Effect of particle size and gradation on compressive strength of MICP-treated calcareous sand

Abstract

Calcareous sand is a type of biological sand deposited from the remains of marine organisms. Although widely used in coastal construction, the reinforcement of calcareous sand is necessary due to its natures of low bearing capacity and high compressibility. Aiming for this, an environmentally bio-grouting technique, microbially induced calcium carbonate precipitation (MICP) was applied to reinforce the calcareous sand. However, MICP treatment is in turn influenced by the properties of calcareous sand, such as particle size and gradation. To reveal the effects of particle size and gradation, the MICP-treated calcareous sands with various median sizes, uniformity coefficients or curvature coefficients, were conducted with the unconfined compressive strength (UCS) tests and a series of laboratory experiments. The results indicated that with the median size or uniformity coefficient increasing, the UCS of the MICP-treated specimens decreased; while with increasing curvature coefficient, the UCS exhibited a trend of increasing before decreasing. Further experiments reveal that particle size and gradation affect the MICP process mainly by changing the amounts and volume of pores. The current study demonstrates the respective effects of particle size and gradation on the treatment of MICP and provides a theoretical reference for reinforcing calcareous sand in marine engineering.