Reducing The Pain of Piles - Fugro Presentation PDF
December 23, 2022 | Author: Anonymous | Category: N/A
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Reducing the Pain of Piles ...
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Nick Ramsey 22 October 2012
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rGAD This talk is primarily about driven steel pipe piles
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The Prologue
•
Why it s not always simpe to make reiabe predictions of the capacity of drven pes
•
Recommended approaches or approprate ste nvestigaton, seection o characterstc soil parameters and methods of assessng ple capacity.
•
The advantages and disadvantages o several dierent methods of predicting pile capacty
•
The potential commercia mpacts o making wrong decisons durng the desgn process wv..fgro com wv
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Why it is not always simple to make reiabe predictions of the capacity of driven piles
• Recommended approaches for appropriate investigation, seection of characteristic oi site parameters and methods of assessing pie capacity. •
The advantages and disadvantages of severa dierent methods of predicting pie capacity
•
The potentia commercia impacts of maing wrong decisions during the design process w fgr fgr.. cm
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Inferring the properties of the pile material is - relatively easy
Steel manufactured in Australia
Steel
Steel
manufactured
manufactured
in China
in the USA
Steel manufactured in the UK
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In contrast, soils can, and do, vary laterally and veically over very small distances
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Soils are not linearly elastic 20
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Drained behaviour is not the same as undrained behaviour 20 S1an ct r
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Stages in the life of a pile driven in SAND - In Inst stal allat latio ion n --
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Hammer blows
+ +
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Stress on sand n front of tip rises
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Large strans as sand s pushed radally outwards
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Large stran leads to crtcal state frction angle
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Stresses reduce as sand moves around tp to shaft
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1. Installaion w .fgro fgrocom
Stages in the life of a pile driven in SAND - Fr Fric icti tion on fatig fatigue ue Hammer blows
tL 2 � cycles +-,N
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• During pile drving sand is subject to cyclc shearing • result Sand contracts as a • Horzontal stress reduces • As you get higher above tip (h increases) horzontal stress and shaft resistance decreases
2. Fricton fatigue
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Friction fatigue
Profiles of unit skin friction for 356mm square concrete pile (Vesc, 1970) 't (kPa)
50
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4
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150 Friction fatigue reduces the shear stress mobilized at a given depth, as the distance
z (m) s
10 · . 12 -P -Pilee Trp atat 9.21250l� · · tL PiPil�m 14
(h) to the pile tip ncreases.
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Stages in the life of a pile driven in SAND - Res Resid idual ual str stress ess n
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Drven pies are not "wshed in pace
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Stresses tend to be "locked in at the base and ower zones of shaft
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3. Residual stress w .fgr fgr.. com com
Stages in the life of a pile driven in SAND Loading
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Load
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Increase in horzontal effective stress occurs close to t o the sh shaf af
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Dilaton close to pile-soil nterface
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Due to complicated lfe cycle of of pile there s no simple lnk ln k between n-stu sol conditions and those at failure
4. Loading
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Stages in the life of a pile driven CLA Y driven in CLAY - In Insta stalla llati tion on
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Hammer bows
n
+', N
•
Increase in horizonta tota stress and consequenty pore pressure
•
Pore pressure change dependent on stress history
•
Change in horizontal effective stress dependent on stress history
cycle less 1. Installation
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Stages in the life of a pile driven in CLAY - Fr Fric ictio tion n Fatigue Fatigue --------� --- -----� Hammer blows ,-
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Reduction in total and eective eec tive horizontal horizonta l stress with increasing height above tip
•
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Reorientation of cay partices to residual e I 8 conditions
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Stages in the life of a pile driven in CLAY - Equ Equali alisat satio ion n --
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So cay: excess pore pressure dissipates. Significant rise in horizontal eective stress (set-up) Sti cay excess pore pressure dissipates, eective stress can be greater than or less than, before instalation. As a consequence set-up or setdown can be observed
3. Equalsation
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Stages in the life of a pile driven in CLAY CL AY - Lo Load adin ing g
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Load
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4. Loading
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Increase in horizontal effective stress occurs close to the sha
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Due to complicated life cycle, there is no simple link between in-situ soil conditions and those at
•
failure Correlations with CPT are thought to represent complicated life-span better w fg fgr r .com
fGRD What about the effect of pile plugging? -
Plugged Sol moves down with pile Partal pluggng: Sol moves slower than ple Unplugged Soil n ple stays statonary
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