Experience with friction-micropiled-raft foundation on soft soils

Proc. XIII ECSMGE, Vaniöek et ul. (eltr. O CG\S, Ptueue, ISBN 8t)-i36769-01-l (yal. 2)
<strong>Experience</strong> <strong>with</strong> <strong>friction</strong>-<strong>micropiled</strong>-<strong>raft</strong> <strong>foundation</strong> on soft soils
Une expdrience avec Ia micropieux-base de frottement dans les
H.-G- Kempfen & F. Böhm,
Lniversirl ofKassel, iwtitute ofGeotechnics, Kasse!, Cernßn!-; geo,eth@uni-kossel.de
sols mous
KEYWORDS: <strong>friction</strong>-micropilcd-<strong>raft</strong> <strong>foundation</strong>, maintained load grouted pile test, setllement, soft
soil
ABSTRACT: A new foundatioo system for buildings on soft soils using micropiles is reported irr this
paper. The preseDted frictioo-micrupiled-<strong>raft</strong> <strong>foundation</strong> has successtitlly been realised for new buildings
on soft soils to stabilise the underground and redrLce the settlement. An exemplcry comparison of
practical projects in terms of measured settlements of a rafi loundation <strong>with</strong> the <strong>friction</strong>-<strong>micropiled</strong><strong>raft</strong>
<strong>foundation</strong> on noamal consolidatcd soft soils has proven the eff'ectiveness of the new <strong>foundation</strong>
system.
RESUME: Le papier prdsente une solution pour construite les t_ondltions des bätiments sur les sols
mous avec micropierx- La tbndation avec lcs micropieur llottants a dte construit avec succCs dans
nouveaux bätiments sur les sols mous pour stabiliser le sous-sol et pour r€duire le tassemeot.
L'efficacitd du nouveau systöme est confiün€e au moyen de la comparaison des tassements des radiers
de fondation avec les tassemenls des foüdations avec micropieux dans plusieurs constructions sur les
sols mous normal consolid€es.
I INTRODUCTION
Several construction measures have been realised in the southem Germrny <strong>with</strong> a piled-<strong>raft</strong> <strong>foundation</strong>
\rith micropiles on soft soils. Beside the stabilisarion elfecr ofrhe new <strong>foundation</strong> system, a sie
nificant settlement reduclion against rali fouodations could be obscwcd. Kenpferr (1986) rcponed
about the tirst positive experiences ofsuccessfully strcngthening an old raihay bridges abutment <strong>with</strong>
the illusüated <strong>foundation</strong> system.
ln particular in urban areas, sefilements due to very thick layers of soft soils c:rn negative]y influence
the neiuhbouring buildings <strong>with</strong> shallow tbundations, for example additional settlements due to
nexly built sfucfures. Such seftiements can lie <strong>with</strong>in the iange of decimetres. The new <strong>foundation</strong>
system preseotcd in this paper enablcs to limil settlements to an admissible size, hence limiting possible
negalive intluences on neighbouring buildings.
A research project financed by the central public funding organisation for academic research in
Gemany (DFC) is utrder way at the lnstitute of Geotechnics, University of Kassel, covering all aspects
ofthe beadlg caprcity ofinjection micropiles on soft normally coosolidated soils. ln the present
paper the effectiveoess of the <strong>friction</strong>-piled-rafi <strong>foundation</strong>s <strong>with</strong> grouted micropiles is iilustrated
based on case studies ofpracrical projects-
Micropiles were originally designed by the ttalian Zi:i to support and safegua.d <strong>foundation</strong>s at risk
and patenled in 1952. Since theq micropiles have been used world-wide tb. distinct building measures.
Bruce et a!. (1997) and Armour et al. (20001 summarised a rcpofi ofworld wide realiscd projects sDch
as <strong>foundation</strong> underpinning, slopc stabilisrtion, slope r€inforcement and gravity retaining strrctures.
