Assessment of the bio-cementation effect on shale soil using ultrasound measurement

Abstract

The assessment of bio-cementation effect using nondestructive testing methods is important for the application of microbial-induced carbonate precipitation (MICP) technique. In this study, a special grouting system was designed to conduct the bio-grouting of shale soils on a testing model. The ultrasound technique was used to evaluate the effectiveness of bio-cementation. A method was derived to estimate the distribution of ultrasonic wave velocity values within the testing model based on the average values measured on the model surfaces. From the changes of isosurfaces of velocity values, the evolution of soil improvement within the model corresponding to the different number of grouting cycles was analyzed numerically and visually. The SEM imaging technique was used to illustrate the mechanism of influence of the calcium carbonate precipitation on the wave velocity of the bio-cemented specimen. The linear relationships were established among the ultrasonic wave velocity, unconfined compressive strength (UCS), and the amount of CaCO3 precipitations formed in the MICP process. In combination with the application of the ultrasound measurement technique as demonstrated in this work, the relationship provides a very useful nondestructive testing tool to assess the effectiveness of bio-cementation within a large soil body.