Effects of carbonate distribution pattern on the mechanical behaviour of bio-cemented sands: A DEM study

Microbially induced carbonate precipitation is a promising ground improvement technique which can enhance the mechanical properties of soils through the precipitation of calcium carbonate. Experimental evidences indicate that the precipitated carbonate can display different distribution patterns. Crystals can develop at grain–grain contacts (contact cementing), connect soil grains that were initially not in contact with each other (bridging), precipitate on the grain surface (coating), or fill in the void space (pore filling). This paper investigates the role of the aforementioned distribution patterns on the mechanical behaviour of lightly bio-cemented soil samples using discrete element modelling. Bio-cemented samples with different distribution patterns and carbonate contents are built, and a series of drained triaxial compression simulations are carried out at different confining pressures. The results show that cementation in the form of bridging and contact cementing leads to obvious improvement in stiffness, strength and dilatancy. In contrast, cementation in the form of coating contributes only slightly to mechanical improvement, and pore filling exhibits negligible influence on the mechanical response of the material. The findings suggest that, to gain strength improvement in the most effective way, treatments should be tailored to precipitate calcium carbonate crystals in the form of bridging.