A discrete element model for the development of compaction localization in granular rock

Wang, Baoshan; Chen, Yong; Wong, Teng-fong

doi:10.1029/2006jb004501

Cited by 67 publications

(89 citation statements)

References 56 publications

(138 reference statements)

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“…Apart from differences in average contact length, which varies with grain size, composition and degree of cementation, one can again clearly distinguish Bentheim and Diemelstadt sandstones with nearly identical narrow contact length distribution, from the Rothbach sandstone which shows significantly broader distribution. As proxies for grain-scale heterogeneity, these statistics of CT-number and grain contact length strongly support the idea that discrete compaction bands are promoted in a relatively homogeneous granular material, in agreement with recent numerical simulations using network (KATSMAN et al, 2005) and discrete element (WANG et al, 2008) models. Vol.…”

Section: Microstructural Origin Of the Mechanical Anisotropysupporting

confidence: 88%

Microstructural Inhomogeneity and Mechanical Anisotropy Associated with Bedding in Rothbach Sandstone

Louis

Baud

Wong

2009

Pure appl. geophys.

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This study present the result of conventional triaxial tests conducted on samples of Rothbach sandstone cored parallel, oblique (at 45 degrees) and perpendicular to the bedding at effective pressures ranging from 5 to 250 MPa. Mechanical and microstructural data were used to determine the role of the bedding on mechanical strength and failure mode. We find that samples cored at 45 degrees to the bedding yield at intermediate level of differential stress between the ones for parallel and perpendicular samples at all effective pressures. Strain localization at high confining pressure (i.e., in the compactive domain) is observed in samples perpendicular and oblique to the bedding but not in samples cored parallel to the bedding. However, porosity reduction is comparable whether compactive shear bands, compaction bands or homogeneous cataclastic flow develop. Microstructural data suggest that (1) mechanical anisotropy is controlled by a preferred intergranular contact alignment parallel to the bedding and that (2) localization of compaction is controlled by bedding laminations and grain scale heterogeneity, which both prevent the development of well localized compaction features.

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Section: Microstructural Origin Of the Mechanical Anisotropysupporting

confidence: 88%

Microstructural Inhomogeneity and Mechanical Anisotropy Associated with Bedding in Rothbach Sandstone

Louis

Baud

Wong

2009

Pure appl. geophys.

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“…The observation that many shear bands in the semibrittle faulting regime show relatively large offsets (with offset to length ratio of up to~3%; Table 2) suggests that the bands are long-lived. This inference agrees with permanent, mesoscale bands predicted from models where grain contacts lose shear strength once slip occurs (Wang et al, 2008;Zheng et al, 2016), but differs from short-lived bands shown in models where the once-slipped contacts regain the strength (Aharonov & Sparks, 2002).…”

Section: Role Of Mesoscale Shear Bands On Granular Deformationsupporting

confidence: 82%

Brittle to Semibrittle Transition in Quartz Sandstone: Energetics

Kanaya

Hirth

2018

JGR Solid Earth

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Triaxial compression experiments were conducted on a quartz sandstone at effective pressures up to 175 MPa and temperatures up to 900°C. Our experiments show a transition from brittle faulting to semibrittle faulting with an increase in both pressure and temperature. The yield behavior of samples deformed in the semibrittle regime follows a compactant elliptical cap at low strain, but evolves to a dilatant Mohr–Coulomb relationship with continued compaction. Optical microscopy indicates that semibrittle deformation involves cataclastic flow through shear‐enhanced compaction and grain crushing; however, transmission electron microscopy shows evidence for dislocation glide in limited portions of samples. To constrain the relative contribution of brittle and crystal plastic mechanisms, we estimate the partitioning of the inelastic work into the dissipation energy for microcracking, intergranular frictional slip, and dislocation glide. We conclude that semibrittle deformation is accommodated primarily by cataclastic mechanisms, with only a limited contribution from crystal plasticity. Mechanical data, acoustic emission records, and analysis of surface energy all indicate the activation of subcritical cracking at elevated temperature. Hence, we infer that the enhancement of subcritical cracking is responsible for the transition to semibrittle flow through promoting distributed grain‐scale fractures and millimeter‐scale shear bands. Subcritical cracking promotes the nucleation of microfractures at lower stresses, and the resulting decrease in flow stress retards the propagation of transgranular microfractures. Our study illuminates the important role of temperature on the micromechanics of the transition from brittle faulting to cataclastic flow in the Earth.

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“…[22][23][24][25][26][27] Moreover, DEM models provide an avenue to investigate the effect of microscopic properties on the macro-scale response, like role of grain interlocking on strength, 28 effect of porosity on the deformability and strength, 29,30 effect of pore size and pore distribution. 31 The advantage of DEM over other continuum methods is its ability to explicitly model the initiation and propagation of cracks from micro-scale to macro-scale without applying complex constitutive laws.…”

Section: Numerical Methodologiesmentioning

confidence: 99%