- Effects of temperature and thermally-induced microstructure change on hydraulic conductivity of Boom Clay
- W.Z. Chen ; Y.S. Ma ; H.D. Yu ; F.F. Li ; X.L. Li ; X. Sillen
- Book Title / Journal: Journal of Rock Mechanics and Geotechnical Engineering
- Year: 2017 , Volume: 9
- Rock Engineering
- Keywords: Boom clay ; permeability ; Thermal effect ; Anisotropy ; microstructure
- Abstract
Boom Clay is one of the potential host rocks for deep geological disposal of high-level radioactive nuclear waste in Belgium. In order to investigate the mechanism of hydraulic conductivity variation under complex thermo-mechanical coupling conditions and to better understand the thermo-hydro-mechanical (THM) coupling behaviour of Boom Clay, a series of permeability tests using temperature-controlled triaxial cell has been carried out on the Boom Clay samples taken from Belgian underground research laboratory (URL) HADES. Due to its sedimentary nature, Boom Clay presents across-anisotropy with respect to its sub-horizontal bedding plane. Direct measurements of the vertical (Kv) and horizontal (Kh) hydraulic conductivities show that the hydraulic conductivity at 80 °C is about 2.4 times larger than that at room temperature (23 °C), and the hydraulic conductivity variation with temperature is basically reversible during heating–cooling cycle. The anisotropic property of Boom Clay is studied by scanning electron microscope (SEM) tests, which highlight the transversely isotropic characteristics of intact Boom Clay. It is shown that the sub-horizontal bedding feature accounts for the horizontal permeability higher than the vertical one. The measured increment in hydraulic conductivity with temperature is lower than the calculated one when merely considering the changes in water kinematic viscosity and density with temperature. The nuclear magnetic resonance (NMR) tests have also been carried out to investigate the impact of microstructure variation on the THM properties of clay. The results show that heating under unconstrained boundary condition will produce larger size of pores and weaken the microstructure. The discrepancy between the hydraulic conductivity experimentally measured and predicted (considering water viscosity and density changes with temperature) can be attributed to the microstructural weakening effect on the thermal volume change behaviour of Boom Clay. Based on the experimental results, a hydraulic conductivity evolution model is proposed and then implemented in ABAQUS. Three-dimensional (3D) numerical simulation of the admissible thermal loading for argillaceous storage (ATLAS) III in situ heating test has been conducted subsequently, and the numerical results are in good agreement with field measurements. PDF |
- Characteristics of structure evolution of expansive soil and loess during loading and wetting
- Z. Chen ;
- Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, September 2-6 2013
- Year: 2013
- Structural Geology
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- An ABAQUS Implementation of the XFEM for Hydraulic Fracture Problems
- Z. Chen
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 36
- Discrete Element
- Keywords: Hydraulic fracture ; Extended Finite Element Method ; internal pressure
- Description
- A new finite element has been implemented in ABAQUS to incorporate the extended finite
element method (XFEM) for the solution of hydraulic fracture problems. The proposed element includes the desired aspects of the XFEM so as to model crack propagation without explicit remeshing. In addition, the fluid pressure degrees of freedom have been defined on the element to describe the fluid flow within the crack and its contribution to the crack deformation. Thus the fluid flow and resulting crack propagation are fully coupled in a natural
way and are solved simultaneously. Verification of the element has been made by comparing the finite element results with the analytical solutions available in the literature.
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- The Impact of the Near-Tip Logic on the Accuracy and Convergence Rate of Hydraulic Fracture Simulators Compared to Reference Solutions
- B. Lecampion ; A. Peirce ; E. Detournay ; X. Zhang ; Z. Chen ; An. Bunger ; C. DetournayC ; J. Napier ; S. Abbas ; D. Garagash ; P. Cundall
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 43
- Numerical & Constitutive Modeling
- Keywords: hydraulic fracture simulators ; near-tip logic
- Description
- We benchmark a series of simulators against available reference solutions for propagating
plane-strain and radial hydraulic fractures. In particular, we focus on the accuracy and
convergence of the numerical solutions in the important practical case of viscosity dominated
propagation. The simulators are based on different propagation criteria: linear elastic
fracture mechanics (LEFM), cohesive zone models/tensile strength criteria, and algorithms
accounting for the multi-scale nature of hydraulic fracture propagation in the near-tip region.
