Quantifying the Erodibility and Geotechnical Strength of Cohesive Alluvial Soils Following Streambank Reconstruction: Fid-Bau Portal

Quantifying the Erodibility and Geotechnical Strength of Cohesive Alluvial Soils Following Streambank Reconstruction

Lovern, S. B. / Fox, G. A. / Miller, R. B.

Post-construction data following streambank restoration and stabilization projects are currently lacking relative to the resistance of cohesive streambanks to geotechnical failure and fluvial erosion. This research sought to quantify differences in erodibility and geotechnical properties of natural and restored banks after construction. The streambank environments varied with respect to the presence or type of construction and resulting bank slopes. Streambank conditions included modified fill bank plots, modified cut bank plots, and nonmodified control bank plots. Geotechnical resistance to failure was quantified using the Iowa borehole shear test (BST) to measure the in-situ drained shear strength of soils. Fluvial resistance to erosion was measured using an in-situ "mini" jet erosion test ("mini" JET) to estimate the erodibility coefficient and critical shear stress. Bulk densities were affected by construction activities with a general trend toward higher bulk densities with greater construction modification. Geotechnical strength, in terms of the soil's effective cohesion for the modified fill bank plots, differed between the modified cut bank plots and the nonmodified control plots but additional samples are needed for statistical relevance. Surprisingly, fluvial resistance to erosion may not be influenced by streambank modification based on "mini" JETs conducted to date. Variability in fluvial resistance parameters within each treatment was as large as differences between treatments. These modifications to the streambank fluvial and geotechnical resistance properties should be considered when modeling the impact of stabilization practices on streambanks.