Similar Simulation Experiment Study on Delineation of Protective Range of Protective Layer under Inclined and Pseudo-inclined Layer
In recent years, China's coal and gas outburst accidents have occurred frequently, and it has become one of the major disasters in China's coal mines. Protective layer mining is considered to be one of the most economical and effective regional anti-burst measures [1], many scholars [2-] 3] has conducted in-depth research. However, the study on the rule of delineation of the protective cover of the protective layer under the inclined pseudo-slant is not very deep. Therefore, after the mining of the protective layer under the inclined pseudo-spike, it is of great significance to study the redistribution law, displacement variation law, mining fissure characteristics and pressure relief protection range of coal mine and gas. (2) After the similar simulation experiment, the displacement field of the overburden layer of the lower protective layer changes greatly, which makes the protective layer fully relieved. This kind of parts are used for John deere , A hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically containing glycol ethers or diethylene glycol, to transfer pressure from the controlling mechanism to the braking mechanism.In a hydraulic brake system, when the brake pedal is pressed, a pushrod exerts force on the piston(s) in the master cylinder, causing fluid from the brake fluid reservoir to flow into a pressure chamber through a compensating port. This results in an increase in the pressure of the entire hydraulic system, forcing fluid through the hydraulic lines toward one or more calipers where it acts upon one or more caliper pistons sealed by one or more seated O-rings (which prevent leakage of the fluid). Hydraulics Parts For John Deere Hydraulics Parts For John Deere,John Deere Hydraulic Cylinder Parts,John Deere Hydraulic Pump Spare Parts,John Deere Hydraulic Pump Parts Hangzhou Holdwell Mechanical&Electrical Co.,LTD , https://www.dieselpart.nl
1 similar simulation experiment
1.1 Test Mine Prototype The test was based on the 1601 working face of Xinglong Coal Mine. The 4# coal seam and 6# coal seam of the working face all have outstanding dangers. The 6# coal seam with less dangerous danger is selected as the protective layer, the 4# coal seam is used as the protected layer; the 1601 working face and the wind lane elevation is +300m. The elevation of the machineway is +250m, the working face is slanted by 86m, the strike length is 400m, and the working surface adopts a pseudo-oblique angle of 30°. The specific simulation conditions are shown in Table 1. 
1.2 Determination of similarity constant and similar material ratio According to the similarity theorem [4], the apparent density of the simulated material is 1.5g/cm3, and the simulation range is 200m×200m×30m. The similarity constant is obtained according to the strength of each rock layer ( See Table 2). Then, the similar material ratio was continuously adjusted, and a plurality of cylindrical models were fabricated for the uniaxial compression test. The similar materials of each model are shown in Table 3.
1.3 Model Loading The model is loaded to simulate the self-weight of the overlying strata. Through the calculation of the prototype conditions, the console needs to be pressurized 6.875 MPa. In this experiment, the principle of leverage is adopted. The power arm: resistance arm = 10:1, there are 5 pressure plates on the upper part of the model, and 5 steel plates are placed on each pressure plate, 10kg per steel plate, which meets the test requirements.
1.4 Model mining (1) Install the logo paper. After the model reaches the maintenance period, install the paper in the model area where the displacement is to be observed; cut the paper 1cm × 1cm, number it, and use a pin to pass from the center of the paper to the model, the paper spacing is 10cm × 10cm, and Make sure that the center of the paper in the same row is on the same line; where the I line is located approximately at the bottom of the protected layer and the position of the II line is approximately at the top of the protective layer.
(2) Install an HD camera. The camera is fixed at a distance of about 3 m from the model test bed, and an automatic photographing function is set, and the side on which the model is mounted with the paper is automatically photographed at a pitch of 1 to 3 minutes.
(3) Install the strain gauge. Connect the pressure box to the 16-way static strain gauge, connect the strain gauge according to the compensation method; check the strain gauge and debug it, prepare the data after the debugging is normal, and the collection time starts when the model is excavated.
