Sand stabilization with exo-polymeric substance producing bacteria isolated from a naturally cemented site

Saswati Ghatak, Suvendu Manna, , Debasis Roy, Prosenjit Saha, Suman Roy

In the proceedings of: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Soil Stabilization III

ABSTRACT: Geotechnical subsurface investigation data from a site underlain by cemented tailings sand generated from a placer mining and microbiological observations provided circumstantial evidence that the cementation was at least partially biogenic. From the cemented sand samples a strain of Bacillus foraminis (Gene Bank accession number HQ436339) was especially noted for its ability to produce exo-polymeric substances (EPS) and magnesium salts of cementitious nature. A strain of Bacillus megaterium (Gene Bank accession number HM371417) isolated from a riverbank silt deposit was also noted for its similar cementing activity. Production of EPS and magnesium salts by these strains were investigated. Laboratory drained triaxial tests on water pluviated sand samples hosting the bacteria also showed evidence of cementation particularly when the samples were loose. Increased dilatancy and cohesion of these sand samples were found to correlate with EPS and magnesium salt production.

RÉSUMÉ: Données d'enquête du sous-sol géotechniques d'un site sous-tendu par les résidus de sable cimenté généré à partir d'une extraction de l'or et des observations microbiologiques ont fourni des preuves circonstancielles que la cimentation a été au moins partiellement biogénique. A partir des échantillons de sable cimenté une souche de Bacillus foraminis (Banque Gene numéro d'accession HQ436339) a été surtout remarquable pour sa capacité à produire des substances exo-polymères (EPS) et des sels de magnésium de nature à base de ciment. Une souche de Bacillus megaterium (Banque Gene numéro d'accession HM371417) isolés à partir d'un dépôt de limon de rivière a également été noté pour son activité cimentation similaire. Laboratoire drainé essais triaxiaux sur l'eau des échantillons de sable pluviated hébergeant les bactéries ont également montré des preuves de cimentation en particulier lorsque les échantillons étaient desserrés. Augmentation de dilatance et la cohésion de ces échantillons de sable ont été trouvés en corrélation avec EPS et la production de sel de magnésium. 1 INTRODUCTION Microbes can precipitate a variety of cementitious materials, e.g., calcite (non-ureolytic or ureolytic), exo-polymeric substances (EPS) and mineral salts such as struvite. Amongst these bioprocesses precipitation of calcite through urease catalysis using Sporosarcina pasteurii has been studied by several research groups interested in developing sustainable ground improvement technologies (DeJong et al., 2006; Whiffin et al., 2007; Van-Paassen et al., 2010). Microbially produced EPS also can be used for sand stabilization. EPSs are high-molecular-weight polymers comprised mainly of sugar residues secreted by a microorganism outside of their cell wall, lipid molecules, protein molecules and dead cells (Fleming et al., 2007). The cementitious behavior of EPS is due to the mixture of exocellular polysaccharides present within the biofilm. Because of their viscous nature (Asthaputre and Shah, 1995) and surface tension (Satpute et al., 2010), EPS also acts as a cementitious material aggregating cells and soil particles particularly in harsh external environments (Godinho and Saroj, 2009). Although the efficacy of biogenic EPS in soil stabilization has also received some attention, the results lead to ambiguous inference about the effectiveness of EPS. Banagan et al. (2010), for instance, report increased cohesion and liquefaction resistance of sand treated with a strain of pathogenic, EPS-producing and non soil-residing bacteria, Flavobacterium johnsoniae. In contrast, no systematic increase in shear strength and liquefaction resistance was observed for sand samples treated with a strain of ultra-microbacteria developed from soil-residing and EPS-producing Klebsiella oxitaca (Perkins et al., 2000). It therefore appears a systematic understanding is yet to develop on the applicability of EPS driven bio cementation in soil stabilization. The inactive dune deposits of sand tailings at a placer east coast (Figure 1) were characterized with unusually high SPT blow counts over the top 4 to 5 m (BH2, Figure 2). Similar elevated level or penetration resistance was not observed underneath active dunes and in the low lying areas in between the +++

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