Understanding Timber Piles: Exploring Pros, Cons, Categories, and Protection

Piles, those sturdy foundations that bear the weight of structures, go deep into the ground, ensuring stability. They’re essentially long, slender columns that either transfer loads through friction or by resting on solid ground. If a foundation’s length is more than three times its width, it’s classified as a pile foundation. Today, our focus is on timber piles, which are made from the trunks of trees.

Timber Piles Unveiled

Timber piles, essentially tree trunks stripped of branches, are designed to handle 15 to 25 tons of load per pile. Bolting fish plates to the sides enhances their strength, making them last around 30 years. With a breadth ranging from 12 to 16 inches, these piles find use in supporting structures with moderate loads or temporary constructions.

Advantages of Timber Piles

1. Economic Value: Timber piles come at a low cost per running length, making them an economical choice.
2. Resilience: Thanks to the resilient nature of timber, these piles are excellent at absorbing impact.
3. Easy Installation: Installing timber piles is a straightforward process.
4. Flexibility: If needed, uninstalling timber piles is a hassle-free task.

Disadvantages of Timber Piles

1. Limited Bearing Capacity: Timber piles have a relatively small bearing capacity.
2. Durability Concerns: Untreated timber piles above groundwater may not last indefinitely.
3. Susceptibility to Damage: Hard driving can damage timber piles.
4. Challenges in Tough Terrain: Timber piles struggle with hard stratum or boulders.
5. Length Limitations: Longer timber piles might not always be readily available.

Timber Pile Quality and Classification

For a timber pile to qualify as a foundation,it must meet specific criteria. The quality, treatment, and constructional characteristics play a crucial role.

Quality Criteria

A sound timber pile should be free of defects, straight, and have a uniform taper. The quality is determined by factors like decay, splits, twists in wood grains, knot size, and the presence of holes.

Classification of Timber Piles

According to ASCE Manual no 17, timber piles fall into three classes based on quality and dimensions:

• Class A Pile: Minimum diameter of 14 inches, suitable for heavy loads or large unsupported lengths.
• Class B Pile: Diameter ranging from 12 to 13 inches, ideal for medium loads.
• Class C Pile: Minimum diameter of 12 inches, used for temporary structures.

Preservative Treatment of Timber Piles

When timber piles extend above water, they face decay from fungi, insect attacks, and borers. Untreated piles below the groundwater table can be considered permanent. The most common preventive measure is treating piles with preservatives, such as creosote oil.

Best Practices for Preservative Treatment

• Impregnation: Proper impregnation of creosote oil ensures excellent protection against decay and attacks.
• Handling: Treated piles require careful handling; cutting, framing, and drilling should be done before treatment.
• Protection: Cuts and abrasions should be covered with coats of creosote for added protection.

Over-driving Challenges with Timber Piles

A notable drawback of timber piles is the risk of damage during over-driving. To mitigate this, a design capacity limit of around 25 tons is empirically set. Careful observation of pile behavior during driving operations is crucial, with immediate cessation if doubts arise.

In summary, timber piles offer cost-effective solutions with their advantages, yet precautions such as proper treatment and handling are necessary to overcome their limitations.