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Flat Jack Outfit (AIM 220)

The method consists of cutting a slot, thereby relieving the stresses perpendicular to the slot, resulting in the deformation of the slot, which is measured. Flat Jack is then embedded in the slot and grouted. Hydraulic Pressure is applied through the flat jack until the displacements which took place on slot cutting are reduced and finally cancelled. By measuring the cancellation pressure in two mutually perpendicular directions, the in-situ stress close to the rock surface can be assessed approximately.