Improvement of the Mechanical Properties of Cohesionless Soil by Microbially-Induced Mineral Precipitation

This technique would have broad applications in the area of Soil Improvement for Civil Infrastructure Construction purposes, including earthquake hazard mitigation, foundation construction, seepage control for a variety of purposes, and stabilizing tunnels and excavations. Earthquake hazard mitigation is perhaps the most immediate application. Liquefaction of loose, saturated sand is a major source of earthquake damage. In some recent earthquakes, it has been the major source of damage, responsible for tens of millions of dollars of direct damage and even more indirect damage (due to the social and economic consequences of the direct damage). Numerous bridges and roadways and port and harbor structures, thousands of commercial buildings, and tens of thousands of residential structures are at risk from earthquake-induced liquefaction in the western United States and other parts of the world. Conventional methods to mitigate liquefaction hazards are expensive and / or cause ground movements that are damaging to adjacent structures, making liquefaction hazard mitigation prohibitive for existing structures and for sites in a dense urban setting. Since changes to the building code in 2000 that mandate evaluation of liquefaction potential in seismic zones, many homeowners in some southern California communities have been unable to get permits for renovations and additions to their homes. This technique offers the potential for a cost-effective non-disruptive means of mitigating the potential for earthquake-induced liquefaction in these and other situations. Other potential applications of this technique include improving the bearing capacity of shallow foundations on loose sand, thereby allowing the use of cost-effective shallow foundations (versus deep foundations) for taller buildings and heavier foundation loads, enhancing the seismic stability of dams and embankments, stabilizing running and flowing sands in tunnel headings and braced and open excavations, reducing earth pressures on temporary and permanent retaining walls and on tunnel linings, and improving the lateral capacity of driven piles and drilled piers. The method may even be useful for reducing under-seepage of levees and cut-off walls, a common source of failure of levees (including those in New Orleans).