There are a large number of microorganisms such as bacteria and fungi in the soil, which affect the physical and mechanical properties of the rock and soil. Microbial solidification technology is the use of microbial metabolism to induce mineral precipitation, thereby changing the soil structure and improving the physical and mechanical properties of the soil. This article uses microbial activated magnesium oxide solidification technology to treat red clay samples, and explores the effects of magnesium oxide content, bacterial solution concentration, and initial moisture content on the shear strength and disintegration of red clay. The experimental results are explained reasonably through scanning electron microscopy experiments and ImageJ quantitative analysis software. The experimental results show that the shear strength of red clay is positively correlated with the content of magnesium oxide and bacterial solution concentration, but negatively correlated with the initial moisture content; The hydrated magnesium carbonate generated in the experiment is the key reason for the improvement of shear strength. Hydrated magnesium carbonate can play a role in bonding red clay particles and filling the pores of red clay; Significant reduction in disintegration of microbial magnesium oxide solidified red clay.

This study proposed an improved bio-carbonation of reactive magnesia cement (RMC) method for dredged sludge stabilization using the urea pre-hydrolysis strategy. Based on unconfined compression strength (UCS), pickling-drainage, and scanning electron microscopy (SEM) tests, the effects of prehydrolysis duration (T), urease activity (UA) and curing age (CA) on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed. The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80% high water content. A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing, which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples. Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield, but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates (HMCs), which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples. The optimum formula was determined to be the case of T = 24 h and UA = 10 U/mL for dredged sludge stabilization. A 7-day CA was enough for bio-carbonized samples to obtain stable strength, albeit slightly affected by UA. The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization. This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil, such as dredged sludge. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).