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United States Department of Agriculture

Agricultural Research Service

Research Project: Technologies for Managing Water and Sediment Movement in Agricultural Watersheds

Location: Watershed Physical Processes Research Unit

Title: Laboratory soil piping and internal erosion experiments: evaluation of a soil piping model for low-compacted soils

Authors
item Fox, Garey -
item Felice, Rachael -
item Midgley, Taber -
item Wilson, Glenn
item Al-Madhhachi, A.T. -

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 14, 2013
Publication Date: December 16, 2013
Citation: Fox, G., Felice, R., Midgley, T., Wilson, G.V., Al-Madhhachi, A. 2013. Laboratory soil piping and internal erosion experiments: evaluation of a soil piping model for low-compacted soils. Earth Surface Processes and Landforms. p. 1-9 doi:10.1002/esp.3508.

Interpretive Summary: Flow through large soil pores (soil pipes) has been blamed as a cause of failure of dams, levees, hillslopes, and streambanks. Mathematical models have been proposed to predict flow through soil pipes and the erosion of the insdie of the pipe. However, very little research has been conducted under controlled conditions to evaluate these models. The objective of this study was to utilize a soil box (50 cm long x 50 cm wide x 20 cm tall) that maintains a constant water level on a soil pipe to derive flow and internal erosion data for two soils packed at uniform bulk densities but different initial moisture contents. Soils included a clay loam from Dry Creek in northern Mississippi and a sandy loam from Cow Creek in northern Oklahoma. Initial moisture contents were 10, 12 and 14% by weight for Dry Creek soil and 8, 12, and 14% for Cow Creek soil. A 1-cm diameter rod was placed horizontally along the length of the soil bed during packing and carefully removed after packing to create a soil pipe that extended the length of the bed. A constant water level was maintained at the inflow end of the soil pipe. Flow rates and sediment concentrations were measured from the pipe outlet. Jet Erosion Tests (JETs) were conducted to measure erosion properties of the soil bed on samples packed at the same moisture contents as the box experiments. Flow rates from the box experiments were used to calibrate the model based on erosion properties. The influence of the initial moisture content of the packed soil was apparent, with some pipes (8% moisture content) expanding so fast that limited data was able to be collected during the experiment. The model was able to estimate equivalent flow rates to those observed in the experiments, but had difficulty matching observed sediment concentrations when the pipes rapidly enlarged by internal erosion. The JETs predicted similar erosion properties compared to the model for the more erodible cases (8 and 12% moisture content), but not for the less erodible cases (14% moisture content). Improved models are needed that better define the changing size and shape of a soil pipe during internal erosion.

Technical Abstract: Soil piping has been attributed as a potential mechanism of instability for embankments, hillslopes, dams, and streambanks. In fact, deterministic models have been proposed to predict soil piping and internal erosion. However, limited research has been conducted under controlled conditions to evaluate these models. The objective of this study was to utilize a constant-head soil box (50 cm long x 50 cm wide x 20 cm tall) to conduct soil pipe experiments and derive flow and internal erosion data for two soils packed at uniform bulk densities but different initial moisture contents. Soils included a clay loam from Dry Creek in northern Mississippi and a sandy loam from Cow Creek in northern Oklahoma. Initial gravimetric moisture contents were 10, 12 and 14% for Dry Creek soil and 8, 12, and 14% for Cow Creek soil. A 1-cm diameter rod was placed horizontally along the length of the soil bed during packing and carefully removed after packing to create a continuous soil pipe. A constant head was maintained at the inflow end of the soil pipe. Flow rates and sediment concentrations were measured from the pipe outlet. Submerged jet erosion tests (JETs) were conducted to derive erodibility parameters for repacked samples at the same moisture contents as the box experiments. Flow rates from the box experiments were used to calibrate the deterministic model based on erodibility parameters. The influence of the initial moisture content of the packed soil was apparent, with some pipes (8% moisture content) expanding so fast that limited data was able to be collected during the experiment. The deterministic model was able to estimate equivalent flow rates to those observed in the experiments, but had difficulty matching observed sediment concentrations when the pipes rapidly expanded by internal erosion. The JETs predicted similar erodibility coefficients compared to the deterministic model for the more erodible cases (8 and 12% moisture content), but not for the less erodible cases (14% moisture content). Improved models are needed that better define the changing cross-section of a soil pipe during both supply-limited and transport-limited internal erosion.

Last Modified: 10/25/2014
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