Principle of the interlaced polygon course Emergency stop Trens GPS Satellite Access tunnel Mules Portal Fortezza Portal network Polygon course First of all, a geodetic reference frame was created to carry out the survey work necessary for the construction of the Brenner Base Tunnel. This creates a link between the plans and the topography and serves as a starting point for the underground tunnel construction. The geodetic reference frame (see illustration on the opposite page) is a network made up of measurement points (highlighted in yellow), which are distributed over a wide area along the stretch of the Brenner Base Tunnel. Together with the GPS system, the geodetic measurement points form the basis for the topographic measurements of the Brenner Base Tunnel. Using satellite measurement technology, 28 base points were established to form the geodetic reference frame. To accomplish this, the project area was measured twice for 24 hours using GPS. The achieved degree of accuracy is seven millimetres. These 28 points, defined using satellite measurement technology, form the basis for the further topographic measurement of the tunnel. This is performed using the principle of the interlaced polygon course, whereby progressive angles and distances up into the tunnel are determined. The construction of a long railway tunnel requires highest precision. Reliable and precise surveying methods guarantee the accuracy required for this task. 25 BRENNER BASE TUNNEL
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