Fracture Characterization and Rock Mass Damage Induced by Different Excavation Methods in the Horonobe URL of Japan

Tokiwa, T.; Tsusaka, Kimikazu; Aoyagi, Kazuhei

doi:10.1007/s40999-016-0126-y

Int J Civ Eng

2017

DOI: 10.1007/s40999-016-0126-y

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Fracture Characterization and Rock Mass Damage Induced by Different Excavation Methods in the Horonobe URL of Japan

T. Tokiwa

Kimikazu Tsusaka

Kazuhei Aoyagi

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Cited by 6 publications

References 16 publications

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Effects of flow dimension in faulted or fractured rock on natural reductions of inflow during excavation: a case study of the Horonobe Underground Research Laboratory site, Japan

Ishii

2023

Hydrogeol J

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Major inflows of groundwater can occur during excavation in faulted or fractured rock masses, even if pre-excavation grouting is applied; postexcavation grouting may then be required to reduce these inflows. However, the diffusion equation for fluid pressure suggests that inflows may reduce naturally by 50–90% or more within days or weeks when the dimension of the flow in faults or fractures that feed the inflow (flow dimension) is close to 1, but inflow reduction is minimal when the flow dimension is close to 3. Therefore, if the flow dimension is close to 1, the natural reduction in inflow may obviate countermeasures. Nevertheless, this natural reduction being dependent on flow dimension is seldom considered explicitly when planning excavations or countermeasures. To verify the applicability of the relationship between natural changes of inflow and the flow dimension, this study measured changes in inflow at six locations at the Horonobe site, Japan, where major inflows occurred during excavations of tunnels or shafts in faulted or fractured siliceous rocks. The flow dimension at each location was assessed using pre-excavation packer tests in surface-based boreholes. The results confirm that changes in the inflows during the days and weeks immediately after their commencement depended consistently on the assessed flow dimension. Natural reductions in inflow during excavation are predictable based on the flow dimension, which can be estimated using pre-excavation borehole investigations or from the initial changes in inflow during the first several days. This approach may be helpful for improving the efficiency of excavations.

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Effects of flow dimension in faulted or fractured rock on natural reductions of inflow during excavation: a case study of the Horonobe Underground Research Laboratory site, Japan

Ishii

2023

Hydrogeol J

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Assessment of rock drillability by the method of analytic hierarchy process combined with fuzzy comprehensive evaluation

et al. 2021

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Evaluation of temporal changes in fracture transmissivity in an excavation damaged zone after backfilling a gallery excavated in mudstone

Aoyagi,

Ishii

2024

Environ Earth Sci

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The long-term geological disposal of high-level radioactive waste relies on predictions of future changes in a disposal facility's hydro-mechanical characteristics in order to assess potential leakage through fractures in the excavation damaged zone (EDZ) after back lling the facility. This study evaluated the transmissivity of EDZ fractures using in situ hydraulic tests around the area of a full-scale, experimental, engineered barrier system in the Horonobe Underground Research Laboratory, Hokkaido, Japan. After their installation, the buffer blocks swelled, altering the stresses within the EDZ fractures. The effects of these changing stresses on the fractures' transmissivity were assessed over a period of four years. The transmissivity continuously decreased in this period to about 26% of its value measured prior to the swelling. Using the Barton-Bandis normal-stress-dependent fracture-closure model, the decrease in transmissivity is quantitatively attributed to closure of the EDZ fractures, which was caused by the swelling pressure increasing up to 0.88 MPa. Evidence of fracture closure came from seismic tomography surveying, which revealed a slight increase in seismic velocity in the study area with increasing swelling pressure. The results show that EDZ fractures were closed by swelling of the fullscale buffer material. They also demonstrate the applicability of the Barton-Bandis model to preliminary estimation of the long-term transmissivity of EDZ fractures in facilities for the geological disposal of radioactive waste.

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Fracture Characterization and Rock Mass Damage Induced by Different Excavation Methods in the Horonobe URL of Japan

Cited by 6 publications

References 16 publications

Effects of flow dimension in faulted or fractured rock on natural reductions of inflow during excavation: a case study of the Horonobe Underground Research Laboratory site, Japan

Effects of flow dimension in faulted or fractured rock on natural reductions of inflow during excavation: a case study of the Horonobe Underground Research Laboratory site, Japan

Assessment of rock drillability by the method of analytic hierarchy process combined with fuzzy comprehensive evaluation

Evaluation of temporal changes in fracture transmissivity in an excavation damaged zone after backfilling a gallery excavated in mudstone

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