In situ stress measurement at the 350 m Loop Gallery East at the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei  ; Sakurai, Akitaka; Niunoya, Sumio*

The objective of this report is to investigate the three dimensional stress state in the 350 m Loop Gallery (East) at the Horonobe Underground Research Laboratory. For the measurement, three boreholes, which are 17.0 m in length, were drilled. Hydraulic fracturing was applied as a stress measurement method. For the analysis, shut-in pressure of a transverse fractures, reopening pressure of longitudinal fractures and stress condition causing borehole breakouts were integrated into the equation; then stress state was calculated by inversion technique. As a result, considering the stress condition causing breakouts, the value of the maximum principal stress was 3.73 MPa, which is much smaller than the overburden pressure (about 6.0 MPa). The orientation of the maximum horizontal stress is almost vertical. The stress state is normal faulting.