Application
Multi-Level VW Piezometers are used to monitor pore-water pressure at different zones in the borehole.
Operation
The multi-level system consists of VW piezometers in multi-level housings, as shown in the photograph at right, and PVC placement pipe. The piezometers are assembled in-line with the PVC pipe and installed downhole. Signal cables are brought to the surface through the PVC placement pipe. The borehole is then backfilled with a bentonite-cement grout, using the placement pipe to deliver the grout. When the grout cures, each piezometer is isolated from the zones above and below it, but is highly responsive to changes in pore-water pressures at its own elevation.
Advantages
Slope Indicator's multilevel system solves or avoids the problems associated with traditional multi-level piezometer installations:
- In the traditional method, placing sensors at their intended depth is difficult, and the difficulty increases with the number of sensors. With the multi-level system, piezometers are installed in-line with PVC pipe. The pipe controls the elevation and relative spacing of the piezometers.
- In the traditional method, placement of sand intake zones and bentonite seals is time-consuming and uncertain. The multi-level system entirely eliminates sand intake zones and bentonite seals. Instead, the entire borehole is filled with a bentonite-cement grout.
- In the traditional method, signal cables from the piezometers pass through the seals that isolate the various intake zones. The cables can form channels for migration of water between zones. With the multi-level system, signal cables from each piezometer run to the surface through the PVC placement pipe. The pipe itself is watertight and is later filled with grout. This completely eliminates communication between zones.
- In the traditional method, cables can be twisted and permanently damaged in the process of withdrawing drill casing or auger sections. With the multi-level system, cables are encased in the PVC pipe and are much less likely to be twisted or damag
- ed.
