Evaluation of porosity in biogrouted sand using microfocus X-ray CT

Abstract

Biogrouting is a method employed for ground improvement based on microbially induced calcium carbonate precipitation. It is commonly believed that biogrout has environmental and economic benefits. However, there remains the need to clearly understand the internal structure of biogrouted soil. In this study, we use microfocus X-ray computed tomography (CT) to evaluate the porosity in biogrouted sand. X-ray CT is useful as a non-distractive inspection tool. First, we prepare small specimens using coral sand at different dilution rates of culture solution. After carrying out a solidification test for 2 wks., we perform an unconfined compressive strength (UCS) test and measure the porosity of the specimens. Our aim is to investigate the influence of the dilution rate on the UCS and the porosity of sand specimens. The results show that a lower dilution rate resulted in a lower sand-specimen porosity and an increase in the UCS. We investigate the precipitation that fills a void. Then, we investigate the relationship between UCS and the ratio of porosity. There was a negative correlation between UCS and porosity, which closely agrees with previous research. We confirm the validity of the result, and we determine the UCS from the porosity.