A constitutive law for low‐temperature creep of water‐saturated sandstones

Ngwenya, Bryne T.; Main, Ian; Elphick, Stephen C.; Crawford, Brian; Smart, Brian George Davidson

doi:10.1029/2001jb000403

Cited by 81 publications

(49 citation statements)

References 53 publications

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“…In turn, this would allow us to quantify the effect of other experimental variables of interest in a more sample and time efficient manner. The stress‐stepping approach has previously been used and has shown to provide reliable data [ Lockner , 1993a; Maranini and Brignoli , 1999; Ngwenya et al , 2001, among others].…”

Section: Resultsmentioning

confidence: 99%

Time‐dependent brittle creep in Darley Dale sandstone

Heap¹,

Baud

Meredith³

et al. 2009

J. Geophys. Res.

318

246

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[1] The characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of the Earth's crust. The chemical influence of pore water promotes time-dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Here, we report results from a study of time-dependent brittle creep in water-saturated samples of Darley Dale sandstone (initial porosity, 13%) under triaxial stress conditions. Results from conventional creep experiments show that axial strain rate is heavily dependent on the applied differential stress. A reduction of only 10% in differential stress results in a decrease in strain rate of more than two orders of magnitude. However, natural sample variability means that multiple experiments must be performed to yield consistent results. Hence we also demonstrate that the use of stress-stepping creep experiments can successfully overcome this issue. We have used the stress-stepping technique to investigate the influence of confining pressure at effective confining pressures of 10, 30, and 50 MPa (while maintaining a constant 20 MPa pore fluid pressure). Our results demonstrate that the stress corrosion process appears to be significantly inhibited at higher effective pressures, with the creep strain rate reduced by multiple orders of magnitude. The influence of doubling the pore fluid pressure, however, while maintaining a constant effective confining pressure, is shown to influence the rate of stress corrosion within the range expected from sample variability. We discuss these results in the context of microstructural analysis, acoustic emission hypocenter locations, and fits to proposed macroscopic creep laws.

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Section: Resultsmentioning

confidence: 99%

Time‐dependent brittle creep in Darley Dale sandstone

Heap¹,

Baud

Meredith³

et al. 2009

J. Geophys. Res.

318

246

View full text Add to dashboard Cite

show abstract

“…Figure 9 shows plots of the data and fits to equation (3) at four selected effective confining pressures, corresponding to the tests used in Figure 7. The curves were fitted using an iterative nonlinear regression technique [ Ngwenya et al , 2001], and confirm that the three‐parameter model fits the data with high correlation coefficients, ranging from 0.970 to 0.987. It is also apparent in Figure 9 that the relationship is log linear at low effective confining pressures, but becomes increasingly nonlinear as effective confining pressure increases.…”

Section: Analysis and Interpretationmentioning

confidence: 99%

Permeability evolution during progressive development of deformation bands in porous sandstones

et al. 2003

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[1] Triaxial deformation experiments were carried out on large (0.1 m) diameter cores of a porous sandstone in order to investigate the evolution of bulk sample permeability as a function of axial strain and effective confining pressure. The log permeability of each sample evolved via three stages: (1) a linear decrease prior to sample failure associated with poroelastic compaction, (2) a transient increase associated with dynamic stress drop, and (3) a systematic quasi-static decrease associated with progressive formation of new deformation bands with increasing inelastic axial strain. A quantitative model for permeability evolution with increasing inelastic axial strain is used to analyze the permeability data in the postfailure stage. The model explicitly accounts for the observed fault zone geometry, allowing the permeability of individual deformation bands to be estimated from measured bulk parameters. In a test of the model for Clashach sandstone, the parameters vary systematically with confining pressure and define a simple constitutive rule for bulk permeability of the sample as a function of inelastic axial strain and effective confining pressure. The parameters may thus be useful in predicting fault permeability and sealing potential as a function of burial depth and fault displacement.

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“…In recent years, this phenomenon has been studied by running series of brittle creep experiments (called static fatigue experiments in the engineering literature) on various rock types: sandstone (Baud and Meredith, 1997;Ngwenya et al 2001;Heap et al, 2009a-b), granite (Kranz, 1980;Lockner, 1993;Brantut et al, 2012;Wang, 2012) and basalt (Heap et al, 2011). In most cases, the evolution of rock microstructure during creep has been monitored using several proxies for crack damage: strain, porosity change, acoustic emission output and changes in acoustic wave velocities.…”

Section: Introductionmentioning

confidence: 99%

Mechanics of Time-Dependent Deformation in Crustal Rocks

et al. 2013

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The characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of the crust. Here we report results from a study of brittle creep in Darley Dale sandstone under triaxial stress conditions. We present new results from a series of constant strain rate experiments and conventional brittle creep experiments. We then apply a micromechanical model for brittle creep in rocks to our experimental data. This model shows that the acceleration of the strain rate observed experimentally prior to failure is due to the increasing importance of crack interactions. Finally, if we compare long-term creep failure under a constant stress with short-term failure under an imposed constant strain rate, we find a mechanical work deficit. The magnitude of the deficit in the mechanical work rate is by definition a stress deficit. Our analysis implies that rock deformation under both constant stress (creep) and constant strain rate conditions are controlled by the same underlying chemo-mechanical processes.

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A constitutive law for low‐temperature creep of water‐saturated sandstones

Cited by 81 publications

References 53 publications

Time‐dependent brittle creep in Darley Dale sandstone

Time‐dependent brittle creep in Darley Dale sandstone

Permeability evolution during progressive development of deformation bands in porous sandstones

Mechanics of Time-Dependent Deformation in Crustal Rocks

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