Assessment of SPT-based Methods of Pile Bearing Capacity-Analysis of A Database
Assessment of SPT-based Methods of Pile Bearing Capacity-Analysis of A Database
Assessment of SPT-based Methods of Pile Bearing Capacity-Analysis of A Database
net/publication/305657928
CITATION READS
1 5,533
1 author:
Ali BOUAFIA
Saad Dahlab University
174 PUBLICATIONS 234 CITATIONS
SEE PROFILE
Some of the authors of this publication are also working on these related projects:
All content following this page was uploaded by Ali BOUAFIA on 27 July 2016.
10000
3 INTERPRETATION OF PILES LOADING
TESTS 5000
2
friction angle of sand, by Caquot-Kerisel’s empirical
correlation:
1
e.tgϕ =m (7)
where m is an empirical factor ranging between
0.40 and 0.60 for silica sands. The analysis made 0
0 10 20 30 40 50 60 70
by the author on 59 sandy samples subject to direct
shear tests from different sites has shown the above Ne
relation fits the best the experimental data with m=
Figure 3. Variation of the adjustment factor λ versus Ns
0.50 (Bouafia, 2000).
Table 1. Summary of features of the different methods
5 ASSESSEMENT OF PREDICTIONS
According to table 1, this fact may be explained by
Table 2 summarises some statistics related to each relatively high values of factors Ks and ns.
method tested. µ is defined as the ratio of predicted The same explanation is possible for Aoki and Vel-
baring capacity to the one experimentally derived. losos’s method which has overpredicted almost all
SD and COV respectively mean standard deviation the cases with an average value of 1.91 for µ.
and coefficient of variation (ratio average/SD) of the Meyerohf’s method and CFEM(1985) have un-
ratio µ. The underprediction rate is defined as the derpredicted most of cases with an average value of
percentage of cases underpredicted. 0.70 for the ratio µ. The pessimistic prediction
From table 2, since the coefficient of variation is which may justify the large use of this method was
almost same for all the methods, it can be concluded already highlighted by many authors working on
that these methods are characterised by the same similar databases ( Turnbull and Kaufmann 1956,
level of dispersion of predictions with respect to the Mansur & Focht 1960). According to table 2, the
mean values of µ. factor ns of Meyerhof’s method for bored piles is the
Figure 4 shows that Decourt’s method in all the smallest one. Moreover, N values used in this
cases has overpredicted the bearing capacity. method are to be reduced by the so-called depth ef-
fect.
Table 2. Results of assessment of the methods
20000 50000
30000
Qe
10000
.= 15000
pred 20000
Q
10000
5000 10000
5000
0
0 0 5000 10000 15000 20000
0
0 5000 10000 15000 20000 0 5000 10000 15000 20000
Qexp.
Qex(kN)
p. (kN)
20000 20000
20000
Reese-O'Neill Shioi-Fukui Hansen-Burland adjusted
15000 15000
15000
0 0 0
0 5000 10000 15000 20000 0 5000 10000 15000 20000 0 5000 10000 15000 20000
20000
20000
Robert 20000
Bazarra-Kurkur Lopes-Laprovitera
15000 15000
15000
Q pred. (kN)
10000 10000
10000
5000 5000
5000
0
0 0 0 5000 10000 15000 20000
0 5000 10000 15000 20000 0 5000 10000 15000 20000
Qexp. (kN)
Figure 4. Comparison of predicted and experimental values of bearing capacity of bored piles for each method
20 Aoki-Velloso
0
0,0 0,5 1,0 1,5 2,0 2,5 3,0
20 Meyerhof
0
0,0 0,5 1,0 1,5 2,0 2,5 3,0
20 Shioi-Fukui
0
0,0 0,5 1,0 1,5 2,0 2,5 3,0
Number of cases
20
Reese -O'Neill
0
0,0 0,5 1,0 1,5 2,0 2,5 3,0
20 Hansen-Burland
0
0,0 0,5 1,0 1,5 2,0 2,5 3,0
20 Lopes-Laprovitera
0
0,0 0,5 1,0 1,5 2,0 2,5 3,0
20 Bazarra-Kurkur
0
0,0 0,5 1,0 1,5 2,0 2,5 3,0
20 Robert
0
0,0 0,5 1,0 1,5 2,0 2,5 3,0
As illustrated by figure 4, methods of Robert, pile bearing capacity calculation was undertaken.
Lopes & Laprovitera, Bazarra & Kurkur and Han- The quality of prediction of these methods is as-
sen & Burland seem giving the best prediction with sessed by direct comparison of the predicted limit
a range of µ between 0.93 and 0.98. They can be vertical load carried by the pile to the one experi-
considered as rather pessimistic since almost two mentally derived from static pile loading test.
third of cases were underpredicted by these meth- Decourt and Aoki-Velloso’s methods were
ods. found optimistic in most of the cases studied
The prediction of the semi-empirical Hansen- whereas Meyerhof’s method is rather pessimistic.
