This is a three dimensional overcore tool. It is a glue in cone cell that is locked at its end into a pilot hole. The cone is of very shallow angle and behaves fairly similarly to a normal pilot hole. Twenty strain gauges are at different orientations and locations on the cell wall and this provides a high degree of redundancy in the measurements.
The process is similar to that shown in the two dimensional overcore tool except that the pilot hole is tapered and the cell is glued into the tapered section. The glue will work in clean water drilling fluid. The glue will take at least 8 hours to reliably set, depending on rock temperature. Practically, this means leaving it in place for a 12 hour shift. As the cell is locked into a pilot hole and glued to the wall of the taper the system is very resistant to drilling vibration.
The tool can be used in any orientation with HQ, HQ-3 or HQ-U coring systems.
The tool may also be fitted with a cable for stress change monitoring.