NEESR II

Principal Investigators

Student Researchers

Edward Thomas Reinert, UCLA, Ph.D. Student
Jay M. Merani, UCLA, B.S. Student
Nicky Galloway, UCLA, B.S. June 2009
Etheline Cimatu, Cal Poly, B.S. Student
Erland Mowinckel, Cal Poly, B.S. Student
Chenin Krieger, Cal Poly, B.S. Student
Taki Chrysovergis, Cal Poly, B.S. Student

Technical Advisory Panel

News and Results

March 26th, 2009: Hand augering was performed at the Blacklock site to determine the type of soil beneath the levees. The site stratigraphy consisted of medium plasticity unsaturated brown clay over high plasticity saturated soft Bay mud with organics. Some fibrous peat material was encountered within the clay matrix at a depth of about 8 feet below the levee crest. We are currently performing laboratory testing to assess whether the material at the site is appropriate for our project goals.

March 10th, 2009: A test site in the Suisun Marsh called Blacklock is currently being evaluated for our proposed testing. Scott Brandenberg met with a group of environmental scientists at the Environmental Coordination Advisory Team meeting on March 10th to present the project. A group visited the test site afterward. Blacklock is a promising site because levees have been deliberately breached as part of an environmental restoration project, and any damage caused by our testing is therefore acceptable.

Project Summary

The Sacramento-San Joaquin Delta levees are critical components of California’s water distribution system. The Delta supplies fresh water to over 22 million people in southern and central California as well as eastern portions of the bay area and directly supports California's $400 billion/year economy. The “islands” circumscribed by the network of levees are commonly 3 to 5 meters below sea level, and are protected by only about 1 to 1.5 meters of freeboard at high tide. A breach in a levee causes water from the channel to flow into the island thereby inundating farmland and wildlife habitat, and potentially locally reversing the direction of flow in the channels thereby drawing saline water into the Delta from the west. Simultaneous inundation of multiple islands, as predicted for a moderate earthquake in the region, could degrade water quality to the point that delivery would be halted. Delta risk assessment has recently gained a significantly enhanced priority in the wake of (1) an unexplained breach of Jones Tract in the Delta in 2004, causing over $100 million in losses and (2) the catastrophic levee failures in New Orleans following hurricane Katrina. The risk posed to the Delta by a strong earthquake is particularly onerous due to the potential for widespread simultaneous levee failures that would overwhelm a disaster recover system that often struggles to rapidly repair a single breached levee. The influence of earthquake shaking on the behavior of the levees is uncertain because the cyclic deformation potential of the underlying peaty organic soils not well understood, and there is an urgent need to investigate the behavior of these materials to clarify likely failure mechanisms.

This project will involve full-scale testing of an existing levee or earth embankment to investigate the in situ deformation potential of peaty organic foundation soils under realistic stresses and boundary conditions. The test conditions and instrumentation will be designed to measure the deformation mechanisms that can result in a critical loss of freeboard leading to a breach. Data of this sort is essential for the development of more rational (and meaningful) analysis tools for assessing the seismic vulnerability of levees. The field testing will be supplemented by an extensive laboratory testing program to further investigate key material response characteristics such as cyclic pore pressure generation and its effects on shear strength and post-cyclic reconsolidation. The improved knowledge of levee seismic vulnerability will be broadly applicable wherever these earth structures are founded on organic soils. The proposed testing activities are being closely coordinated with stakeholders and environmental regulators at potential test sites in the Delta and Suisun Marsh.