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Borehole gauge for in-situ measurement of stress and other physical properties.
U S Patent 4,389,896, 1983 Jun; :1-8
This invention relates to a method of gathering information from sensors from which the Young's modulus, Poisson's ratio, and the two principal stresses can be obtained. The absolute secondary principal stresses can also be obtained. The method involves the placement of two inclusions of different, but known, physical properties in a single bore hole with a strain or displacement rosette sensor placed in each inclusion and oriented so as to measure physical properties on a plane normal to the bore hole axis. It is extremely important that intimate contact exists between the inclusions and the bore hole surface, because the physical properties of the two inclusions are different and the interactions between each inclusion and the rock mass will be different. The measurements from each rosette sensor and the known physical properties of each inclusion, the Young's modulus, the Poissons ratio, and the two principal stresses for the rock mass can be derived by known mathematical formula. Also, by overcoring at the end of the test period, the absolute secondary principal stresses can also be obtained.
U.S. Patent No. 4,389,896