Slope Erosion Testing – Identifying “Critical” Parameters

Various large-scale tests have been used to evaluate the performance of erosion control products. These tests typically are performed using boundary conditions that attempt to simulate field conditions. When evaluating slope erosion, for instance, a full-scale slope is generally eroded by rainfall impact and associated sheet runoff forces resulting from a simulated rainfall event. A certain combination of steepness, width and length of slope is selected, and the soil type, thickness, and compaction characteristics are chosen. The amount of soil loss from a protected condition is compared to that of the unprotected, or control, in order to establish product performance. In one such procedure, 6-inch thick compacted soil plots placed on a free draining tilt-table platform measuring 6 ft x 30 ft are used. Other tilting bed facilities use shorter and narrower plots, and different synthetic rainfalls. Still other facilities do the testing in-situ, out-of-doors, with even different dimensions, rainfall conditions, and soil type, preparation, and subgrade drainage. With this variety of approaches to testing, it is important to understand what mechanisms may or may not develop under modeled conditions and whether the associated mechanism depends on the type of erosion control product being tested and/or how it is installed. Specifically, some products armor the slope, encouraging efficient overland runoff, while other products encourage infiltration by absorbing the rainfall. Still other products seek to balance the two approaches to erosion control. Excess runoff may overwhelm surface “armoring”, while high infiltration rates may lead to slope instability, especially for steeper slopes.

This paper uses the Revised Universal Soil Loss Equation (RUSLE) to consider the various parameters associated with large-scale slope evaluations and identifies the “critical” parameters associated with slope stability. Practical test results are also presented to support the analytical findings and demonstrate that the ASTM 6459 protocol reasonably agrees with theoretical RUSLE-based calculations. It is not clear if other (tilting bed) protocols similarly correlate.

Keywords: slope testing; slope erosion control; RUSLE, large-scale testing; mass wasting