Undrained Load Capacity of Torpedo Anchors in ... - laceo - UFRJ

varies from 0 to 0.90m. The self-weight of the anchor was kept
constant and equals to 850kN.
Although the undrained shear strengths were different, all
the scenarios have the same anchor penetration. A study based
on the theoretical model presented by True [11] was conducted
only for soil B and the four flukes anchor. The penetration
achieved by the top of the anchor was equal to 16m and this
value was used in all analyses.
Moreover, in the performed analyses, the extension cone
approximation, Eq.(14), is employed.
Several FE meshes were developed. In average, they have
53770 nodes, 93830 elements leading to a problem with
161310 degrees of freedom.
Results
Figure 10 – Dimensions, in m, of the analyzed torpedo
anchor.
Effect of different undrained shear strengths
Figures 12 to 14 present the variation of the displacement
at the top of the anchor with the applied load. These curves
were obtained in the analyses of the torpedo anchor with 4
flukes embedded in soils A, B and C, respectively. In these
figures, loads are at an angle of 45° with the plane of the flukes
(plane 1, Fig. 11a) and several different load inclinations with
respect to the horizontal plane are accounted.
These figures point that the ratio between the displacement
change and the applied load varies with the load inclination
and, consequently, there is a significant difference between the
vertical and lateral soil stiffness.
7000
6000
Figure 11 – Torpedo anchor cross-sections: (a) four, (b)
three and (c) no flukes.
In all analyses, seven load inclinations with respect to the
horizontal plane were considered: 0° (horizontal load), 15°,
30°, 45°, 60°, 75° and 90° (vertical load). All loads, F a , were
applied at the top of the anchor, as pointed out in Fig. 10.
The soil is considered to be purely cohesive and isotropic
with Young modulus varying with depth and given by the
expression:
() z
E( z)
= 550⋅ S
(25)
u
Three different undrained shear strength profiles were
considered in this numerical-based study:
kPa
Soil A: S u ( z)
= 1.5⋅
⋅ z
m
kPa
Soil B: S u ( z)
= 3.0 ⋅ ⋅ z
m
kPa
Soil C: S u ( z)
= 6.0 ⋅ ⋅ z
m
where z is the depth bellow mudline in m.
(26)
Load (kN)
5000
4000
3000
0°
15°
2000
30°
45°
60°
1000
75°
90°
0
0.00 0.05 0.10 0.15 0.20 0.25
Displacement at anchor top (m)
Figure 12 – Load vs displacement curves of a torpedo
anchor with 4 flukes considering different load inclinations
with the horizontal plane: soil A, 45° with the flukes.
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