2758
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Research on the Load-Bearing Behaviour of Bored Piles with Different Enlarged Bases
18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
[m]
[%]
1** (b)
1.10
0.95
3.60
2** (b
f
)
1.58 1.44
1.96
3.40
-5.90
3++ (b)
1.50
1.77
4.20
4++ (b
f
)
2.04 1.36
3.27
3.20
-31.30
5## (b)
1.10
0.95
3.80
6## (b
f
)
1.53 1.39
1.84
3.60
-5.60
7*+ (b)
1.50
1.77
3.80
8*+ (b
f
)
2.10 1.40
3.46
4.00
-5.00
Own Tests
Pile
b
resp.b
f
[m]
Ratio
b
f
resp.
b [-]
Pile foot
base
area
[m²]
σb(s
gr
)
(1)
resp.
σb
f
(s
gr
)
(1)
[N/mm2]
σb(s
gr
)
(1)
to
σb
f
(s
gr
)
(1)
[%]
1xD
(b)
3.60
1017.90
1.01
-
2xD
(b
f
)
7.20
2.00
4071.50
0.92
-10.20
3xD
(b
f
)
10.80
3.00
9160.90
0.98
-3.00
(1)
σb(s
gr
) resp. σb
f
(s
gr
)
= R
b
(s
gr
) resp. R
bf
(s
gr
) / ((b resp.bf) · π) / 4)
s
gr
= 0.1 · b resp. b
f
**, ++, ##, *+ Comparable piles comparable lengths, Without base
enlargement (b) /with base enlargement (b
f
)
Note: Pile No. 4 is not comparable because of a shorter pile
length, i.e. not included in the evaluation.
In summarizing, two informative results come from the test
loadings on the scale model test piles. This is on the one hand the
realization that the base enlargement of a drilled pile to three times
it’s shaft diameter would increase the load-bearing resistance
expected due to the effect of D
2
was fair.
On the other hand it turned out that a pile base enlargement
according to DIN 1054 (or EA-Pfähle) using the reducing
coefficient α
enlarged
= 0.75 for calculating the pile base resistance
contains a high safety factor.
Fundamentally, it is to be noted, however, that in the context of
this work the results obtained are based on tests at a small scale
(model tests). Further, are factors (ground-water flows,
inhomogeneous soils) that were left out of consideration, which
could possibly have an influence on the bearing behavior of in situ
piles. This is especially true if, due to pile settlement, a
displacement of the soil in the area of the pile foot base can take
place. Therefore no clear conclusions on the actual bearing behavior
of large drilled pile with base enlargements can be drawn.
Table 5: Evaluation of In Situ Load Tests by Franke/garbrecht for
various related Settlements, s/D
Pile
Pile base
dia-
meter [m]
Pile
foot
area
[m²]
s/D
(2)
[-]
Settle-
ment
[cm]
σb(s)
(3)
resp.
σb
f
(s)
(3)
[N/mm2]
R
b
(s)
resp.
R
bf
(s)
[MN]
0.02
2.2
1.7
1.6
0.03
3.3
2.0
1.9
1**
(b)
1.10
0.95
0.10
11.0
3.6
3.4
0.02
3.2
1.8
3.5
0.03
4.7
2.1
4.1
2**
(b
f
)
1.58
1.96
0.10
16.0
3.4
6.7
0.02
3.0
1.7
3.0
0.03
4.5
2.3
4.1
3++
(b)
1.50
1.77
0.10
15.0
4.2
7.4
0.02
4.1
1.4
4.6
0.03
6.1
1.7
5.6
4++
(b
f
)
2.04
3.27
0.10
20.4
3.2
10.5
0.02
2.2
1.5
1.4
0.03
3.3
1.8
1.7
5##
(b)
1.10
0.95
0.10
11.0
3.8
3.6
0.02
3.1
1.3
2.4
0.03
4.6
1.8
3.3
6##
(b
f
)
1.53
1.84
0.10
15.3
3.6
6.6
7*+
1.50
1.77
0.02
3.0
1.5
2.7
0.03
4.5
2.0
3.5
(b)
0.10
15.0
3.8
6.7
0.02
4.2
1.9
6.6
0.03
6.3
2.3
8.0
8*+
(b
f
)
2.10
3.46
0.10
21.0
4.0
13,9
(2)
D = b
f
resp.b
(3)
σb(s) resp. σb
f
(s) =
= R
b
(s) resp. R
bf
(s) / ((b resp.bf) · π) / 4)
s = s/D · b resp. b
f
**, ++, ##, *+ Comparable piles comparable lengths, Without base
enlargement (b) /with base enlargement (b
f
)
Note: Pile No. 4 is not comparable because of a shorter pile length, i.e.
not included in the evaluation.
However, since there appears to be a discrepancy between
theory and practice, a continuing analysis would be meaningful and
necessary based on full-scale tests up to the 1:1 scale, since the
reliable data collection on the influence of manufacturing
variabilities can only be investigated in full-scale tests. This
evaluation is valid in particular under the aspect that there are new
techniques and geometries for pile base enlargement – as were
considered in this presentation – to produce new types of pile foot
base enlargements with positive influences on the bearing behavior
or the piles.
Thus, these drilled piles represent a new system for deep
foundation with a special capability regarding the loads and the
deformation limitations. It is of special importance that all of the
new pile cutting equipment for pile foot base enlargement
according to DIN EN 1536 – including the largest – can assuredly
manufacture piles in the soils envisaged for it by specialized
foundation engineering.
If these investigations would lead to a confirmation of available
findings, a safe and economic adjustment of the reducing
coefficient would be possible. Therefore, the work on this topic
should be continued.
6
REFERENCES
DIN EN 1536: Ausführung von Arbeiten im Spezialtiefbau –
Bohrpfähle,Deutsche Fassung EN 1536:2010, Beuth-Verlag Berlin,
2010
DIN 4014:
Bohrpfähle – Herstellung, Bemessung
und
Tragverhalten,Beuth-Verlag Berlin, 1990
Franke/Garbrecht: Lastsetzungslinien von Großbohrpfählen mit und
ohne Fußverbreitung bei 2,5 m Einbindung in Sand und
verschiedenen Pfahllängen (nach Franke/Garbrecht 1976). In:
Smolczyk, U.: Grundbau-Taschenbuch, 4. Auflage, Teil 3, S. 210.
Ernst & Sohn, Berlin, 1992
BAUER: Firma BAUER Spezialtiefbau Schrobenhausener Tage 2006
(unveröffentlicht) / Firmenunterlagen, 2006
Herrmann, Lauber: Vergleichende Untersuchungen zur Kompatibilität
zwischen den nationalen und europäischen Grundbaunormen und
sonstigen Regelwerken – Band 1: Bohrpfähle – Vergleich DIN
4014 mit DIN EN 1536, Beuth-Verlag Berlin, 2000
Herrmann, Lauber: Vergleich DIN 4014 mit DIN EN 1536,
fahlsymposium 2001, TU Braunschweig,
Heft
Nr.
65,
Braunschweig, 2001
Tinteler, Herrmann: Untersuchungen zum Tragverhalten von
Großbohrpfählen mit unterschiedlichen Fußaufweitungen, Institut
für Geotechnik der Universität Siegen, 2012
DIN 1054: Baugrund – Sicherheitsnachweise im Erd- und
Grundbau,Beuth-Verlag Berlin, 2005 / 2010
EA-Pfähle: Empfehlungen des Arbeitskreises “Pfähle” der DGGT, 2007
