Comparison of frictional material models with respect to shear band initiation

Molenkamp, F.

doi:10.1680/geot.1985.35.2.127

Cited by 73 publications

(11 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Formation and progression of SBs in contractant clays is difficult to model due to the non-unique solutions and ill posedness of the governing equations (Rudnick and Rice, 1975;Vardoulakis, 1980Vardoulakis, , 1996aMolenkamp, 1985;Vermeer, 1990;Brinkgreve, 1994;Saada et al, 1999). In contrast, no specific regularization technique has been developed for contractant clays because an appropriate micro-structural length parameter had not been identified until the work of Jostad et al (2006), Thakur (2007), and 1 Particle image velocimetry results (incremental displacement field) for a contractantant clay subjected to undrained shearing at 3%/h normalized rate of deformation under plane strain condition Thakur (2011).…”

Section: Shear Bands In Contractant Claysmentioning

confidence: 99%

Orientation of locally drained shear bands in contractant clays

Thakur¹

2013

International Journal of Geotechnical Engineering

View full text Add to dashboard Cite

A slip surface or shear band orientation of 45u from the minor principal stress is obtained when contractant clays are numerically analyzed while assuming undrained conditions. This orientation occurs because the shear band is modeled as undrained and with no volume change. However, thin shear bands induce the dissipation of pore water to the outside body, and depending on the degree of local drainage, the incipient shear bands are then no longer at 45u. In drained conditions, the incipient shear band inclination to the minor principal stress is controlled by the friction angle, the dilatancy angle or a combination of both. This paper examines the orientation of a developing shear band, accounting for the effects of local pore water pressure flow away from the shear band to investigate whether the orientation of the band is controlled by the degree of drainage (i.e. volume change) or the mechanisms of shear band orientation under fully drained conditions. The numerical results show that the band's inclination can be .45u for globally undrained contractant clays sheared at rates of #10%/h, rates that are normal in laboratory testing.

show abstract

Section: Shear Bands In Contractant Claysmentioning

confidence: 99%

Orientation of locally drained shear bands in contractant clays

Thakur¹

2013

International Journal of Geotechnical Engineering

View full text Add to dashboard Cite

show abstract

“…While many criteria exist to ascertain the onset of localization for plastic materials (Hill & Hutchinson 1975; Rudnicki & Rice 1975) and for granular materials under high stress (Molenkamp 1985; Koenders et al 1990; Vermeer 1990), a simple approach is taken here. The material condition is assumed to be such that there is a time point after the imposition of a uniform deformation field at which no unique shear stress increment can be found.…”

Section: Rheology Of Rate Dependent Dilatant Materialsmentioning

confidence: 99%

Shear-induced pressure changes and seepage phenomena in a deforming porous layer-III

Koenders

Petford²

2007

Geophysical Journal International

View full text Add to dashboard Cite

S U M M A R YWe report the results of an analytical investigation into the deformation behaviour of ratedependent granular material as a refinement of previous studies on seepage phenomena during shear. The rheology has two components-a compliant part of the constitutive law associated with grain contacts as deformation takes place (dilatancy), and a rate-dependent viscous force transmitted by the melt phase. This formulation allows intermediate, time-dependent behaviour to be assessed for the dilatant porous medium. A key result is that during shear, the magnitude of the excess pore pressure first decreases then increases back to its initial value. Two characteristic timescales are identified that control the rate-dependent dilatancy of the mixture, τ 1 , the time constant that rules the increase of the magnitude of the excess pore pressure, and τ 0 that controls its decline. We consider the dilatant effect to be an internal constraint in deforming magmas in the lithosphere and other porous (partially molten) regions in the solid earth. When such regions are exposed to external loading, secular pressure changes should drive fluid flow independent of local buoyancy forces, for the duration of the governing rate-dependent timescales. The accumulated heave of the process is also estimated.

show abstract

“…Post‐failure the material has become degenerate, though not unconstrained. The transition between the two regimes is marked by some form of bifurcation, see for instance Molenkamp (1985) or Vermeer (1990) for continuum‐mechanical descriptions in the context of elasto‐plasticity.…”

Section: Granular Materialsmentioning

confidence: 99%

Shear-induced pressure changes and seepage phenomena in a deforming porous layer - I

Petford¹,

Koenders²

2003

Geophysical Journal International

View full text Add to dashboard Cite

S U M M A R YWe present a model for flow and seepage in a deforming, shear-dilatant sensitive porous layer that enables estimates of the excess pore fluid pressures and flow rates in both the melt and solid phase to be captured simultaneously as a function of stress rate. Calculations are relevant to crystallizing magma in the solidosity range 0.5-0.8 (50-20 per cent melt), corresponding to a dense region within the solidification front of a crystallizing magma chamber. Composition is expressed only through the viscosity of the fluid phase, making the model generally applicable to a wide range of magma types. A natural scaling emerges that allows results to be presented in non-dimensional form. We show that all length-scales can be expressed as fractions of the layer height H, timescales as fractions of H 2 (nβ θ + 1)/(θ k) and pressures as fractions of Rċ 0 H 2 /(θ k). Taking as an example the permeability k in the mush of the order of magnitude 10 −15 m 2 Pa −1 s −1 , a layer thickness of tens of metres and a mush strength (θ ) in the range 10 8 -10 12 Pa, an estimate of the consolidation time for near-incompressible fluids is of the order of 10 5 -10 9 s. Using mush permeability as a proxy, we show that the greatest maximum excess pore pressures develop consistently in rhyolitic (high-viscosity) magmas at high rates of shear (ċ 0 > 10 −1 Pa s −1 ), implying that during deformation, the mechanical behaviour of basaltic and rhyolitic magmas will differ. Transport parameters of the granular framework including tortuosity and the ratio of grain size to layer thickness (a/H) will also exert a strong effect on the mechanical behaviour of the layer at a given rate of strain. For dilatant materials under shear, flow of melt into the granular layer is implied. Reduction in excess pore pressure sucks melt into the solidification front at a velocity proportional to the strain rate. For tectonic rates (generally 10 −14 s −1 ), melt upwelling (or downwelling, if the layer is on the floor of the chamber) is of the order of cm yr −1 . At higher rates of loading comparable with emplacement of some magmatic intrusions (∼10 −10 s −1 ), melt velocities may exceed effects due to instabilities resulting from local changes in density and composition. Such a flow carries particulates with it, and we speculate that these may become trapped in the granular layer depending on their sizes. If on further solidification the segregated grain size distribution of the particulates is frozen in the granular layer, structure formation including layering and grading may result. Finally, as the process settles down to a steady state, the pressure does not continue to decrease. We find no evidence for critical rheological thresholds, and the process is stable until so much shear has been applied that the granular medium fails, but there is no hydraulic failure.

show abstract

Comparison of frictional material models with respect to shear band initiation

Cited by 73 publications

References 3 publications

Orientation of locally drained shear bands in contractant clays

Orientation of locally drained shear bands in contractant clays

Shear-induced pressure changes and seepage phenomena in a deforming porous layer-III

Shear-induced pressure changes and seepage phenomena in a deforming porous layer - I

Contact Info

Product

Resources

About