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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
For the 40 centimeter pile sample, the data of the works
done, obtained during the excavation of 10,00 meter depth piles,
once a load test was made on a pile with those characteristics,
close to boring SPT 1 (Table 2), which results are marked with
grey color in Table 2. Silva (2011) submited all the collected
data to normality tests that evaluate if the frequency distribution
of a data group adheres to the Normal Distribution and verified
that the data adheres to the normal distribution. The central
tendency measures, mean and median, the standard deviation
and the variance are presented in Table 4.
Table 4– Características estatísticas da população e da amostra
Estacas
População
Amostra
Média (MJ)
5,56
3,97
Mediana (MJ)
5,70
3,80
Desvio Padrão (MJ)
1,56
0,84
Variância (%)
29
21
It is observed in this case that the mean and the variance of
the sample was smaller than the population. Such fact was
expected for the mean once it refers to a very folded profile, the
load test was made on the pile with a small depth in favor of
safety. The smaller value of variance is perfectly justified
because in accordance with the methodology, a region with
small variability must be chosen what was assured, in the case,
by the sampling in a restricted area, on the contrary concerning
the piling which was executed taking all the area and
consequently all its variability. Then to assure that the bearing
capacity could be achieved, the SCCAP methodology was
applied during the piling execution, in the case, the first criteria
by considering that the mean is a good representative of the
population, the criterions are:
• It will be accepted the pile which when achieving the
minimum design depth did during excavation a required and
measured work (w) greater than the mean (µ) of the work
measured from the sample (W
≥
µ);
• It will be accepted the pile which when achieving the
minimum design depth did during excavation a required and
measured work (w) greater than the mean (µ) plus the standard
deviation (
σ
) of the work measured from the sample (W
≥
µ+
σ
);
• It will be accepted the pile which when achieving the
minimum design depth did during excavation a required and
measured work (w) greater than the mean (µ) plus two times the
standard deviation (
σ
) of the work measured from the
population sample where they belong (W
≥
µ+2.
σ
).
For the analyses, hypothetical applications were done from
the first and second criterion. Comparing the work done (W) in
each pile during its excavation (Table 3) with the mean (µ) of
the required work to execute the piles of the sample, first
criterion (W
≥
µ), it is observed that it would be necessary to
correct or increase the depth of 4 piles with a diameter of 40 cm
for them to present a cumulative work smaller than the mean
obtained for the sample. By using the second criterion, which is
more conservative, it is noticed that eliminating the piles which
have been excluded from the previous analysis, even though 8
piles with a diameter of 40 cm would be refused.
Once the results presented in Table 3 were set in the
chronological execution sequence of the piling and knowing
that the piling was executed sequentially till the total area of the
construction was covered, it can be verified, for example, in
Table 3, that the piles refused by criterions 1 and 2 are arranged
in group, that is, those piles are neighbors and probably are
founded in regions with NSPT mean value smaller than what
was expected or they were founded on synclinal folds.
It is clear that the adoption of the SCCAP methodology gives
more reliability to the piling in terms of bearing capacity.
4 RELIABILITY
Trying to measure the reliability of CFA pilings, Silva
(2011) from a data file made with energy or wok done records
to execute each pile of the piling, he evaluated the reliability in
bored pilings. He considered the concept that the bearing
capacity of each pile and its deformability are directly related
with the measured energy or the required work to bore it, he
used the proposal of Ang & Tang (1984), which defined the
continuous random variables, in the case, their probability
distributions that define the demanding forces and piling
resistance: X= resistance or resistant capacity of the system; Y=
demanding load acting in the system.
The goal was to assure that the event (X > Y) happens
during the whole life of the foundation. This condition or
warranty can be verified in terms of the which represents the
piling reliability. On the contrary, the probability of failure is
the measurement which corresponds to the completing event.
Once fixed to the shape of the demanding action curves
(loads on foundations) and of resistances (bearing capacity of
piles); and knowing their coefficients of variety and the global
safety factor of the piling, the reliability index can be
determined and the probability of failure of the piling,
interpreted by Cardoso e Fernandes (2001). From that proposal,
Silva (2011) showed that the reliability index (
β)
of the piling
increased a great deal, going from 2,69 to 3,14.
4 CONCLUSIONS
The routines of quality control proposed by the SCCAP
methodology are showing their great importance in
constructions controlled by such technique, assuring quality for
the whole process of excavation. Mainly because it can assure
that all design assumptions in terms of bearing capacity and
deformability are guaranteed through the decrease of the
variability and the increase of reliability. Another important
issue which was observed is that the SCCAP methodology
offers stopping criteria for the boring which has a
complementary and corrective role, contributing to risk
reduction in the construction once it reduces the probability of
failure and increasing the reliability..
5 ACKNOWLEDGEMENTS
The authors would like to thank the foundation company
Empresa Sul Americana de Fundações S/A and Embre
Engenharia for the availability of the data files analyzed in this
study.
6 REFERENCES
CARDOSO, A.S. & FERNANDES, M.M. (2001). Characteristic Values
of Ground Parameters and Probability of Failure in Design
according to Eurocode 7. Geotechnique 51, 6: 519-531.
CLOUGH, R.W. & PENZIEN, J. Dynamics of Structures, 1st Ed., New
York-NW, McGraw-Hill, 634 p., 1975.
SILVA, C.M. Energy and Reliability in Continuous Flight Auger Type
Foundation Works. PhD Thesis, Publication G.TD - 070/11, Civl
and Environmental Department, University of Brasilia, Brasilia,
DF, 303p, 2011. (in portuguese).
SILVA, C.M.; CAVALCANTE, A.L.B.; CAMAPUM DE
CARVALHO, J. On Modelling Continuous Flight Auger Pilings by
means of Energy. International Journal of Science and Engineering
Investigations vol. 1, issue 9, October 2012, ISSN: 2251-8843.
