A system for measuring borehole diametric deformation based on mechanical contact and micro-optical imaging

Quantifying diametric deformations of boreholes is vital in rock engineering due to its applications in the determination of in-situ stresses using the stress relief methods. New methods are desired to overcome the harsh environment featuring high temperature and high pressure in deep boreholes. Therefore, this study develops an apparatus using rigid probes combined with microscopic camera to measure borehole diametric deformation. The structural design of the rigid probe and package of the measuring device avoid the advert impact of environmental factors. The usage of multi-probes and high resolution micro-optical imaging technique enables simultaneous collection of multi borehole diametric deformation data. Furthermore, using these data, a new method of borehole shape measurement is proposed at high speed compared with traditional methods that measure one diametric deformation at a time. The feasibility of the system is verified by conducting laboratory tests. This system can be readily used in the in-situ stress measurement based on borehole shape analysis.