Comprehensive Experimental Study of Affecting Factors on Rectangular Roadway Stability

In this paper, two methods of orthogonal numerical simulation test and similar material simulation test are used to study the influence of five factors on the stability of rectangular roadway: roadway width, roadway height, roadway buried depth, lateral pressure coefficient of surrounding rock, and comprehensive strength of surrounding rock. The results show that five factors have influence on the stability of roadway, but the degree of influence is different. The depth of the tunnel and the coefficient of the side pressure of the surrounding rock are positively correlated with the stability of the tunnel; the comprehensive strength of the surrounding rock is negatively correlated with the stability of the tunnel, but the correlation between the width and height of the tunnel and the stability of the tunnel is not obvious. The results of orthogonal numerical simulation test and similar material simulation test verify each other. The results of the field practice of the Fucun coal mine are basically consistent with the results of the two test methods, which shows that the research results have a certain guiding effect on the field roadway support.

Similar Material Simulation Study on Protection Effect of Steeply Inclined Upper Protective Layer Mining with Varying Interlayer Distances

Protective layer mining, as a dominating regional prevention measure, is generally adopted to prevent and control gas disasters in highly gassy or outburst mines of China. Interlayer distance is one of the most important factors that influences protection effect. However, how does interlayer distance affect the protection effect of steeply inclined upper protective layer mining is not understood fully. According to the engineering practice in Nantong mining district, a new method for similar material simulation experiment of steeply inclined upper protective layer mining is proposed, in which an orthogonal test of similar materials comprising of sand, cement (containing gypsum and fly ash), and water mixture is conducted to obtain relations between proportioning parameters and mechanical properties using a multiple regression method. And then the method is applied to study the protection effect of steeply inclined upper protective layer mining with varying interlayer distances. The results show the following. (1) The proportioning parameters of similar material have strong linear relations with its mechanical properties, and mechanical behaviors of such similar material denote that it can simulate most coal-rock lithologies in coal mine. (2) Both pressure-relief curves and swelling strain curves for protected layer present convex shapes; protection angles at lower excavation boundary are greater than those of upper excavation boundary; with the increase of interlayer distance, the pressure-relief curve evolves from pattern “∩” to pattern “∧” and corresponding pressure-relief region becomes narrower, the center of pressure-relief region tends to transfer to the corresponding center of upper protective layer excavation region, the stress concentration coefficient decreases, the protection angles change little, and the length of the protection region reduces dramatically. (3) The protection region and protection angle calculated based on swelling strain of 3‰ are less than the empirical values based on the dip angle in Provisions, denoting that the method proposed in this study is safer than that in Provisions. The research results provide a useful guide for layouts of roadway and gas drainage boreholes to prevent gas disaster in Nantong coal mine district.

Application of DICM on Similar Material Simulation Experiment for Rock-Like Materials

The digital image correlation method (DICM) has been applied to similar material simulation experiments for rock-like materials, to overcome the weakness of traditional measurements, for example, data discontinuous. In this paper, the movement and fracturing process of the overlying strata during excavation are observed and studied, and the distributions of stress, strain, and deformation in the overlying strata are obtained based on similar material simulation. The DICM is applied to improve the testing method and to optimize the discontinuity of testing points; of course, the difference of rock deformation in the overlying strata during excavation is considered. Full-field deformation and strain are analyzed by the DICM. To verify the accuracy of the DICM, results obtained from the DICM, numerical simulation and similar material simulation, are compared. The DICM can reflect the characteristics of locality and randomness of rock-like materials more real than numerical simulation, and comparing with similar material simulation, it can directly reproduce the movement and fracturing process of the overlying strata during full-field excavation. It shows that, the DICM is entirely feasible to using in the large scale full-field deformation measurement on complex rock structure, and it is of theoretical importance for testing for rock-like materials.

Research on the Height of Water-Flowing Fractured Zone under the Weak Roof Strata and Fully Mechanized Caving Condition

The first working face production has suspend because of the great roof water inrush in Mindongyi coal mine, which has weak roof strata and mining use the fully mechanized caving method. In order to detect the height of water-flowing fractured zone, loses of drilling fluid observation method has carried on the flied test, the results showed that while the full-mechanized caving mining thickness is 7.7 m, the height of water-flowing fractured zone is 79.78 m, and the ratio of height to thickness is 10.36, meanwhile, the numerical simulation and similar material simulation have proved the test results are correct. The study enriched the domestic research fruits of the height of water flowing fractured zone, and provided technical references for Mindongyi coal mine mining.

Experimental Study on Low-Strength Similar-Material Proportioning and Properties for Coal Mining

Similar-material simulation test is an effective tool to study the practical problems in mining and civil engineering. This paper conducts an orthogonal study on low-strength similar materials comprising sand, fly ash, and plaster and analyses the sensitivity of the materials. The mechanical properties of the similar materials strongly depend on the proportioning ratio, and they can satisfy different similar-material simulation tests. The compression strength and elastic modulus of the similar material decrease as the sand-binder ratio or cement ratio increases. There are approximately linear relations between the compression strength/elastic modulus and sand-binder ratio and approximately power relations between the compression strength/elastic modulus and sand-binder ratio. Sensitivity analysis employing the range method shows that the effects of the cement ratio on the compression strength and elastic modulus are more obvious than the effects of the sand-binder ratio. Finally, one of similar materials is used in a simulation test of coal backfill mining.

Research on the Rules of Overlying Rock Movement by Similar Material Simulation in Fully Mechanized Top Coal Caving Mining with High Cutting Height

In order to study overlying rock movement rules of fully mechanized top coal caving mining with high cutting height, taking 8100 working face of Tongxin mine as the engineering background, basing on the similarity theory and similarity simulation experiment, the paper analyzed overlburdens deformation, failure and movement laws after mining. Through research, results obtained first cave pace of immediate and basic roof, three zones characteristics and overburden displacement characteristic, which could provide a basis for coal mining under similar conditions, a reference for studying overburden movement rules of fully mechanized top coal caving mining with high cutting height and a guide for safe production.

A Method for Subsidence Monitoring of Similar Material Simulation Test in Coal Mining

To accurately monitoring the subsidence of similar material simulation test in coal mining, a static deformation measurement system is proposed based on the digital image processing and photogrammetry techniques. Firstly pastes reference points and observation points on model frame and working face respectively. Before exploitation, calculates the 3D coordinates of those artificial points, transfers the default coordinate system to user defined coordinate system using 3-2-1 transformation method, and defines this stage as basic stage. Then start mining, records enough images from different position and angle, and calculates the 3D coordinates of the deformation stage. Finally aligns the single deformation stage to the basic stage, by tracking and comparing the 3D coordinates of the homonymous points, the subsidence of observation points are obtained. One similar material simulation tests were conducted which prove good performance of the proposed measurement system.