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| Testing method and system application of circumferential deformation of cylindrical rock and soil specimens based on angle measurement |
| WANG Hanpeng1，LI Qingchuan1，LI Shucai1，ZHANG Qiangyong1，YUAN Liang2，LIU Zhongzhong1 |
(1. Research Centre of Geotechnical and Structural Engineering，Shandong University，Jinan，Shandong 250061，China；
2. School of Ming and Safety Engineering，Anhui University of Science and Technology，Huainan，Anhui 232001，China) |
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Abstract In order to obtain the accurate circumferential deformation and the mechanical characteristics of post-peak dilation of the standard cylindrical specimen during the whole process of stress-strain test，a new type of circumferential deformation test method for standard specimens was proposed with the angle measurement based on the MTS chain circumferential extensometer. The principle of measurement was described in the paper. A chain rolling belt connected with the angle sensor is used in the system to twine around the standard circular specimen. The data acquisition system programmed by LABVIEW is used to achieve the automatic high precision acquisition and rapid recording. The measurement accuracy is 0.004 mm and the measurement range is 30 mm，which is adequate for many loading environments such as the gas-solid coupling loading and the tri-axial loading. The reliability and accuracy of this system were verified by the MTS chain extensometer and the close-range photogrammetry. The adsorption degradation test of coal with different gases was carried out. The briquettes with the same prefabricated strength were filled with the gases under the same pressure(He，N2，CH4 and CO2)，and then the axial loading test was carried out after the full adsorption. The deformation and instability of coal body during loading were obtained. The effects of gas properties on the volume expansion，the strength and fracture development of coal were compared and analyzed. The experimental results show that with the improvement of gas adsorption，the coal enters the expansion stage from the compaction stage earlier，and the position of the ultimate load value and volume expansion point reached earlier with the sequence for gases：CO2＞CH4＞N2＞He. The impregnation of He without adsorption does not degrade the coal，but the coal body strength is significantly reduced by adding the adsorptive CO2. The peak strength decreases by 32.05% after the CO2 adsorption under the pressure of 1.0 MPa. The whole system is made of modules and can work synchronously with the axial LVDT displacement meter.
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2018, Vol. 37 
