NEESR II: Evaluation of Seismic Levee Deformation Potential by Destructive Cyclic Field Testing
Sponsored through the George E. Brown Network for Earthquake Engineering Simulation
August 29th, 2011 The field test was completed over the span of approximately one week leading up to August 29, 2011. The MK-15 shaker imposed dramatic dynamic loads on the embankment as it visibly rocked and translated, and Rayleigh and Love waves propagated through the soft peat soil. Despite the dramatic ground surface motion induced by shaking, little demand was exerted on the underlying peat soil. However, this is not necessarily evidence of good performance of a real levee because the groundwater table depth was approximately 2m at the time of shaking. The watertable is typically above the peat surface for levees that impound water. Saturated peat is much softer and weaker, and the unsaturated crust layer likely shielded the underlying saturated peat from the shaking energy. We are working on a plan to reshake the embankment during late Spring of 2012 when the watertable is shallower. We are currently in the process of uploading the experimental data to the NEES data repository.
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August 3rd, 2011 Construction of our test specimen began on July 27th, 2011 and finished on August 1st, 2011. A time-lapse video on the images page shows the construction sequence, which spanned four days. John Lemke from GeoDaq helped set up a data acquisition system to remotely record pore pressure and settlement during consolidation of the embankment. The data can be viewed at http://geodaq.com/servlet/login1 using username: ucla and password: geodaq. Doug Wahl, a UC Davis graduate student, helped us conduct a cone penetration test with shear wave velocity and pore pressure measurements using the nees@UCLA CPT rig. The peat thickness is approximately 11m at our site. We are processing the CPT data and will make it available in the NEES data repository soon.
June 15th, 2011 A team of five researchers from UCLA and Cal Poly performed a hand auger site investigation on Sherman Island at our site location. The upper 1.5m of peat above the water table was unsaturated and fairly strong, whereas the saturated peat below 1.5m was very soft. Vane shear measurements indicated that the peak undrained shear strength ranged from about 10 to 20 kPa in the saturated peat, with residual undrained strengths around half of the peak. The peat is so soft and weak that a 75mm (3") diameter hand auger could be monotonically pushed vertically through the peat through a distance of about 2m without turning the auger (Click to see video). We retrieved some 150mm (6") diameter undisturbed samples using the hand piston sampler from Prof. Riemer's lab at UC Berkeley, and will be testing the specimens this summer. Prof. Moss performed ReMi measurements to obtain a shear wave velocity profile, and we will follow this up with SCPT and SASW. Construction of the mound will begin next month. Vane shear and ReMi data will be uploaded to the repository in the coming weeks.
June 8th, 2011 Permit applications have been approved by the US Army Corps of Engineers and the Central Valley Regional Water Quality Control Board.
March 8th, 2011 Permit applications have been submitted to the US Army Corps of Engineers and the Central Valley Regional Water Quality Control Board are currently being evaluated, and we anticipate the permit applications will be approved in mid-April. This will allow us to begin the field testing on May 1st. Testing can only be performed from May to October since this is the active time for the Giant Garter Snake, and activities during their dormant time is prohibited.
August 10th, 2010: The Sherman Island Reclamation district agreed to the legal agreement formulated by DWR, UCLA and the Reclamation District. We are now awaiting approval from DWR, and completion of the CEQA process before beginning our testing. We hope to perform a geotechnical site investigation in September prior to constructing the test specimen at the site.
March 24th, 2010: We visited Sherman Island to make geophysical measurements of ambient vibrations and small-scale active sources to quantify tolerable levels of shaking during the embankment test. Based on the measured test data, we predict that the shaking levels at the levees (several hundred meters away from our test site on the interior of Sherman Island) will be smaller than the ambient vibrations. Hence our test program poses essentially no risk to the existing levees. Download Report
February 24th, 2010:We coordinated a meeting in Sacramento with key personnel from the California Department of Water Resources to discuss our plan to construct an embankment on peaty organic soil on the interior of an island for our testing. The site conditions at Blacklock were inappropriate for our test since soil at the site is clay rather than organic peat. Hence, our focus has shifted to constructing an embankment on the interior of an Island, with likely candidates being Sherman Island, Twitchell Island, Prospect Island, or Dutch Slough. We planned a follow-up meeting in about a month and a possible site visit.
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.