Experimental study on the reinforcement performance of unloading-damaged mudstone by microbial grouting

Abstract To address the structural deterioration and water-induced swelling of mudstone caused by unloading damage during foundation excavation, grouting reinforcement tests using MICP and volcanic ash-assisted MICP were conducted. Mudstone specimens with unloading damage degrees of 70%-90% were prepared through triaxial unloading tests. Combined with lateral constrained swelling tests, triaxial compression tests, and SEM analysis, the swelling deformation, mechanical properties, and micro-mechanisms of unloading-damaged mudstone under different reinforcement methods were systematically investigated. The results show that unloading damage significantly weakens the strength of mudstone and enhances its swelling sensitivity. Both MICP and volcanic ash-assisted MICP can effectively inhibit swelling deformation and improve strength. Specifically, MICP increased the residual strength by 7.41%-13.98% and the peak strength by 2.49%-6.34%, while volcanic ash-assisted MICP increased them by 13.45%-20.61% and 5.36%-9.45%, respectively. SEM results show that the mineralization products improve the structural integrity of mudstone by filling pores, sealing cracks, and enhancing interparticle cementation. The incorporation of volcanic ash further promotes mineral precipitation and the formation of a composite cementation structure, resulting in a better reinforcement effect than that of conventional MICP.