An investigation of strain rosette relief methods of measuring rock stress

Full-scale laboratory experiments have been performed to determine the effectiveness of borehole strain rosette relief methods of measuring rock stress. The effect of the stress acting parallel to the borehole axis cannot be neglected when analysing the data. The stress distribution in the block of rock used in these experiments seems to conform closely to the three-dimensional photoelastic pattern for stresses around the flattened end of a borehole, determined by Galle and Wilhoit. It appears that independent information concerning the orientation of at least one of the principal stress directions is necessary before this type of borehole strain relief technique can be used. If the direction of one of the principal stresses is known, the effect of the stress acting parallel to the borehole axis on the measured strains taken into account, and the elastic moduli of the rock determined under stress conditions similar to those acting during the strain relief test, the method of strain rosette relief on the flattened face of a borehole gives a good estimate of the rock stress.