This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Liquefaction is an important cause of damage to civil infrastructures during earthquakes, and techniques that can minimize the liquefaction susceptibility of a site, with no ground disturbance can greatly impact geotechnical earthquake engineering practice. While many factors affect liquefaction resistance, laboratory and field observations demonstrate that the presence of plastic fines reduces liquefaction susceptibility. With this premise, previous work explored the use of bentonite-based thixotropic slurries for liquefaction mitigation. This work showed a ten fold or greater increase in cyclic resistance in presence of 3% bentonite in the sand pores; demonstrated that permeation of concentrated bentonite suspensions is possible through treatment of the clay with Na-pyrophosphate; and established that increased cyclic resistance is due to the rheology of the pore fluid formed in presence of bentonite.
This work has the potential to be further advanced through the use of laponite, a synthetic, inert, high purity, highly plastic nano-clay, ten times smaller in size than bentonite. As bentonite, laponite does not pose environmental concerns and benefits from the experience base in geotechnical engineering with clays. Early results suggest that, compared to bentonite, smaller percentages of laponite may be required to obtain the same improvement in cyclic resistance; and that, thanks to the delayed gel time, permeation is possible with no chemical treatment of the clay (although chemical modification may be necessary to extend the time window for permeation).
The research is based on an absolutely novel approach to soil improvement ? one that relies on engineering the pore fluid, rather than the soil skeleton. It also represents the first attempt in civil engineering to utilize laponite. Hence, the research has the potential to be transformational providing a next generation solution to the problem of soil improvement for liquefaction mitigation.
The overall scope of the research is to provide sound laboratory evidence of the effectiveness of this treatment and address key issues that will enable field testing. The specific objectives are to: quantify the improvement in cyclic resistance of sand following permeation with laponite; identify the mechanism(s) responsible for this behavior; determine the chemo-physical modification of the laponite that can optimize treatment; and explore means by which to verify the delivery of the laponite inside a sand matrix. These objectives will be pursued through an experimental program that will include: cyclic triaxial tests and resonant column tests on sand specimens permeated with laponite; permeation tests of laponite suspensions in laboratory prepared sand columns; characterization of the rheology and of the microstructure of the laponite pore fluid using advanced rheometrical techniques, and cryo-scanning electron microscopy; study of the surface chemistry of laponite through XRD, FTIR and thermal analyses; and bench-scale tests exploring changes in electrical, physical and chemical properties of the treated sand volume, that may be helpful to define field verification methods.
