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Multi-Level Vibrating Wire Piezometers

The multi-level vw piezometers 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.

piezo vw multi level dwg

Advantages

Durham Geo Slope Indicator’s multi-level vw piezometers 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 damaged.
Specifications

 

Piezometer specification

Sensor type Pluck-type vibrating wire sensor with built-in thermistor or RTD
Range 3.5 or 7 bar (50 or 100 psi).
Resolution 0.025%FS
Accuracy ±0.1% FS
Maximum pressure 1.5x range pressure
Filter 50 micron sintered stainless steel
Temperature coefficient < 0.04% FS per °C
Materials Stainless steel

 

Housing specification

Length 305mm
Diameter 71mm
Couplings 1.25" schedule 40 slip coupling. 
Pipe requirements  1.25 inch, schedule 40 PVC pipe can accommodate signal cables for a maximum of six piezometers and offers convenient handling to depths of 45 m (150').
Weight 0.64 kg
Product Datasheet and Specification