A study on the triaxial shear behavior and microstructure of biologically treated sand specimens
Date
2010
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Publisher
University of Delaware
Abstract
The use of microbial calcite cementation for ground improvement presents a relatively new ground improvement option for geotechnical engineers, one that particularly has the potential to revolutionize the way that we improve soils to prevent liquefaction-induced damage. This technique uses non-pathogenic organisms which are found naturally in a soil environment to cement sand particles together at their particle-to-particle contacts. There is significant potential for a reduction in environmental concerns on various types of projects; in the long-term, this technique may also prove to be an extremely sustainable form of ground improvement. Consequently, the goal of the research described herein is to enhance the state-of-theart with respect to our understanding of controlling biological cementation processes in soil. This thesis describes the results from an experimental study that was conducted to examine the factors that influence microbial calcite cementation in sands. Bio-treatment of the sand was performed using a commonly encountered ureaproducing soil microorganism called Sporosarcina Pasteurii (ATCC-6453). Ottowa sand was selected as the soil for this initial study, as widespread information about this soil is available in the technical literature, and it has been used by a variety of other researchers studying similar phenomena. In this study, triaxial test specimens were prepared using dry pluviation and moist tamping, which achieves a relatively loose initial void ratio that is more prone to collapse during soil shear. Microorganisms that are suspended in solution are introduced to the soil, and over time the microorganisms are supplied with necessary nutrients via cycling with a peristaltic pump. After biotreatment, the specimens were back pressure saturated, isotropically consolidated, and sheared under undrained conditions. The shear behavior of bio-treated specimens is presented and compared to untreated specimens that have been prepared in a similar fashion. Additional scanning electron microscope (SEM) testing was also performed to examine the soil microstructure over a range of specimen curing periods to assess the nature of any cementitious bonds that may have formed.