| With the increasing of mining range and mining depth,mylonite coal and extremely broken coal rock mass are increasing day by day.This kind of coal is small in particle size,mostly granular and earthy,low in strength,difficult to resist the impact of high stress,prone to coal and gas outburst,resulting in safety accidents,grouting method is often used in engineering reinforcement.Conventional inorganic grouting materials and organic grouting materials often have the disadvantages of poor injectability and environmental pollution,so it is necessary to study an environment-friendly grouting material with good solidification effect.Microbial induced calcium carbonate deposition(MICP)technology is a new environmental protection reinforcement technology.The loose and broken coal particles can be cemented into a complete whole by using calcium carbonate crystals induced by bacterial metabolism,so as to improve its strength.This paper focuses on the related research on the reinforcement of coal body with MICP technology,solidifies the coal with different particle size by different grouting times and grouting speed,analyzes the physical characteristics and microstructure of the solidified specimen,and studies its solidification mechanism.The conclusions are summarized as follows:(1)It is effective to reinforce the coal body with MICP technology,and the mechanical properties of the solidified specimen are improved obviously.(2)The number of bacteria and urease activity reached a high level after 25 hours of culture.The number of bacteria remained unchanged and urease activity still reached a high level when the bacterial solution was kept for 12 hours.The best choice of cementation solution is the mixture of urea and calcium chloride with the molar ratio of 1:1.After the bacteria were injected into the coal,the bacteria adsorption rate could reach the highest after standing for 2 hours.(3)After curing,the strength of the specimen is controlled by the content of calcium carbonate and the uniformity of calcium carbonate distribution.The higher the content of calcium carbonate in the specimen,the more uniform the distribution,the higher the strength.The increase of grouting times is beneficial to increase the accumulation of calcium carbonate crystal content in the specimen,so as to improve the strength of the specimen.Increasing the flow rate of cementation liquid is beneficial to optimize the uniformity of calcium carbonate crystal distribution,but it will lead to the decrease of calcium carbonate crystal content.The particle size has a significant impact on the reinforcement effect.Too large or too small particle size is not conducive to the improvement of strength.(4)With the increase of grouting times,calcium carbonate crystals gradually accumulate in the internal pores of the specimen,resulting in the decrease of permeability of the specimen.After 8 rounds of grouting,although the permeability of most specimens is greatly reduced,it still has a certain permeability.The faster the grouting speed is,the better the permeability of the solidified specimen is.The grouting times can be increased by increasing the grouting speed.(5)XRD results show that calcium carbonate is mainly calcite.SEM experiments show that bacteria act as nucleation sites between coal particles,and form space skeleton structure among coal particles after wrapping coal particles as a whole,so as to enhance their strength.(6)Compared with the MICP technology,the common chemical method has no obvious effect on the consolidation of coal particles due to the lack of nucleation sitesThe thesis has 36 pictures,5 tables,and 58 references... |
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