Timber piles in marine applications are exposed to the harsh intertidal and subtidal zone environments, resulting in deterioration – and at worst structural failure – if left unprotected. Timber does not deteriorate due to aging alone, with the service life of timber piles dependent on protection from a number of other environmental factors. Pile jackets are one form of protection that can be applied prior to pile installation or to repair, strengthen and protect them after installation and deterioration has occurred.

Deterioration of timber in marine environments

While other materials used in marine environments – such as concrete or steel – are highly susceptible to corrosion from the saltwater, timber is much less so, with deterioration typically due to biological, physical and chemical factors. 

• Biological deterioration is caused by fungi and insects that use the timber for food or nesting material. In particular, recent successes in cleaning the waterways have led to the return of marine borers and shipworms that eat away the wood in timber piles. 
• Physical deterioration and loss of cross section can be a result of overstressing from the dry-wet cycles the piles are subject to. Overstressing is caused by a number of factors, including: high mechanical loads from the recurrent impact of waves, shingles, sand, ice and other solid fragments; high moisture content of the wood; and high impact loading from berthing and mooring ships.
• Chemical deterioration is less common for the timber itself, but can occur when it comes in contact with certain strong acids or alkalis. Most commonly, chemical deterioration of wooden components is associated with metal fasteners, iron nails, screws and bolts.

If left unprotected and deterioration is allowed to advance unchecked, the timber piles can prematurely fail, leading to costly repairs or replacement, and safety concerns for those who use the structure.

Pile jackets to repair, restore and protect

Pile jackets are one form of repair and restoration that can help strengthen the piles and protect them from further damage, and have been used extensively worldwide for underwater pile repair.

In the past, GFRP jackets have been used as they are lightweight and moisture tolerant, however they also have one or two weak seams along the height of the jacket that provide an entry point for water and oxygen to weaken the system over time. Furthermore, older systems in particular only come in standard sizes which lead to larger annular spaces, leading to increased grout costs, lead times, and dead load to the host pile.

PileMedic laminates overcome these shortfalls, offering a variety of engineered solutions for repair and strengthening of piles. When wrapped around a pile, the jacket creates a seamless shell with tremendous confining pressure. As the axial capacity of a pile is proportional to the degree of confinement, the more layers of PileMedic that are wrapped around the pile, the higher the axial capacity of the pile. The annular space between the jacket and the pile is filled with grout or resin and optional FRP or steel reinforcing bars. It is the only system on the global market that provides this 360 degree confining pressure, enabling tensile strengths between 62,000 to 155,000psi – three to ten times higher than other pile jacket systems available. Full capacity of the pile is reached or surpassed within 24 hours of the installation being completed.

PileMedic is wrapped around the pile at the waterline and slid down the pile while another laminate is wrapped around the pile with a small overlap on the previous jacket; there is no need for divers to assemble jacket shells underwater. This is the quickest and most economical method to wrap piles. Furthermore, it is one size fits all so it can be cut to fit any size or shape pile, eliminating the need to order in advance when repairs need to take place. 

PileMedic jackets are also coated with a special epoxy paste – such as QuakeWrap

Pile Jacket Epoxy – and wrapped two or more times around the pile to create a multi-ply impervious shell. This process results in a seamless shell around the pile that will keep all moisture and oxygen out, bringing the corrosion rate to a near halt.

PileMedic in action

In November 2021, Hychem supplied the PileMedic 14.13 Jacket System and QuakeWrap Pile Jacket Epoxy for a project in Blackwattle Bay, NSW, that required the structural remediation of four timber piles.

The PileMedic PLG14.13 structural UV stable jacket system – installed by certified contractor Marine & Civil Maintenance (MCM) – was used to repair the badly damaged timber piles. 

Prior to installation, the piles were prepared by water blasting to remove all the marine growth and loose timber. The jacket system was then measured, cut to size and installed. The project was completed on time and on budget.

The system has increased the axial compressive capacity of the structure and flexural (bending) enhancement under compliant conditions, as well as significantly reducing future maintenance costs by reducing the future rate of corrosion and deterioration due to the seamless shell.