Behavior of Biocemented Sands under Cyclic Loading

Abstract

In the past ten years, intensive research efforts were undertaken to study a newly emerging soil improvement technique that uses calcite-inducing reactions to produce natural cementation in soils. Given the fact that current ground improvement techniques are energy consuming, it is imperative that research in the soil improvement field be directed towards more sustainable eco-friendly techniques. Microbial induced calcite precipitation is a sustainable technique that allows for solid sandstone-like material to be produced from naturally loose sand. The technique uses bacterial species to produce urease enzymes, which catalyze the chemical reaction and induce calcite precipitation. Another way for inducing calcite precipitation is to directly use the urease enzyme, leading to enzyme-induced calcite precipitation. Researchers have studied the behavior of biocemented sand using conventional triaxial tests and compressive strength tests. However, the cyclic behavior of these samples is not yet significantly explored and/or understood.

Thus, the objective of this study was to investigate the behavior of biocemented sand subjected to cyclic loading. The study focused on: (1) Measuring the improvement obtained on sand samples due to calcite precipitation by using “continuous” shear velocity measurements from embedded bender elements. (2) Studying the effect of increasing the calcite precipitation on the sand resistance to cyclic loading. The sand type and properties, percentage of cementation, curing time, and vertical confinement were also investigated.

The study concluded with a significant improvement in treated samples which was noticed through the increase in the shear wave velocity, compared to the non-treated samples, and depending on the quantity of cementation solution. In addition, the samples showed resistance to cyclic loading as we increase the cementation, which implies resistance to liquefaction. Finally, the improvement measured using the cone penetration test was in compliance with the shear wave velocity readings.