Insight into the Properties of Surface Percolated Biocemented Sand

Abstract

Most traditional soil improvement methods are time-consuming, expensive, require heavy machinery and environmentally detrimental. As a more ecofriendly ground improvement method, the biocementation of soil offers an alternative to traditional soil improvement techniques. This method is based on microbial precipitation of calcium carbonate serving as cementing or bonding agents between soil grains. To achieve this bonding, the method of in situ soil stabilization by surface percolation under free drainage of solutions containing either bacteria or calcium ions was chosen. This paper investigates the effects of this method on the strength improvement and microstructure of a dry loose poorly-graded sand after bioimprovement. To evaluate the success of treatment, a series of laboratory experiments was conducted, including, shear wave velocity, unconfined compressive strength, calcium carbonate content, triaxial shear test, scanning electron microscopy, etc. The study revealed that this newly emerging biomediated technique causes the improvement of soil strength as a result of the cementation of sand particles via crystal precipitation and the surface percolation method has the potential of stabilizing the loose sand with desirable depth. Results also showed that strength increase depends not only on calcium carbonate content but also on its precipitation location and particle-to-particle binding strength and numbers. In addition, scanning electron microscopy images and X-ray diffraction showed precipitation of biological calcium carbonate is different in polymorph type throughout the sand column.