The Mohr–Coulomb criterion for intact rock strength and friction – a  re-evaluation and consideration of failure under polyaxial stresses

Hackston, Abigail; Rutter, E. H.

doi:10.5194/se-7-493-2016

Cited by 56 publications

(38 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Frictional sliding in the Pennant sandstone samples was stable, without stick-slip and the friction coefficient (μ) = 0.665 ± 0.005 (1 standard error) ( Figure 5). Hackston and Rutter (2016) previously showed this to be the same as the friction coefficient on freshly faulted surfaces.…”

Section: Sliding Frictionmentioning

confidence: 53%

“…A large, homogeneous block was obtained from a monumental mason. Samples from the same block were used in rock mechanics studies by Hackston and Rutter (2016) and Rutter and Hackston (2017). Pennant sandstone displays a weak grain shape orientation parallel to bedding (Figure 1), but the bedding orientation is not well defined by microstructural layering or inhomogeneities.…”

Section: Test Materials and Experiments Performedmentioning

confidence: 99%

See 1 more Smart Citation

Influence of Normal and Shear Stress on the Hydraulic Transmissivity of Thin Cracks in a Tight Quartz Sandstone, a Granite, and a Shale

Rutter

Mecklenburgh

2018

JGR Solid Earth

Self Cite

View full text Add to dashboard Cite

Transmissivity of fluids along fractures in rocks is reduced by increasing normal stress acting across them, demonstrated here through gas flow experiments on Bowland shale, and oil flow experiments on Pennant sandstone and Westerly granite. Additionally, the effect of imposing shear stress at constant normal stress was determined, until frictional sliding started. In all cases, increasing shear stress causes an accelerating reduction of transmissivity by 1 to 3 orders of magnitude as slip initiated, as a result of the formation of wear products that block fluid pathways. Only in the case of granite, and to a lesser extent in the sandstone, was there a minor amount of initial increase of transmissivity prior to the onset of slip. These results cast into doubt the commonly applied presumption that cracks with high resolved shear stresses are the most conductive. In the shale, crack transmissivity is commensurate with matrix permeability, such that shales are expected always to be good seals. For the sandstone and granite, unsheared crack transmissivity was respectively 2 and 2.5 orders of magnitude greater than matrix permeability. For these rocks crack transmissivity can dominate fluid flow in the upper crust, potentially enough to permit maintenance of a hydrostatic fluid pressure gradient in a normal (extensional) faulting regime.

show abstract

Section: Sliding Frictionmentioning

confidence: 53%

Section: Test Materials and Experiments Performedmentioning

confidence: 99%

Influence of Normal and Shear Stress on the Hydraulic Transmissivity of Thin Cracks in a Tight Quartz Sandstone, a Granite, and a Shale

Rutter

Mecklenburgh

2018

JGR Solid Earth

Self Cite

View full text Add to dashboard Cite

show abstract

“…In the shales tested here, the failure stresses measured in the bedding-parallel and bedding-perpendicular orientations are very similar. Hackston and Rutter (2016) found a substantially steeper dependence of 1,fail on 3 in Pennant sandstone than is observed here. The trend presented here in Pennant sandstone was determined from only three Journal of Geophysical Research: Solid Earth 10.1029/2018JB017207 Note.…”

Section: Anisotropy In Failure Strength and Stress At Onset Of Nonlincontrasting

confidence: 46%

Fluid Injection Experiments in Shale at Elevated Confining Pressures: Determination of Flaw Sizes From Mechanical Experiments

et al. 2019

Self Cite

View full text Add to dashboard Cite

Triaxial experiments and direct fluid injection experiments have been conducted at confining pressures up to 100 MPa on Mancos shale, Whitby mudstone, Penrhyn slate, and Pennant sandstone. Experiments were conducted with sample axes lying both parallel and perpendicular to layering in the materials. During triaxial failure Penrhyn slate was stronger for samples with cleavage parallel to maximum principal stress, but the two orientations in the shales displayed similar failure stresses. Initial flaw sizes of around 40 μm were calculated from the triaxial data using the wing crack model, with the shales having shorter initial flaws than the nonshales. During direct fluid injection, breakdown was rapid, with no discernible gap between fracture initiation and breakdown. Breakdown pressure increased linearly with confining pressure but was less sensitive to confining pressure than expected from existing models. A fracture mechanics‐based model is proposed to determine the initial flaw size responsible for breakdown in injection experiments. Flaw sizes determined in this way agree reasonably with those determined from the triaxial data in the nonshales at low confining pressures. As confining pressure rises, a threshold is reached, above which the fluid injection experiments suggest a lower initial flaw length of around 10 μm. This threshold is interpreted as being due to the partial closure of flaws. In the shales an initial flaw length of around 10 μm was determined at all confining pressures, agreeing reasonably with those determined through the triaxial experiments.

show abstract

“…Pennant sandstone is a quartz sandstone deposited in South Wales during the Upper Carboniferous (Kelling, 1974). The samples used here were taken from the same block as used by Hackston and Rutter (2016), who used Scanning Electron Microscopy (SEM) chemical mapping to find a composition of 70% sutured quartz grains and 15% feldspar with the interstitial space containing clusters of muscovite, oxides, and clay minerals. Figure 3 shows example curves of the load, P, as a function of the actuator displacement, x.…”

Section: Sample Materialsmentioning

confidence: 99%

Correlative Optical and X‐Ray Imaging of Strain Evolution During Double‐Torsion Fracture Toughness Measurements in Shale

et al. 2018

View full text Add to dashboard Cite

Mode‐I Fracture Toughness, KIc, was measured in six shale materials using the double‐torsion technique. During loading, crack propagation was imaged both using twin optical cameras, and with fast X‐ray radiograph acquisition. Samples of Bowland, Haynesville, Kimmeridge, Mancos, Middlecliff, and Whitby shales were tested in a range of orientations. The measured fracture toughness values were found to be in good agreement with existing literature values. The two imaging techniques improve our understanding of local conditions around the fracture‐tip, through in situ correlation of mechanical data, inelastic zone size, and fracture‐tip velocity. The optical Digital Image Correlation technique proved useful as a means of determining the validity of individual experiments, by identifying experiments during which strains had developed in the two “rigid” specimen halves. Strain maps determined through Digital Image Correlation of the optical images suggest that the scale of the inelastic zone is an order of magnitude smaller than the classically used approximation suggests. This smaller damage region suggests a narrower region of enhanced permeability around artificially generated fractures in shales. The resolvable crack‐tip was tracked using radiograph data and found to travel at a velocity around 470 μm/s during failure, with little variation in speed between materials and orientations. Fracture pathways in the bedding parallel orientations were observed to deviate from linearity, commonly following layer boundaries. This suggests that while a fracture traveling parallel to bedding may travel at a similar speed to a bedding perpendicular fracture, it may have a more tortuous pathway, and therefore access a larger surface area.

show abstract

The Mohr–Coulomb criterion for intact rock strength and friction – a re-evaluation and consideration of failure under polyaxial stresses

Cited by 56 publications

References 48 publications

Influence of Normal and Shear Stress on the Hydraulic Transmissivity of Thin Cracks in a Tight Quartz Sandstone, a Granite, and a Shale

Influence of Normal and Shear Stress on the Hydraulic Transmissivity of Thin Cracks in a Tight Quartz Sandstone, a Granite, and a Shale

Fluid Injection Experiments in Shale at Elevated Confining Pressures: Determination of Flaw Sizes From Mechanical Experiments

Correlative Optical and X‐Ray Imaging of Strain Evolution During Double‐Torsion Fracture Toughness Measurements in Shale

Contact Info

Product

Resources

About