In situ strength characterisation of peat and organic soil using full-flow penetrometers

Boylan, Noel; Long, Michael; Mathijssen, F.A.J.M.

doi:10.1139/t11-023

Cited by 39 publications

(12 citation statements)

References 22 publications

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“…The two sites in the Netherlands were investigated as part of a joint UCD / TU Delft research project, which is described elsewhere (Boylan et al, 2011;Mathijssen et al, 2008) Sampling techniques varied from site to site and the specific technique used depended on resources available, the conditions of the site and health and safety considerations. For instance, hand carving of block samples was only carried out at shallow depths where there is minimal risk to sampling personnel from collapse of the excavation.…”

Section: Overview Of Sitesmentioning

confidence: 99%

Evaluation of peat strength for stability assessments

Boylan

Long

2014

Proceedings of the Institution of Civil Engineers - Geotechnica

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SynopsisIn this paper guidance is given for the assessment of peat strength for stability assessments based on laboratory undrained simple shear tests (SS). When considering the stability of peat, these tests will yield a conservative estimation of the in-situ strength of the peat mass. The study was motivated by recent interest in renewable energy developments in upland peat areas. The results of more than 111 SS tests from 16 sites in Ireland, Scotland and the Netherlands were studied. It was found that peat strength is strongly influenced by its stress history and also varies as a function of the water content and degree of decomposition (fibre content). The normally consolidated normalised strength ratio (s u /σ v ') from SS tests of peat was found to be approximately 0.4, which is towards the lower bound of previously published data for peat. Comparisons of strengths derived from SS and field vane tests showed the ratio of the strength derived from the two tests was influenced by the degree of decomposition and that previously published correction factors for field vane strengths are inappropriate. Guidance is given for engineers working on future schemes on upland peat areas.

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Section: Overview Of Sitesmentioning

confidence: 99%

Evaluation of peat strength for stability assessments

Boylan

Long

2014

Proceedings of the Institution of Civil Engineers - Geotechnica

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“…At the mid-face (midway between the tip and equator), the pore pressure response will be somewhat between that at the tip and that at the equator. Each of these three measurement locations have been considered in previously reported centrifuge and field studies (Boylan and Long, 2006;Boylan et al, 2010;Kelleher and Randolph, 2005;Low et al, 2007;Mahmoodzadeh and Randolph, 2014) (Figure 1), but with no current consensus as to the 'optimal' location; noting that the optimum may be more than one concurrent measurement. Kelleher and Randolph (2005) showed that pore pressure measured at the piezoball equator location exhibited a greater sensitivity to changes in the soil stratigraphy compared with the piezocone.…”

Section: Introductionmentioning

confidence: 99%

Experience with a dual pore pressure element piezoball

Colreavy

O’Loughlin

Randolph

2016

International Journal of Physical Modelling in Geotechnics

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Piezoballs, which are full-flow ball penetrometers incorporating pore pressure measurements, are an attractive soft soil characterisation tool as they allow measurement of the intact and remoulded strength and the consolidation coefficient in a single test. The merit of full-flow penetrometers as a reliable tool that is superior to the cone in quantifying the strength of soft clay is gaining acceptance. Much of the recent focus on piezoballs has been on the pore pressure measurement location. Prompted by recent studies that highlight the merit of measuring pore pressure concurrently at more than one measurement location, this paper considers a new centrifuge-scale piezoball, with simultaneous pore pressure measurement at the equator and mid-face positions. Results from centrifuge tests in normally consolidated kaolin clay form the basis for the examination and yield coefficients of consolidation that are consistent with values derived using a number of different methods. Although the mid-face position appears to be the more sensible pore pressure measurement position for dissipation tests, consideration of the values measured at both positions provide strong indications of the drainage response during penetration that is shown in the paper to be important for deriving coefficients of consolidation from subsequent dissipation phases.

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“…Greater difficulties are encountered with peats, which are harder to sample and often manifest exceptionally high ö9 and pore pressure ratios in undrained laboratory tests, but not clear failure: see Yamaguchi et al (1985), Den Haan & Kruse (2006) or Zwanenburg et al (2012). Low resistances, potential rate effects, possible anisotropy and fibrous inclusions also hinder in situ shear strength test interpretation; Landva (2007) and Boylan et al (2011).…”

Section: Introductionmentioning

confidence: 99%

Laboratory, in situ and full-scale load tests to assess flood embankment stability on peat

Zwanenburg¹,

Jardine²

2015

Géotechnique

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Laboratory, in situ and full-scale load tests to assess flood embankment stability on peat C. ZWANENBURG Ã a n d R . J. JA RD IN E †The low submerged unit weights of peats usually lead to low effective self-weight stresses, stiffnesses and undrained shear strengths. These features, in combination with high compressibility, a propensity to creep and the uncertain effects of fibrous inclusions, make foundation stability hard to assess reliably. It is usual to apply high safety, or strong material reduction, factors in foundation design. However, over-conservatism can lead to undesirable environmental and financial costs. This paper describes full-scale field tests conducted on peat, with and without pre-loading, at Uitdam on the borders of Lake Markermeer, north of Amsterdam. The experiments investigated the peat layers' consolidation behaviour and their response under loading, including full shear failure. Noting the complex final test geometries and the large displacements developed, simple numerical analyses were undertaken to help interpret the failures within a Tresca and 'consolidated undrained shear strength' framework. The trials that included modest pre-loading developed large vertical consolidation strains (up to 35%) and significant bearing capacity improvements. The field experiments provide a rich resource for testing advanced numerical techniques. They also allowed a range of practical characterisation techniques to be assessed and calibrated for flood dyke applications.

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In situ strength characterisation of peat and organic soil using full-flow penetrometers

Cited by 39 publications

References 22 publications

Evaluation of peat strength for stability assessments

Evaluation of peat strength for stability assessments

Experience with a dual pore pressure element piezoball

Laboratory, in situ and full-scale load tests to assess flood embankment stability on peat

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