Guidance on Applied Pressure Heads for Quantifying Cohesive Soil Erodibility with a Jet Erosion Test (JET)

Abstract

Highlights Jet erosion test (JET) is a commonly used instrument for quantifying soil erodibility. Uncertainty remains on an appropriate applied pressure head to ensure high-quality JET data. Numerical analysis was used to derive minimum and maximum heads for four soil classifications. Ideal applied pressure heads depend on soil erodibility parameters and user-selected JET characteristics. Abstract. The Jet Erosion Test (JET) is one of the few instruments available for measuring cohesive soil erodibility in situ, but uncertainty remains regarding an appropriate initial applied pressure head for the test. Users typically iterate on an initial applied pressure head setting when testing soil. This iteration is necessary to ensure a reasonable erosion rate and the total amount of scour while imposing applied shear stresses that match the expected application range when using JET-derived erodibility parameters. This research used a numerical analysis of simulated JETs to determine both minimum and maximum applied pressure heads, ensuring a logistically appropriate estimation of soil erodibility parameters. First, the minimum head was set to generate at least 25 mm of scour, established based on data from previous in situ JETs. Second, the maximum applied pressure head was set to ensure that no excessively large initial applied shear stress impacted the estimation of erodibility parameters from a linear regression on erosion rates. Analyses were conducted for four selected soil erodibility classes: highly erodible, more erodible, erodible, and moderately resistant soils. Curves showing the ideal applied pressure ranges were generated for initial time intervals of scour depth measurements of 60, 90, 120, 180, 240, and 360 s and dimensionless initial nozzle heights of 1.00, 1.25, and 1.50. The appropriate range in the applied pressure head depended not only on the soil erodibility classes but also on the initial time interval for scour depth measurements, total test duration, and dimensionless initial nozzle height above the soil surface. Users should ensure that a minimum applied pressure head is exceeded for resistant soils. Maximum applied pressure heads should be considered for erodible, more erodible, and highly erodible soils, dependent on the initial time interval for scour depth measurements and dimensionless initial nozzle heights. Wider ranges of acceptable applied pressure heads were observed with smaller initial time intervals. The procedure presented in this research can be readily adapted by JET users to reflect specific testing conditions (e.g., different data collection intervals and test durations) for ensuring the a priori use of effective pressure head settings. Keywords: Cohesive soils, Erodibility, Jet erosion test, Pressure head, Soil erodibility.

Streambank Erosion Phenomena and Understanding: Current Research and Future Directions

“…However, questions remain with regard to standard operating practices among JET users, including selecting a pressure head (h). Fox et al (2022) performed numerical analyses and documented a procedure to provide guidance on appropriate ranges of h values for predetermined soil types and JET settings. Pre-determined soil types were selected based on the classification system proposed by Hanson and Simon (2001) using average values of τ c and k d for highly erodible, more erodible, erodible, and moderately resistant soils.…”

“…Lastly, both the upper and lower limits of the range of appropriate h values were found to increase as the initial jet orifice height increased, with a much greater impact on the upper limit of such a range. Fox et al (2022) recommended that JET users should select h values near the middle of the numerically derived appropriate range to account for assumptions and simplifications in the analyses (e.g., soil homogeneity). Overall, the work of Fox et al (2022) contributes towards the establishment of more consistent standard operating practices for the JET.…”

“…Fox et al (2022) recommended that JET users should select h values near the middle of the numerically derived appropriate range to account for assumptions and simplifications in the analyses (e.g., soil homogeneity). Overall, the work of Fox et al (2022) contributes towards the establishment of more consistent standard operating practices for the JET.…”

“…Relevant examples of available process-based models include FLU-VIAL-12 (Chang, 1998), CONCEPTS (Langendoen et al, 2001), SWAT (Arnold et al, 1998), and the coupled HEC-RAS 1D with BSTEM (CEIWR-HEC, 2015). Studies from this special collection contributed to advancing data collection methods (e.g., Knox and Mittelstet, 2021;Fox et al, 2022) and characterizing the variability of site-specific parameters (e.g., Wilson et al, 2022). However, previous studies that have assessed streambank erosion simulation typically find that process-based models have difficulty capturing the complexity of erosion processes (Myers et al, 2021).…”