Theory and Comments on Standard Dilatometric Back Analysis

ThedilatometerprobedevelopedbySolexpertsAG (Switzerland)has beensuccessfully used for more than 30 years. Determination of the mechanical properties of the rock mass is based on real-time measurement of the applied pressure and the resulting deformation ‐ the change of the borehole diameter. The dilatometer probe consists of a metal core, which holds three potentiometeric displacement transducers placed in the centre of the core, Figure 1. The axes of the transducers are oriented 120˚ to each other and vertical distance between the transducers is 75 mm. The borehole wall is loaded by means of a reinforced one meter long packer sleeve fixed to the core of the probe at its both ends. The packer can be expanded by compressed nitrogen or air via a high-pressurehoseconnected to either nitrogen bottles or a compressor. The deformation of the borehole wall is directly measured by the transducers, which contact the borehole wall through steel pins with spherical heads. The installation of the probe into the borehole is usually done with a drilling rig. A dilatometer test has usually two to four loading cycles, as described in the example from the investigation for the Brenner Base Tunnel, Figure 2. At first,