Use of bacterial ureolysis for improved gelation of silica sol in rock grouting

Abstract

Low pH silica-based grouts suitable for penetrating fine aperture fractures are increasingly being developed for use in engineering applications. Silica sol has an initial low viscosity and mixing with an accelerator destabilises the suspension producing a gel. The influence of sodium, calcium and ammonium chloride accelerators on gel time, rate of gelation and shear strength of the resulting gel were investigated in this study. For the first time the potential use of bacterial ureolysis as an accelerator for the destabilisation of silica sol was also explored. This study demonstrates that bacterial ureolysis can be used to control the gelation of silica sol. The rate of ureolysis increases with increasing bacterial density, resulting in faster gel times and higher rates of gelation. In addition, for grouts with similar gel times, using bacterial ureolysis to induce destabilisation results in a higher rate of gelation, a higher final shear strength and a more uniform gel than direct addition of the corresponding chemical accelerator. These results suggest that bacterial ureolysis could potentially be used in rock grouting to achieve long gel times and hence greater penetration, while also maintaining sufficiently rapid gelation to minimise issues related to fingering and erosion of the fresh grout

Biomediated control of colloidal silica grouting using microbial fermentation

“…In the study by Cheng et al (2019) 30 , fermentative activity was established by inoculating soils with a mixed microbial culture obtained from activated sludge and provided in solutions containing alginate and glucose (pH initial = 7.5). Although using a different microbial pathway, Maclachlan et al (2013) 31 demonstrated that microbial urea hydrolysis could be used to mediate the gelation of initially acidic colloidal silica grouts through increases in solution ionic strength and pH. In this study, mediation of the process via ureolysis was found to achieve a more uniform gel structure, faster gelation, and a higher gel shear strength when compared to gels formed using chemical accelerants, albeit with the generation of aqueous ammonium resulting from urea hydrolysis.…”

“…Collectively, outcomes from both studies suggest that microbial glucose fermentation activity can provide a viable pathway to control the gelation of colloidal silica grouts. Although similar in principle to the work by Maclachlan et al (2013) 31 , the use of glucose fermentation activity was expected to address limitations related to the use of microbial ureolysis by providing a method capable of improving soils under more acidic conditions and eliminating the production of ammonium by-products.…”

Application of numerical simulation of microbial reaction to biogrout with ureolytic bacteria

“…3.05×10 -7 3.21×10 -3 Whiffin (2004) 25) 2.00×10 -7 0.2 van Paassen (2009) 3) -0.055 Tobler et al (2011) 26) 1.15×10 -11 -6.32×10 -10 -Maclachlan et al (2013) 27) 8.33×10 -10 -2.22×10 -9 -Tobler et al (2014) 28) 1.92×10 -8 -Mahanty et al (2014) 29) 9.60×10 -12 -1.73×10 -10 -Lauchnor et al (2015) 30) 8.92×10 -8 0.305…”