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A preliminary laboratory testing program was conducted to investigate the potential effect of vegetation on the hydraulic conductivity of soils used to construct levee structures. The testing program was conducted using a silty sand soil with a simulated root system. Testing apparatus included rigid-wall-double-ring permeameters and flexible-wall permeameters. The simulated roots were made using Balsa wood having a square cross section of 1.65 by 1.65 mm and approximately 12 to 25 mm in length. The measured hydraulic conductivity for specimens without simulated roots decreased as a function of the moisture content from approximately 1 × 10-3 cm/s to 5 × 10-4 cm/s. Values obtained using the flexible-wall device were less than those measured using the rigid-wall device by a factor of approximately 2. The addition of 1% simulated roots decreased the measured hydraulic conductivity, k. The reduction in k increased from less than 10% at a molding water content of 10% to approximately 50% at a water content of 25%. Similar behavior was observed in the case of specimens with 2% simulated roots. For γdry of 10 kN/m3, the estimated k values were 1 × 10-5 cm/s for the case of 2% roots versus 3 × 10-4 cm/s for the case of 1% roots. The k values decreased as the unit weight of the specimens was increased for both cases. In addition, the difference between k values obtained for specimens containing 1% and specimens containing 2% simulated roots increased as the dry unit weight of the specimens was increased.
Assistant professor, West Virginia University, Morgantown, WV
Research assistant, West Virginia University, Morgantown, WV
Research engineer, Geotechnical Laboratory, Army Corps of Engineer, Waterways Experiment Station, Vicksburg, MS
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