Wood poles are popular and widely used in the Power Supply Industries in all over the world because of their high strength per unit weight, low installation and maintenance costs and excellent durability. Reliability of these components depends on a complex combination of age, usage, component durability, inspection, maintenance actions and environmental factors influencing decay and failure of components. Breakdown or failure of any one or more of these components can lead to outage and cause a huge loss to any organisation. Therefore, it is extremely important to predict the next failure to prevent it or reduce its effect by appropriate maintenance and contingency plans. In Australia, more than 5.3 million wooden poles are in use. This represents an investment of around AU$ 12 billion with a replacement cost varying between AU$1500-2500 per pole. Well-planned inspection and maintenance strategies considering the effect of environmental and human factors can extend the reliability and safety of these components. Maintenance and sophisticated inspection is worthwhile if the additional costs are less than the savings from the reduced cost of failures. Objectives of this research are to: * Investigate decay patterns of timber components based on age and environmental factors (e.g. clay composition) for power supply wood pole in the Queensland region. * Develop models for optimizing inspection schedules and Maintenance plans. Deterioration of wood poles in Queensland is found mostly due to inground soil condition. It is found that the moisture content, pH value (Acidity/ alkalinity), bulk density, salinity and electrical conductivity have influence over the deterioration process. Presence of Kaolin or Quartz has some indirect effect on the degradation process. It allows more water to be trapped inside the soil that cause algae, moss and mould to grow and attack the wood poles. On the other hand, by virtue of permeability, soils with high quartz content allows more water to infiltrate, preventing the growth of micro-organism. This research has increased fundamental understanding of inground wood decay process, developed testing methods for soil factors and proposed integrated models for performance improvement through optimal inspection, repair and replacement strategies considering durability, environmental and human factors in maintenance decisions. A computer program is also developed to analyse "what if" scenario for managerial decisions. This research has enhanced knowledge on the wood decay process in diverse environmental conditions. The outcomes of this research are important, not only to users of timber components with ingrond decay but also to the wood industry in general (the housing sector, railways for wooden sleepers and other structural applications such as timber bridges). Three refereed conference papers have already come out of this research and two more papers for refereed journal publication are in the process. This research can be extended to develop models for: * Qualitative as well as quantitative research database on lab/field wood decay process; * Assessment of the residual life of timber infrastructure; * Optimal condition monitoring and maintenance plans for timber components showing inground decay; And * Cost effective decisions for prevention of timber components and mitigation. Findings of this research can be applied to other equipment or assets showing time dependent failure rate and can be extended further to consider age/usage replacement policies, downtime and liability costs.