At present therc are just few re,llised triction-piled-ral't <strong>foundation</strong> on soft soil reported in literature-
.\loin Session 1 'Foundanons in urban ureas'
::9

'proc. XLLI ECSMGE, l/aniöek et al. (eds). @ CGß, Prague, ISBN 8G86769-01-l (yot. 2)
Exampies of buiiding <strong>foundation</strong>s <strong>with</strong> micropiles found in literature are mainly deep <strong>foundation</strong>s,
where the pile toe penetrates the underlying bearing layer. An overview of<strong>foundation</strong>s on soft soils in
Mexico city is given by Auviaet {2002). He investigated the reaction ofthe <strong>foundation</strong> system to seismic
excitation in additio[ to the static loads.
Over the years, different types and manufacturing methods ofmicropiles werc invenred. The piles
discussed hereafter are ofthe GEwl type, DY-WIDAG System (see D.t1f2002))
2 FOTINDATION SYSTEM AND SIJBSOIL
Two <strong>foundation</strong>s of neighbouing buildings <strong>with</strong>ia the same location are compared hereafter- One of
them, located south west (Fr'gure 1), consists of seven independent buildings <strong>with</strong> up to 4 storeys. The
overall oute. size of the building is 100 x 42 m and it is founded on <strong>raft</strong> <strong>foundation</strong>. A new 4-storey
building <strong>with</strong> mainly two pais alld a size of 15 x 43 m is located east ofthe described building- It is
fomded on a ftiction-<strong>micropiled</strong>-<strong>raft</strong> <strong>foundation</strong> <strong>with</strong> 95 injection type piles.
o4
Fi$re 1, Siie map
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(-_)
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(:)
(._]
F;r. B r
Tkr.cti
The micropiles <strong>with</strong> a length of 16.25 m (GEWI-pile, DYWIDAG System) each and a diameters of
150 mm were installed in a drilled hole <strong>with</strong> casing in a grid of2 to 3 m. Then the piles were grouted
under prcssue of 25 to 30 bar at a depth of9 m and 14 m below the ground surface- A second pressurc
grouting was carried out once more <strong>with</strong> prcssures of 27-5 to 38.5 bar. F;gure 2 shows a typical cross
sections ofthe investigated buildings and <strong>foundation</strong>s.
230
Session 1 'Foundalions in arban area|"
^,Iain

Proc. XII LCS^,(GE, I/a\iöek et at. (edg. A CGIS, Prasrc, LSBN 8A-86769-AI I (ot. 2)
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Figure 2. Cross section and subsoil profile (section A-A)
.l
1t
iI
fi dion-micropaled-<strong>raft</strong> foondalion
The ground condition encountered in the southem Germany arcund lake Constance consists ofnormal
cotsolidated soft soils which extends up to a depth of60 m- The site investigation at the sire (Figure 2)
revealed a 2 - 3 m made ground overlying a very young normally consolidated soft soil layer, consisting
of clayey silts <strong>with</strong> pulpy to soft consistency and sorne organic componeots. This soil material is
described hereefier as upper lacustrine clay. At a depth of 12 to 15 m below sulface, a transition layer
ftom upper lacustrine clay to a lower lacustrine clay can be observed whjch consists ol soft to stiff
clayey silts <strong>with</strong> inclusions ofthin horizontal flne sand bands. Beneath the lower lacustrine clay layer
a moraine layer consisting ofclayey silts <strong>with</strong> large components ofsand aüd boulder was encountered
at a depth of24 to 36 m.
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Figure 3- Compilation ofwater contents, vane shear tests. penetration tests and heavy penetration tests
A water oontents around 30 %, and partly up to 90 o/o was measuled both in the uppe.lacusAine ciay
and lower lacustrine clay (Figure 3). The same hgute shows a diagram oftwo tield vane test, a typical
Mai Sessian 4 'Foundatialß inurban areas ' 231

Proc. XII ECSMGE, ,anlöek et al. (edt. A ÖGtS, Pra|ue, ISBN 80-86769-0t-j lrot. tt
cone pcnetration and heavy pcnetration tes! lesults. The average number ofblous in ihe upper lacustrine
clay was Nro = 5and the maximum measured was Nro = 9.
