Cracked Embankment Erosion Research
Project ID: 8284
Principal Investigator: Peter Irey
Research Topic: Condition Assessment
Funded Fiscal Years: 2015
Keywords: erosion, hole erosion test, probability of erosion initiation, cracked embankment, hydraulic shear stress.
Reclamation owns and operates over 250 urbanized canals that sum to over 1000 miles of canal embankments. Several canal failures and numerous incidents occur each year. Canal failures in urbanized areas have the potential to result in loss of life, significant property damage, environmental impacts, loss of project benefits, litigation, and decrease Reclamation's credibility. The purpose of this testing is to better understand the potential for internal erosion and embankment failure due to cracking either by using deterministic or risk-based procedures. Cracking can lead to sudden failures because the cracks, and water flowing through them, may not be detected immediately, and an embankment that is susceptible to internal erosion could quickly fail and release the reservoir. Risk-based procedures are increasingly being adopted for canal and levee embankments. A significant amount of research has been completed by the University of New South Wales (UNSW) on developing a repeatable experiment to determine the hydraulic shear stress required to initiate erosion rate and the erosion rates of various soils. From the UNSW research the Hole Erosion Test (HET) was created to determine the initial hydraulic shear stress required to initiate erosion. Several tests were performed on a variety of typical embankment materials. From this research Reclamation, United States Army Corps (USACE), UNSW, and URS Corporation created tables for designers to use when evaluating the potential for internal erosion to initiate through a cracked embankment. However, there is concern, from both the USACE and Reclamation, that the probability of erosion initiating within a cracked embankment is not accurately predicted by the HET. This proposed research will determine if results from the HET should be used in the risk-based evaluation process USACE has adopted for much of their dam and levee inventory and Reclamation has adopted for their dam embankments and used for evaluating canals.
Need and Benefit
Cracking of embankments is a significant canal safety concern and can occur due to desiccation, deformation from earthquakes, differential settlement, slope instability, poor compaction around a turnout structure, or a host of other causes. Currently, guidance on initiation of erosion through cracked embankment material comes from research completed by Chi Fai Wan and Robin Fell using the Hole Erosion Test (HET) and Slot Erosion Test (SET). This research was used to develop a table comparing likelihood of erosion initiation and hydraulic shear stress (i.e. gradient along a crack) according to material type. This table is referred to often in risk analyses, but it has never been an independent evaluation or verification of the initiation information.
The new model will help determine erosion rates when water flows through a realistic crack (similar to the upper reaches of a canal embankment). This research will help designers (USACE, Reclamation, or private industry) model internal erosion failure modes, perform risk assessments, and design better remediation/new structures. This research will provide examples of particular soil types in order to see how flaws, or cracks, in the embankment can erode under different conditions.
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