Due to the interlayered sandstone and shale geological condition of many nature slopes in Taiwan, failure of anchored slopes is usually resulted by a combination of causes. The most commonly encountered is a shallow slip behind or above the anchored slope retaining structure followed by a total failure of the entire anchor system. Rainfall infiltration and weathering of slope surface material are the main causes to trigger shallow landslip. But, totally or partially loss of tieback anchor load due to poor corrosion protection is often the reason for the failure of anchored slopes under the adverse geological and weather conditions of Taiwan. So it is necessary to carry out a systematic investigation on current status of anchors which had been in service for decades to understand the corrosion condition of anchors and to keep the safety of anchored slope. This paper summarizes the common cases and failure types of anchors and anchored slopes failures in Taiwan. Some counter-measures against anchor corrosion are proposed including the routine anchor investigation program and the improved details of corrosion protection measure for the entire anchor (e.g., anchor head, steel strands in fixed and free ends of the anchor).
This study collects the cases of ground anchor construction and investigation, analyzes the factors affecting the quality and performance of ground anchor. Some key points of the anchor design and construction for the corrosion inhibiting consideration were discussed through the cases. The preliminary investigation results are compiled as well.
Using ground anchors has become a controversial issue after the failures of several slopes, which have caused significant casualties, in Taiwan. A great part of engineers are against anchors to be used in permanent structures. However, ground anchors offering high resistance are one of the most efficient methods to stabilize a retaining wall or a slope. Sometimes ground anchors will be the only option in a very steep slope which can not be easily accessed with heavy machinery. Thus, to improve ground anchors to be a reliable construction method is still the present issue for engineers. This paper focuses on the defects of existing ground anchors in the aspects of investigation, design, construction and maintenance for the reference of the improvement of ground anchors. For permaent anchors, the most important issuse is the longterm corrosion protection of the anchor head, the free length of tendon and the fix length of tendon. In the same time, the maintenance management is also very important. Under regular maintenance, most defets will be found and be remedied when they just happened.
In Taiwan, anchors were first used in slope protection engineering in Techi Dam in 1970s. Since then anchors were often used in slope stability for construction of roads and communities on hillsides. In the past 40 years engineers have accumulated a lot of experience in using anchors, but there are still certain problems needed to be solved. Especially in 2010 after the failure of anchored slope at mileage 3.1K on Highway No. 3, the function of existing anchors and the safety of anchored slopes have raised a lot of concern. This paper introduces examining items, methods and processes of functional inspection of existing anchors. Also, 16 functional inspection results of existing anchors in western Taiwan are analyzed. It is hoped to show the common problems of existing anchors and the preliminary improving methods for engineering reference.
Prestressed ground anchors were first applied for Derchi dam project in 1975 in Taiwan. Since then many prestressed ground anchors have been installed and put in service for the past 40 years. However, the prestressed ground anchors installed in Taiwan have not fully satisfied the newest international standard for permanent anchors owing to the inferior or inadequate corrosion protection technique and lack of continuous post-construction maintenance plans throughout the life span of an anchor system. In this article, installation methods, corrosion protection technique, and durability requirement of the prestressed ground anchors were discussed based on the relevant construction codes from different countries. Consequently, the discussion aims at providing insights into improvements of current installation codes and maintenance plans of prestressed ground anchor systems in Taiwan, hoping to be capable of reducing possible failures in the future.
This article reviews aspects ignored frequently in current permanent ground anchor design and provides design recommendations. Lessons learned from major ground anchor failure cases are also discussed and included in the design recommendations. In addition, suggestions to the future permanent ground anchor design are provided considering the latest developments of permanent ground anchor in the world and practical needs in Taiwan.
Owing to improper design, construction, creep of stratum or rust of strand at the completion service stage of prestressed ground anchor, the design capacity may reduce to severe hazard under completion usage stage due to less or exceeding tensile force, or loss of prestressed force. Therefore the establishment of maintenance and management system for ground anchor is an important issue for government and engineer to avoid disaster. This paper is to discuss how to strengthen the maintenance and management work of ground anchor by unitary, systematic, effective maintenance and management system and functionality test of ground anchor. Thus, the function and public safety can be secured during the life cycle of ground anchor.
The traditional corrosion protection on ground anchor was used mostly by cement. However, it may gradually lose effectiveness because of the cracks happening in the cement caused by the afterword anchor deformation or harden shrinkage. This paper compares the evolution of ground anchor construction in Taiwan with Japan. The problems of ground anchor corrosion are discussed. The applications of new material and technology for ground anchor corrosion protection are introduced.