Direct Shear Characteristics of Enzymatically Cemented Sands

A laboratory study was conducted to investigate the shear strength of bio cemented sands using enzyme-induced carbonate precipitation (EICP) via the direct shear test. Several specimens were prepared using four different application methods of EICP solution, namely spraying, mix-&-compact, percolation, and injection. Potential use of EICP for improving the sand-concrete interaction strength was also studied. Results indicated that the adopted application method of introducing the EICP solution to the soil affects the distribution pattern of CaCO3 precipitation in the soil matrix, thereby shear strength. Each method yielded a different response when sheared compared to untreated sand. The injection method was found to achieve higher shear strength and interparticle cementation under controlled rate and distribution followed by percolation. The spraying and mix-&-compact methods produced specimens with weaker particles’ bond and lower shear strength measurement but still showed relatively better performance than the untreated sands. Better cementation of soil grains was achieved in medium sand and when fine and organic materials were removed. Sands response to EICP-treatment was inferred to vary depending on the geotechnical characteristic of the soils. Moreover, the interfacial strength between sand and concrete was found to be enhanced after applying the EICP treatment as it coarsened soil particles.