Predicting ground conditions ahead of the tunnel face by vector orientation analysis

Tunnel construction frequently makes use of radial displacements to monitor tunnel support performance, particularly in complex ground conditions. In recent years, absolute displacement monitoring methods have replaced the more traditional radial convergence measurements. It has been suggested by Schubert and Budil (1995) [The importance of longitudinal deformation in tunnel excavation. In: Fujii, T. (Ed.), Proceedings of the 8th ISRM Congress on Rock Mechanics, Tokyo, vol. 3. A.A. Balkema, Rotterdam, pp. 1411-1444.] that these near-face displacements could also be used to forecast the tunnel conditions ahead of the advancing tunnel face. This paper presents the results from a series of detailed three-dimensional analyses in varying ground conditions, which compares vertical (radial) displacements measured at the roof, vector orientations associated with these roof displacements and tunnel face displacements (extrusion). These numerical results suggest that in all cases vector orientation provided additional information not obtained from traditional radial displacements or face extrusion. If interpreted correctly the vector orientations could provide advanced warning of changing ground conditions in the vicinity of the tunnel face.