Inclinometers are used to measure displacements in ground and in structures that lie below ground level (e.g. retaining walls).
To make inclinometer measurements a plastic (ABS) tube (the inclinometer casing) is installed in a borehole (for ground measurements) or a void former (for measurements inside a concrete structure) and the annulus between the ground or the concrete structure is filled with a cement/bentonite grout.
The inclinometer casing has four orthogonal grooves along the inside and these are used to guide an inclinometer probe along in order to survey the line of the inclinometer casing.
An inclinometer probe contains orthogonal sensors that measure the angle that the body of the probe makes with vertical (for vertical and inclined casings) or horizontal (for horizontal casings). Inclinometer probes also have sprung wheels to hold them in the centre of the inclinometer casing as the survey is taking place.
The sum of the angles in each direction enables the shape of the inclinometer casing to be determined and the difference between the shape of a casing at any particular time and the shape of the same casing at a reference time represents the displacement that occurred between the two times.
At Geotechnical Observations we read each inclinometer casing twice with two independent inclinometer probes and we compare the results for each pair of readings to ensure that they lie within the random error associated with the survey. One probe is then used for all of the subsequent readings and the other probe is used as a back-up in case the routine probe is subsequently unavailable or if the subsequent readings with the routine probe require checking.
All of our inclinometer measurements are examined for sources of systematic error such as bias, changes in alignment of the sensors and depth positioning. Adjustments are applied if required and noted. Our reports and presentations also include details of the ground profile and construction progress where appropriate.