Validation Of An Injection Protocol For Micp And Preliminary Results Of Undrained Triaxial Tests

Benoit St-Onge

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: PROBLEMATIC SOILS - I Soft, Collapsible, Residual Soils

ABSTRACT: During the last decade, biocalcification has been recognized as a promising method of soil improvement. Microbial Induced Carbonate Precipitation (MICP) increases both stiffness and shear strength of granular soil. This article presents the elaboration and validation of an injection protocol for MICP treatment and CIU tests conducted on three average levels of cementation: 10.5 %, 12.5 % and 14.5 %. By injecting the bacteria during their exponential growth phase and using a cementing liquid ratio of 7:4:4, a high efficiency of precipitation has been observed. An average reduction of 30 % of pore volume was measured for every specimen. During the shearing, all specimens showed two phases, elastic and plastic. The elastic phase can be characterized by high stiffness and contracting behaviour. During this phase, the loading path has a slope of 3:1 and the stress ratio shows a clear peak, which increases with higher calcite content. The top of all specimens broke into several pieces during shearing and their base remains whole with a slightly conical shape. During the plastic phase, specimens showed a clear dilatant behaviour. The residual strength is higher by third in comparison to untreated specimens. Finally, the residual stress ratio tends to the same value of untreated specimens for all levels of cementation.

RÉSUMÉ: Le traitement des sols granulaires par MICP (Microbially Induced Calcite Precipitation) est considéré comme un procédé novateur et écologique face aux méthodes de cimentation actuelles. Ce nouveau procédé de Sporosarcina pasteurii dans un milieu urée. S. pasteurii permet une augmentation locale du pH, ce qui conduit à une formation de été conduits et analysés. Les résultats permettent ainsi de caractériser les phases élastiques et plastiques des sols traités. Lors de la phase élastique, les échantillons traités ont un comportement contractant et fortement rigide. essentiellement conditionnée par la cohésion à une résistance par friction. Le sol devient alors fortement dilatant et il subit un écrouissage positif.

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