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United States Department of Agriculture

Agricultural Research Service

Title: Pressure Forces in a Fractured Matrix

Authors
item Robinson, Kerry
item Kadavy, Kem

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings
Publication Acceptance Date: July 27, 2001
Publication Date: July 30, 2001
Citation: Robinson, K.M., Kadavy, K.C. 2001. Pressure forces in a fractured matrix. American Society of Agricultural Engineers Meetings Paper No. 012081.

Interpretive Summary: As water flows over soil and rock, these earthen materials are subject to erosion. In the simplest of circumstances, predicting this erosion can be challenging. The presence of cracks or fracture patterns in earthen materials further complicates erosion prediction. These cracks can accelerate the erosion by allowing large pieces of material to be removed by the flowing water. Hydraulic pressure forces have a major impact on how large pieces of material are removed. This study examines the fundamental characteristics of the pressure forces transmitted through fractured materials. The pressure forces were measured and described. The cracks act to decrease the maximum pressures, but they spread the pressure over a wider area. The pressure increased as the overfall height increased and as the crack spacing decreased. These results should be of interest to other researchers and engineers responsible for water resources structures built in earthen materials. This information enhances our understanding of how pressure forces and fracture patterns can influence soil and rock erosion.

Technical Abstract: Substantial pressure forces can be transmitted to an overfall boundary as water flows over a headcut. These pressure forces, acting with the hydraulic shear stress, cause soil erosion, scour, and headcut instability. Fracture patterns or cracks can naturally occur in earth materials (soil and rock), and these cracks can accelerate soil erosion and headcut advance. This project examines how pressure forces are transmitted through a fractured matrix in the impingement area of an overfall. Two crack spacings and two overfall heights were tested over a range of flow rates. Pressure forces were measured below a fixed block matrix, and the ability of these forces to remove material was examined. Pressure magnitude and variance was observed to be greatest near the point of nappe impingement. Piezometers placed below two layers of fractured block material indicated that the fractured matrix dramatically dampened the boundary pressure magnitude but spread the pressure over a wider area. This paper describes the magnitude and location of pressure forces downstream of an overfall with and without blocks. This research should enhance our understanding of how pressure forces and fracture patterns can influence soil and rock erosion.

Last Modified: 8/21/2014
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