Inherent and stress-state-induced anisotropy in very small strain stiffness of a sandy gravel

Jiang, Guanlu; Tatsuoka, Fumio; Flora, Alessandro; Koseki, Junichi

doi:10.1680/geot.1997.47.3.509

Cited by 85 publications

(26 citation statements)

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“…Thus, I proceeded to compare velocities and strains measured under hydrostatic pressure and under a test that I called quasihydrostatic discussed in Chapter 3. Although the work of indicates that sands are expected to be intrinsically isotropic, I found that P-wave velocity anisotropy for the quasi-hydrostatic stress also is affected by the intrinsic anisotropy in sands corroborating previous work (Jiang et al, 1997;Tai and Sadd, 1997;Chen et al, 1998;). This result led me to investigate more the intrinsic anisotropy and P-wave velocity anisotropy in the sands and glass beads discussed in Chapter 4.…”

Section: Dissertation Outlinesupporting

confidence: 86%

“…Wong and Arthur (1985) showed that intrinsic anisotropy in sand affects the induced strain anisotropy; the stress-strain relation depends on the direction of the applied stress when the grain deposition is in the symmetry plane of the major principal stress. In sandy gravels, Jiang et al (1997) found static Young's modulus anisotropy in samples with intrinsic and induced anisotropy. Hock and Totsuka (1998) found that the strain anisotropy and the static Young's modulus anisotropy in sands and gravels become higher as the stress state become more anisotropic.…”

Section: Soft Sediments and Anisotropy Overviewmentioning

confidence: 99%

“…Most of the studies have been done on packings structure and deposition (Bernal and Mason, 1960;Makse et al 1997;Makse et al, 2000), motion of the grains (Savage, 1993), granular hydrodynamics (Blanc and Hinch, 1993), and stress distribution ) mainly for one simple grain constituent; and mechanical or static (Wong and Arthur, 1985;Jiang et al, 1997;Hoque and Tatsuoka, 1998;Chang, 1998) and acoustic or dynamic properties Kopperman, 1982;Zeng, 1999;Cascante and Santamarina, 1996;Fratta and Santamarina, 1996;Modoni et al, 2000;Fiovarante and Capoferri, 2001) mainly for soft sediments. The studies of properties of simpler granular materials, such as those having only a single grain constituent, can help us to understand more complex granular materials, such as soft natural sediments.…”

Section: Soft Sediments and Anisotropy Overviewmentioning

confidence: 99%

“…They found that the dependence of the shear modulus with shear stress and the dependence of strain with stress in the induced anisotropic samples were slightly higher than in the intrinsic anisotropic samples. Research in soft sediments and stress anisotropy has been done on static properties, such as Young modulus, stress versus strain, strength (Wong and Arthur, 1985;Jiang et al, 1997;Hoque and Tatsuoka, 1998). Research on stress-induced anisotropy of dynamic properties, i.e., acoustic velocities, has been done for a wide range of compressive stresses in consolidated rocks (Nur and Simmons, 1969;Best et al, 1994;Cruts et al, 1995;Furre et al, 1995;).…”

Section: Soft Sediments and Anisotropy Overviewmentioning

confidence: 99%

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Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Mavko¹

2006

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Summary of Accomplishments and ResultsWe completed our planned work on anisotropy in loose unconsolidated sediments.An important accomplishment was to understand the seismic velocity anisotropy resulting from the combined roles of depositional stratification and stress in unconsolidated sands. This work has lead to one Ph.D. dissertation, and two conference presentations (SEG, 2003). The expanded abstracts from the conference proceedings were attached in the annual report for [2003][2004]. The completed Ph.D. dissertation is forms part of this final report as attachment A.The dissertation presents an experimental study of velocity anisotropy in unconsolidated sands at measured compressive stresses up to 40 bars, which correspond to the first hundred meters of the subsurface. Two types of velocity anisotropy are considered, that due to intrinsic textural anisotropy, and that due to stress anisotropy.Three types of tests were performed: (1) hydrostatic pressure, (2) quasihydrostatic stress, in which, cubic samples are placed in the polyaxial cell and approximately equal forces are applied in each of the three principal directions; and (3) uniaxial strain, in which, cubic samples are placed in the polyaxial cell and an axial stress is applied in the Zdirection, while the horizontal platens are held fixed, at approximately zero displacement. The hydrostatic pressure test is used to compare the standard velocity measurements with the velocity anisotropy measured in the polyaxial cell. The quasi-hydrostatic stress test is used to study the velocity anisotropy resulting from intrinsic anisotropy of the granular materials. The uniaxial strain test is used to study the velocity anisotropy resulting from stress anisotropy in sands. We found that intrinsic and stress-induced anisotropy can be detected in sands using Vp. The intrinsic velocity anisotropy was studied using P-wave velocities and the textural anisotropy was studied using the spatial autocorrelation function of sediment images for sands and glass beads. The results suggest that P-wave velocity anisotropy and textural anisotropy are related for grain segregation or stratification. We found that sand samples display a bi-linear dependence of velocity anisotropy with stress anisotropy. There exists a transition stress beyond which the stressinduced anisotropy outweighs the intrinsic anisotropy for three different sands. In addition, the dissertation discusses the problem of extrapolating acoustic velocities measured under hydrostatic pressure to quasi-hydrostatic stress. Measured Vp under hydrostatic pressure is higher than Vp measured under quasi-hydrostatic stress in the sand, for the same depositional anisotropy and similar isotropic stress. This difference might be due to boundary effects in the apparatus, and due to complexity of the stress field inside of the granular material samples. Finally, we found that the model of Norris I find that intrinsic and stress-induced anisotropy can be detected in sands using Vp. I study the intrinsic velocity anisotropy usi...

