2285
Inspection and Capacity Assessment of Anchored Slopes
Inspection et évaluation des capacités des pentes renforcées par ancrage
Yeh H.n-S., Wang C.-S., Wei C.-Y.
Taiwan Area National Freeway Bureau, MOTC
Lee S.-M., Ho T.-Y., Hsiao C.-A., Tsai L.-S.
CECI Engineering Consultants, Inc., Taiwan
ABSTRACT: In Taiwan, anchors were first used in the Techi Dam for slope protection in 1970s. Since then, anchors were often used
for stabilizing slopes in the construction of roads or communities. Lots of anchor experience of engineering practices have been
accumulated in the past 40 years, however, it still remains some problems to be solved. In particular, after the failure of anchored
slope at station 3.1K of Highway No. 3 in 2010, the function of existing anchors and the safety of anchored slopes have raised lots of
concern. This paper introduces examining items, methods and processes of functional inspection of existing anchors. Also, results of
16 functional inspection of existing anchors in western Taiwan are presented. It is expected that the concepts and suggestions
described in this article would be helpful for an engineer in gaining the ability of the analysis of slopes so that the more effective
design can be developed for such a problem in the future.
RÉSUMÉ : A Taiwan, les renforcements par ancrages ont d'abord été utilisé dans le barrage Techi pour la protection des talus dans les
années 1970. Depuis lors, les ancrages étaient souvent utilisés pour la stabilisation des pentes dans la construction de routes.
Beaucoup d'expérience dans les pratiques d'ingénierie d’ancrages a été accumulées au cours des 40 dernières années. Cependant, il
reste encore quelques problèmes à résoudre. En particulier, après la rupture d’une pente ancrée à la station 3.1k de la route n
o
3 en
2010, l’efficacité des ancrages existants et la sécurité des talus ancrées ont soulevé beaucoup d'inquiétude. Cet article présente
l'examen des ancrages, des méthodes et des processus de contrôle du fonctionnement des ancrages existants. En outre, les résultats
d'inspection de 16 talus renforcés par ancrages existants dans l'ouest de Taiwan sont présentés. Il est prévu que les concepts et les
suggestions décrits dans cet article soit utilisable par un ingénieur via l’acquisition d’outils d'analyse des pentes de sorte qu’une
conception plus efficace puisse être développé à l'avenir.
KEYWORDS: Landslides, anchor, lift-off test, anchor inspection, maintenance and management.
1 INTRODUCTION
Taiwan’s area is approximately 3,600,000 hectare, and of it
moderately flat area comprises about 26% while sloped and
forested land make up the remaining 74%. Therefore Taiwan is
mostly mountainous with lesser plains topography, though in
the recent decade with the economic growth and the pursuit of
comfort and ease of transportation, the trend of developing
public infrastructure such as roadways and public facilities is
moving toward hillsides and slopes.
Ground anchoring usage over steep slope has its certain
advantages. Ground anchoring technique originated since the
1970s in Taiwan. Since 1988, Northern Taiwan Second
Highway construction had begun, as its alignment laid
predominantly among mountainous ranges and slopes, this type
of method had proved itself to be an effective technique under
such natural constraints and coupled with rapid economic
growth, many new projects had begun to adopt this method in
many sloped terrain community developments. Until today,
ground anchorage technique has proven to be a reliable method
and have been widely used, as well as the design and field
installation has vastly improved since its earlier days. However,
there are still many ground anchoring failure instances in recent
years, one of which is the quite high profiled case of the 1997
Xizhi Lincoln Mansions disaster and 2010 National Highway
No. 3 at 3.1k accident. Both failure cases are considered ground
anchoring accidents and attributed to parallel landslide as the
cause.
According to Briaud et al.(1998), Bruce and Wolfhope
(2007),
Liao et al. (2011), Ho et al.(2011), Jeng et al.(2011) and
various domestic and foreign ground anchoring case studies,
failure instances involved most commonly pre-stressed losses.
The main cause of that include 1) free section of
tendon(unbounded tendon) rusted and cracked, 2) ground
anchoring wedges rusted or had sub-standard quality, 3)
Installation did not conform to the specification, as the steel
tendon had not gone far enough into the earth, 4) change of
terrain layer, and 5) ground cave in at bottom of the bearing
plate.
After the National Highway No. 3 incident involving ground
anchoring failure, see
Figure 1,
a complete study had done on
ground anchor inspection and assessment. Even so, the findings
of the study were routine and not consistent among the
investigators. This article will introduce and explain the
currently most adopted ground anchoring inspection, procedure,
and assessment. In addition, this article will propose a new way
of ground anchoring assessment, in hoping to establish a
standardized quantitative analysis procedure for professional
reference.
Figure 1. National Highway No. 3 at 3.1k accident
