Development of Precise Stress-strain Measurement System by Employing Electronic Speckle Pattern Interferometry

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The aim of research is to develop a new type of crustal-strain and -stress measurement system by employing the technique of Electronic Speckle Pattern Interferometry (ESPI), which enables, as well as holographic interferometry, two or three dimensional deformation of object to be measured quantitatively in terms of the wavelength of laser light without any contacting the object. Moreover, the ESPI technique has some attractive feature compared with holographic interferometry, i.e, short exposure time and no need for wet photographic processing, because this technique does not use a holographic plate instead a video camera to record interference fringe patterns.In 1991, we developed a borehole module of the ESPI stress measurement system. The module is designed to be very compact (10cm in diameter and about 50cm in length) and to be used in a small borehole.In January, 1992, The first field experiment using the ESPI borehole stressmeter was carried out in a tunnel at the Hiraki mine, Hyogo Prefecture.