Anisotropic Closure in Squeezing Rocks: The Example of Saint-Martin-la-Porte Access Gallery

In this paper, we analyse the convergence measurements recorded in a gallery excavated in severely squeezing ground. The procedure consists in a preliminary geometrical treatment of the raw data to evaluate the principal axes of deformation by assuming an elliptic deformation of the walls of the gallery. Then the convergence law proposed by Sulem et al. (Int J Rock Mech Min Sci Geomech Abstr 24(3):145–154, 1987a), which is extended to account for anisotropic closure, is fitted on the displacements along the two axes of the obtained ellipse. This procedure is more robust and relevant than fitting the convergence recorded on the most deforming segment or fitting the average value of the convergence along the various segments. An attempt is made to correlate the amount and the direction of anisotropic deformation with the lithology and some geological features described by the dominant discontinuity families.