Large-Scale Bio-Cementation Improvement of Sands

Microbially induced calcite precipitation (MICP) is one of the most promising emerging environmentally conscious soil improvement techniques. The bio-cementation process offers an alternative to traditional mechanical, Portland cement, and silicate based ground improvement methods, by utilizing microbial activity to induce calcite precipitation on soil particle surfaces and at particle contacts. Despite extensive demonstration of the process at the laboratory-scale, few large and field-scale applications have been completed to demonstrate and understand the biogeochemical process at the meter scale. An instrumented large-scale bio-cementation test was performed using a 1.7-meter diameter tank containing 0.7 m³ of a poorly-graded natural sand, and treated with three wells positioned in a triangular pattern at a well-to-well spacing of 1.2 m. Eight non-uniform cementation treatment injections were completed to determine the extent to which the improvement level could be spatially controlled, and to establish a cementation gradient for study of improvement across a broad range of cementation levels. Prior to treatment, miniature cone penetrometer soundings were used to assess pre-treatment conditions. During treatment, tank specimens were monitored spatially for shear wave velocity changes. Following treatment, cone penetration soundings were performed to assess improvement spatially, and discrete soil samples were obtained for calcite content measurements. Post-treatment measurements indicated that a gradient of cementation was achieved, with highly cemented locations reaching shear wave velocities near 970 m/s, calcite contents in excess of 5.0%, and increases in penetration resistances near 545%.