An Optical Instrument for in-situ Stress Measurement in Rocks
Final rept. 1 Nov 1972-31 Nov 1974
TRW SYSTEMS GROUP REDONDO BEACH CA
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A laboratory model of a holographic instrument, essentially a logging tool, has been designed and tested for measuring in-situ stress in a 9-inch diameter blind exploratory drill hole. The apparatus can ultimately operate remotely at depths of thousands of feet. It has been tested in a simulated borehole in the laboratory on prestressed samples granite which upon stress relief produced displacements on the order of .3 micrometers. Data, in the form of holographic plates are stored, on board, the instrument. Displacement fields are stored in fringe patterns covering the holographically recorded images of the strained surface. The holographic instrument consists of separate core drill, optics, and laser modules and associated electrical and plumbing connections. The performance of the holographic instrument in a dry and water- flooded simulated borehole was excellent. Good quality holographic interferograms were obtained by double exposure, before and after drilling, in a water-flooded environment, of prestressed slabs of granite under loads in the 130 to 300 bar range.
- Geology, Geochemistry and Mineralogy
- Civil Engineering