NEW DEVELOPMENT OF THE LNEC STRESS TENSOR GAUGE.

A new development is presented of the LNEC stress tensor gage, in the form of a hollow cylinder 2 mm thick (I. D. 31 mm, O. D. 35 mm), with electrical resistance strain gages embedded midway from the inside to the outside surface. The recent plastic gage, to be installed like its solid forerunner in a standard EX borehole, is claimed to substantially reduce the incidence of practical situations where the gage to rock bond fails on stress-relief overcoring. Analytical expressions are deduced and checked, which enable the complete state of stress in the studied rock mass to be determined from the nine strains measured with the gage.