All the simulators tested here are able to capture the analytical solutions of the different configurations tested, but at vastly different computational costs. Algorithms based on
the classical LEFM propagation condition require a fine mesh in order to capture viscosity dominated hydraulic fracture evolution. Cohesive zone models, which model the fracture
process zone, require even finer meshes to obtain the same accuracy. By contrast, when
the algorithms use the appropriate multi-scale hydraulic fracture asymptote in the near-tip
region, the exact solution can be matched accurately with a very coarse mesh. The different
analytical reference solutions used in this paper provide a crucial series of benchmark tests
that any successful hydraulic fracturing simulator should pass.
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- Monitoring and Measuring Hydraulic Fracturing Growth During Preconditioning of a Roof Rock over a Coal Longwall Panel
- R.G. Jeffrey ; Z. Chen ; K.W. Mills ; S. Pegg
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 45
- Rock Engineering ; Mining
- Keywords: hydraulic fracturing
- Description
- Narrabri Coal Operations is longwall mining coal directly below a 15 to 20 m thick conglomerate sequence expected to be capable of producing a windblast upon first caving at longwall startup and producing periodic weighting during regular mining. Site characterisation and field trials were undertaken to evaluate hydraulic fracturing as a method to precondition the conglomerate strata sufficiently to promote normal caving behaviour at longwall startup and reduce the severity of periodic weighting. This paper presents the results of the trials and illustrates the effectiveness of hydraulic fracturing as a preconditioning technique. Initial work was directed at determining if hydraulic fractures were able to be grown with a horizontal orientation, which would allow efficient preconditioning of the rock mass by placing a number of fractures at different depths through the conglomerate from vertical boreholes drilled from the surface. The measurements and trials were designed to determine the in situ principal stresses, the hydraulic fracture orientation and growth rate, and whether the fractures could be extended as essentially parallel fractures to a radius of at least 30 m. Overcore stress measurements were used to determine the orientation and magnitude of the in situ principal stresses, a surface tiltmeter array was used to determine the hydraulic fracture orientation, and stress change monitoring, pressure monitoring and temperature logging in offset boreholes were used to establish the fracture growth rate, lateral extent, and that the fractures maintained their initial spacing to a radial distance of greater than 30 metres. The measurements and trials demonstrated that horizontal fractures could be extended parallel to one another to a distance of 30 to 50 m by injection of 5,000 to 15,000 litres of water at a rate of 400 to 500 L/min. Results from the trial allowed a preconditioning plan to be developed and successfully implemented.
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- Polymer addition to enhance healing and self-healing of kaolin clay
- S.Z. Chen ; Y.X.D.W. GanandAirey
- Australia - New Zealand Conferences on Geomechanics - 13th Australia New Zealand Conference on Geomechanics
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- Ground Improvement
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- Characteristics of structure evolution of expansive soil and loess during loading and wetting
- Z. Chen
- International Conference on Soil Mechanics and Geotechnical Engineering - 18th International Conference on Soil Mechanics and Geotechnical Engineering (Paris)
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- Soil Mechanics
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- Numerical simulation of heat and mass transfer during the in-situ thermal remediation process of NAPLs-impacted soil
- Z. Chen
- International Conference on Soil Mechanics and Geotechnical Engineering - 20th International Conference on Soil Mechanics and Geotechnical Engineering (Sydney)
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- Experience with the Search of Minimum Factor of Safety of Slopes
- Z. Chen
- Australia - New Zealand Conferences on Geomechanics - 6th Australia New Zealand Conference on Geomechanics (Christchurch, 1992)
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- Slope Stability
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