Experimental study on grouting reinforcement characteristics of limestone with different length cracks under fluid solid coupling

It is difficult to fully develop coal resources in the north of the Yellow River due to the influence of mine water disaster. Grouting technology is an important means to solve the problem of mine water disasters at present. The in-depth study of grouting technology can not only liberate a large number of coal resources threatened by water disasters, but also have positive significance for the protection of groundwater resources. Laboratory tests were conducted on limestone samples obtained from Qiuji Coal Mine in the Yellow River North Coalfield to observe the microscopic characteristics of the limestone. The mechanical properties and grouting reinforcement characteristics of limestone with different lengths of cracks under fluid solid coupling were obtained. Through theoretical analysis, the variation law of the cracking strength of limestone with the change of prefabricated crack length was obtained, and the grouting reinforcement mechanism was analyzed. The test results show that the strength and toughness of the rock after grouting have been significantly improved, the limestone before grouting has obvious brittleness characteristics, and the brittleness of the limestone after grouting has decreased and the ductility has increased; The damage degree of grouting plus solid is more and more severe with the increase of crack length. When the crack length is large, it is accompanied by horizontal fracture development; The pre-peak permeability of grouting plus solid decreases slightly, and the post-peak permeability decreases significantly. The maximum stage of limestone permeability occurs in the post-peak stage, while the minimum stage of permeability occurs in the linear elastic stage of the stress-strain curve. The longer the fracture length, the easier the double-peak phenomenon of permeability appears. Based on the theory of continuous medium mechanics, the formulas for calculating the crack initiation strength and fracture toughness of grouting plus solid are derived. It is theoretically proved that the strength of grouting plus solid is greater than that of the original rock sample; The greater the difference between the elastic modulus of rock and the elastic modulus of the combination formed by grouting, the weaker the impact of grouting on rock strength.