Effect of biocementation on the strength and stability of termite mounds

Termite mounds are bioengineered granular ensembles that remain stable over decades, a vital requirement for termite societies that house millions of individual termites. An experimental study on the mechanobiology of mounds and mound soil of the fungus-growing termite Odontotermes obesus (Rambur) demonstrated that termites are capable engineers. Mound soil was significantly different in its physical and mechanical properties compared to the surrounding or 'control' soil. However, mound and control soils did not differ in clay mineralogy. Utilising the finer soil fraction, termites altered the soil significantly by cohering grains through their secretions into units called boluses, in the presence of water. Termites modulated the amount of water close to the plastic limit of the soil while preparing these boluses such that the soil could be effectively moulded. The cementation effected by termites using their secretions and/or excretions enhanced the strength of the soil tenfold, which may not be achievable otherwise. The soil modification achieved by the termites decreased mound susceptibility to erosion and collapse. Termites successfully cemented foreign materials, suggesting a wide range of cementation abilities. Slope stability analysis with intact mound soil revealed a significant increase in the safety factor of the mound compared to that of reconstituted soil.