ABSTRACT
During the winter 1988/89 hydraulic fracturing and the hydraulic tests on preexisting fractures (HTPF) method were used to measure the horizontal stresses in a vertical, 508 meter deep core drilled borehole in Lulea. Both rock stress measurement methods employed identical test equipment based on a multihose test unit. The pressures required to initiate hydrofractures were selected as the pressures where the curves begin to deviate from linearity, shortly before peak pressures are reached. If time and cost are deciding factors the HTPF method should replace the hydrofracturing technique only when none of the principal stresses are expected to be parallel to the borehole axis or when marked weakness planes exist in the rock mass. A source of error in the HTPF method is the assumption that the fracture orientation at the borehole wall correspond to the fracture orientation further out in the rock mass where the stress normal to the fracture plane is measured.
