Liquefaction Mitigation
Over the past forty years, the Bay Area has been preparing for the next “big one,” and, like much of the Bay Area, Oakland is experiencing an influx of new businesses, industries, and homes that are revitalizing many of the older, unused buildings and their communities. As with any old building, they were built using old building codes and must be rehabilitated to meet modern earthquake standards. One aspect of those standards is to ensure its resiliency to earthquakes and preparedness for a phenomenon called liquefaction.
Liquefaction is a process where liquefiable soils behave similarly to a liquid when exposed to intense vibration. As you can imagine, liquefaction can cause buildings serious stress, such as sinking, moving, or the foundation splitting. Stabilizing liquefiable soils cost-effectively has become a trending conversation within the Earthquake Engineering community and EagleLIFT has developed a cost-effective solution for doing just that.
When the old Z Hotel was being converted into an apartment complex, the developers went through stringent engineering analysis to ensure that it was up to code. A survey, performed by Geo-Engineering Solutions, Inc., found that liquefiable soil was encountered just below the existing footings, and could not be relied on to safely support the building in case of a major earthquake.
The owner started seeking solutions for stabilizing the liquefiable soils. After a webinar with CALGEO, where EagleLIFT presented its research with the University of California San Diego (UCSD) showing the effectiveness of geotechnical resins in mitigating liquefaction, Geo-Engineering Solutions determined the application was a good fit.
Solutions and Results
The solution, called Deep Stratum Injection, is a process where an expandable light-weight geotechnical resin is injected on a gridded pattern at multiple depths to achieve soil consolidation and stabilization. Based on shake table tests performed by UCSD, the process has been proven to result in soil densification, cementation, lateral confinement, and reduce liquefaction induced settlement by 97%. The beautiful part is the cost-effective process requires no excavation, improves soil bearing capacity, and requires minimal interruption to project schedules.
Once onsite, EagleLIFT prepared injection locations around the perimeter and interior footers and support columns by driving rods down to the 8’ and 12’ target depths at every 3’. It injected on both sides of the footings, both interior and exterior. The goal was to ensure resin permeation around and below the footers to stabilize the liquefiable soils. Once injected, the geotechnical resins permeate the soils in liquid form and then expand up to 25 times its initial liquid volume. The expansion consolidates the base soils, underpins the treatment area, and displaces any present water, and improves soil bearing capacity.
“Even at 8’ injection depths, we were seeing the resin travel all the way to the surface. This means that in addition to the liquefaction mitigation, the Deep Stratum Injection was also resulting in filling present voids and improving soil conditions all the way to the foundation itself,” stated Cliff Frazao, President of EagleLIFT.
The project took place over 3 weeks and with zero interruption to the multitude of renovation and demolition contractors onsite, which is a vast improvement over the expected 2–3-month installation time of the alternative earthquake retrofit solutions. Results were also confirmed via pre and post Cone Penetration Testing (CPT). EagleLIFT stabilized the entire perimeter and interior column supports of the building during this period, placing the foundation on solid ground and a stabilized base.
