During the past four years, WSP has installed over 100 VWPs using the fiberglass rod method, offering clients a combination of innovation, high-quality work, and a commitment to safety.
“All field work requires a firm handle on the method, potential pitfalls and the flexibility,” Kennealy said. “All of our field personnel are trained hydrogeologists with the expertise to make timely, site-specific decisions to address issues that can arise while in the field.”
VWPs are installed using a 1/2-inch fiberglass rod after a pilot hole is fully grouted using a cement-bentonite mixture. Multi-level VWPs use grouted-in pressure transducers, set at different depths within the same hole, to measure pore pressures and gradients in, and across, geologic units and structures. The resulting data can be compared with geotechnical design targets to manage and track slope depressurization, and provide a basis for calibrating 2D and 3D pit-slope pore-pressure models.
“The most accurate pore pressure gradients are measured in vertical VWPs,” Kennealy said. “However, in areas where data is needed but access for vertical holes is not available, we have adapted the fiberglass rod assembly for a secondary use.”
Traditional geophysical tools rely on gravity to run logs, but WSP has worked with a geophysical sub-contractor to use the rigid – yet flexible – fiberglass rod to push the geophysical tools to the terminal point of a horizontal drain hole. The logging tool can then be pulled out of the hole at a constant rate, providing an accurate log. The VWP is then installed using the traditional pipe method.
The process requires strong, continuous collaboration with the client, on-site drillers, and other WSP project managers for both time-saving ideas and equipment improvements.
“Every installation seems to be unique,” Kennealy said. “On each installation something new or different arises, so the equipment and the installation process are continuously refined.”