US Foundations : Foundation Pile Driving
Pile Driving is used to provide support for retaining walls, bulkheads, bridges, piers, or building foundations.
Deep & Driven Foundations
This type of foundation is distinguished from shallow foundations by the depth they are embedded into the ground.
There are many reasons a geotechnical engineer would recommend a deep foundation over a shallow foundation, but some of the common reasons are very large design loads, a poor soil at shallow depth, or site constraints (like property lines). There are different terms used to describe different types of deep foundations including piles, drilled shafts, caissons and piers. Deep foundations can be made out of timber, steel, reinforced concrete and pre-tensioned concrete. Deep foundations can be installed by either driving them into the ground or drilling a shaft and filling it with concrete, mass or reinforced.Prefabricated piles are driven into the ground using a pile driver. Driven piles are either wood, reinforced concrete, or steel. Wooden piles are made from trunks of tall trees. Concrete piles are available in square, octagonal, and round cross-sections. They are reinforced with rebar and are often prestressed. Steel piles are either pipe piles or some sort of beam section (like an H-pile). Today, splicing is common with steel piles, though concrete piles can be spliced with difficulty. Driving piles, as opposed to drilling shafts, is advantageous because the soil displaced by driving the piles compresses the surrounding soil, causing greater friction against the sides of the piles, thus increasing their load-bearing capacity.
Timber
As the name implies, timber piles are piles made of wood.
Historically, timber has been a plentiful, locally-available resource. Today, timber piles are still more affordable than concrete or steel. Compared to other types of piles (steel or concrete), and depending on the source/type of timber, timber piles may not be suitable for heavier loads. A main consideration regarding timber piles is that they should be protected from deterioration above groundwater level. Timber will last for a long time below the groundwater level. For timber to deteriorate, two elements are needed: water and oxygen. Below the groundwater level, oxygen is lacking even though there is ample water. Hence, timber tends to last for a long time below groundwater level Timber that is to be used above the water table can be protected from decay and insects by numerous forms of preservative treatment (ACQ, CCA, Creosote, PEC, Copper Napthenate, etc.
Pipe Piles
Pipe piles are a type of steel driven pile foundation.
Pipe piles can be driven either open end or closed end. When driven open end, soil is allowed to enter the bottom of the pipe or tube. If an empty pipe is required, a jet of water or an auger can be used to remove the soil inside following driving. Closed end pipe piles are constructed by covering the bottom of the pile with a steel plate or cast steel shoe.In some cases, pipe piles are filled with concrete to provide additional moment capacity or corrosion resistance, corrosion protection is provided by allowing for a sacrificial thickness of steel or by adopting a higher grade of steel. If a concrete filled pipe pile is corroded, most of the load carrying capacity of the pile will remain intact due to the concrete, while it will be lost in an empty pipe pile.
The structural capacity of pipe piles is primarily calculated based on steel strength and concrete strength (if filled). Steel pipe piles can either be new steel manufactured specifically for the piling industry or reclaimed steel tubular casing previously used for other purposes such as oil and gas exploration.
Pre-Cast or Pre-Stressed Concrete Pile
Pre-cast or pre-stressed concrete piles are commonly used in the pile market. We drive concrete piles on more than forty percent of our jobs. The pre-cast pile is one of the most cost effective pile types due to material cost, custom pile lengths, and availability.
- The cost of concrete pile varies based on design loads, dimensions and length, but typically a concrete pile is more cost effective.
- After the completion of an indicator program pile lengths can be customized to site specific soil conditions prior to ordering production pile avoiding costly material waste.
- In most cases, concrete piles can be ready to drive in fourteen days, as opposed to steel piles which can require a mill rolling taking six to eight weeks.
Standard concrete pile sizes are 12-inch square, 14-inch square, 15-inch octagonal, 16-inch square, and 16-inch round. Other pre-cast concrete pile sizes such as 18-inch square, 20-inch square, 24-inch square, and 24-inch octagonal are used occasionally depending on the project requirements.