and is highly resistant to wear. After hardening and tempering, 45 steel substrate has great tenacity so the combined structure meets the performance requirements for the construction of shearer sliding boots.

Laser triangulation theory was used to develop a novel contact-free method for measuring the coal level in a silo under harsh environmental conditions found in coal mines, such as the presence of dense dust, high humidity, and low illumination. A laser source and a camera were mounted at the top of the silo. The laser spot projected into the silo was imaged by the camera. The pinhole imaging principle allows the level to be found from the lateral shift of the spot image on the sensor. A pre-calibrated look-up table of the coal depth versus spot position was used to obtain the depth. The measurement accuracy depends on the step size used during pre-calibration. The actual application of a device designed according to these principles shows that it is easy to implement. The detection of the coal level in a silo at the low illumination level found in coal mines is demonstrated.

Low grade siliceous manganese ores from the iron ore group of the Bonai-Keonjhar belt, Orissa, India are found mostly in shear zones. The ore characteristics of siliceous manganese ore samples from three different mines, viz. the Shankar (Barbil OMC lease hold area), the Sone-Patuli (Patmunda, OMM lease hold area), and the Musaghar (Roida, OMDC lease hold area), were studied. These siliceous manganese ores are of three types, respectively: (i) spongy-granular; (ii) massive-mosaic; and (iii) hard-mylonitized. The spongy-granular type contains granular, saccharoidal quartz and the major manganese mineral present is pyrolusite. The second type contains well crystallized quartz and cryptomelane, while the third has cherty, fine grained quartz (mylonite) along with romanechite. All three ores were subjected to physical beneficiation under similar conditions. Both gravity and magnetic separation techniques were employed. The mineral-fabric of the ores has been correlated to the extent of their beneficiation using these physical techniques. Of these three ores only the spongy-granular type responded well to upgrading. The feed with 22% Mn content could be upgraded to 44% with a 28% yield and a 49% recovery. The good response to beneficiation of the spongy-granular sample could be due to the large euhedral crystals of pyrolusite and the friable nature of the saccharoidal quartz. This study reveals the influence of mineral-fabric on beneficiation of low grade ore, siliceous Mn ore in particular.

Deployment of nodes based on K-barrier coverage in an underground wireless sensor network is described. The network has automatic routing recovery by using a basic information table (BIT) for each node. An RSSI positioning algorithm based on a path loss model in the coal mine is used to calculate the path loss in real time within the actual lane way environment. Simulation results show that the packet loss can be controlled to less than 15% by the routing recovery algorithm under special recovery circumstances. The location precision is within 5 m, which greatly enhances performance compared to traditional frequency location systems. This approach can meet the needs for accurate location underground.

Curvature-driven diffusion (CDD) principles were used to develop a novel gradient based image restoration algorithm. The algorithm fills in blocks of missing data in a wireless image after transmission through the network. When images are transmitted over fading channels, especially in the severe circumstances of a coal mine, blocks of the image may be destroyed by the effects of noise. Instead of using common retransmission query protocols the lost data is reconstructed by using the adaptive curvature-driven diffusion (ACDD) image restoration algorithm in the gradient domain of the destroyed image. Missing blocks are restored by the method in two steps: In step one, the missing blocks are filled in the gradient domain by the ACDD algorithm; in step two, and the image is reconstructed from the reformed gradients by solving a Poisson equation. The proposed method eliminates the staircase effect and accelerates the convergence rate. This is demonstrated by experimental results.

A neural network is applied to high-quality 3-D seismic data during micro-seismic facies analysis to perform the waveform analysis and training on single reflection events. Modeled seismic channels are established and the real seismic channels are classified. Thus, a distribution of micro-seismic facies having a high precision over a flat surface was acquired. This method applied to existing geological data allows the distribution of areas rich in coal bed methane to be clearly defined. A distribution map of the micro-seismic facies in the research area is shown. The data accord well with measured methane contents, indicating that the analysis using micro-seismic facies is reliable and effective. This method could be applied to coal bed methane exploration and is of great importance to future exploration work and to an increase in the drilling success rate.

Coal mining under thin bedrock or thick unconsolidated soil layers brings mining problems related to these special geological conditions. The meaning of the term “thin bedrock” is defined through the thickness statistics of the coal seam and the bedrock layer. The coal-bearing strata having thick, unconsolidated aquifers and thin bedrock located at the Taiping Coal Mine in Shandong province were taken as a geological prototype for subsequent study. The geological, hydro-geological and engineering characteristics of the thin bedrock were analyzed. An engineering geological model was than established. Overburden failure and the development of “Three Zones” were studied by physical model tests. The rupture pattern and rock failure were analyzed for mining conditions under thin bedrock. The height of the caving zone and the freely flowing water fractured zone of different mining thicknesses were separately calculated. The results show that a mining thickness greater than 3.5 m causes the height of the freely flowing water fractured zone to be sufficient to touch the weathered zone and the bottom of the Quaternary system aquifer, to various degrees. This, then, would lead to water and sand inrush into the working face. Measures to prevent water and sand flow inrush disasters by eliminating the power source are put foreword. A field dewatering scheme was designed and observational data were obtained. The dewatering project had an obvious effect and the water level at working face number 8309 dropped to a safe level. The average draw down of the groundwater was observed to be 7.86 m. This showed that the dewatering project played a role in decreasing the hydraulic pressure and ensuring safety mining.

Coal is the principal form of energy used in China. Hence, coal price variations are expected to have some influence on merchandise prices. Monthly data from January, 2002, to October, 2010, were used to construct a varying-parameter state space model, and an error correction model, to estimate the influence of coal prices on Chinese merchandise prices. The time lag and the dynamic relationship were determined from the data. A long term equilibrium relationship between coal price and the PPI, and the CPI, can be observed. The long term influence of coal price fluctuations on the PPI is 0.263%. The corresponding value for the CPI is 0.157%. The PPI shows an influence from coal price change in the first period of observation: by eight periods the influence is obvious, after which it diminishes. The effect of coal price change on the CPI is rather weak and has no long term memory. Analysis of variance shows a similar situation. The elasticity coefficient of coal prices on the CPI, or the PPI, fluctuates over the 2002–2004 period. From 2002 to 2007 the influence elasticity on the CPI declined and subsequently levelled off after 2009.