Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Popular Publication
Publication Acceptance Date: July 22, 1999
Publication Date: July 30, 1999
Citation: Robinson, K.M., Hanson, G.J., Cook, K.R., Kadavy, K.C. 1999. Erosion of fractured materials. American Society of Agricultural Engineers Meetings Papers No. 99-2038. Interpretive Summary: Soil and rock materials often exist with naturally occurring fracture patterns or cracks. These cracks influence how quickly water can erode these materials. This research was conducted to determine how these fracture patterns influence the rate of erosion. For a range of block sizes, orientations, and overfall heights, concrete blocks were tested by slowly increasing the flow rate until the blocks failed. The failure discharge was observed to decrease as the overfall height increased. If the block was oriented with the long axis in the vertical direction, a higher failure discharge was required. Block failure also occurred more rapidly when the crack spacings between blocks was increased. These results are important to researchers, engineers, and dam owners interested in predicting the rate of erosion of fractured materials. This information can be used in many areas such as stilling basin stability, headcut erosion, and dam foundation stability.
Technical Abstract: The natural fracture patterns that often exist in soil and rock materials are believed to have a major influence on how these materials erode. The objective of this study was to investigate the dominant parameters that cause failure of a fractured block matrix. A study was conducted by placing a matrix of blocks downstream of an overfall. The discharge over the overfall was increased until the block matrix failed due to the forces transmitted by the impinging flow. The block size, block orientation, and overfall height were varied systematically over a range of flow rates. The failure discharge was observed to decrease as the overfall height increased. The failure discharge was also observed to increase if the block orientation was placed with a long axis oriented vertically. The repeatability of these fractured material tests was also examined, as was the block layer thickness. In addition to the hydraulic erosion of fractured materials, preliminary results on the measurement of pressure forces below a block matrix are also discussed. This paper provides fundamental research information concerning scour hole development and headcut erosion in fractured materials.