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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Table 2. Results of one-sided Student’s T-test with unequal variance of
mean pull-out resistances
R
a
for reference and alternative anchors.
RCP/D
RCP/D-K RCP/D-Z
RCP/D-I
Mean
980
1132
620
925
Variance
47770
19965
32622
70263
Standard deviation 218,6
141,3
180,6
265,1
Coef. of variation
0,223
0,125
0,291
0,287
RCP/D
–
RCP/D-K
13,0 %
–
RCP/D-Z
0,7 %
0,1 %
–
RCP/D-I
70,3 %
17,3 %
7,1 %
–
5 CONCLUSIONS
Based on the theoretical background of bond length behaviour
of a prestressed ground anchor and the patents of Barley and
Škrabl, three types of anchors with alternative concepts of bond
lengths inside PE encapsulation (RCP/D-K, RCP/D-Z and
RCP/D-I types) were designed, installed and tested at a test
field. The behaviour of alternative types of anchors was
compared with the behaviour of the reference RCP/D anchors.
Different aspects of design (especially limited anchor bond
length of 7 m, the diameter of available type of corrugated PE
duct), formation, manufacturing details and installation of
testing field anchors resulted in different pull-out resistances
R
a
and they indicate the relations among bond length capacities of
different anchor types.
Test results of 25 anchors showed that the maximum values
of pull-out resistance
R
a
were reached at the modified RCP/D-K
anchors with increased stiffness of bond length - the mean
values of
R
a
of RCP/D-K anchors exceeded the mean values of
R
a
of RCP/D anchors by 16 %. Although the free space within
the corrugated PE duct of bond length of the RCP/D-K anchors
was very restricted, allowing only
∅
5 mm additional steel
wires to be installed (instead of originally planned
∅
12.5 mm
steel strands), high values of pull-out resistances of RCP/D-K
anchors were obtained. The behaviour of RCP/D-Z and RCP/D-
I anchors was probably influenced by the surface contamination
with vaseline as well as the configuration of strands in the bond
length. Additional impairment of the conditions within the
corrugated PE duct was caused by the use of soft and relatively
spacious packing connections in the transition between anchor
units bond and free length. The RCP/D-Z anchors demonstrated
the poorest performance of all tested anchors (the bond length
of RCP/D-Z anchors failed at low force levels of IT and CST).
In all cases local debonding at the strand/grout interface resulted
in the pull-out of strands. With improvement of particular
technological details of alternative anchors, higher values of
pull-out resistances can be expected. According to the
experiences of Barley with multiple anchors, the pull-out
resistances of RCP/D-Z anchors should attain (and probably
exceed) the pull-out resistances of reference RCP/D anchors,
provided that the pull-out of strands from cement grout, placed
within the corrugated PE duct, is prevented. At least it is
necessary to provide the immaculate condition of bare strands in
the bond length within the PE encapsulation. Moreover, it is
also possible that instead of RCP/D-K anchors the highest
values of pull-out resistance could be achieved at one of the
other alternative types (RCP/D-I or RCP/D-Z).
With the intention to increase the efficiency of alternative
types of permanent prestressed anchors (RCP/D-K, RCP/D-Z
and RCP/D-I) the following improvements are suggested:
• Results of field testing confirm the already known fact
(Littlejohn, 1993, Hanna, 1982) that for effective performance
of bond length the bare strands should be covered with
sufficiently thick layer of cement grout, irrespective of the
anchor bond length design.
• The efficiency of anchor bond length could be improved
with the increase of corrugated PE duct diameter. In that case
the region around bare strands within corrugated PE duct could
be reinforced (spiral micro reinforcement, cement grout with
admixed fibres, etc.). Simultaneously, extra space would be
gained for noding or local deforming of strands.
• The efficiency of RCP/D-Z and RCP/D-I anchors could also
be improved by upgrading the technological detail of anchor
unit packing connections at the transition between strand bond
and free lengths. Performance of RCP/D-z and RCP/D-I
anchors could also be improved if the greased and sheathed
strands in the free length would possibly be replaced with some
other solution that offers higher stiffness in radial direction.
• For specific design of RCP/D-Z and RCP/D-I anchors the
combination of strand and anchor unit noding is suggested,
whereat the minimal anchor unit strands bond length should be
2.5 m (in case of the increased diameter of corrugated PE duct)
and 3.0 m (in case of the unchanged diameter of corrugated PE
duct).
6 ACKNOWLEDGEMENTS
The authors are grateful to the Slovenian motorway agency
DARS, for their financing of the research project. We are also
much obliged to the manufacturer CA.TI. Carnica Tiranti, Srl,
Italy for their donation of the anchors, and to the contractor
GEOT for successful installation and in-situ testing of anchors.
7 REFERENCES
Barley A.D. 1990. Ground anchorage containing a multiple of ground
anchorages : patent number EP 0 356 215 A2. European Patent Office.
Barley A.D. and Windsor C.R. 2000. Recent advances in ground anchor
and reinforcement technology with reference to the development of the
art. International conference on geotechnics and geotechnical
engineering, vol. 1. 19th – 24th November 2000, Melbourne,
Australia. Basel, Lancaster: 1157-1252.
Bruce M.E.C., Gómez J., Traylor R.P. 2007. Repeated lift-off testing of
single bore multiple anchors for dam retaining wall over a 5-year
period. V: Littlejohn, G.S. (ed.). International conference on ground
anchorages and anchored structures in service. ICE London,
November 2007. London, Thomas Telford: str. 111-119.
Hanna T.H. 1982. Foundations in tension : ground anchors. Trans Tech
Publications. New York, McGraw Hill Book Co.
Hutchinson D. and Diederichs M. 1996. Cablebolting in underground
mines. Richmond, Canada, BiTech Publisher Ltd.
Klemenc I. 2011. Investigation tests of permanent prestressed strand
ground anchors with various designs of tendon bond length : doctoral
thesis (in Slovene). Ljubljana.
Limelette test fields results. 2008. Proceedings of the international
symposium ground anchors. 14 May 2008, Brussels, Belgium.
Littlejohn S. 1993. Overview of rock anchorages. Hudson, J.A. (ed.).
Comprehensive rock engineering : excavation, support and
monitoring, vol. 4. Oxford, Pergamon Press.
Ostermayer H. 1975. Construction, carrying behaviour and creep
characteristics of ground anchors. Conference on Diaphragm Walls
and Anchorages. ICE London, September 1974, 141-151.
Škrabl S. 2004. Prestressed ground anchors of variable stiffness : patent
number 21320 (in Slovene). Ljubljana : SIPO.
