Application
Typical applications for the VW piezometer are:
- Monitoring pore water pressures to determine safe rates of fill or excavation.
- Monitoring pore water pressures to determine slope stability.
- Monitoring the effects of dewatering systems used for excavations.
- Monitoring the effects of ground improvement systems such as vertical drains and sand drains.
- Monitoring pore pressures to check the performance of earth fill dams and embankments.
- Monitoring pore pressures to check containment systems at land fills and tailings dams.
Operation
The VW piezometer converts water pressure to a frequency signal via a diaphragm, a tensioned steel wire, and an electromagnetic coil. The piezometer is designed so that a change in pressure on the diaphragm causes a change in tension of the wire. When excited by the electromagnetic coil, the wire vibrates at its natural frequency. The vibration of the wire in the proximity of the coil generates a frequency signal that is transmitted to the readout device. The readout device processes the signal, applies calibration factors, and displays a reading in the required engineering unit.
Installation Overview
Grout-In Method: The piezometer is lowered, filter-end up, to the specified depth in the borehole. Then the borehole is filled with a bentonite-cement grout.
Sand Filter Method: The borehole is flushed with water or biodegradable drilling mud. A sand filter is placed around the piezometer which is positioned at the specified depth. A bentonite plug is formed at the top of the sand filter. Then the remainder of the borehole is filled with a bentonite-cement grout.
Push-In: The special-body, push-in piezometer is pushed into soft, cohesive soil at the bottom of a borehole. The piezometer must be monitored to ensure that it is not overpressured as it is pushed in. The borehole is then filled with a bentonite-cement grout.
Embankments: The piezometer is embedded in sand and then covered with hand-compacted select fill. Signal cables are routed though trenches and covered with compacted fill. Bentonite water stops are placed at appropriate locations. Readings become available when the surrounding soil becomes saturated.
Advantages
High Resolution: VW piezometers provide a resolution of 0.025% of full scale.
High Accuracy: Slope Indicator's automated, precision calibration system ensures that all VW piezometers meet or exceed their accuracy specifications.
Groutable: The VW piezometer can be installed without a sand filter or a bentonite seal. This greatly simplifies same-hole installation of multiple piezometers or piezometers with inclinometer casing.
Rapid Response: VW piezometers offer rapid response to changes in pore water pressure, whether they are grouted in, pushed into cohesive soils, or embedded in a sand filter zone.
Reliable Signal Transmission: With properly shielded cable, signals from the VW piezometer can be transmitted long distances.
Temperature Measurement: All VW piezometers are equipped with a temperature sensor.