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Section: Dissertation Outlinesupporting

confidence: 86%

Section: Soft Sediments and Anisotropy Overviewmentioning

confidence: 99%

Section: Soft Sediments and Anisotropy Overviewmentioning

confidence: 99%

Section: Soft Sediments and Anisotropy Overviewmentioning

confidence: 99%

See 2 more Smart Citations

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Mavko¹

2006

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“…The effect of gravity settling on natural stratification in granular materials has been shown through lab tests and theoretical simulations (Makse et al, 1997;Baxter et al, 1998;Cizeau et al, 1999). This textural anisotropy influences the anisotropy of mechanical properties (Wong and Arthur, 1985;Jiang et al, 1997;Hoque and Tatsuoka, 1998). The directional dependence of mechanical properties becomes more pronounced at higher stresses.…”

Section: Introductionmentioning

confidence: 99%

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

Mavko¹

2003

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As part of our study on "Relationships between seismic properties and rock microstructure", we have studied 1. Methods for detection of stress-induced velocity anisotropy in sands.2. We have initiated efforts for velocity upscaling to quantify long-wavelength and short-wavelength velocity behavior and the scale-dependent dispersion caused by sediment variability in different depositional environments. INTRODUCTIONIn this quarter, we submit results of our research on: pore textural mapping and its relation to centimeter-scale core measurements of impedance and measurements of seismic properties of unconsolidated sediments at very low effective pressures. The special effect of stress anisotropy on velocity anisotropy is investigated. Two papers have been submitted for publication. This report presents preprints of our research relevant to this project on impedance mapping, soft-sediment measurements, stress anisotropy, and scale effects. PAPER 1Vega, S., Prasad, M., Mavko, G., and Nur, A., Detection of stress-induced velocity anisotropy in sands. Submitted to GRL In this paper, we present a preliminary study on stress-induced velocity anisotropy in two different sands. We describe the method used for sample preparation, and the polyaxial apparatus used for velocity, strain, and stress measurements. Furthermore, we examine the velocity response as a function of stress in different directions of applying uniaxial strain test to the samples. The strains and velocities of the two sands are also compared. We show that stress-induced velocity anisotropy exists and is detectable in sands. A stress anisotropy of 87% corresponds to a velocity anisotropy of 29%-34%, and there is a linear dependency of velocity anisotropy on stress anisotropy in the sands. We apply different statistical methods for characterizing heterogeneity and textures from scanning acoustic microscope (SAM) images of shale microstructures. Characterizing and understanding the microgeometry, their textures, scales, and textural anisotropy is important for better understanding the role of microgeometry on effective elastic properties. We analyzed SAM images from Bakken shale, Bazhenov shale, and Woodford shale. Our analysis, based on spatial autocorrelation functions shows that there is a small positive correlation between the degree of heterogeneity and the mean spatial correlation length of the microstructure. The textural anisotropy ranges from 10% to 80%. There is considerable variability within each image, as well as from one image to another. A singular value decomposition (SVD) spectral analysis showed that the shale microstructures have characteristics in common with fractal stochastic images. We also obtain a correlation between maturity and textural heterogeneity. The textural heterogeneity increases with increasing maturity (decreasing kerogen content), while there is a general decrease in textural anisotropy with maturity. The accompanying paper A4 in this volume relates the textural characteristics obtained from image processing ...

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A multilaminate constitutive model accounting for anisotropic small strain stiffness

Schädlich

Schweiger

2012

Num Anal Meth Geomechanics

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SUMMARY In this paper an extension of existing multilaminate soil models is presented, which can account for inherent and stress‐induced cross‐anisotropic elasticity in the small strain range and its dependency on the load history. In the multilaminate framework, material behaviour is formulated on a number of local planes in each stress point, and the macroscopic response of the material is obtained by integration of the local contributions. Strain‐induced anisotropy, which adds to the stiffness anisotropy inherently present in the material, is therefore intrinsically taken into account. Micro–macro relations between local parameters on plane level and global parameters on macroscopic level are obtained by the spectral decomposition of the global elastic compliance matrix. The model is implemented into a finite‐element code, and model predictions are compared with experimental data of triaxial tests on different soils involving small and large load cycles. The importance of cross‐anisotropic elasticity within the small strain range for predicting ground deformations in geotechnical boundary value problems is discussed at the example of an excavation problem. Copyright © 2012 John Wiley & Sons, Ltd.

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Inherent and stress-state-induced anisotropy in very small strain stiffness of a sandy gravel

Cited by 85 publications

References 4 publications

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

A multilaminate constitutive model accounting for anisotropic small strain stiffness

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