1

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

2

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

3

FOUNDATIONFOUNDATIONShallow foundation

strip footing-strip footing-spread footing cantilever footing-cantilever footing

-raft footing

Deep footingi-piers

-caissons il-piles

4

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

5

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

7

FOUNDATION ALTERNATIVESFOUNDATION ALTERNATIVES

8

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

9

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

10

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 

11

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

13

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

14

EFFECT OF RAFT THICKNESSEFFECT OF RAFT THICKNESSAs raft thickness increases:

- differential settlement reduces- maximum bending moment reduces-resist punching shear

15

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

16

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

17

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

18

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

19

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

21

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

24

CONTD…………CONTD………… Factor of safety

against vertical block movement: <2against lateral block movement: >2against overturning :=5

25

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

27

FOUNDATION DESIGNFOUNDATION DESIGN

28

(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.

29

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

30

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.

31

32