Effect of fibre-reinforced microbial-induced calcite precipitation on the mechanical properties of coastal soil

Coastal erosion is a global environmental concern, threatening infrastructure, human livelihoods and ecosystems. Recently, microbial-induced calcite precipitation (MICP) has emerged as a promising ground improvement technique. The present study examined the effects of adding three different fibre reinforcements, namely carbon, basalt and polypropylene, on the physical and mechanical properties of coastal soil through MICP. The fibre content used was 0.20%, 0.40% and 0.60% of soil weight. A comprehensive biotreatment investigation was conducted using Sporosarcina pasteurii (S. pasteurii) in a 0.5 molar cementation solution. The samples prepared for this study had aspect ratios of 2:1 and 1:1. These samples were subjected to biotreatment, consisting of a 24-h cycle for 9 and 18 days. Unconfined compressive strength (UCS), split tensile strength (STS) and ultrasonic pulse velocity (UPV) tests were conducted on the biotreated samples to evaluate the effect of fibre reinforcement on the mechanical properties of the biotreated samples. The amount of calcite precipitation, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to interpret biocementation. Results suggest that adding fibres to the MICP process enhances the mechanical properties of coastal soil. The optimum fibre content for carbon and basalt fibre was 0.40%, whereas, for polypropylene, it stood at 0.20%. The maximum UCS, STS, UPV and average CaCO3 were observed in a basalt fibre-reinforced biotreated sample with a fibre content of 0.40%, subjected to 18-day biotreatment. Conversely, the sample without fibre-reinforcement, biotreated for 9 days, exhibited the lowest values for these parameters. Samples subjected to 18 days of treatment have higher values of UCS, STS, UPV and CaCO3 content than 9-day-treated soil samples. SEM revealed the presence of CaCO3 precipitates on the surfaces of soil grains and their contact points, and the EDS spectrum corroborated this observation.