3 SETTLEIVIENI
Settlement gauges were installed at different location ofthe buildings, in *.hich senlements of the <strong>raft</strong>
fbundations rvere evaluated from the inclination mersurement ofthe individual buildings, The contact
pressure lies between 50 to 70 kN/mr. A back analysis result sho*s a seulement values berween 40 to
180 mm. Figure 4a shows settlements ofthe individual buildings <strong>with</strong> <strong>raft</strong> foundätion-
The contact pressure utrder the <strong>friction</strong>-<strong>micropiled</strong>-<strong>raft</strong>-fouodation lies around ?0 kN/m,. Measured
maximum sertlements at building comer points was 17 mm, whereby the <strong>foundation</strong> have not
ceased to settle so far. Extrapolated total settlements according to Srery'amounts ro about 18.2 n]m.
The measured and calculated settlements of the buildings \1 ith the <strong>friction</strong>-micropi]ed-<strong>raft</strong>-<strong>foundation</strong>
are shown in Figure 4b.
a) b)
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E z
:90
IkN/m.l time ldl
100
1000
_3 60
;
=0
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Figure 4. a) Top view and setllement of<strong>raft</strong> building b) Sculoment measuremenr of<strong>friction</strong>-<strong>micropiled</strong>-<strong>raft</strong>
<strong>foundation</strong>
4 PILE TEST RESULTS
The skin <strong>friction</strong> of a single pile (GEWI-pi1e, DYWIDAG System) in soft soils was esrimated from
pile tests under tension forces. The observed pile head djsplacement ol two pile rests are presented in
Figure 5.
A maximum pile resistance of432kN was measured liom rhe pile rest I wirh a pile length of
15.5 m. The unrecoverable settlemert after force removal amounted to 32,1 mm (Figtire 5a). A further
pile test on a 14.7 m pile sho*ed a maximum pile resistance of 800 kN and unrecoverable settlement
of7.8 mm (Figure 5b). Similar pile tests showed a maximum pile resistance ofabout 800 kN.
Altematively a pile load test under compression \r.as caftied out on a 32 m long reinforced concrete
pile (300 x 300 üm), in order to investigate the usability of such piles as <strong>friction</strong> piles. Thc pile
ißelfconsisted ofthree sepamte parts <strong>with</strong> a length of9 m, 14 m and 9 m. Such consrrucrion had been
chosen in order to conduct a dynamic test of the pile interconnections. The pile was driven up to a
depth of7 m \',ithout any major driving energy. Betweeo a depth of3 and 7 m, a pile slip <strong>with</strong>oul no-
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232 Main Sessiotl 4 'Faukdatians in utban aleas '

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ticeable <strong>friction</strong> was obseryed in areas of low
number ofblorvs are shown in Figure 6.
a)
50
pile resistance R [kNl
100 200 300 400 500
'r'
B.;
E]I
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0
Figure 5. Resisrance herve; a) pile test I b) pile resr 2
20
25
shear strength. The driving energy rcqLrired and the
b)
E E
c 15
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5
pile rcsisiance R IkNl
200 400 600 800 1000
The dynamic pile load tests were carricd out by means ofthe CASE and CAPWAP methods. The tcst
results were analysed a! dillerent penetration depths olthe reinlbrced concrete pile. Figure 6 shorvs lhe
test results as well as the idle time after driving the pile to the respective depth. The piie resistance at a
depih ofaround 17.5 m and aller l0 min idlc time $as 400 kN, alier 1.5 h it lvxs 600lcN. The increase
of the pile resistance is aitributed to the dissipation of the pore pressure <strong>with</strong> time. Fudher pile load
Iest at a penctration depth of 22 m sholved a pile resislanr of about 500 kN. Ar a depth of 31 m. the
pile shaft was already I m deep in the moruine layer. A pile .esistsDce of rbout 650 kN was measured
irnmediately after end of pile drjving. Afler further 4 days, the pile was loaded once more and a pile
resishncc il50 kN was calculated accordins to the CASE method and 1050 kN accordins to CAP-
a.) b) c)
: drlving €iergy [[,INm] nurnber oi blows per m
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after 10 m'n:500 kN/ -
after '1 h: 650 kN/ -
after 5 d: 1150 kN/1050
a 2 4 6 I 105 15 25 35 45
drjving energy [NlNm/m] nurnber of strokes l-l
Figure 6. Tcst loading ofa rcinforccd concrete pile: a) i$erted penerration energvl b) number ofstrokes; c) results
ofpile tests
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Main Session 1 "Foundutions in ürban areas' 233
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Proc. XII ECSI,IGE, Ildniiek et dl. led:). A ÖG6, prague, ISBN 80-36769-At -t A,ot. 2)
A comparable injeciion 14.7 m pile (6 150 mm) located immediately next to the dynamic pile load test
had shown a pile resistance of 800 kN at a penetration depth of 19.?0 m (Figure 5b).
