<p><p><figure id='attachment_2531' style='max-width:1183px' class='caption aligncenter'><img class="wp-image-2531 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Diagram of various bio-treatments in levee system including bio-reinforcement preventing erosion, bio-mineralization stabilizing a slope, bio-film preventing groundwater seepage, bio-mineralization immobilizing carbon, and bio-dechlorination of contaminants." width="1183" height="564" /><figcaption class='caption-text'> Overview of Bio-Treatment Soil Improvement Dystems (Jason DeJong, personal communication, 2012)</figcaption></figure><h2>Basic Function:</h2>Biological processes have the potential to change the physical and mechanical properties of earth materials through precipitation in such a way that in-situ weak and unstable soils can be made sufficiently strong and durable, and also improve the sustainability of geotechnical engineering practices<br><h2>Advantages:<em> </em></h2><ul> <li>Is a true <em>in situ</em> process with low invasive nature</li> <li>Low investment and maintenance costs</li> <li>Process is ecological and environmentally friendly</li> <li>Process doesn’t interfere with hydraulic properties of the treated soil</li> <li>Great microbial diversity and fast reproduction rate of microorganisms are responsible for the ubiquitous presence and high efficiency in the geoenvironment</li></ul><h2>General Description:</h2>Bio-treatment involves a chemical reaction network that is managed and controlled within soil through biological activity and whose byproducts alter the engineering properties of soil. Bacteria produce extracellular polymeric material, which tends to bind soil particles together like “biological glue”, whereas the fungal colonies produce microscopic, hair-like hyphae, which at small scale have an effect similar to plant roots. Microbial activity can directly or indirectly affect the physical properties of soils on a permanent or temporary basis. To date experiments involving biological processes for soil strengthening have been largely confined to laboratory studies.<br><h2>Geologic Applicability:</h2>Both cohesive and cohesionless soils can be improved with bio-treatment<br><h2>Construction Methods:</h2>Bio-treatment is an emerging technology. Engineered microorganisms that produce polymeric materials or cause precipitation of inorganic cementing material or “growing” foundations using biological processes in a manner similar to root growth. Will need to be injected into the ground. Methods for accomplishing this have not yet been developed. Experiments to date involving biological processes for soil strengthening have been largely confined to laboratory studies of the precipitation of carbonate as a cementation material in sands and as a crack filler. Much more research is needed to fully evaluate the full potential for soil stabilization and improvement to levels necessary for their use as a pavement subgrade material, the potential uniformity of the treatment zone in field, and the longevity of the treated soil properties.<br><h2>Additional Information:</h2>Many bio-treatments are in very early developmental stages, and it is unclear whether these can be advanced sufficiently to stabilize in-situ soils and subgrades in practice. The key obstacles to more widespread use of the technology are lack of knowledge about the mechanisms, means for implementation in the field, quantification of results, and conditions favoring its application. Applied research would be necessary to advance technologies that have been developed and basic applied, research is regarded for those in early stage of development.<br><h2>SHRP2 Applications:</h2><ul> <li>Roadway and embankment widening</li> <li>Stabilization of pavement working platforms</li></ul><h2>Example Successful Applications:</h2><ul> <li>Mining Road, Casablanca area, Morocco</li> <li>Heavy Farm Road, Bangkok area, Thailand</li></ul><h2>Complementary Technologies:</h2>Mechanical or chemical stabilization.<br><h2>Alternate Technologies:</h2>Geogrid reinforcement, Geocell reinforcement, thicker unreinforced base/subbase, lime or cement-stabilized subgrade, over-excavation and replacement of subgrade.<br><h2>Potential Disadvantages:</h2><ul> <li>The microbial process is more complex than the chemical one because microbial activity depends on many environmental factors such as temperature, pH, concentrations of donors and acceptors of electrons, concentrations and diffusion rates of nutrients and metabolites.</li> <li>Labor intensive at present</li> <li>Potentially invasive sampling required</li> <li>Pore size limitations reduce effectiveness</li></ul><h2>Key References for this technology:</h2>DeJong J.T., Mortensen B.M., Martinez B.C. and Nelson D.C. (2010). “Bio-mediated soil improvement”. <em>Ecological Engineering</em>, Volume 36, Issue 2, pages 197-210.</p><p>Mitchell J.K. and Santamarina J.C.(2005). “Biological Considerations in Geotechnical Engineering”. <em>Journal of Geotechnical and Geoenvironmental Engineering, </em>131(19): 1222-1233.</p><p>Ivanov V. and Chu J. (2008). ‘Application of microorganisms to geotechnical engineering for bioclogging and biocementation of soil in situ”. <em>Rev Environ Sci Biotechnol, </em>7:139–153.</p></p>