2370
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
are quite similar in the two cases and affect only a quite limited
area of the foundation soil.
Table 3. Computed factors of safety (on strength parameters)
Factor of safety
Consideration of
cyclic loading
Wave force =
341.6 kN/m
1000 impacts
Wave force =
1011.6 kN/m
40 impacts
Yes
1.48
1.18
No
1.55
1.40
Table 2. Characteristics of the design storm
Number of waves
Wave
height
(m)
H
s
=
3m
(24 h.)
H
s
=
4m
(24 h.)
H
s
=
5m
(24 h.)
H
s
=
5.9m
(24 h.)
Wave
force
(kN/m)
Force
height
(m)
1-2
3124 1661 593
150 213.4
9.77
2-3
2203 1693 720
199 341.6
10.28
3-4
848 1133 626
198 475.0
10.62
4-5
195
545
427
161 685.0
10.65
5-6
28
194
236
111 825.4
10.74
6-7
2
52
108
66
870-5
10.80
7-8
0
11
41
34
920.0
10.00
8-9
0
2
13
16 1011.5
10.36
9-10
0
0
3
6
1410.1
11.46
10-11
0
0
1
2
1528.0
11.15
11-12
0
0
0
1
1559.3
11.38
6 CONCLUDING REMARKS
Finally, a new stability analysis is performed with the new
distribution of undrained shear strength of the foundation soil
for the two cases considered. The analysis also considers the
influence of the dynamic uplift caused by the storm loading,
derived from the physical model tests carried out for this
particular breakwater design. The results, in terms of factor of
safety for strength reduction, are shown in Table 3. It can be
seen that consideration of cyclic loading has a moderate but
noticeable impact on the factor of safety. Given the exceptional
character of the design storm and the conservative assumptions
made in the analysis, the factor of safety obtained was
considered adequate for accepting the design.
A key design feature of a breakwater is the assessment of the
stability of the breakwater when subject to extreme storms. This
is particularly the case for caisson breakwaters in which the
effects of wave action are significantly stronger than for the
classical rubble mound type. A proper consideration of the
dynamic effects would require the performance of a full
dynamic analysis. Here, a simplified stability analysis is
proposed that takes into account the potential reduction of the
shear strength of the soil due to cyclic loading. It is based on the
experimental determination of the interaction diagrams that
provide criteria to identify the conditions for which the soil can
undergo cyclic mobility and strength degradation. The
corresponding strength reduction is then taken into account in
conventional stability analyses. The procedure has been
illustrated by a specific application to a caisson breakwater that
is part of the extension works of the Barcelona Harbour.
7 ACKNOWLEDGEMENTS
The authors are grateful for the technical and financial support
provided by APB (Autoritat Portuaria de Barcelona).
8 REFERENCES (TNR 8)
-80
-60
-40
-20
0
20
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60
80
100
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Goulois, A.M., Whitman, R.V., and Hoeg, K. (1985). Effect of
sustained shear stress on the cyclic degradation of clay.
Proceeding,
Symposium on Strength Testing of Marine Sediments
, R.C. Chaney
and K.R. Demars, eds., ASTM STP 883, ASTM, Philadelphia, 336-
351.
NGI. (2002). Laboratory Testing. Geotechnical Testing Report. March
2002.
Tsuchida, T. (2000). Evaluation of undrained shear strength of soft clay
with consideration of sample quality.
Soil & Foundations
40, No 3,
29-42.
Figure 8. Foundation zones exceeding the interaction diagram criterion.
Wave load = 341.6 kN/m and 1000 cycles.
-80
-60
-40
-20
0
20
-100
-80
-60
-40
-20
0
20
40
60
80
100
120
Figure 9. Foundation zones exceeding the interaction diagram criterion.
Wave load = 1011.5 kN/m and 40 cycles.
