ETH Zürich is establishing an underground geoscience laboratory in the Bedretto Tunnel located in the Swiss Central Alps. The purpose of the laboratory is to host meso-scale in situ experiments with the focus on hydraulic stimulation (geothermal energy) and fault reactivation (induced seismicity). Currently, the stress measurement via classic hydraulic fracturing technique is ongoing in multiple boreholes around the BUL. The preliminary stress measurement results indicate that the BUL is generally in a normal faulting and/or strike-slip stress regime, and is near critically-stressed. The estimated stress components are: Sv ≈ 26.5 MPa; SHmax ≈ 0.8∼1 *Sv; Shmin ≈ 13∼16 MPa; Pp = 3-6 MPa. The estimated SHmax direction is approximately N100E, albeit with some variations. In this case, the E-W striking and steeply-dipping fractures can potentially be activated with elevated pore pressure perturbation. These serve as important constraints to the future in situ experiment design.

1 Introduction

ETH Zürich and the Swiss Competence Center for Energy Research - Supply of Energy (SCCERSoE) are establishing a deep underground geoscience laboratory in the Swiss central Alps. The purpose of the laboratory is to host meso-scale in situ experiments in crystalline rocks. The current experimental focus is on hydraulic stimulation for deep geothermal energy research and fault reactivation for better understanding of induced and triggered seismicity.

The laboratory is located in the Bedretto tunnel (a branch of the Furka railway tunnel) (Figure 1). The Bedretto Underground Laboratory (BUL) sits in an enlarged section of the tunnel (between TM2000-2100) from its south entrance. The tunnel axis trends ∼N43°W, generally along the mountain ridge line above. The altitude at the tunnel south entrance is ∼1480.5 m above sea level, from which the overburden gradually increases to a maximum of 1650 m at Pizzo Rotondo (TM3100). The overburden directly above the BUL is between 1000 and 1030 m.

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