Application of microbial biocementation to improve the physico-mechanical properties of sandy soil

Abstract

Biological process in soil improvement which is known as biocementation soil improvement technique has shown greater potential in geotechnical engineering applications such as slope stabilization and increasing sand strength. Egypt has more than 50,000 km irrigation and drainage channels. The main type of soil constituting a soil layer of most of the canal embankment in the Nile delta is the loosely soil. It is exposed to slope stability problems. This work focused on studying stabilization of the loosely soils via biocementation process and it was applied on sands to improve their mechanical properties by different treatment methods using bacteria named Sporosarcina pasteurii. These methods are injection with and without fixations, and mixing method. The main results showed that the injection methods of the bacteria with fixation solution in the treated soil was effective than the injection without fixation solution at the same conditions. Also, it is suggested to add solutions gradually to prevent precipitation of calcite on the surface of sand. Furthermore, using a growth media without sterilization has no negative effect on the bacterial activity. Meanwhile, using a growth media without centrifuge processes and bacteria incubation at 12 h instead of 24 h were more economy. This method leads to improvement of soil of large scale in site with low effort and relatively at short time when using the mixing method. The studied physicomechanical properties were significantly increased in biocemented sand for all methods used and they were superior for the injection with fixation method. The XRD results and SEM images indicated the deposition of calcium carbonates in biocemented sand. It is concluded that Sporosarcina pasteurii can be used commercially for sand biocementation process.