2031
In-situ tests of permanent prestressed ground anchors with alternative designs of
anchor bond length
Essais in situ des tirants d'ancrage précontraints permanents avec des conceptions alternatives de
la longueur de scellement
Klemenc I.
Slovenian National Building and Civil Engineering Institute
Logar J.
University of Ljubljana, Faculty of Civil and Geodetic Engineering
ABSTRACT: Some concepts of cost efficient ground anchors with enhanced pull-out resistance from single borehole already exist:
single bore multiple anchors (Barley, 1990) and prestressed ground anchors of variable stiffness (Škrabl, 2004). A third alternative
with anchor bond length of increased stiffness has been proposed. All three concepts have been combined with the concept of
comprehensive corrosion protection. Five anchors of all three design alternatives as well as ten investigation tests on standard
permanent prestressed ground anchors were tested in-situ on a large retaining wall in N-E Slovenia. The paper presents the design of
each type of anchor bond length, test procedure and test results. The test results of our in-situ research on the specific location show
that the highest anchor pull-out resistance was obtained for the anchor bond length of increased stiffness.
RÉSUMÉ: En plus des conceptions existantes d'augmentation de la résistance des tirants d'ancrage dans un même forage avec un bon
rapport coûts-efficacité, tels les tirants à torons multiples (technologie SBMA – Barley, 1990) et les tirants précontraints de rigidité
variable (Škrabl, 2004), nous proposons une troisième alternative: les tirants d'ancrage à rigidité renforcée. Les trois types étudiés ont
été combinés parallèlement avec une conception de protection anti-corrosion. Nous avons testé in situ des ensembles de cinq groupes
de chacun des trois types proposés et de dix tirants d'ancrage standard, sur une construction de soutènement importante réalisée dans
la partie nord-est de la Slovénie. Dans cet article nous présentons le dimensionnement de la longueur de scellement de tous les types
de tirants d'ancrage ainsi que le déroulement et les résultats des essais effectués. Les résultats des essais in situ démontrent que la
résistance maximale est obtenue avec la longueur de scellement du tirant à rigidité renforcée.
KEYWORDS: ground anchor, design of bond length, pull-out resistance, in-situ test, comprehensive corrosion protection.
1 INTRODUCTION
In 1934 the first prestressed ground anchors were built during
the raising of the Cheurfas Dam (Algeria). Such anchors have
been increasingly used since then, in cases, where the execution
of other geotechnical measures is significantly more difficult,
more expensive or even impossible. The most widespread is the
use of the friction tensile type of ground anchors (Limelette,
2008), with which the technological design and implementation
of the corrosion protection has reached a level that promises a
long-term operation (provided that adequate maintenance is
ensured). This especially applies to anchors with a
comprehensive corrosion protection, which was two decades
ago developed in Switzerland: the steel parts of these anchors
are encapsulated by a waterproof polyethylene (PE) cover,
which also provides electrical isolation of steel parts against the
environment. In parallel with technological improvements, the
price of anchors has also grown. Therefore, increasing
tendencies to rationalize anchors have appeared.
Three different simple modifications of a permanent
prestressed anchor bond length were designed and investigated
in order to achieve higher values of pull-out resistances and
better efficiencies of anchors. The prototypes of such alternative
anchors were installed and tested in a testing field. The obtained
results were compared with those of reference anchors.
2 ALTERNATIVE DESIGNS OF BOND LENGTHS
The starting-point in the task of searching for the most effective
concept of permanent prestressed ground anchors with the
tendon contained within joint PE cover were reference
(standard) anchors
RCP/D
. These anchors were used in a
retaining wall that served as a test site. The total length of each
individual anchor is
l
= 35 m with the tendon bond length of
l
v
=
7 m, consisting of six low-relaxation strands
∅
15.2 mm
(
f
p0.1k
/
f
pk
= 1670/1860 MPa).
Figure 1. Conceptual designs of bond lengths of permanent prestressed
strand anchors with joint PE encapsulation: reference anchor RCP/D,
alternative types of anchors RCP/D-K (increased stiffness of bond length),
RCP/D-Z (multiple anchor) and RCP/D-I (anchor of variable stiffness).
Three different conceptual designs of anchor bond lengths
(Fig. 1) were conceived and implemented with the intention to
improve stress distribution along the tendon bond length and to
consequently increase the pull-out capacity of anchors:
•
anchors with increased stiffness of bond length
, with which
six additional steel wires
∅
5 mm were placed in empty spaces
among bond lengths of strands (type
RCP/D-K
with strand free
lengths of 28 m and strand bond lengths of 7 m),
•
multiple anchors with staggered anchor units
based on the
idea of Barlay's anchors SBMA, only that three anchor units
