A fluidized bed technique for estimating soil critical shear stress

Authors: NOUWAKPO, S - Purdue University; Huang, Chi Hua

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2012
Publication Date: 7/1/2012
Citation: Nouwakpo, S., Huang, C. 2012. A fluidized bed technique for estimating soil critical shear stress. Soil Science Society of America Journal. 76:1192-1196.

Interpretive Summary: Soil erodibility is a term that describes the soil’s resistance against erosive forces before the soil can be detached. A common way of measuring soil erodibility is to apply different levels of erosive forces and empirically fit the measured erosion data through a proposed erosion equation to come up with the value of soil erodibility. In our recent research, we found that many erodibility measurements are affected by field conditions prevailing during the measurements, and therefore the resulting soil erodibility values are not inherent to the soil. We developed a fluidized bed technique that can measure intrinsic soil cohesion and this technique on four soils with varying soil properties. Our results showed that the fluidized bed measured soil cohesion correlated well with empirically measured critical shear stress from a field experiment. This method is a simple alternative to traditional rainfall or runoff experiments with the advantage of being independent of external factors, hence is a true measure of soil cohesion.

Technical Abstract: Soil erosion models, depending on how they are formulated, always have erodibilitiy parameters in the erosion equations. For a process-based model like the Water Erosion Prediction Project (WEPP) model, the erodibility parameters include rill and interrill erodibility and critical shear stress. These erodibility parameters are commonly determined from rainfall and runoff experiments. Recent developments in soil erosion research suggest that these experimentally determined parameters are affected by field conditions prevailing during the measurement, and therefore are not inherent to the soil. The quest for fast and accurate alternatives to rainfall and runoff experiments for estimating soil erodibility parameters is an active research area. In this paper, the fluidized bed technique for intrinsic soil cohesion measurement was improved and tested on four soils with varying intrinsic soil properties, along with two low-cohesion materials, sand and glass beads. A strong correlation (R2 = 0.82) was found between cohesion per unit length C0 and published critical shear stress, when the C0 values were multiplied by a sub-millimeter dimension equivalent to a hypothetical layer removed at the onset of erosion, the range of stress yielded overlapped that of the published critical shear stress. This method is a simple alternative to rainfall / runoff experiment with the added advantage of being independent of extrinsic factors.