Effect of fibre content and structure on anisotropic elastic stiffness and shear strength of peat

HendryMichael, T; SharmaJitendra, S; Martin, C. Derek; Lee, BarbourS.

doi:10.1139/t2012-003

Cited by 50 publications

(27 citation statements)

References 19 publications

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“…Excessive settlements that necessitate increased amounts of maintenance are not uncommon for peat deposits acting as pavement subgrades or foundations for railroad embankments (Hendry et al, 2012). Calculations routinely involve effective stress analysis, with the general consensus being that the principles of effective stress and routinely-used soil mechanics strength models (e.g.…”

Section: Introductionmentioning

confidence: 99%

Consolidated-Drained Triaxial Compression Testing of Peat

O’Kelly

Zhang

2013

Geotechnical Testing Journal

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Abstract:Recent peat soil problems, including failures of dykes, foundations and slopes in peat deposits, have focused greater attention on understanding the mechanical behavior of peat. Stability calculations routinely involve effective stress analysis, with pertinent strength and stiffness parameters often determined from standard triaxial testing, without special consideration given to internal tensile reinforcement provided by the fiber content and also the high compressibility of the peat material. This paper investigates consolidated-drained triaxial compression testing applied to peat soils. Significant differences in mini-structure and fiber content between test-specimens of undisturbed, reconstituted and blended peat materials were found not to cause significant differences in shear resistance under drained triaxial compression, with mobilized shear resistance increasing approximately linearly with increasing axial strain. Hence it was concluded that c and  deduced from drained triaxial -2-compression testing of peat are unlikely to be intrinsic material properties, and rather are largely a function of strain level, with higher values of  deduced for higher strain levels.End of primary consolidation should be deduced from pore-water pressure measurements rather than volume change response; although the repeatability of the triaxial consolidation tests was generally found to be poor on account of the natural variability of peat and small size of the test specimens.

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Section: Introductionmentioning

confidence: 99%

Consolidated-Drained Triaxial Compression Testing of Peat

O’Kelly

Zhang

2013

Geotechnical Testing Journal

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“…The extent of cross-anisotropy not only increases with increasing fibre content (Hendry et al, 2012) and for lower levels of humification, but also tends to be affected by the type of peat deposit (fen, bog, reed etc.). In other words, the decomposition of fibrous peat material reduces its level of structural anisotropy (Pichan and O'Kelly, 2012;O'Kelly and Pichan, 2013).…”

Section: Botanical Composition Degree Of Humification and Strength Pmentioning

confidence: 99%

“…RS tests on Escuminac Sphagnum peat, Landva and La Rochelle (1983) presented a technique for estimating the apparent increase in lateral resistance provided by the fibres and the resulting effect on the shearing behaviour of fibrous peat. Hendry et al (2012) proposed a procedure for estimating the interparticle frictional strength of fibrous peat from CU triaxial testing of 38 mm dia. specimens, while Cola and Cortellazzo (2005) presented a bilinear failure criterion for fibrous peats based on soil-reinforcement interaction mechanisms.…”

Section: Cu Tc Testingmentioning

confidence: 99%

“…specimens, while Cola and Cortellazzo (2005) presented a bilinear failure criterion for fibrous peats based on soil-reinforcement interaction mechanisms. To measure (isolate) the effects and contributions of the peat fibres, fibre content and in situ structure on the strength and stiffness properties, Cola and Cortellazzo (2005) performed CU triaxial tests on undisturbed specimens and reconstituted specimens without fibres, while Hendry et al (2012) performed CU triaxial and DS tests on Shelby peat specimens, remoulded peat specimens and fibre-only remoulded specimens. (Koumoto and Houlsby, 2001;Kulhawy and Mayne, 1990;Ladd and Foott, 1974), 38 mm dia.…”

Section: Cu Tc Testingmentioning

confidence: 99%

“…In an intact state, the peat fibres themselves have relatively high tensile strength and they also provide conduits for the preferential flow of water through the bulk material (Hobbs, 1986;O'Kelly, 2015a;O'Kelly and Pichan, 2013). For peat deposits, the fibre deposition and subsequent large vertical strains experienced during the onedimensional (1D) consolidation in situ produce an inherent structural cross-anisotropy (Helenelund, 1967;Landva and Pheeney, 1980;Yamaguchi et al, 1985a), the degree of which is dependent on the material's level of humification (Hendry et al, 2012), although an exception is upland blanket bog peat material (Long and Jennings, 2006).…”

