Field implementation of enzyme-induced carbonate precipitation technology for reinforcing a bedding layer beneath an underground cable duct

Abstract

A suitable bearing capacity of foundation is critical for the safety of civil structures. Sometimes foundation reinforcement is necessary and an effective and environmentally friendly method would be the preferred choice. In this study, the potential application of enzyme-induced carbonate precipitation (EICP) was investigated for reinforcing a 0.6 m bedding layer on top of clay to improve the bearing capacity of the foundation underneath an underground cable duct. Laboratory experiments were conducted to determine the optimal operational parameters for the extraction of crude urease liquid and optimal grain size range of sea sands to be used to construct the bedding layer. Field tests were planned based on orthogonal experimental design to study the factors that would significantly affect the bio-cementation effect on site. The dynamic deformation modulus, calcium carbonate content and long-term ground stress variations were used to evaluate the bio-cementation effect and the long-term performance of the EICP-treated bedding layer. The laboratory test results showed that the optimal duration for the extraction of crude urease liquid is 1 h and the optimal usage of soybean husk powder in urease extraction solution is 100 g/L. The calcium carbonate production rate decreases significantly when the concentration of cementation solution exceeds 0.5 mol/L. The results of site trial showed that the number of EICP treatments has the most significant impact on the effectiveness of EICP treatment and the highest dynamic deformation modulus ( E vd ) of EICP-treated bedding layer reached 50.55 MPa. The area with better bio-cementation effect was found to take higher ground stress which validates that the EICP treatment could improve the bearing capacity of foundation by reinforcing the bedding layer. The field trial described and the analysis introduced in this paper can provide a practical basis for applying EICP technology to the reinforcement of bedding layer in poor ground conditions.