Experimental study on load-bearing failure characteristics and repeated seepage resistance performance of immobilized...

Repeated mining in thick coal seams and close-distance coal seam groups induces recurrent development of overburden fractures, resulting in persistent loss of groundwater bodies. Immobilized microbial cement materials are expected to achieve the goal of "one-time grouting with repeated seepage-resisting" for managing water-conducting fractures in overburden strata. Through saturated water absorption tests, nuclear magnetic resonance (NMR) detection, uniaxial compression tests, acoustic emission (AE) monitoring, scanning electron microscopy (SEM) imaging, X-ray diffraction (XRD) analysis, and triaxial seepage experiments, this study investigated the load-bearing failure characteristics and repeated seepage-resisting performance of a certain immobilized microbial cement. Compared with ordinary cement, the calcium carbonate produced by the biochemical action of this immobilized microbial additive can densify the microstructure of the specimens and reduce their porosity; however, it may induce internal stress concentrations within the specimens. Together with its retarding effect on the hydration of cement clinker, this leads to a reduction in compressive strength and makes the tensile failure characteristics of the specimens more pronounced. Under experimental conditions simulating a formation stress of 3 MPa and a formation water pressure of 0.5 MPa, the pre-cracked specimens grouted with cement and with microbial cement completed 1 cycle and 3 cycles of repeated seepage-resisting experiments, respectively. This indicates that the biocarbonation effect and hydration-retarding effect of the immobilized microbial additive can, under laboratory conditions, prevent continuous leakage of mobile water within fractures induced by repeated mining, without the need for additional nutrient solution. The water flow rate over time during the experiments follows an exponential-type function, and through coefficient fitting with a correlation above 95%, it can be expressed as an equation closely related to the repeated seepage-resisting cycle number *n* and seepage time *t*. This study can provide a theoretical basis and experimental reference for research on strata seepage control under repeated mining conditions.