In-Situ Stress Measurement at 1550-Meters Depth at the kISMET Test Site in Lead, S.D.

We conducted a series of u stress measurements in a 100-meter deep hole (kISMET 003) drilled vertically from the 4850-ft level (1478-meters depth) of the Sanford Underground Research Facility (SURF) located in Lead, South Dakota. We used the method of hydraulic fracturing for u stress measurements (Haimson and Cornet, 2003) at total overburden depths between 1520 and 1550 meters The minimum horizontal stress magnitudes were taken to be the shut-in pressures obtained from dP/dt analysis (Lee and Haimson, 1989) of pressurization cycles 3 and 4 in each test. The values ranged between 20.0 and 24.1 MPa (2900 and 3494 psi), and averaged 21.7 MPa (3146 psi). The direction of maximum principal stress was obtained from analysis of an acoustic borehole televiewer log following the hydraulic fracturing. The fractures are striking at an average of N86°E with a dip of 78° to the southeast. The fact that the fractures are not following foliation but have a non-vertical, though very steep, dip indicates that one of the principal stresses may be inclined slightly off vertical.