Overbank Soil Erosion Model Validity for Plastic Riverbed Soils




Alam, Muhammad Tasnim

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Critical shear stress is the hydraulic stress at which soil erosion initiates. An estimate of critical shear stress is needed to predict bridge scour; however, there is no unifying equation for predicting the critical shear stress of plastic soils based on soil properties. Therefore, the current design approach by most State Departments of Transportation is to use an in-house empirical equation, an overly conservative minimum critical shear stress based on an assumed soil property, or by direct measurement. For example, the Kansas Department of Transportation (KDOT) developed an empirical critical shear stress model in 2021 by analyzing 13 soil parameters based on 70 soil samples collected from overbanks. Critical shear stress is a function of the soil's physical, chemical, and biological properties, and these properties are dynamically linked. For this research, ten riverbeds with soils with plasticity were identified and sampled from Kansas. One sample from each site was tested in an erosion function apparatus to determine the critical shear stress. An additional sample was collected and used for measuring the same 13 soil parameters used to develop the previous KDOT model, as well as organic content. When the new data from the ten riverbed samples were combined with the original KDOT model data, the power of the KDOT model was found satisfactory. Furthermore, this study established a new model boundary limit, which improved the power of the overall KDOT model. Therefore, it is recommended that the existing overbank model be used for all riverbed sediments to predict critical shear stress and, ultimately, scour for bridge design in Kansas.



erosion, riverbed, Engineering


Alam, M. T. (2023). Overbank soil erosion model validity for plastic riverbed soils (Unpublished thesis). Texas State University, San Marcos, Texas.


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