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confidence: 99%

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Measurement, interpretation and recommended use of laboratory strength properties of fibrous peat

O’Kelly

2017

Geotechnical Research

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Peat deposits are complex natural formations encountered in many geographical areas. Peat itself is considered as a challenging geomaterial, with many aspects of its behaviour seemingly remaining enigmas. This state-of-the-art review paper provides an extensive summary of current knowledge on the strength and shear behaviour of fibrous peats. Critical assessments and interpretations of the undrained strength, effective-stress strength and at-rest earth pressure coefficient parameter values determined for fibrous peat materials using standard and advanced laboratory apparatus are presented, focusing particularly on the consolidated undrained triaxial compression and direct simple shear approaches. Based on documented case histories of embankments, dikes and natural peat slopes, guidance is given for operational shear strength assessments in peat, aimed at bearing capacity and slope stability calculations, considering both the normalised undrained strength ratio and limit equilibrium effective-stress strength approaches. In particular, the botanical origin, structural anisotropy, humification level, likely initial overconsolidated state, tensile resistance associated with the peat fibres and possible scale effect related to the test-specimen size are discussed in the context of the strength mobilised for different testing apparatus. The test methodologies and interpretations of experimental results presented for fibrous peat in this paper should be transferable to other fibrous soil and soil-like materials. Notation

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A study of wave propagation and stiffness anisotropy in anisotropically loaded granular material-synthetic fiber binary systems

Ren

Senetakis

et al. 2022

Granular Matter

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The influence of polypropylene fiber inclusion on the wave propagation parameters and stiffness anisotropy of granular materials was examined through vertically and laterally positioned bender elements, by which, shear wave velocities were measured leading to the quantification of elastic stiffness Gmax(vh), Gmax(hv) and Gmax(hh) (the first subscript corresponds to the direction of wave propagation and the second subscript corresponds to the direction of particle perturbation as v:vertical and h:horizontal). Various stress paths were considered to comprehensively study stiffness anisotropy of the specimens and grain-scale laboratory tests were additionally performed to provide, partly, some multi-scale insights into the mechanisms of wave propagation of the sandfiber granular composites. For the back-calculation of elastic stiffness from the wave propagation experiments, Biot's theory was adopted, in which case an equivalent density was used to interpret the high-frequency test results taking into account the relative movement of the solid and fluid phases, which approach provided much better convergency of the results from bender elements and resonant column tests. In this case we assumed that the solid skeleton is composed of the sand particles and the fibers. The test results indicated that when subjected to isotropic stress state, the presence of fibers led to a decrease of Gmax(vh) and Gmax(hv) but an increase of Gmax(hh). The extent of Gmax(hh) increase was dependent on the characteristics of the host sand and could be attributed to the structural anisotropy with preferred horizontal orientation of the fibers leading to more pronounced development of rigid-soft contacts in the vertical direction. The contribution of the rigid-soft contacts in stiffness reduction could be linked to the microscopic influence of the softer synthetic fibers in reducing the normal contact stiffness and increasing the energy dissipation of the granular system as the grain-scale experiments suggested. When subjected to anisotropic stress state, the stiffness anisotropy was affected by fiber content in a way that with increasing amount of fiber inclusion, the reduction of the stiffness anisotropy became larger. The stiffness anisotropy of the sand or sand-fiber binary system increased with the increase of the stress ratio. Further analysis of the test results revealed that stress induced anisotropy was directly linked to the influence of deviatoric stress on the volumetric strain.

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Effect of fibre content and structure on anisotropic elastic stiffness and shear strength of peat

Cited by 50 publications

References 19 publications

Consolidated-Drained Triaxial Compression Testing of Peat

Consolidated-Drained Triaxial Compression Testing of Peat

Measurement, interpretation and recommended use of laboratory strength properties of fibrous peat

A study of wave propagation and stiffness anisotropy in anisotropically loaded granular material-synthetic fiber binary systems

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