2690
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Table 3. Moments of the distribution of R = log (P
CTL
/P
D&Q
) for Janbu
nd Chellis formulas
a
Pile driving formula
Mean
Variance
CTL=Janbu (set-based)
0.05977
0.05339
CTL=Chellis (rebound-based
0.02339
0.04523
Once again correlations with the Chellis formula exhibit a
smaller variance that those with Janbu’s.
6 APPLICATION AND RESULTS
Application of the proposed procedure was guided by the final
goal of developing plots that could provide sound statistical
justification to field operational rules that will lead to more
economical pile foundation solutions, such as shorter piles, with
the very same probability of failure (or reliability index,
).
Figures 4 and 5, developed by means of equations 3 to 6
with data from Tables 1 to 3, show the updated global safety
factor required to maintain the same reliability index (
) after
the distribution of the predicted ultimate load of the pile is
updated on the basis of field control measurements and the
corresponding pile driving formulas. The x-axis values are
possible observable results of the ratio P
OBS
/P
PRED
. In Figure 4,
set is the field control and Janbu is the formula used for P
OBS
prediction. In Figure 5 the performance of set and rebound are
compared for an intra-site variance of 0.08, while results in
Figure 4 explore four possible values of intra-site variance.
Figure 5 confirms previously discussed indications that
rebound-based control is slightly superior to set-based control.
Updated F from Janbu-interpreted set measurement,
for constant
(see legend for intra-site variances adopted)
1,5
1,75
2
2,25
2,5
0,5
0,75
1
1,25
1,5
P
OBS
/P
D&Q
F
0,08
0,12
0,16
0,20
D&Q only
Figure 4 - Comparison of code-prescribed global safety factor (F=2)
with set-updated F values, for the same reliability index (
)
Updated F from interpreted set (Janbu)
or rebound (Chellis), for constant
Intra-site variance = 0,08
1,5
1,75
2
2,25
2,5
0,5
0,75
1
1,25
1,5
P
OBS
/P
D&Q
F
Janbu
Chellis
D&Q only
Figure 5 - Comparison of the performance of set and rebound field
controls for updating the safety factor while preserving the same
reliability index (
)
7 CONCLUSIONS
Duly interpreted field control measurements, recorded during
pile driving, facilitate more economical pile foundation design,
while maintaining the same safety level required by code-
prescribed safety factors. Figure 5, for example, sets a sound
foundation for operational rules that provide safe guidance for
early interruption of pile driving.
8 REFERENCES
Aoki, N., Alonso, U. R. Correlation between different evaluation
procedures of static and dynamic load tests and rebound.
XII
ICSMFE – 12th International Conference On Soil Mechanics And
Foundation Engineering
, Rio de Janeiro.
Baecher, G.B., Rackwitz, R. 1982. Factors of safety and pile load tests.
International
Journal for Numerical and Analytical Methods in
Geomechanics
, v. 6, 409-424.
Bilfinger, W. 2002. Safety criteria of foundations of driven piles using
field control methods.
PhD Thesis. Polytechnic School, University
of São Paulo
(in Portuguese).
Bilfinger, W., Hachich, W. 2006. Influence of pile length in the
variability of axial resistance.
XIII COBRAMSEG – Congresso
Brasileiro de Mecânica dos Solos e Engenharia Geotécnica,
ABMS, Curitiba (in Portuguese).
Briaud, J. L., Tucker, L. M. 1988. Measured and Predicted Axial
Response of 98 Piles.
Journal of Geotechnical Engineering –
ASCE
, 114 (9), 984-1001.
Décourt, L. 1982. Prediction of the Bearing Capacity of Piles based
exclusively on N values of the SPT.
2
nd
European Symposium On
Penetration Testing,
Amsterdam.
Décourt, L. 1991. Bearing Capacity of displacement piles in residual
soils on basis of SPT.
SEFE II – 2O Seminário De Engenharia De
Fundações Especiais, São Paulo
, São Paulo.
Décourt, L., Quaresma, A. R. 1978. Capacidade de Carga de Estacas a
partir de Valores de SPT.
VI COBRAMSEF – 6o Congresso
Brasileiro De Mecânica Dos Solos E Engenharia De Fundações,
Rio de Janeiro.
Kay, J.N. 1976. Safety factor evaluation for single piles in sand.
J. of
the Geot. Engng. Div.
, ASCE, V. 102.
Kay, J.N. (1977) Factor of safety for piles in cohesive soils.
IX
International Conference on Soil Mechanics and Foundation
Engineering
, Tokyo.
Hachich, W., Falconi, F., Santos, M.S. 2008. Foundation safety:
incorporating load test results.
11º Congresso Nacional de
Geotecnia
, SPG, Coimbra, Portugal (in Portuguese).
Hachich, W., Santos, M.S. 2006. Safety updating for piles based on load
tests.
XIII COBRAMSEG – Congresso Brasileiro de Mecânica dos
Solos e Engenharia Geotécnica
, ABMS, Curitiba (in Portuguese).
Martz, H.F., Waller, R. A. 1982.
Bayesian reliability analysis
. John
Wiley & Sons.
Meyerhof, G. G. 1956. Penetration Tests and bearing capacity of
cohesionless soils.
J. Soil Mechanic and Foundation Division -
ASCE
, 82 (SM1), 1-19.
Poulos, H. G., Davis, E. H. 1980. Pile Foundation Analysis and Design,
New York.
Poulos, H. G. 1989. Pile behaviour – theory and application.
Géotechnique
39(3), 365-415.
Poulos, H. G., CARTER, J. P., SMALL, J. C. 2001. Foundations and
retaining structures – research and practice,
XII IXSMGE – 12th
International Conference On Soil Mechanics And Geotechnical
Engineering
, Istambul, 2001.
Rosa, R. L. 2000. Proposition for the modification of Chellis and Uto et.
Al. Driving formulas using CASE method results.
MSc Thesis,
Polytechnic School, University of São Paulo
.(in Portuguese).
Santos, M.S. 2007. Bayesian inference for the evaluation of foundation
safety of displacement piles.
MSc Thesis, Polytechnic School,
University of São Paulo
(in Portuguese), 183 p.
Terzaghi, K. 1943. Theoretical Soil Mechanics.
John Wiley and Sons
,
New York.
Vrouwenvelder, A. 1992. Effects of inspection on the reliability of
foundation piles. In: Barends, F.B.J. (ed),
Application of Stress
Wave Theory to Piles
, Balkema, Rotterdam.
Zhang, L. 2004. Reliability Verification Using Proof Pile Load Tests.
Journal of Geotechnical and Geoenvironmental Engineering
,
ASCE, V. 130, n.11.
