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Laboratory Method for Predicting Boundary Conditions of Soil Textures that Support Fracture Development

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Applied Engineering in Agriculture. 26(6): 973-982. (doi: 10.13031/2013.35913) @2010
Authors:   E. K. Kim, Y. W. Kang, A. D. Christy, J. Weatherington-Rice
Keywords:   Sand, Silt, Clay, Cracks, Soil physical properties, Porous media, Soil structure, Soil water movement

Desiccation cracking is important in geotechnical, agricultural, and environmental engineering because it contributes to problems including failures of dams, embankments, landfill liners and caps, and contamination of groundwater. Soil textures (sand, silt, and clay) identified by previous field investigations of fracturing in glacially-derived soils were analyzed and the range of known fracture-prone textures extended using new controlled fracturing experiments, called "mud-pie tests." The purpose of this study was to establish a protocol to predict fracturing in natural settings. Experiments were performed on naturally fractured field soil samples and mixtures of those field soils with pure silica sand. Grain sizes were determined according to USDA classifications. Methods included grinding soil samples, adding water and silica sand, drying them, and photo-documenting final presence or absence of fractures. Fractures and volume shrinkage occurred on all mud-pies made with original fractured field soil samples. As sand content increased, some mixtures no longer supported fracturing. Results graphed on ternary diagrams indicated that soils having greater than 6.5% clay and/or less than 79% sand were more likely to support fracturing. The texture classes predicted to sustain fracturing were mainly clay, loam, clay loam, silty clay loam, and silty clay, but fractures were supported in all textures except sand and loamy sand. Laboratory mud-pie tests can establish a baseline for the clay minerals found in a region, allowing investigators to develop a graphical tool to predict fracturing in the field without need for test pit excavation or additional laboratory analyses.

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