The state of stress in the Earth's crust

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Abstract
This article is limited to a short state of the art report on available methods of stress determination in situ and a summary of findings to date.Stress determination at depth requires the drilling of a hole to the level of interest. Most of the methods employ sophisticated instrumentation down the hole and require overcoring for relieving the stresses. Because of the necessity to overcore, hole length is limited to 30–40 m. Hence these methods are useful only in stress measurements near the surface of the earth or at depth if previous access has been obtained through underground chambers, tunnels, or mine openings. A variety of measuring methods have been developed which determine either changes in hole diameter or strain on the bottom of the hole resulting from the complete relief of the stress due to overcoring.