Experimental study of relationship between uniaxial compression strength and CaCO 3 bonding strength of a biogrouted rock-like material

Abstract

Abstract Biogrout is a promising soil/rock improvement method in which CaCO3 crystals are formed in between sand grains or rock fractures through a microbial induced calcium carbonate precipitation (MICP) process. One of the limitations of biogrout is that it is not effective to be applied to coarse sand or rock fractures with broad aperture (i.e., fracture width is larger than 1mm), as a number of rounds of treatments are required to produce sufficient amount of CaCO3 in soil pore spaces or rock fractures. A new biogrouting method using biogrout containing bioslurry has been proposed to overcome this difficulty. Bioslurry contains pre-formed urease active CaCO3 crystals. The use of bioslurry will reduce considerably the number of treatment. However, the mechanical properties of sand treated with biogrout containing bioslurry, a type of rock-like material are more complicated as bioslurry may not contribute to microbial bonding strength as much as pure biogrout. The objective of this study is to investigate the micro-mechanisms of strength improvement behind the use of biogrout containing bioslurry as well as the relationship between the uniaxial compression (UC) strength and CaCO3 bonding strength based on a series of biogrouting experiments on various sand. A new method to evaluate the bonding strength of biogrouted sand using the acoustic emission (AE) technique is proposed. By detecting AE hits and AE energy of bonding damages during a UC test, the relationship between AE energy and elastic strain energy that induces bonding damage is established. The experimental results indicate the bonding strength of the specimen treated by biogrout containing bioslurry is weaker than that by pure biogrout and the UC strength of biogrouted sand is primary controlled by the mean bonding strength. The higher the mean bonding strength, the greater the UC strength.