Rock Mechanics

Wittke, Walter

doi:10.1007/978-3-642-88109-1

Cited by 159 publications

(21 citation statements)

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“…Assuming that the ''background'' permeability in the absence of fissures is isotropic (equal to k 0 I), we aim at expressing the change of permeability due to cracks K À k 0 I as a function of the proper microstructural parameter. It is usually assumed that permeability due to several families of fissures is a simple superposition of the individual permeabilities, the underlying assumption being that energy losses at intersections can be neglected (Wittke, 1990). This implies that a-type tensor that sums up the individual fissure contributions, is adequate.…”

Section: Effective Transport Propertiesmentioning

confidence: 99%

On quantitative characterization of microstructures and effective properties

Kachanov

Sevostianov

2005

International Journal of Solids and Structures

250

118

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Section: Effective Transport Propertiesmentioning

confidence: 99%

On quantitative characterization of microstructures and effective properties

Kachanov

Sevostianov

2005

International Journal of Solids and Structures

250

118

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“…Making use of limiting equilibrium methods, John [4], Londe et al [5], Hendron et al [6], Hoek and Bray [7], Warburton [8], Priest [9], and Goodman and Shi [1] considered case (a) (wedge sliding) only. Pioneered by Wittke [10,11], the study of rotational failure modes (b) and (c) in Figure 2 was also pursued using analytical methods by Chan and Einstein [12], Mauldon and Goodman [13], and Tonon [14]. These analytical methods cannot handle general simultaneous sliding and rotation; Yeung and co-workers [15][16][17] thus used a numerical method, such as the discontinuous deformation analysis (DDA), to overcome the problem.…”

Section: Introductionmentioning

confidence: 98%

Analysis of single rock blocks for general failure modes under conservative and non‐conservative forces

Tonon

2007

Num Anal Meth Geomechanics

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SUMMARYAfter describing the kinematics of a generic rigid block subjected to large rotations and displacements, the Udwadia's General Principle of Mechanics is applied to the dynamics of a rigid block with frictional constraints to show that the reaction forces and moments are indeterminate. Thus, the paper presents an incremental-iterative algorithm for analysing general failure modes of rock blocks subject to generic forces, including non-conservative forces such as water forces. Consistent stiffness matrices have been developed that fully exploit the quadratic convergence of the adopted Newton-Raphson iterative scheme. The algorithm takes into account large block displacements and rotations, which together with nonconservative forces make the stiffness matrix non-symmetric. Also included in the algorithm are in situ stress and fracture dilatancy, which introduces non-symmetric rank-one modifications to the stiffness matrix. Progressive failure is captured by the algorithm, which has proven capable of detecting numerically challenging failure modes, such as rotations about only one point. Failure modes may originate from a limit point or from dynamic instability (divergence or flutter); equilibrium paths emanating from bifurcation points are followed by the algorithm. The algorithm identifies both static and dynamic failure modes. The calculation of the factor of safety comes with no overhead. Examples show that the equilibrium path of a rock block that undergoes slumping failure must first pass through a bifurcation point, unless the block is laterally constrained. Rock blocks subjected to water forces (or other non-conservative forces) may undergo flutter failure before reaching a limit point.

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“…To date there has been little overlap between work of this nature and laboratory experiments. This has been due to difficulties in conducting experiments on similar timescales and spatial extents between real-world and (Wittke and Sykes, 1990;Deer et al, 1992). computational systems. While these obstacles are likely to remain in place for some time, the feldspars may offer the opportunity to address this deficit by providing qualitative corroboration between computational and laboratory results.…”

Section: Introductionmentioning

confidence: 99%

Not all feldspars are equal: a survey of ice nucleating properties across the feldspar group of minerals

et al. 2016

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Abstract. Mineral dust particles from wind-blown soils are known to act as effective ice nucleating particles in the atmosphere and are thought to play an important role in the glaciation of mixed phase clouds. Recent work suggests that feldspars are the most efficient nucleators of the minerals commonly present in atmospheric mineral dust. However, the feldspar group of minerals is complex, encompassing a range of chemical compositions and crystal structures. To further investigate the ice-nucleating properties of the feldspar group we measured the ice nucleation activities of 15 characterized feldspar samples. We show that alkali feldspars, in particular the potassium feldspars, generally nucleate ice more efficiently than feldspars in the plagioclase series which contain significant amounts of calcium. We also find that there is variability in ice nucleating ability within these groups. While five out of six potassium-rich feldspars have a similar ice nucleating ability, one potassium rich feldspar sample and one sodium-rich feldspar sample were significantly more active. The hyper-active Na-feldspar was found to lose activity with time suspended in water with a decrease in mean freezing temperature of about 16 • C over 16 months; the mean freezing temperature of the hyper-active K-feldspar decreased by 2 • C over 16 months, whereas the "standard" K-feldspar did not change activity within the uncertainty of the experiment. These results, in combination with a review of the available literature data, are consistent with the previous findings that potassium feldspars are important components of arid or fertile soil dusts for ice nucleation. However, we also show that there is the possibility that some alkali feldspars may have enhanced ice nucleating abilities, which could have implications for prediction of ice nucleating particle concentrations in the atmosphere.

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Rock Mechanics

Cited by 159 publications

References 0 publications

On quantitative characterization of microstructures and effective properties

On quantitative characterization of microstructures and effective properties

Analysis of single rock blocks for general failure modes under conservative and non‐conservative forces

Not all feldspars are equal: a survey of ice nucleating properties across the feldspar group of minerals

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