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Fig. 4 | Geothermal Energy

Fig. 4

From: An open-access stress magnitude database for Germany and adjacent regions

Fig. 4

Implementation of the overcoring method on the example of the Borre probe (Sjöberg and Klasson 2003); the principles can be applied to any overcoring method (Sjöberg et al. 2003). Figure and description was adapted from Sjöberg et al. (2003). (1) Drill main borehole (76 mm diameter) to measurement depth. Grind borehole bottom using a planing tool. (2) Drill pilot hole (36 mm diameter) and recover the core for appraisal. Flush the borehole to remove drill cuttings. (3) Apply glue to strain gauges. Insert the probe with installation tool into hole. (4) Let the probe tip with strain gauges enter the pilot hole. Release the probe from installation. A compass released at the same time is recording the installed probe orientation. Gauges are bonded to pilot hole wall. (5) Pull out installation tool and retrieve to surface. The probe is bonded in place. (6) Allow glue to harden overnight. Then overcore the probe and record strain data using the built-in data logger. Break the core and recover it to the surface

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