Vibrating wire piezometers are used to monitor pore-water pressure in soils. They are typically sealed in boreholes but can also be embedded in fills, or suspended in a well. Typical applications include evaluating slope stability, dewatering and drainage schemes, overpressure in silt and clay soils, permeability and hydraulic gradients in dams, and also ground water levels. They can also be used to monitor up-lift pressures in gravity dams.
? Dams and fill embankments
? Measurement of ground water
? Dewatering activities
? Landslides monitoring
? Natural or cut slope sites
? Monitoring of up-lift pressure
? Long-term stability
? Cable length does not affect reading
? Long working life and reliability
? Built-in surge protection (overvoltage)
? Built-in temperature sensor
? Hermetically sealed
The vibrating wire pressure sensor contains a steel wire held in tension between a flexible outer diaphragm and rigid inner bulkhead. The sensor is configured so that water pressure acting on the diaphram changes the tension in the wire. As pressure increases, tension of the wire decreases, and vice versa. Tension in the wire is measured by setting it into vibration with a series of electromagnetic pulses from a coil. The wire then vibrates primarily at its natural resonant frequency.
When excitation ends, the wire continues to vibrate and a sinusoidal signal, at the resonant frequency, is induced in the coil and transmitted to the readout unit. A built-in bipolar gas discharge tube protects the sensor against voltage transients. A built-in thermistor provides temperature data and can be used for thermal corrections.