A magnetic anisotropy sensor is built on the principle of the magneto-strictive effect in which changes in magnetic permeability due to deformation of a ferromagnetic material is measured in a nondestructive manner, which then can be translated into the absolute values of stresses existing on the surface. This technique was applied to measure stresses of H-beams, used as tunnel support structures, to confirm expected measurement accuracy. The results show that this method could be one of the promising technologies for non-destructive stress measurement for safe construction and probably maintenance of rock structures.
