Timber utility poles play a significant role in the infrastructure of Australia as well as many other countries. There are over 5 million timber utility poles currently used in Australian energy networks, which are more than 80% of total utility poles in the network. Due to the advanced age of Australia’s timber pole infrastructure, significant efforts are undertaken by state authorities on maintenance and asset management to prevent utility lines from failure. However, the lack of reliable information regarding their in-service condition, including the embedment length or the degree of deterioration or damage below ground level makes it extremely difficult for the asset managers to make decisions on the replacement/maintenance process with due consideration to economy, operational efficiency, risk/liability and public safety. For example, in order to avoid any failure and considering the public safety, each year approximately 300,000 poles are replaced in the Eastern States of Australia with up to 80% of them still being in a very good serviceable condition, resulting in significant waste of natural resources and money.
In order to address this problem, an R&D program commenced in 2011 at the University of Technology Sydney in collaboration with the Electricity Network Association of Australia. The aim of this study is to design and develop a Non-Destructive Testing (NDT) method with acceptable accuracy, whilst being cost efficient for the condition assessment of the in-service timber utility poles. This research project contains three phases, which will be explained briefly in the following paragraphs.
Several stress wave based NDT methods are currently available and have been used in field applications over the past decades as simple and cost-effective tools for identifying the condition and underground depth of embedded structures, such as poles or piles in service. In this regard, in the first phase of this research, the applicability and efficiency of the currently available NDT methods on the condition assessment of the timber utility poles is investigated through simulation and laboratory tests. Results of the first phase reveal that these surface NDT methods face significant challenges in the condition assessment of the timber utility poles. These challenges are due to presence of uncertainties such as complicated material properties and imperfect body (i.e. timber pole natural cracks), environmental conditions, interaction of soil and structure, defects and deteriorations as well as an impact excitation type. It is necessary to mention that access to the top of the in-service timber utility poles is prohibitive due to the presence of the electrical or communication wires. In this regard, the hammer impact is applied to the timber pole on its side.
In order to address these complicating factors, in the second phase of this research some advanced digital signal processing methodologies are selected, modified, and employed from different groups of methodologies that can most probably provide solutions. The efficiency of these methodologies is investigated through simulation, laboratory, and field tests. Results of the second phase of this research illustrate that the behaviour of the timber pole under the lateral hammer impact excitation is very complicated. In fact, if dealing with this high level of complexities is not impossible, it is a very difficult task.
In this regard, in the third phase of this research a novel, fast, and accurate ultrasonic narrowband NDT method is proposed as an alternative proposition for the condition assessment of the timber structures. The efficacy of the proposed methodology is verified through the laboratory experiments.