Abstract: Staphylococcus epidermidis X-NM1 is a highly efficient carbonate-mineralizing bacterial strain isolated from soil near
a saline lake. This study is focused on the heavily sandy dolomite from the Yuxi section of the Central Yunnan Water Diversion Project, using Staphylococcus epidermidis X-NM1 for its solidification. The effects of inoculum size, calcium source type and concentration, and bacterial grouting strategies on urease activity and calcium carbonate precipitation were systematically examined. The solidification performance was comprehensively evaluated by integrating unconfined compressive strength tests, micro-penetration tests, and scanning electron microscopy (SEM) to assess the strength, uniformity, and microstructures of the treated samples. The results show that: (1) The inoculum size significantly affected bacterial growth and metabolism, with an optimal inoculum size of 10%, at which the OD600 value of the bacterial solution and urease activity reach 2.19 and 3.3 mM urea/min, respectively, achieving the optimal growth level; (2) Among the bacterial grouting strategies, the mixed bacterial solution method yields the best bacterial adsorption effect, with an adsorption rate as high as 97.91%; (3) Calcium source screening shows that calcium chloride was most conducive to calcium carbonate generation, significantly outperforming calcium acetate, calcium lactate, and calcium oxide; (4) When calcium chloride is used as the calcium source, the solidified specimens exhibit the highest unconfined compressive strength, reaching 355 kPa and 817 kPa at cementation solution concentrations of 0.5 M and 1.0 M, respectively, with the best uniformity observed in the specimens. (5) Microbially induced calcium carbonate crystals effectively filled the pores of the heavily sandy dolomite, thereby enhancing the overall strength of the specimens.  Among all the calcium sources, calcium chloride demonstrated the most superior and stable cementation effect.

Key words: sandy dolomite, MICP, staphylococcus epidermidis X-NM1, calcium sources, inoculum size, microstructure