Experimental study on reconstruction of aquiclude by MICP under the back ground of water preserved coal mining in Northern Shaanxi

Northwest China is rich in coal resources,but its ecological environment is fragile.Coal mining results in the destruction of the soil layer,water resources leakage,soil erosion and ecological environment degradation.Therefore,the research on the reconstruction of the water-proof soil layer has important theoretical and practical significance.Based on the field conditions of water conservation and coal mining in Northern Shaanxi,including temperature characteristics,environmental characteristics,mining fracture characteristics,fracture filling material characteristics,microbial calcium source characteristics,a series of laboratory tests about MICP (microbial induced carbonate precipitation) reconstituted aquiclude had been conducted.The characteristics of Bacillus megaterium in different temperature,adaptability in different environment and adaptability in different temperature had been studied by UV spectrophotometer tests and calcium carbonate production tests.Using concentrated high calcium clean mine water as calcium source and inorganic salt source,coal gangue powder,loess and sand as fracture filling material of mining soil,and urea as nitrogen source,a series of experiments of MICP technology to solidify mining fracture soil had been done,including unconfined compression contrast tests under microbial solidification and variable head permeability comparison tests,X-ray diffraction tests of solidified body and recovery tests of mining physical models.The results show that the experimental strains can be preserved for 3 months at 3 ℃,and the activity of the microbial samples inoculated for 3 months at 0 ~ 20 ℃ has a certain influence,but it can still be used for the fracture repair of mining soil.The OD600 value of the three inoculated strains exceeded 2.0 in 7 days,which indicated that the microorganisms could adapt to the local environment.Compared with the 30 ℃ constant temperature curing,the simulated temperature curing samples in May in Northern Shaanxi had a higher calcium carbonate production in the same period,while the microorganism domesticated in the research background area had a higher calcium carbonate production in the same period.Although the curing effect of concentrated high calcium clean mine water as solidified calcium source is slightly worse than that of calcium chloride reagent,the curing effect can be partially compensated by four times of repeated injection.When the mass ratio of coal gangue powder,clay and sand is 1∶1∶2,the physical and mechanical properties of the fractured soil can be considered as well as the hydraulic restoration effect,which is beneficial to the subsequent joint phytoremediation.The results of physical simulation show that the effect of aquiclude reconstruction by MICP technology is significant.After four times of solidification of the model mining fissure soil,the water head of 3 m in 1 h only drops 0.1 m.The results provide experimental support for the industrialization of MICP technology.