Interfels Hydrostatic Profile Gauge has been specially designed for monitoring and measuring vertical ground settlement or heave under embankments and foundations or subsidence of landfill areas. The system offers high heave or settlement range and yet renders readings with desired resolution and accuracy.

This system comprises a probe (with a gas/water rubber membrane interface) attached to a differential pressure transducer in a reel assembly via a pressurised double-wall nylon tube. The outer and inner tubes carry gas and de-aired water respectively. The reel has a Bluetooth transmitter which sends data from the pressure transducer to a PDA (Personal Digital Assistant).

The basic operation of the HPG system is to "hang" a column of water from the pressure transducer at one end while being unsupported at the probe end. The column of water is pressurised by a gas pressure (e.g. air) in the outer tube, transmitted to the water via the rubber membrane interface inside the probe. This ensures positive water pressure throughout the working range and prevent break-up of the water column.

The system measures relative elevations of the probe inside the installed horizontal borehole deduced from the pressure transducer output. As the probe is pulled through the borehole, it's elevation with respect to the pressure transducer changes which is displayed and saved by the PDA. Such elevation reading facilities determining a profile of vertical settlement along the borehole. By comparing the settlement readings against an initial set of readings (before construction), the progress of construction (e.g. an embankment) can be monitored and controlled.