Study on the improvement of grouting stone properties in coal mine goafs using combined denitrifying bacteria

Grouting can effectively reduce residual deformation of coal mine goafs, but fly ash grouting materials suffer from poor flowability and slow early strength development. Microbially Induced Calcite Precipitation(MICP), with its high environmental compatibility and minimal disturbance to geotechnical bodies, effectively improves the injectability of grouting slurry in goafs. This study combined Castellaniella denitrificans and Sporosarcina pasteurii to induce calcite precipitation, preparing cement-fly ash slurry with varying water-solid ratios, solid ratios, and denitrifying bacteria concentrations. The physical properties of the slurry and the mechanical properties of the grouted stone bodies under sealed curing conditions were measured. Results showed that the strength of the stone bodies cured by MICP increased rapidly within 7 days, and the strength reached the standard 2.03 MPa at 28 days under conditions of low solid ratio and high water-solid ratio. At a water-solid ratio of 1:1.2 and a solid ratio of 15%, initial and final setting times were 97.46 and 127.31 hours, respectively, indicating that MICP enhances slurry fluidity, providing more time for grouting construction in goafs. Dual-bacteria MICP improves stone body performance by enhancing cohesive, frictional, and interlocking forces, with the best compressive strength at a denitrifying bacteria concentration with an optical density of 0.8 at 600 nm wavelength.

注浆工艺可有效降低煤矿采空区的残余变形，但粉煤灰注浆材料存在流动性差、早期强度发展缓慢的缺陷。微生物诱导碳酸钙沉淀（Microbially Induced Calcite Precipitation，MICP）具备环境相容性高、对岩土体扰动极小的特点，可显著改善采空区注浆浆液的可注入性。本研究选取脱硝基卡斯泰尔氏菌（Castellaniella denitrificans）与巴氏芽孢八叠球菌（Sporosarcina pasteurii）联合诱导碳酸钙沉淀，制备了一系列不同水固比、固含量及反硝化细菌浓度的水泥-粉煤灰浆液。测试了密封养护条件下浆液的物理性能，以及注浆结石体的力学性能。结果显示，经MICP固化的结石体强度在7天内快速提升，在低固含量、高水固比的工况下，其28天抗压强度可达2.03 MPa，符合相关规范要求。当水固比为1:1.2、固含量为15%时，浆液的初、终凝时间分别为97.46小时与127.31小时，表明MICP可有效提升浆液流动性，为采空区注浆施工预留了更为充足的作业时间。双菌联合MICP通过增强粘结力、摩擦力与咬合力来优化结石体性能，当反硝化细菌在600 nm波长下的光密度为0.8时，结石体的抗压强度达到最优水平。