piled raft foundation
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CONTENTSCONTENTS
1 INTRODUCTION1.INTRODUCTION2.FOUNDATION3.PILED RAFT FOUNDATION4.CLASSIFICATION OF PILED RAFT5.ADVANTAGES OF PILED RAFT FOUNDATION6.CASE STUDY-BURJ DUBAI7.CASE STUDY- MESSE TURM TOWER,FRANKFORT8.CONCLUSION9.REFERENCES
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INTRODUCTIONINTRODUCTION
Number of skyscrapers are high in recent years(source: commons.wikimedia.org )
Proper foundation is adequatePiled raft foundation is economicalBearing capacity of both pile and raft utilized
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FOUNDATIONFOUNDATIONShallow foundation
strip footing-strip footing-spread footing cantilever footing-cantilever footing
-raft footing
Deep footingi-piers
-caissons il-piles
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RAFT FOUNDATIONRAFT FOUNDATION
Large concrete slab
(source: commons.wikimedia.org )
gSupports column of entire structureDifferential settlement compensated by rigidity of raftp y g yDepth of footing < 1m
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PILE FOUNDATIONPILE FOUNDATIONVertical or slightly inclined membersTransmit load of superstructure to lower depthLoad transfer-
1)skin friction2)end bearing2)end bearing
6(source: commons.wikimedia.org )
PILED RAFT FOUNDATIONRAFT
LOAD ON SUPERSTRUCTUREPILE
RAFT PILE
CONTACT WITH SOIL
SKIN FRICTION
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FOUNDATION ALTERNATIVESFOUNDATION ALTERNATIVES
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LOAD SETTLEMENT BEHAVIOURLOAD SETTLEMENT BEHAVIOUR
Curve 0: Raft only (settlement excessive)
f i h ilCurve 1: Raft with pile designed for conventional safety factorCurve 2: Raft with piles designed for lower safety factor using reduced number gof pilesCurve 3: Raft with piles designed for full utilizationdesigned for full utilization of capacity using reduced number of piles
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FAVOURABLE AND UNFAVOURABLEFAVOURABLE AND UNFAVOURABLE CIRCUMSTANCE FOR PILED RAFT
FAVOURABLEsoil profile withsoil profile with
1) stiff clay2) d d2) dense sand
UNFAVOURABLEUNFAVOURABLEsoil profile with
1) soft clay and loose sand1) soft clay and loose sand2) soft compressible layers at shallow depth
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CLASSIFICATION OF PILED RAFT• W<L• Insufficient bearing capacity of
raftSMALL PILED raft• Piles added to increase factor of
safetyRAFT
W>L• W>L• sufficient bearing capacity• Piles added to decrease settlement
LARGE PILEDRAFT Piles added to decrease settlementRAFT
W‐WIDTH OF RAFTL‐ LENGTH OFPILE
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FACTORS WHICH AFFECT THE PERFOMANCE OF PILED RAFTPERFOMANCE OF PILED RAFT
No: of piles Type of loadingEffect of raft thicknessRelative length of pilesPile configurationPile configurationPile group width to raft width ratio
12(Source:www.wikipedia.org)
NO. OF PILESNO. OF PILESAs no. of piles increases:
-maximum settlement decreases -load carried increases
Upper limit exist
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TYPE OF LOADING
Maximum settlement and maximum bending moment i t t d l di > M i ttl t din concentrated loading > Maximum settlement and maximum bending moment in uniform loading
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EFFECT OF RAFT THICKNESSEFFECT OF RAFT THICKNESSAs raft thickness increases:
- differential settlement reduces- maximum bending moment reduces-resist punching shear
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RELATIVE LENGTH OF PILESRELATIVE LENGTH OF PILESFor a given no of piles:
L/D ti ias L/D ratio increases -differential settlement decreases-maximum moment decreases
Most effective strategy:To increase the length of pile than
increasing no of pileL- Length of pileD- Diameter of pilep
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PILE CONFIGURATIONPILE CONFIGURATION Depends on:
