Effect of chemical treatment used in MICP on engineering properties of cemented soils

Despite the large number of studies concerned with microbially induced carbonate precipitation (MICP) on soils, little attention has been paid to the effect of the chemical concentration used in the treatment on the precipitation pattern of calcium carbonate and their influence on engineering properties of MICP cemented soils. In this study, unconfined compressive strength tests were conducted on sand samples treated using 01,0-25,0-5 and 1 M urea-calcium chloride solutions. It was found that, although the strength of tested samples all increased after MICP treatment, the magnitude of this increase depended on the concentration used in the treatment and that the use of a low-chemical-concentration (i.e. urea and calcium chloride) solution resulted in stronger samples. Permeability test results showed that the use of a high-urea-calcium chloride-concentration solution resulted in a rapid drop in permeability at the early stage of calcite precipitation, whereas the use of a low-chemical-concentration solution was found to result in a more gradual and uniform decrease in permeability. This observed effect of chemical concentration on the strength and permeability of MICP cemented soils can have implications for the design of MICP for field applications

Application of Bio-Stimulated Calcite Precipitation to Stabilize Expansive Soils: Field Trials

This paper presents the results of a field implementation of microbial induced calcite precipitation to stabilize expansive soils in Marsing, Idaho. The field test was done by drilling 2.5” (6.35 cm) diameter holes at a spacing of 16” to 30” (40.6 cm to 76.2 cm) into the ground and, injecting bio-enrichment followed by bio-cementation solutions to stimulate the native bacteria and subsequently achieve calcite precipitation. The pH level of the soil, the calcite content, and free swelling potential were monitored over time by collecting periodic soil samples from the injection points. An increase in pH from 8.3 to 9.7 was seen in the first seven days after the injection of bio-enrichment solution. The calcite content in the soil increased and the free swelling potential decreased consistently with each subsequent injection of bio-cementation solution. The calcite content increased from 3% to 8% and the free swell index dropped from 114% to 29%. The results show that microbial induced calcite precipitation can be successfully replicated in the field for the stabilization of expansive soils

Biogeochemical processes and geotechnical applications: Progress, opportunities and challenges

Consideration of soil as a living ecosystem offers the potential for innovative and sustainable solutions to geotechnical problems. This is a new paradigm for many in geotechnical engineering. Realising the potential of this paradigm requires a multidisciplinary approach that embraces biology and geochemistry to develop techniques for beneficial ground modification. This paper assesses the progress, opportunities, and challenges in this emerging field. Biomediated geochemical processes, which consist of a geochemical reaction regulated by subsurface microbiology, currently being explored include mineral precipitation, gas generation, biofilm formation and biopolymer generation. For each of these processes, subsurface microbial processes are employed to create an environment conducive to the desired geochemical reactions among the minerals, organic matter, pore fluids, and gases that constitute soil. Geotechnical applications currently being explored include cementation of sands to enhance bearing capacity and liquefaction resistance, sequestration of carbon, soil erosion control, groundwater flow control, and remediation of soil and groundwater impacted by metals and radio-nuclides. Challenges in biomediated ground modification include upscaling processes from the laboratory to the field, in situ monitoring of reactions, reaction products and properties, developing integrated biogeochemical and geotechnical models, management of treatment by-products, establishing the durability and longevity/reversibility of the process, and education of engineers and researchers