Measuring Erodibility of Embankment Soils Containing Gravel
Project 8442 (Physical Hydraulic Modeling of Canal Breaches) studied breach development processes in canal embankments and showed that erodibility of the embankment material was critically important for accurate prediction of rates of erosion, time for breach development, and potential breach outflow rates. Submerged jet erosion tests were used to quantify erodibility of test embankment materials, but there are difficulties with applying this test in the field when embankments are constructed from soils containing significant amounts of gravel. If gravel comprises less than 40-50 percent of the gradation, erodibility is likely to be controlled by the fine-grained fraction of the material, but the presence of gravel interferes with the ability to perform the jet test. Thus, materials must be brought into the lab and screened to allow testing of the fine-grained fraction. Soils containing gravel are commonly screened at the #4 sieve for compaction testing or the #40 sieve for evaluation of Atterberg limits (plasticity). Since erodibility is known to be strongly associated with both compaction and plasticity, the appropriate division for screening materials for jet testing is uncertain. This research would attempt to answer the question of how to screen materials prior to jet erodibility testing and how to interpret results from tests of screened materials.
Need and Benefit
The Bureau of Reclamation (Reclamation) has experienced at least three notable canal embankment failures since 2006 (A-Line Canal, Hermiston ID 2006; Truckee Canal, Fernley NV 2008; Franklin Canal, El Paso TX 2011). Reclamation is now actively working to assess issues related to canals in urban areas, and the ability to measure the erodibility of embankment soils is crucial to evaluating the risks associated with potential canal breaches. Successful measurements of soil erodibility will allow Reclamation to identify canal reaches that pose the greatest hazard to downstream populations and property, which will allow prioritization of hazard mitigation efforts.
This research also has potential benefits in other application areas. For instance, the Seismotectonics & Geophysics Group in the Technical Service Center (TSC) is currently using the submerged jet test to determine the erodibility of soils in alluvial flood plains, where gravel can be encountered.
Bureau of Reclamation Review
The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.
Measuring Erodibility of Gravelly Fine- Grained Soils (final, PDF,
By Tony Wahl
Report completed on September 18, 2014
procedures overcome difficulties with performing the test on soils containing significant quantities of gravel or coarse sand.