NATM (New Austrian Tunnelling Method)
The NATM integrates the principles of the behaviour of rock masses under load and monitoring the performance of underground construction during construction. Often described as a "design as you monitor" approach, based on observed convergence and divergence in the lining and mapping of prevailing rock conditions.
Potential deformations of the excavation must be carefully monitored. NATM requires installation of sophisticated measurement instrumentation which is embedded in lining, ground, and boreholes.
To make sensors easier to use we can characterise their behaviour as linear even though their output is not exactly linear. Non-linearity is the percentage of variation from the measured value of the device to the calculated linear value with respect to the full scale of the sensor. This is often specified as linearity on datasheets but non-linearity and linearity can be taken as the same thing. It is often termed linearity as it is the linearity of the sensor that we are trying to ascertain but the value given is actually the % of non-linearity.