Burland’s method seems better than many other The semi-empirical Hansen-Burland’s method
purely empirical methods, which encourages to allows very good prediction in comparison with
improve the quality of adjustment of this approach. the other empirical approaches.
According to figure 5, histograms of µ counts Methods of Robert, Lopes & Laprovitera, Ba-
may be fitted by a Gaussian distribution. If one de- zarra & Kurkur and Hansen & Burland give an
fines the criterion of ranking of these methods as average value of the ratio µ (ratio load predicted to
the frequency counts of µ between 0.8 and 1.0, experimental load) ranging between 0.93 and 0.98.
Robert, Lopes & Laprovitera, Bazarra & Kurkur According the ranking criterion defined as the fre-
and Hansen & Burland are respectively character- quency count of µ ranging between 0.8 and 1.0,
ised by the frequencies of 30.8 %, 28.9%, 24.3% methods of Robert, Lopes & Laprovitera, Bazarra
and 21.5%. & Kurkur and Hansen & Burland are respectively
characterised by the frequencies of 30.8 %, 28.9%,
24.3% and 21.5%. However, al the methods tested
6 CONCLUSIONS express some dispersion of prediction with a coef-
ficient of variation of about 30% with respect to
On the basis of a database comprising 46 static the mean value.
pile loading tests carried out in 27 silty sand an
evaluation study of nine SPT-based methods of
7 REFERENCES Lopes,R.F, Laprovitera,H.1988. On the prediction of the
bearing capacity of bored piles from dynamic penetration
Aoki,N & Veloso,D.1975.An approximate method to esti- tests. Proceedings of Deep foundations on bored and au-
mate the bearing capacity of piles. Proceedings of the 5th ger piles BAP’88, Van Impe (ed), pp: 537-540.
Pan-American Conference on soil Mechanics and Foun- Meyerhof,G.G.1956. Penetration tests and bearing capacity
dation engineering,Vol 1, pp : 367-376, Buenos-Aires. of piles in cohesionless soils. Proceedings of ASCE,
Journal of SMFE, Vol.82,No. SM.1, January 1956.
Bazarra, A.R & Kurkur,M.M.1986. N-values used to predict Meyerhof,G.G.1976. Bearing capacity and settlement of pile
settlements of piles in Egypt. In: Use of In-situ tests in foundations. Journal of Geotech. Engg. ASCE, Vol.102,
geotechnical engineering, ASCE Geotech. Special Publi- No.3, pp :1-19.
cation, Clemence ed., Vol. 6, pp : 462-474. Peck,R.B et Al.1973. Foundation engineering. 2nd edition,
Bouafia,A. 2000. Some comments on e-ϕ correlation for John Wiley & sons editors, 514 pages.
sandy soils. Internal publication (in French), Department Reese,L.C & O’Neill,M.W. 1989. New design method for
of Civ.Engg. Univ. of Blida, 6 pages. drilled shafts from common soil and rock tests. Proceed-
Bouafia, A.2001. Pile foundations bearing capacity –The ings of Congress foundation engineering-Current princi-
UAE experience, World of Engineering, Journal of the ples and practices,ASCE, Vol 2, pp :1026-1039.
UAE society of Engineers, 7 pages. Robert,Y,1997. A few comments on pile design. Can. Geo-
Briaud,J.L, L.M.Tucker.1988. Measured and predicted axial tech. J. Vol.34. pp : 560-567.
response of 98 piles. Journal of Geotech. Engg., Shioi,Y & Fukui,J.1982. Application of N-value to design of
Vol.114,No.9, September 1988. foundations in Japan, Proceeding of the 2nd ESOPT, Vol.
Burland,J.B.1973. Shaft friction piles in clay-A simple fun- 1, pp 159-164.
damental approach, Ground Engineering, vol. 6, N°3, PP. Tornbull,W.J & Kaufmann,R.I .1956.Discussion on the paper
30-42. :Penetration tests and bearing capacity of piles in cohe-
Bustamante,M et Al.1991. Evaluation dequelques méthods sionless soils by :Meyerhof, proceedings of ASCE, Jour-
de calcul des pieux forés (in French), RFG, French Geo- nal of SMFE, Vol.82, No. SM.1, January 1956.
tech. Journal No.54, pp :39-52, january 1991.
CGS.1985. Canadian Foundation Engineering manual
CFEM, 2nd edition, Canadian Geotechnical Society, C/o
Bitech publishers Ltd.,Vancouver, BC.
Decourt,L.1982. Prediction of the bearing capacity of piles
based exclusively on N-Value of the SPT. Proceedings of
2nd European Symposium on penetration testing, Vol 1,
pp :29-34, Amsterdam.
Hansen, J.B.1970. A revised and extended formula for Bear-
ing Capacity, Danish Geotechnical Institute report No.
28, Copenhagen, 21 pages.