Investigating the effect of ageing on the behaviour of chalk putty

Doughty, L.J.; Buckley, R.; Jardine, Richard J.

doi:10.1680/eiccf.64072.695

Cited by 11 publications

(9 citation statements)

References 8 publications

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“…Supplementary testing at Imperial College examined the interface shear behaviour of the glacial till (Buckley, 2018) and the time-dependent behaviour of the remoulded "putty" chalk that forms around pile shafts during driving (Doughty et al, 2018). Table 2 summarises the index properties of the three main strata; three key additional points are:…”

Section: Laboratory Testingmentioning

confidence: 99%

“…A higher φ′ =36.4° with c′≈200kPa applied to denser samples and these parameters are compatible with the lower end of the ranges for c' of 100kPa to >2MPa and φ′ of 36-42°quoted for intact chalk by Lord et al (2002). Doughty et al (2018) showed that intact Wikinger chalk, whose natural water contents usually lie close to their liquid limit, degrades readily to putty with su≈4kPa under compaction at constant water content. Fall cone tests showed mildly thixotropic behaviour after puttification, with modest increases in su developing through ageing.…”

Section: Laboratory Testingmentioning

confidence: 99%

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Full-scale observations of dynamic and static axial responses of offshore piles driven in chalk and tills

et al. 2020

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This paper describes and interprets tests on piles driven through glacial tills and chalk at a Baltic Sea windfarm, covering an advance trial campaign and later production piling. The trials involved six instrumented 1.37m diameter steel open-ended tubes driven in water depths up to 42m. Three piles were tested statically, with dynamic re-strike tests on paired piles, at 12-15 week ages. Instrumented dynamic driving and re-strike monitoring followed on up to 3.7m diameter production piles. During driving, the shaft resistances developed at fixed depths below sea-bed fell markedly during driving, with particularly sharp reductions occurring in the chalk. Shaft resistances increased markedly after driving and good agreement was seen between long-term capacities interpreted from parallel static and dynamic tests.Analyses employing the sites' geotechnical profiles show long-term shaft resistances in the chalk that far exceed those indicated by current design recommendations, while newly proposed procedures offer good predictions. The shaft capacities mobilised in the low-plasticity tills also grew significantly over time, within the broad ranges reported for sandy soils. The value of offshore field testing in improving project outcomes and design rules is demonstrated; the approach described may be applied to other difficult seabed conditions.

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Section: Laboratory Testingmentioning

confidence: 99%

Section: Laboratory Testingmentioning

confidence: 99%

Full-scale observations of dynamic and static axial responses of offshore piles driven in chalk and tills

et al. 2020

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“…New preliminary design rules have been proposed for piles in low-medium density chalk, which tend to mobilise very low shaft resistances during driving that subsequently increase significantly over time [1,5]. Dynamic compaction can easily de-structure chalk and pile driving creates a zone of very soft puttified material around pile shafts that consolidates to form an annular region of permanently lower water content [1,6,7]. The peak shearing resistances of remoulded chalk, as developed in triaxial tests, generally fall in the 29 < φ peak ′ < 34° range with low cohesion values c′ of 0-10kPa [8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

“…The peak shearing resistances of remoulded chalk, as developed in triaxial tests, generally fall in the 29 < φ peak ′ < 34° range with low cohesion values c′ of 0-10kPa [8][9][10][11][12]. Triaxial tests that have attempted to replicate the effects of ageing observed in the field have shown little change in peak or critical state effective stress shear strength parameters over time, but have indicated significant increases in yield stresses and small-strain stiffness [6,10,13].…”

Section: Introductionmentioning

confidence: 99%

Laboratory investigation of interface shearing in chalk

et al. 2019

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Chalk, a soft fine-grained Cretaceous limestone, is encountered across northern Europe where recent offshore windfarm, oil, gas and onshore developments have called for better foundation design methods, particularly for driven piles whose shaft capacities are controlled by an effective stress Coulomb interface failure criterion. Interface type and roughness is known to affect both interface friction angles, δ′ and the magnitude of dilation required for shaft failure to develop. Site-specific interface ring-shear tests are recommended for offshore pile design in sands and clays to account for driven pile shaft materials, roughnesses and shear displacements. However, few such tests have been reported for chalks and it is also unclear whether δ′ angle changes contribute to the striking axial capacity increases, or set-up, noted over time with piles driven in chalk. This paper describes an interface shear study on low-to-medium density chalk from the St. Nicholas-at-Wade research test site in Kent, UK, where extensive field driven pile studies have been conducted [1, 2]. Direct shear and Bishop ring shear apparatus were employed to investigate the influences of interface material and surface roughness, as well as ageing under constant normal effective stresses (σn'). It is shown that the high relative roughness of the interface compared to the chalk grain size results in the ultimate interface shearing angles falling close to the chalk-chalk shearing resistance angles. The δ′ angles also increased by up to 5° over 38 days of ageing.

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“…Noting the known effects of pile driving, Doughty et al (2018) The piles of interest in this study were 139mm OD open-ended steel tubular piles ( Table 1). The piles were monitored dynamically during driving with strain gauges and accelerometers fitted near the pile head and were subjected to axial static and cyclic loading after installation; Buckley et al (2018b).…”

Section: Description Of Test Sites and Testing Programmesmentioning

confidence: 99%

Pile driveability in low- to medium-density chalk

et al. 2021

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Pile driving in low to medium density chalk is subject to significant uncertainty. Predictions of Chalk Resistance to Driving (CRD) often vary considerably from field driving behaviour, with both pile refusals and free falls under zero load being reported. However, recent field studies have led to better understanding of the processes which control the wide range of behaviour seen in the field. This paper describes the primary outcomes of the analysis of dynamic tests at an onshore and an offshore site and uses the results to propose a new method to predict CRD. The method is based on phenomena identified experimentally: the relationship between cone penetration resistance and CRD, the attenuation of local stresses as driving advances and the operational effective stress interface shear failure characteristics. The proposed method is evaluated through back analyses of driving records from independent pile installation cases that were not included in developing the method, but involved known ground conditions, hammer characteristics and applied energies. The proposed method is shown to lead to more reliable predictions of CRD than the approaches currently applied by industry.

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Investigating the effect of ageing on the behaviour of chalk putty

Cited by 11 publications

References 8 publications

Full-scale observations of dynamic and static axial responses of offshore piles driven in chalk and tills

Full-scale observations of dynamic and static axial responses of offshore piles driven in chalk and tills

Laboratory investigation of interface shearing in chalk

Pile driveability in low- to medium-density chalk

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