Experimental Studies of the PVD Permeameter

Prefabricated vertical drains (PVDs), also known as wick drains, are typically used to increase the rate of consolidation. In addition, PVDs have been used to remediate contaminated soils by serving as mini extraction and injection wells. One of the major factors impacting the design of PVDs is the quantification of the effect of smear (the disturbance of soil surrounding the PVD during installation). A device, dubbed the PVD Permeameter, that measures the in-situ values of hydraulic conductivity and horizontal coefficient of consolidation has been under investigation and development. The PVD Permeameter consists of a short length of PVD material placed in the ground to the desired position using an actual PVD installation rig. The major benefit of this device is that it provides a cost-effective means of determining in situ parameters that already include smear; thus removing the uncertainty of the effects of smear from design. A field study indicated that more refinement was needed in the design of the PVD Permeameter. Specifically, laboratory studies were undertaken to investigate the impact of the length to diameter ratio and to confirm that the equation used to determine the horizontal hydraulic conductivity from the field trial was appropriate. All of the experiments were performed using a sand/kaolinite mixture. The laboratory experiments utilized scaled-down versions of the PVD Permeameter used in the field trial. The laboratory work indicates that the equation used to calculate the horizontal hydraulic conductivity is appropriate and that a larger length to diameter ratio does improve results. This work is an ongoing collaborative effort between researchers at Villanova and The Nilex Corporation, LLC; the laboratory program was originally presented as part of GRI-18.