Numerical Simulation of Forming MICP Horizontal Seepage Reducing Body in Confined Aquifer for Deep Excavation

Abstract

The drawdown outside of a deep foundation pit has to be controlled during excavation. However, the vertical curtain cannot cutoff a deep and thick confined aquifer during deep excavation. In this study, a microbial-induced carbonate precipitation (MICP) horizontal seepage reducing body (HSRB) was proposed to control drawdown combined with a partially penetrating curtain. MICP HSRB is formed by using the seepage field generated by the recharge wells to drive the migration of a Sporosarcina pasteurii solution, stationary solution, and cementation solution into the deep confined aquifer. The migration of each solution was numerically simulated to study the HSRB formation process. The influence of different factors on solute migration was studied. The results show that the solutes in the fixed fluid and cementation fluid can reach the area under the driving of the seepage field, which proves that MICP HSRB can be formed. The calcium ions and urea in the cementation solution are more likely to migrate to the designated area than the bacterial solution. Increasing the injection rate of bacterial solution and adding recharge wells both made the bacterial solution migrate more quickly to the designated area. In the case of multiple grouting, the solute migration in the later stage will be hindered by the plugging of pores caused by calcium carbonate generated in the earlier stage. Therefore, different grouting methods need to be designed to drive the seepage field so that the solute injected in the later stage can continue to migrate. The MICP HSRB grouting technology can be used in foundation pit dewatering, providing reference for similar engineering.

Feasibility of Microbially Induced Carbonate Precipitation to Enhance the Internal Stability of Loess under Zn-Contaminated Seepage Conditions

“…Ureolytic bacteria such as Bacillus pasteurii, Bacillus sphaericus, Bacillus licheniformis, nitrate-reducing bacteria, and other alkaliphilic bacteria are utilized in MICP. Bacillus pasteurii, known for its strong tolerance and ease of cultivation, has been shown in previous studies to play a significant role in calcium carbonate precipitation [25,26,31,38,39]. Sporosarcina pasteurii (CGMCC1.3687) bacteria were obtained from the China General Microbiological Culture Collection Center for this study.…”

“…Sporosarcina pasteurii (CGMCC1.3687) bacteria were obtained from the China General Microbiological Culture Collection Center for this study. The liquid culture medium consisted of urea (20 g/L), peptone (5 g/L), yeast extract (3 g/L), and manganese sulfate (0.01 g/L) as reported by Jiang et al [13] and Wang et al [26].The pH was adjusted to 7.0 using a 10% NaOH solution and sterilized at 121 • C for 20 min in an autoclave. Following cooling, the bacteria were inoculated at a 1:100 ratio and incubated aerobically in a shaking incubator at 30 • C and 180 rpm for 48 h. Bacterial liquid concentration was determined by OD 600 at 600 nm wavelength, and urease activity was measured by the average conductivity change within 5 min.…”

“…While soil stiffness increases with cementation, changes in permeability are minimal, making MICP technology a promising option for internal erosion control. Previous studies [19][20][21][22][23][24][25][26] have highlighted numerous advantages of MICP technology. These benefits include improving soil strength and stiffness, maintaining soil permeability with minimal calcium carbonate precipitation (usually less than 5-6%), providing energy-efficient on-site treatment compared to traditional chemical grouting, and showing rapid biogeochemical reaction rates.…”

A Numerical Bio-Geotechnical Model of Pressure-Responsive Microbially Induced Calcium Carbonate Precipitation

“…Furthermore, field applications have validated its practical feasibility [17][18][19]. To optimise the MICP process further, numerical models have also been produced, which include aspects such as reaction rates, fluid flow, bacteria cell concentrations, and the resulting concentration of calcium carbonate, alongside the reduction in soil permeability [20][21][22][23][24].…”