Applicability of initial stress measurement methods to Horonobe siliceous rocks and initial stress state around Horonobe Underground Research Laboratory

Sanada, Hiroyuki; Niunoya, Sumio*; Matsui, Hiroya ; Fujii, Yoshiaki*

Understanding initial stress in underground is important for construction of HLW repository. Evaluation of initial stress around Horonobe URL was carried out in order to understand initial stress condition and applicability of AE, DSCA and hydraulic fracturing (HF) methods to Neogene sedimentary rock. Initial stress values obtained from AE method is smaller than overburden pressure due to time dependency of Kaizer effect. Principal stress values by DSCA are similar to those by HF tests. Directions of maximum horizontal principal stresses are approximately in E-W and corresponded to HF results. Horizontal maximum and minimum principal stresses increase linearly in HF results. Deviatoric stress is acting at shallow depth. Initial stress condition approaches hydrostatic condition with depth. Direction of maximum horizontal principal stress was in E-W direction which was similar to tectonic movement around Horonobe URL by triangular surveying.