Uncertainty in tacheometric measurement of convergences in tunnels

The variations, along time, of the distances betwee n object points on tunnel cross-sections (convergences) may be used in real time conti nuous tunnel monitoring systems, as decision tools, to activate signals of alert or ala rm. Electronic tacheometers, especially the motorized ones, are frequently used to measure conv ergences. To quantify the levels of alert and alarm one should take into account the converge nce measurement uncertainty. The paper deals with modelling the uncertainty of the converg ence as a function of the instrumental uncertainty parameters, using the general formula f or the propagation of variances. The model is applied to a simulated tunnel, where the special ase of motorized tacheometers with automatic target recognition (ATR) systems is analy sed.