陕北保水采煤背景下MICP再造隔水土层的试验研究

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

我国西北地区煤炭资源丰富,但生态环境脆弱。煤炭开采导致隔水土层破坏,产生水资源漏失、水土流失和生态环境退化。因此,隔水土层再造的研究有重要的理论和现实意义。基于陕北保水采煤现场条件,包括温度特征、环境特征、采煤裂隙特征、裂隙充填物特征、微生物钙源特征等,开展了一系列MICP(微生物诱导碳酸钙沉积)再造隔水土层室内试验研究。采用紫外分光光度计测试和碳酸钙产量测试等方法,研究了巨大芽孢杆菌在不同温度下的保种特性、不同环境的适应性和不同养护温度的适应性。利用浓缩的高钙洁净矿井水作为钙源和无机盐来源,利用煤矸石粉、黏土和砂体作为采动土体裂隙充填物质,利用尿素作为氮源,开展了一系列的MICP固化采动裂隙土体试验,包括微生物固化前后,无侧限抗压强度测试对比试验、变水头渗透对比试验、固化体X衍射实验、采动物理模型修复试验。研究结果表明:本次实验菌种在3℃下可以保种3个月,0~20℃常温条件下保种3个月再接种后的微生物样品活性有一定影响,但仍可用于采动土体裂隙修复。本次实验菌种在接种3次后培养7 d其OD_(600)值超过2.0,说明3次接种后微生物能够适应当地环境。相比较30℃恒温养护,模拟陕北5月温度养护的样品同期碳酸钙产量更高,而在微生物富集阶段采用研究背景区温度驯化的微生物的同期碳酸钙产量进一步提高。利用高钙洁净矿井水浓缩后作为固化钙源虽然固化修复效果相比氯化钙试剂作为钙源固化效果略差,但通过4次反复注入可以部分弥补固化效果。采用煤矸石粉、黏土和砂作为土体裂隙充填物质,其质量比为1∶1∶2时,采动裂隙土体的物理力学和水理修复效果可以兼顾,且有利于后续植物联合修复。物理模拟结果发现MICP技术的隔水层再造效果显著,模型采动裂隙土体4次固化后,1 h内3 m高的水头仅下降0.1 m。研究结果为MICP技术用于隔水土层再造的工业化提供了试验支撑。

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 OD_(600) 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.