Full-Scale Hydro-Mechanical Properties of Vertical Flow Bed Treatment Soils

Abstract

A 15.25 m wide by 30.50 m long by 1.80 m thick, soil test section (test pad) was constructed to determine the hydraulic conductivity of a proof-of-concept vertical flow bed wetland water treatment system. Specifically, in situ and laboratory hydraulic conductivity tests were performed to confirm if the hydraulic conductivity of the treatment soil within the wetland was equal to or greater than the design requirement of 3.33 × 10−5 cm/s. The in situ hydraulic conductivity measurements were obtained by performing a sealed double ring infiltrometer tests and multiple two-stage borehole infiltration tests. Because of the soil conditions and the implementation of in situ sensors, these two tests were modified. Three types of in situ instrumentation including the time domain reflectrometry, heat dissipation water matric potential sensors, and irrometer tensiometers, were installed into the soil to monitor the movement of the water by measuring the changes of water content and suction as water flow through the soil. In addition, four flexible wall permeameter tests were conducted on Shelby-tube samples to validate the field hydraulic conductivity measurements. A comparison between field and laboratory testing results was completed. The laboratory hydraulic conductivity values were significantly lower than in situ hydraulic conductivity values, and also lower than the design requirement value. The in situ tests results met the 3.33 × 10−5 cm/s requirement, with the exception of a few of the values that were obtained from a borehole where highly plasticity clay was observed.