Liquefaction of Partially Saturated Sands

Abstract:

Liquefaction-induced damages to our built environment can be catastrophic. During the past four decades, intensive efforts have been made to understand the mechanism of liquefaction, and to develop procedures for analyzing the liquefaction potential at a site during a given seismic event. While research on liquefaction continues, the geotechnical engineering practice has developed various techniques for site improvement that can mitigate the potential effects of liquefaction. Existing mitigation measures are expensive and often are applicable only for a new project. Mitigating the liquefaction-induced damages to an existing structure in an urban community remains to be a major challenge.
The primary objective of the research is to investigate the scientific and technical feasibility of using entrapped air in liquefaction susceptible sands to mitigate potential earthquake-induced damages. Results from an earlier NSF SGER grant received by the PI and Co-PI demonstrated that small amounts of air introduced into the voids of an otherwise fully saturated sand can significantly increase resistance to liquefaction. Furthermore, monitoring of the degree of saturation of a sand column with entrapped air showed that the degree of saturation of the sample changed little with time, thus indicating the potential long-term entrapment of air bubbles in liquefaction susceptible sand. Hence, potentially, the generation or introduction of air in a sand deposit at a new or an existing site can be a cost-effective site improvement and earthquake hazard mitigation measure.

Based on the NSF SGER results, a number of specific objectives have been formulated for the current research that include:

1. Developing a unique experimental set-up that will integrate advanced sensing technologies including radar and bender elements with generation of gases using electrolysis, with a shaking table facility to permit cyclic and earthquake testing of saturated and air-entrapped sands.
2. Developing a fundamental understanding of the behavior of sand-water-gas mixtures subjected to seismic excitations.
3. Demonstrating that entrapped air can significantly reduce the liquefaction potential of sands, and holds promise as a cost-effective and readily applicable liquefaction mitigation measure.
4. Identifying the important areas of field research that must be conducted to advance the proposed mitigation measure for adoption in engineering practice.

This research will significantly expand our understanding of the seismic response of partially saturated sands and lead to potential development of a cost-effective measure for liquefaction mitigation.

The research will also have a broader impact on improving our ability to reduce the expected losses to a community from an earthquake by cost-effectively mitigating existing sites that otherwise would remain vulnerable. The research will create a mutually beneficial link between the geotechnical earthquake engineering field and the geo-environmental field where air injection is used for site remediation. The proposed collaboration with the Center for Subsurface Sensing and Imaging Systems (an NSF ERC at Northeastern University) will create a unique opportunity for civil engineering faculty and students to learn and transfer advanced technologies into the civil engineering profession. The shaking table experiments will support our educational activities involving graduate students as well as undergraduate students participating in the cooperative program. The PI and Co-PI will continue utilizing their research activities and facility in their current outreach activities especially targeted to minorities and women, as well as heightening public awareness of earthquake hazard.
Previous research “Air entrapment for liquefaction mitigation” was funded by NSF through the small grant for explatory research program (SGER) under award No CMS-0234365. The current research “Liquefaction mitigation using entrapped air” is also supported by NSF under award No CMS-0509894. The support of NSF is greatly appreciated.

 CO PI: Prof. Akram Alshawabkeh

 Ph. D. Student
Fritz Nababan

 Former M.S. Graduate
A. Emre Ortakci

Undergraduate Student
Kaitlin Vacca
(Funded by NSF-REU)

Lab Manager
David Whelpley

Photos and Related Documents;

Relevant Publications:

• Yegian, M. K., Eseller-Bayat, E., Alshawabkeh, A., Ali, S.(2007) . “Induced Partial Saturation for Liquefaction Mitigation: Experimental Investigation.” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 133 (4).
• Yegian, M., Eseller, E., Alshawabkeh, A.(2006). “Preparation and Cyclic Testing of Partially Saturated Sands.” Proceedings of the Fourth International Conference on Unsaturated Soils, GSP 147, April 2-6, 2006, Carefree, Arizona