Seismic Deformation Potential of Peaty Organic Soils Underlying Delta Levees

Start/End: September, 2013 to August, 2015

The Delta Science Fellow leading this project will study the post-earthquake volume change (settlement) of peaty soils. Peaty soils are associated with wetlands and contain high amounts of partially decomposed plant debris. These soils underlie many of the region’s earthen levees and their deformation potential is an important factor in seismic hazard assessment. Though the engineering community is well aware of this mechanism’s importance, most previous studies have focused on understanding the post-seismic response of “traditional” soils such as clay and sand. This project will fill a much needed gap in the ability to evaluate levee stability following the next “big one” by looking more closely at peaty soil dynamics. In the project’s first year, the fellow will conduct laboratory tests on peaty soil samples gathered from Sherman Island, the site of a field-scale model levee test in 2011 and 2012, to measure their seismic deformation potential and cyclic deformation potential. The fellow will utilize a digitally controlled simple shear device, recently modified to perform cyclic shearing under realistic field conditions during and after an earthquake. These modifications will greatly enable relevant soil testing. Findings will further refine and improve seismic hazard assessment within the geologic context of the delta.

Research mentor: Scott Brandenberg, UCLA

Community mentor: Curtis Schmutte, professional engineer and consultant