Fabric characteristics and mechanical response of bio-improved sand to various treatment conditions

Investigation of the enhanced mechanical response of treated soils through microbially induced calcite precipitation requires extensive understanding of the pore structure. Depending on the applied treatment conditions, the resultant material exhibits distinct changes in the solid phase. In this paper, the focus is on the microstructural characteristics of bio-cemented soils derived from different treatment patterns. The objective is to clarify the predominant fabric features as a function of the adopted treatment conditions. For this purpose, microstructural observations with scanning electron microscopy are used to analyse the structure during the treatment and post-treatment. Mesocrystals – that is, aggregates of single particles – are identified as a distinct form of precipitate that provides the crucial grain-to-grain contact surfaces. The cemented samples are subsequently subjected to undrained triaxial shear test to investigate the response in three typical cases of bio-cemented samples produced under laboratory conditions: (a) one of very low calcite content (2·5% w/w), (b) one with inhomogeneous distribution of calcite and (c) for the case of homogeneously distributed calcite mass. Improved characteristics are obtained in all three cases.