Effect of Simulated Roots on the Permeability of Silty Soil
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 ?dry 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.