TY - JOUR
T1 - Shear strength and shear stiffness analysis of compacted Wyoming-type bentonite
AU - Pintado, X.
AU - Kumpulainen, S.
AU - Romero, E.
AU - Lloret, A.
AU - Weber, R. C.
AU - Ferrari, A.
AU - Villar, M. V.
AU - Abed, A.
AU - Solowski, W.
AU - Heino, Ville
N1 - Funding Information:
Financial support of Posiva Oy (Finland) through a collaboration agreement with Mitta Oy is greatly acknowledged, as well as the support by CIEMAT, CIMNE (Spain) and EPFL (Switzerland). The authors appreciate the internal review of the manuscript carried out by Barbara Pastina from the Safety Case at Posiva Oy, and Pirjo Hellä and Núria Marcos from the Long-Term Safety Team at Mitta Oy, the data provided by Peter Eriksson (SKB AB) and the suggestions from Domenico Gallipoli (University of Genoa) and Vicente Navarro (University of Castilla-La Mancha).
Funding Information:
Financial support of Posiva Oy (Finland) through a collaboration agreement with Mitta Oy is greatly acknowledged, as well as the support by CIEMAT, CIMNE (Spain) and EPFL (Switzerland). The authors appreciate the internal review of the manuscript carried out by Barbara Pastina from the Safety Case at Posiva Oy, and Pirjo Hellä and Núria Marcos from the Long-Term Safety Team at Mitta Oy, the data provided by Peter Eriksson (SKB AB) and the suggestions from Domenico Gallipoli (University of Genoa) and Vicente Navarro (University of Castilla-La Mancha).
Publisher Copyright:
© 2023 Elsevier Ltd
PY - 2023/6
Y1 - 2023/6
N2 - Wyoming-type bentonite is one of the materials to be used as part of the Engineered Barrier System (EBS) in deep geological disposal facilities for the safe disposal of spent nuclear fuel. In the KBS-3 type repository, the canisters containing the spent fuel assemblies are surrounded by bentonite buffer. Therefore, it is necessary to understand the bentonite behaviour in shearing conditions for the long-term performance assessment of the canisters. Bentonite shearing could arise, for example, due to potential post-glacial earthquakes. The deviatoric stress at failure and the shear modulus of a compacted Wyoming-type bentonite were measured using different shearing tests. Tests were carried out on unsaturated samples at three laboratories. The shearing tests on unsaturated samples were unconfined and triaxial compression tests, hollow cylinder tests and simple shear tests. Unconfined and triaxial compression tests were also carried out on saturated samples. The failure was quite ductile when tests were carried out with confining pressure. The samples were compacted at different dry densities and degrees of saturation and tested at different confining pressures and strain levels to study their influence on the shear properties. Shear strength and shear modulus were studied based on models that consider the double porosity structure of the bentonites. Previously published triaxial tests and resonant column test results were also included in this study. In combination with these models, several alternatives for the definition of the constitutive stress were checked for the case of bentonite. A novel, approach, involving the results of mercury intrusion porosimetry in estimating the constitutive stress, was introduced. The shear strength calculated by the models showed a good agreement with the measured values. In some cases, unrealistic large tensile stresses were predicted. Furthermore, the models can assess the tendency of the shear modulus as a function of the shear strain, degree of saturation and dry density.
AB - Wyoming-type bentonite is one of the materials to be used as part of the Engineered Barrier System (EBS) in deep geological disposal facilities for the safe disposal of spent nuclear fuel. In the KBS-3 type repository, the canisters containing the spent fuel assemblies are surrounded by bentonite buffer. Therefore, it is necessary to understand the bentonite behaviour in shearing conditions for the long-term performance assessment of the canisters. Bentonite shearing could arise, for example, due to potential post-glacial earthquakes. The deviatoric stress at failure and the shear modulus of a compacted Wyoming-type bentonite were measured using different shearing tests. Tests were carried out on unsaturated samples at three laboratories. The shearing tests on unsaturated samples were unconfined and triaxial compression tests, hollow cylinder tests and simple shear tests. Unconfined and triaxial compression tests were also carried out on saturated samples. The failure was quite ductile when tests were carried out with confining pressure. The samples were compacted at different dry densities and degrees of saturation and tested at different confining pressures and strain levels to study their influence on the shear properties. Shear strength and shear modulus were studied based on models that consider the double porosity structure of the bentonites. Previously published triaxial tests and resonant column test results were also included in this study. In combination with these models, several alternatives for the definition of the constitutive stress were checked for the case of bentonite. A novel, approach, involving the results of mercury intrusion porosimetry in estimating the constitutive stress, was introduced. The shear strength calculated by the models showed a good agreement with the measured values. In some cases, unrealistic large tensile stresses were predicted. Furthermore, the models can assess the tendency of the shear modulus as a function of the shear strain, degree of saturation and dry density.
KW - Bishop's stress
KW - Constitutive stress
KW - Hollow cylinder test
KW - Mercury intrusion porosimetry
KW - Shear strength
KW - Simple shear test
KW - Suction
KW - Triaxial test
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U2 - 10.1016/j.gete.2023.100468
DO - 10.1016/j.gete.2023.100468
M3 - Article
AN - SCOPUS:85158820086
SN - 2352-3808
VL - 34
JO - Geomechanics for Energy and the Environment
JF - Geomechanics for Energy and the Environment
M1 - 100468
ER -