Saturated loose sand deposits subjected to seismic loads are susceptible to liquefaction, a phenomenon in which there is a rapid loss of strength of the soil caused by a sudden increase in porewater pressure. Structures built on these soils may suffer severe deformations or failure during liquefaction due to excessive settlement caused by the loss of support from the foundation soils. At undeveloped sites, proven methods of soil improvement - e.g., dynamic compaction and vibro-compaction - can reduce the likelihood of liquefaction. However, at locations where structures already exist or exist nearby, these methods are either impossible to implement or are impractical as they may cause damage to these structures.
The aim of this research is to determine whether the addition of bacteria, either simple adhering bacteria or biofilm formers, increases the strength and stability of liquefiable soils. It is hypothesized that the microbes will provide some cohesion/cementation between the particles, thereby increasing their resistance to liquefaction. Very little research has been done on the use of microbes to improve the strength properties of soil. Loose sands will be inoculated in separate tests with two organisms, Cytophaga U67 (a biofilm former) and a mutant Cytophaga U67 (a non-biofilm former). Cytophaga are naturally found in a saturated, low-nutrient environment. The attachment of the microbe to the solids is expected to create cohesion/cementation between particles, thereby reducing the susceptibility of the soil deposit to loss of strength during rapid increases in porewater pressure. Cohesive strength gains in the sand will be measured using vane shear tests and/or unconfined compression tests.
This project will provide information on the potential use of microbes in the remediation of liquefiable soils. It will also initiate the first collaborative research project between the civil engineering and biology departments at Lafayette College. The results will be disseminated to the wider scientific community through poster presentations and published research papers.
