Design and calibration of a new triaxial strain cell for rock stress measurement.

The present paper describes the technical characteristics and first laboratory calibration tests of a new Triaxial Strain Cell (TSC) -with re-usable components - conceived for low cost measurement of the 3D state of stress in rock mass through borehole overcoring. The instrument, like other well known triaxial strain cells in litherature (Leeman, 1966; Worotnicki & Walton, 1976), utilizes a set of differently oriented strain gauge rosettes as sensing elements; it is therefore innovative as far as the measurement geometry, the adopted materials and the sensor characteristics are concerned. The in situ installation procedures result very easy and the overall costs of both production and investment are reduced. The instrument is equipped with an onboard, purposely developed, Miniaturized Data Acquisition System (MiDAS) that allows a continuous and remote acquisition of the strains induced by stress relief during tests.