Measurement Methods for Cross-Sections of Tunnels Using Reflectorless Total Stations

Owing to the technical and economic aspects of the project management, pre-estimating the volumes of excavating, shotcreting, and concreting operations have been of great importance for the underground construction industry, especially in metro and highway tunnels. In this respect, we offer a reliable method based on the trigonometric geometry for estimating the required parameters of the conventional tunnels that are manually excavated via explosions and road-header machines. To this end, a geodetic network consisting of dense benchmarks are firstly realized outside the trench and throughout the excavated tunnel. The cross-sections of the tunnel are then mapped in the coordinate frame attached to the reference lines after orienting the reflectorless total station with respect to the geodetic network points and the predesigned reference lines. Consequently, by comparing the resultant coordinates of each cross-section at the excavating, shotcreting, and concreting stages, one can arrive at accurate estimation of the corresponding thickness, areas and volumes during different phases of the tunnel construction. The performance of the proposed method has been evaluated as a function of the central angles between the consecutive points on the arc of tunnel cross-section via a simulated dataset from an assumed D-shape tunnel. The numerical results have indicated that in the case of the consecutive central angle of ۲۵ deg the estimated thickness, area, and volume errors are about ۰.۰۰۵۷ m, ۰.۱۹۹ m۲, and ۰.۳۹۹ m۳, which can be considered as a clear indication of the reliability and applicability of the presented method.