Control Surveys During the Construction of the Channel Tunnel

The Institute for Deposits and Surveying of the Deutsche Montan Technologie (DMT), Bochum, delivered 3 high precision gyrotheodolites GYROMAT to the English-French-syndicate for the construction of the tunnel under the English Channel. The GYROMATS are in use for direction-finding during the construction of the EUROTUNNEL from both sides.Furthermore, DMT surveying teams carried out control surveys both on the French and on the British side to guarantee a successful breakthrough under the English Channel in December 1990.Within 7 surveying campaigns more than 100 km of bored tunnels in the EUROTUNNEL-project were checked.The GYROMAT and the EUROTUNNEL-project will be outlined in this paper.Finally the results of the control surveys and the influence of horizontal refraction on traverse measurements in tunnels are discussed.