load distributionNo: of piles Length of pile
Concentric arrangement of pile with respect toConcentric arrangement of pile with respect to centre give good performance
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PILE GROUP WIDTH TO RAFT WIDTH RATIORATIO
Most influenced element of system geometry-ratio=1,to minimize the average displacement-ratio=0.5,to minimize differential settlement
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ADVANTAGES OF PILED RAFT FOUNDATIONFOUNDATION
(source: wwwmaniacworld com)reduction in the number or length of pilesreduction of maximum and differential settlements
d h i l d b di i f
(source: www.maniacworld.com)
reduces the internal stress and bending moment in raftimprovement of bearing capacity of raftreduction in the heave inside and outside the pit during excavation educ o e e ve s de d ou s de e p du g e c v owork
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CASE STUDYCASE STUDYBURJ DUBAI
Key features:•Height -828m•No of storey-160No of storey 160•Storey garage-4 to 6•Water level-2.5mWater level 2.5m below ground level•Podium developmentPodium development
( b jd b i k )
World’s tallest building 20
(source: www.burjdubaiskyscraper.com)
SUBSOIL CONDITIONSUBSOIL CONDITION-complex
i i ll i-seismically active area
Medium dense to looseMedium dense to loose granular silty sand
Weak sandstone inter bedded
With cement sand
W k t d t l kWeak to moderately weak conglomerates
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FOUNDATION DESIGNFOUNDATION DESIGN
Tower piles:1.5 m diameter47 45 l:47.45 m long
pPodium piles:0.9m diameter :30 m length
Thickness of raft:3.7 mThickness of raft:3.7 m
22source:www.burjdubaiskyscraper.com
23Piled raft foundation for Burj Dubai(source:www.burjdubaiskyscraper.com)
CONTOURS OF THE MAXIMUM AXIAL LOAD
•Maximum load at cornersMaximum load at corners-35MN•Minimum load at centreMinimum load at centre:12-13MN •Centre to centre spacing ofCentre to centre spacing of pile:2.5 x pile diameter
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CONTD…………CONTD………… Factor of safety
against vertical block movement: <2against lateral block movement: >2against overturning :=5
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CASE STUDYMESSE TURM TOWER ,FRANKFORTMESSE TURM TOWER ,FRANKFORT
KEA FEATURESKEA FEATURES:•Height-256m•No of floors-63•No of floors-63•36.3 m high pyramid
Second tallest building in Germany 26source: commons.wikimedia.org
SUBSOIL CONDITIONSUBSOIL CONDITION
FILL+QUARTERNARY SAND +GRAVEL
DEPTH:10M
FRANKFURT CLAY( t bl )FRANKFURT CLAY(unstable)DEPTH:70M
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FOUNDATION DESIGNFOUNDATION DESIGN
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(source: commons.wikimedia.org )
CONCLUSIONCONCLUSIONThe piled raft foundation is extensively applied in last t d dtwo decades.The piled raft is applied not only to control the foundation settlement but also to minimise the required raft thickness to reach the most economic foundation design.
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REFERENCESREFERENCESBakholdin, B. V. (2003), Piled-raft Foundations: “D i d h t i ti f t ti“Design and characteristics of construction procedures”, Soil Mechanics and Foundation E i i V l 40 (5) 185 189Engineering, Vol. 40 (5),pp 185-189Bezerra, J. E, Cunha, R. P. and Sales, M. M (2005), “Optimisation concepts for the design of piled raft foundation system”, Proceedings of 16th ICSMGE, Osaka,pp 1947-1950
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CONTD………………..•Cao X. D., Wong, H. and Chang, M. F. (2004),
h i f d l f i“Behaviour of Model Rafts Resting onPile-Reinforced Sand”, Journal of Geotechnical and G l (ASC ) l ( )Geo environmental Engineering(ASCE), Vol.130 (2), pp 129–138•Desai, C. S. (1974), “Numerical design analysis for piles in sands”, Journal of Geotechnical Engineering (ASCE), , f g g ( ),Vol 100 (6), pp 613-635.
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