5 SIIMMERY
The paper gives a short insight into the application of micropiles in a combined piled-<strong>raft</strong> <strong>foundation</strong>
on soft soils. The positive expedences <strong>with</strong> such bearing <strong>foundation</strong> system could be verified bl' showing
the minimal measured settlement of 17 mm. Moreover, injection piles have proven to contribute in
stabilising the surrounding soils. A compadson olmeasur€d settlement ofa <strong>raft</strong> <strong>foundation</strong> and a similar
building on fiiction-<strong>micropiled</strong>-<strong>raft</strong> <strong>foundation</strong> <strong>with</strong> a similar contact pressue are shown in Figure
7, where the settlements amount 180 ]rlm and 4 mm respectively.
0
20
40
E60
E
_9
124
ßa
160
pile load [KN]
0 100 204 300 400 500
--1":::.'::":7
" ",","""i1,"*ii. ""il*,.i, 60
figure 7. Comparrriv€ setilements ola <strong>raft</strong> fbundation
and a fric!ion-<strong>micropiled</strong>-<strong>raft</strong> foundatioo
The results obtained from various piie load tests underiine the effectiveness oftbe <strong>friction</strong> micropiLes,
which shows a pile resistance ofup to E50 kN. Comparative dynamic pile load tests on reinlorced concrete
piles showed a pile resistance of about 600 kN at a similar penetration depth, at which the pore
waier pressures were noi fully dissipated and hence a reduced pile resistance.
The ample eflectiveness ofthe Aiction-<strong>micropiled</strong>-<strong>raft</strong> <strong>foundation</strong> systems is due to the prestressing
ofthe soft soil between the piles by the injection pressures during pile manufacturing.
6 REFERFNCES
Auvinet. G. (2002). Foundations on solt soils in Mexico ciry. lntemational Workshop ISSMGE-Technical
Comnitlee TC36, 124-131, Mexico
Armour, T., Croneck. -P., Keeley, J., Sharma, S. (2000). Micropile Design and Coostruction Guidelines Implementaiion
Manual, National Technical Information Sysiem Se ice, Springfield
Bruce, D.A-, Juran, L (i997). Drilled and grouted Micropiies: State ofPraciice, Review, Volume I-IV. Nationäi
Technical lnformation System Selvice, Springteld
DlWiDAG-Systems intenational (DSI) (2002). Promotional brochure on GEWI piles, 8 pp- Essen
Kempfer! H.-G. (1986). Gründung aufVerpresspf:thlen in weichen Sedimenten, Geotechnik, H. 2, 73 - 78. Munich
:31 Mai Sessian 1 "Foundatians in urban areas '

w
PROCEEDINGS OF THE Xüth f,L'?OPf,AN CONFERXNCE ON SOIL IVIEC}LANICS
Ä.ND CEOTECIIi\{ICAL ENGINiEERDIG
PR{GIJE, CZECH REPUBLTC, 2s - 28th AUGUST 2003
GEOTECIINICAL PROBLEMS \\TTH MAN-MADE
AND MAN INFLUENCED GROT]NDS
CO!}IPTES RENDUS DU XIIIöME CONGRbS EUROPfEN DE IITCITTqUT
DES SOLS Er DE LA CiOuCU.nrqUr
PRAGUE, RTPUBLIQUE TCHiQUE, 25 - 28 AOÜT 2OO3
LES PROBLTNTSS GfOTECHNIQUES POSfS PAR LES
REMBLAIS ET LES SOLSANTHROPIQUES
Editors,{R6dacteurs:
I. Vaniöek, R. Barvinek, J. Bohäö, J. Jettmar, D. Jiräsko, J Saläk
VOLUME 2
Papers presented tbr Maitl Sessions 4,5,6
(eB
THE CZECH GEOTECHNICAL SOCIETY CICE
eKArr
.G ry
THE CZECH CHAMBER OF CERTIFIED ENGINEERS AND TECIINICIENS