Fibre Bragg Grating
A technique for building optical filtering functions directly into a piece of optical fibre based on interferometric techniques. Usually this is accomplished by making the fibre photosensitive and exposing the fibre to deep UV light through a grating. This forms regions of higher and lower refractive indices in the fibre core. Fibre Bragg Gratings can be made into many different types of Geotechnical sensor including strain gauges, temperature sensors, piezometers, extensometers.
Special Interrogators are required to read and interpret the data from the sensors.
A fibre optic sensor is a sensor that uses optical fibre either as the sensing element. Optical fibres can be used as sensors to measure strain, temperature, pressure and other quantities by modifying a fibre so that the quantity to be measured modulates the intensity, phase, polarization, wavelength or transit time of light in the fibre.
Frequency is the unit of measurement in vibrating wire technology.
When excited by the electromagnetic coil, a vibrating wire sensor 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.
Fully Grouted Method
The fully-grouted method entails installing a piezometer tip in a borehole which is backfilled entirely with cement-Bentonite grout. This method allows multiple piezometers to be installed easily within a single borehole.