Len Carrigan’s scientific contributions

CFRP ground anchors have an integral place in the ground anchor industry, providing designer and contractors with a corrosion resilient anchor which minimises the labour intensive corrosion protection required when using steel strands. Successful anchoring of long strand lengths in a confined ground anchor environment has been the greatest constraint in the development of CFRP ground anchors. Recent research undertaken at Monash University and Geotechnical Engineering has developed a reliable and compact bond type anchorage head system, practical for permanent ground anchor applications. Laboratory and full scale testing has been successfully carried out. This paper provides tests results on a four and ten strand CFRP modified bond type anchor head system with a reduced bond length. Results showed failure of specimens were within the CFRP fibres due to tensile rupture. Negligible movement at the bond anchor head were recorded.

Steel tendon ground anchors are an integral construction technique for numerous civil engineering applications ranging from deep excavation support to resistance of structural uplift and overturning of superstructures. Corrosion and human error generally causes failure of steel tendon ground anchors. Several methods of minimising anchor system corrosion have been adopted over time to minimise ingress of corrosive substances. Anchors are still failing due to corrosion. Advancement in the development of corrosion resistant materials has been at the forefront of materials research. Research and development of FRP materials has enabled the progress of providing the industry with a more potentially robust anchor system aimed at eliminating current limitations encountered with steel strand ground anchors. This paper investigates current developments in FRP materials for ground anchor applications as I an alternative to conventional steel tendon ground anchors.

Steel tendon ground anchors are an integral construction technique for numerous civil engineering applications ranging from deep excavation support to resistance of structural uplift and overturning of superstructures. Failures of steel strand ground anchor systems are rare, but when they occur, corrosion and human error are the primary reason. Several methods of minimising anchor system corrosion have been adopted over time to minimise ingress of corrosive substances. However, anchors are still failing due to corrosion. Advancement in the development of corrosion resistant materials has been at the forefront of materials research. In this respect, research and development of FRP materials is enabling the progress of providing the industry with a more potentially robust anchor system aimed at eliminating current limitations encountered with steel strand ground anchors. This paper provides an overview of current best practices for the application of permanent ground anchors and investigates the current developments in FRP materials for ground anchor applications as an alternative to conventional steel tendon ground anchors. The paper also provides insight into known areas where further research is required to assist the introduction of FRP ground anchors into standards.

High capacity ground anchors currently employ the well established steel strand system using stress relieved post tensioned strands. Although such systems provide rugged tendons with readily available hardware, they are vulnerable to corrosive attack from aggressive ground environments. Current permanent ground anchor standards require the use of double protection systems encapsulating the steel strands, to ensure a serviceable design life. Fibre Reinforced Polymer (FRP) is characterised by its superior resistance to aggressive environments, compared to steel. In recent years, where steel reinforcement use was restricted due to aggressive ground conditions, FRP reinforcement was successfully used as a durable construction alternative. Whilst carbon fibre (CFRP) strands have been researched and developed for use in prestressed concrete members such as bridge construction, minimal research has been devoted to developing FRP strands for use in high capacity ground anchors. The paper summarises current research knowledge and best practices for use of CFRP strands in ground anchor systems. Research work reported in this paper involves investigation into CFRP strand performance in comparison to steel strands, when exposed to extreme aggressive environments. A series of six month long experiments are currently in progress studying these durability effects over a range of accelerated conditions including temperature and concentration levels, whilst specimens are in an unstressed and stressed state. This paper presents the interim results of unstressed CFRP specimens subjected to an alkaline and acidic based groundwater solution and a neutral solution tested under accelerated conditions (60 O C and increased salt concentration) over three months of a six month period. Based on the results of tests, the levels of corrosion protection systems required for CFRP anchor systems are critically assessed. Early progressive research results, presented by the authors, in the field of CFRP durability indicated that there are minimal overall material property changes over time when specimens are exposed to various aggressive groundwater environments.