Geodetic Network Design in Tunnel Surveys

Abstract

The design of surveying networks inside tunnels is of crucial importance because an optimal design enables the network to fulfill its required quality parameters, for instance, precision and reliability. The precision of a geodetic network in a tunnel usually decreases drastically as the network expands inside the tunnel and as the distance to known control points increases. The reliability of tunnel geodetic networks is fairly low due to weak network geometry (limited space in the lateral section of the tunnels). This paper studied the uncertainty of tunnel surveying networks using different observation methodologies in the West Link project, in which an 8-km railway tunnel is to be constructed underneath Gothenburg, Sweden. Adding more free station setups and involving observations from the tunnel wall-bracket points can improve the network uncertainty and reliability. Moreover, including orientation measurements (gyro-observations) has a significant effect on preventing a quick decrease of the precision of networks in long corridors.