(4) Excavation model. The model adopts a full-face mining of one working face and simulates all the slump mining methods for longwall fully mechanized mining. The model is manually excavated, starting from the design excavation area, and excavating from top to bottom along the inclination until all excavation. After the mining is completed, wait for the upper layer of the protective layer to slowly fall under the influence of the overlying pressure. After about 3 to 4 hours, the collapsed form formed by the model is shown in Fig. 1.
It can be seen from Fig. 1 that the overburden layer forms a slump zone, a fracture zone and a curved subsidence zone [5], which is consistent with the "vertical three-band" feature formed during the on-site mining of the coal seam.
2 analysis of experimental results
2.1 Change law of overburden strata displacement The data extracted by Matlab programming [6] obtained the displacement field variation law of the upper rock stratum after excavation (see Figure 2). It can be seen from Fig. 2 that after the protective layer is mined, the upper rock layer is fully moved, so that the protective layer is fully relieved.
2.2 Change law of the top plate During the mining process, the position of the mark installed on the roof of the coal seam is recorded by the camera, and the displacement of each point of the top layer of the protective layer during the mining process is tracked by Matlab, as shown in Fig. 3. It can be seen from Fig. 3 that as the working face advances, the amount of sinking of the roof increases continuously, roughly in the form of "W".
2.3 Pressure-relief protection range The collected stress during the excavation process is converted into strain; and according to the relationship between stress, strain and elastic modulus, the elastic modulus is 10 MPa, and the pressure-deformation deformation curve of the protected layer after excavation is drawn. ,As shown in Figure 4. Then according to the displacement deformation deformation of 3‰, the protection range is defined [7], and the protection range is 95° for the upper boundary and 75° for the lower boundary, which is within the scope of the protective layer on site.
3 Conclusions (1) In the similar simulated mining process, the lower protective layer formed a “vertical three-band†collapse pattern, which is consistent with the on-site mining.
(3) During the similar simulation experiment, the sinking law of the lower protective layer is “Wâ€, and stress concentration is formed at the place where the coal pillar is left.
(4) According to the similar simulation experiment, the protection range delineated by the lower protective layer is very consistent with the site investigation, indicating that the protection range delineated by the similar simulation method is also reliable.
references:
[1] Yu Qixiang. Mine disaster prevention theory and technology [M]. Xuzhou: China University of Mining and Technology Press, 2008.
[2] Wang Hongtu, Huang Guangli, Hu Guozhong, et al. The gas-solid-solid-gas coupling model and protection range of the protective layer mining on the steep slope [J]. Rock and Soil Mechanics, 2014, 35(5): 1377-1382.
[3] Tu Min, Yan Xie Xing, Huang Naibin. Research on deformation law of protected coal seam in remote lower protective layer mining [J]. Journal of Mining and Safety Engineering, 2006, 23(3): 253-257.
[4] Zhang Zhenglin. Study on the law of gas migration in the fracture zone of overburden mining and its extraction and utilization [D]. Xi'an: Xi'an University of Science and Technology, 2001.
[5] Qian Minggao, Shi Pingwu. Mine pressure and rock formation control [M]. Xuzhou: China University of Mining and Technology Press, 2003.
[6] Similar simulation experiment on the evolution law of cracks in the protective layer of Hongling Coal Mine [J]. Journal of Liaoning Technical University, 2012, 31 (2) 186-188.
[7] Yu Fan, Bai Fan, Liu Ming. Coal mine gas prevention and control technology [M]. Beijing: China Economic Publishing House, 1987.
Article source: Mining Technology; 2017.12(1)
Author: Zhao Wenjie, only Shu, Shi Feng; State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
Hong-tu Wang; National and Local Joint Engineering Laboratory for Gas Drainage in Complex Gas Layer, Chongqing University , Chongqing 400044 , China
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