On Accuracy Determining Coordinates Contour Points of Fixed Forehead Tunnel Face during Underground Structures Construction
The solutions discussed in this article are an intermediate result to the method development for measuring the movement in the plane points of the fixed forehead underground structures face in order to indirectly determine the ground pressure intensity ahead of the future structure. The article provides formulas for calculating coordinates of bench marks from measured chords of tunnel lining inner outline. At the same time, all measurement processes should be performed in the following sequence: at the beginning take measurements immediately after installation of tunnel structures and determine the initial coordinates of bench marks; then make chords measurements of inner outline tunnel construction during the tunneling and tunnel operation, and determine changes in coordinates bench marks, that is, their movements, transverse to longitudinal tunnel axis. In the article are shown random errors in measuring lengths of chords when determining the displacements of bench marks affect error in calculating coordinates, and, accordingly, displacements. Error in calculating bench marks was found to be satisfactory. Data obtained can be used for measurements and stresses in tunnel lining and for monitoring its technical condition. In addition, using periodic measurements movements controlled points on anchored forehead tunnel face, in long term we can get information about soil pressure on anchored forehead tunnel face. To do this, it is necessary to take into account membrane efforts in anchored forehead tunnel face, and to determine membrane effort in turn, it is necessary to know movements of bench marks, transverse to longitudinal axis of tunnel.