2086
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
2
2
2
2
2
2
8
2 2 1
8
2 1
2 2 1
s
s
R l
c
L z l lR R
R R l
c
L z l lR
R
(4)
In expressions (3) and (4),
and are the radius and the
length of the tie rod, while
l
and
R L
s
z
stand for the length and
the elevation (with respect to the bottom of the tie rod) of the
steel sockets.
The straightforward solution of system (2) allows of
estimating both
socket
and
int
T
(=
lateral
). The soundness of the
above assumptions has been verified for all the performed
simulations and, in particular, for the full-size analyses (3 m and
7 m embedment) a satisfactory agreement in terms not only of
total pull-out force (errors less than 10%) but also of the single
contributions has been found. Further confirmation is given in
Figures 9 and 10, where the analytical predictions for the radial
(a, circular marked line) and shear (b, square marked line)
stresses along the inner side of the soil wedge are compared
with the FEM results (black solid line).
F
F
4 CONCLUSIONS
The pull-out performance of an innovative soil anchoring
system has been numerically investigated through FEM
analyses. The anchoring device is composed of a tie rod and a
set of steel sockets, the latter to be extruded into the soil; former
in situ tests have shown the steel sockets largely improve the
pull-out performance of the anchorage. The device installation
is fast, flexible and inexpensive, while in most cases additional
soil grouting becomes optional.
In this work, vertical pull-out tests have been first simulated
to explore the SSI mechanisms determining the pull-out
capacity of the device, whence the following conclusions have
been drawn:
the steel sockets contribute to the global pull-out
capacity in a twofold manner. In a direct way, they
sustain a significant part of the total load owing to
their shear/flexural strength; they also provide an
indirect contribution, by increasing the lateral
confinement and the mobilizable friction along the tie
rod;
in all the cases considered, failure develops up to the
free surface through a global mechanism involving a
cylindrical vertical soil wedge;
the pull-out strength increases for deeper anchors. Its
dependence on socket depth has been found to be,
within the investigated range, almost linear;
Figure 9. FEM and analytical stress distributions for the full-size model
with 3m-embedded sockets.
A simplified analytical model was then proposed to
simultaneously estimate the strength contributions – both direct
and indirect – given by the sockets. This relies on a set of
simplifying hypotheses suggested from the results of FEM
simulations, and provides results in good agreement with the
numerical outcomes. Although only vertical pull-out tests were
considered, the above inferences are believed to apply for
inclined anchors as well, since only a slight influence of the
initial in situ stresses was found.
The proposed model clarifies the mechanical working
conditions of the anchoring system and provides practitioners
with a preliminary design framework. In the near future, further
efforts will be devoted to analyse the device in the case of more
complex geological conditions and, as more experimental
results become available, to validate numerical/analytical
predictions with respect to in situ measurements.
5 ACKNOWLEDGEMENTS
JOBSOIL s.r.l and MIDAS/GTS are gratefully acknowledged
for the financial support.
6 REFERENCES
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Earth anchors
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