Characterisation of Excavation-Induced Damage Around a Short Test Tunnel in the Opalinus Clay

Yong, Salina; Loew, Simon; Schuster, Kristof; Nussbaum, Christophe; Fidelibus, Corrado

doi:10.1007/s00603-017-1212-4

Cited by 10 publications

(6 citation statements)

References 25 publications

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“…For shales or argillaceous rocks, changes in the saturation state are directly linked to structural modifications (Valès et al, 2004;Yurikov et al, 2019). In the highly saturated state, a large portion of the pore water is adsorbed onto the clay mineral surfaces, while for high external suction, i.e., desaturation, it is extracted from the rock through the pore network (Zhang et al, 2007).…”

Section: Measured Hydraulic Fracture Aperturementioning

confidence: 99%

“…In the highly saturated state, a large portion of the pore water is adsorbed onto the clay mineral surfaces, while for high external suction, i.e., desaturation, it is extracted from the rock through the pore network (Zhang et al, 2007). Dehydration of claystone leads to a decrease in total porosity (Yurikov et al, 2019) and induces a reduction of pore and swelling pressure, which in turn impedes self-sealing processes (Tsang et al, 2005;Zhang et al, 2007). In addition, secondary shrinking-induced tension fractures can develop parallel to bedding with progressive dehydration (Delage, 2014).…”

Section: Measured Hydraulic Fracture Aperturementioning

confidence: 99%

“…In addition, secondary shrinking-induced tension fractures can develop parallel to bedding with progressive dehydration (Delage, 2014). In contrast, hydration of clay-stones leads to a significantly enhanced creep and swelling capacity (Yurikov et al, 2019;Zhang et al, 2007). In the case of the non-lined EZ-B niche in Mont Terri, self-sealing is inhibited due to a sharp decrease in water content of the rock mass close to the niche caused by sustained ventilation since tunnel excavation.…”

Section: Measured Hydraulic Fracture Aperturementioning

confidence: 99%

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Mechanical and hydraulic properties of the excavation damaged zone (EDZ) in the Opalinus Clay of the Mont Terri rock laboratory, Switzerland

Hale

Ries

Jaeggi³

et al. 2021

Solid Earth

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Abstract. Construction of cavities in the subsurface is always accompanied by excavation damage. Especially in the context of deep geological nuclear waste disposal, the evolving excavation damaged zone (EDZ) in the near field of emplacement tunnels is of utmost importance concerning safety aspects. As the EDZ differs from the intact host rock due to enhanced hydraulic transmissivity and altered geomechanical behavior, reasonable and location-dependent input data on hydraulic and mechanical properties are crucial. Thus, in this study, a hydromechanical characterization of an EDZ in the Mont Terri underground rock laboratory, Switzerland, was performed using three different handheld devices: (1) air permeameter, (2) microscopic camera and (3) needle penetrometer. The discrete fracture network (DFN), consisting of artificially induced unloading joints and reactivated natural discontinuities, was investigated by a portable air permeameter and combined microscopic imaging with automatic evaluation. Geomechanical and geophysical characterization of the claystone was conducted based on needle penetrometer testing at the exposed rock surface. Within the EDZ, permeable fractures with a mean hydraulic aperture of 84 ± 23 µm are present. Under open conditions, self-sealing of fractures is suppressed, and cyclic long-term fracture aperture oscillations in combination with closure resulting from convergence processes is observed. Based on measured needle penetration indices, a uniaxial compressive strength of 30 ± 13 MPa (normal to bedding) and 18 ± 8 MPa (parallel to bedding) was determined. Enhanced strength and stiffness are directly related to near-surface desaturation of the claystone and a sharp decrease in water content from 6.6 wt % to 3.7 wt %. The presented methodological approach is particularly suitable for time-dependent monitoring of EDZs since measurements are nondestructive and do not change the actual state of the rock mass. This allows for a spatially resolved investigation of hydraulic and mechanical fracture apertures, fracture surface roughness, and physico-mechanical rock parameters and their intra-facies variability.

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Section: Measured Hydraulic Fracture Aperturementioning

confidence: 99%

Section: Measured Hydraulic Fracture Aperturementioning

confidence: 99%

Section: Measured Hydraulic Fracture Aperturementioning

confidence: 99%

See 1 more Smart Citation

Mechanical and hydraulic properties of the excavation damaged zone (EDZ) in the Opalinus Clay of the Mont Terri rock laboratory, Switzerland

Hale

Ries

Jaeggi³

et al. 2021

Solid Earth

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show abstract

Section: Measured Hydraulic Fracture Aperturementioning

confidence: 99%

Section: Measured Hydraulic Fracture Aperturementioning

confidence: 99%

Mechanical and hydraulic properties of the excavation damaged zone (EDZ) in the Opalinus Clay of the Mont Terri Rock Laboratory, Switzerland

Hale¹,

Ries²,

Jaeggi³

et al. 2021

Preprint

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Abstract. Construction of cavities in the subsurface is always accompanied by excavation damage. Especially in the context of deep geological nuclear waste disposal, the evolving excavation damaged zone (EDZ) in the near field of emplacement tunnels is of utmost importance concerning safety aspects. As the EDZ differs from the intact host rock due to enhanced hydraulic transmissivity and altered geomechanical behavior, reasonable and location-dependent input data on hydraulic and mechanical properties is crucial. Thus in this study, a hydro-mechanical characterization of an EDZ in the Mont Terri underground rock laboratory, Switzerland, was performed using three different handheld devices: (1) air permeameter, (2) microscopic camera and (3) needle penetration test. The discrete fracture network (DFN), consisting of artificially induced unloading joints and reactivated natural discontinuities, was investigated by a portable air permeameter as well as combined microscopic imaging with automatic evaluation. Geomechanical and geophysical characterization of the claystone was conducted based on needle penetrometer testing at the exposed rock surface. Within the EDZ, permeable fractures with a mean hydraulic aperture of 84 ± 23 µm are present. Under open conditions, self-sealing of fractures is suppressed and cyclic long-term fracture aperture oscillations in combination with closure resulting from convergence processes, is observed. Based on measured needle penetration indices, a uniaxial compressive strength of 30 ± 13 MPa (normal to bedding) and 18 ± 8 MPa (parallel to bedding) was determined. Enhanced strength and stiffness is directly related to near-surface desaturation of the claystone and a sharp decrease in water content from 6.6 wt.-% to 3.7 wt.-%. The presented methodological approach is particularly suitable for time-dependent monitoring of EDZs since measurements are nondestructive and do not change the actual state of the rock mass. This allows for a spatially resolved investigation of hydraulic and mechanical fracture apertures, fracture surface roughness as well as physico-mechanical rock parameters and their intra-facies variability.

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A Model for Pore Pressure Response of a Claystone due to Liberated Residual Stress Dilation

Corkum

2019

Rock Mech Rock Eng

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Characterisation of Excavation-Induced Damage Around a Short Test Tunnel in the Opalinus Clay

Cited by 10 publications

References 25 publications

Mechanical and hydraulic properties of the excavation damaged zone (EDZ) in the Opalinus Clay of the Mont Terri rock laboratory, Switzerland

Mechanical and hydraulic properties of the excavation damaged zone (EDZ) in the Opalinus Clay of the Mont Terri rock laboratory, Switzerland

Mechanical and hydraulic properties of the excavation damaged zone (EDZ) in the Opalinus Clay of the Mont Terri Rock Laboratory, Switzerland

A Model for Pore Pressure Response of a Claystone due to Liberated Residual Stress Dilation

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