Optimization of the Breakthrough Accuracy in Tunneling Surveys

Abstract

Analysis and optimization of the breakthrough accuracy and a proper design of the underground control survey are the most important tasks of the survey engineer in charge of a tunneling project. The breakthrough point P should be treated as two different points P′ and P″ in the accuracy analysis, and the breakthrough error is found from the relative error ellipses calculated for P′ and P″. The accuracy of the underground control surveys (usually open-ended traverses) is much more critical in tunneling surveys than the accuracy of the surface control network. Use of gyrotheodolites decreases the error propagation in underground traverses, particularly when the influence of atmospheric refraction is suspected.