Biogrouting coarse materials using soil-lift treatment strategy

This paper investigates the feasibility of using a soil-lift biogrouting treatment strategy to improve the mechanical properties of coarse sand with the view of applying it to stone columns - sand piles and rammed earth columns type of applications. A two-phase percolation approach was adopted in this study that included percolating a bacterial suspension Sporosarcina pasteurii in the first phase and a cementation solution in the second phase. This process was repeated every two treatments. The study reveals that an increase in the number of soil lifts negatively influenced the mechanical properties of the biocemented coarse sand. However, the minimum strength and stiffness achieved (2.8 MPa) in this study was sufficient to mitigate slumping of a soil column that may occur during installation or excessive radial expansion. Furthermore, it is shown that a single lift treatment can lead to a very high increase in strength and stiffness (up to 8.9 MPa and 2.3 GPa, respectively). However, calcite distributions within biocemented soil columns piles were quite heterogeneous with increasing number of soil-lift treatments. Soil-lift treatment can be seen as a practical strategy that can be used to inject treatment liquids in deeper depths, such as in soil columns piles.