Piling

Some of the common reasons are very large design loads, a poor soil at shallow depth, or site constraints like property lines.

Piles are generally driven into the ground in situ; other deep foundations are typically put in place using excavation and drilling.

A large number of monopile foundations[1] have been utilized in recent years for economically constructing fixed-bottom offshore wind farms in shallow-water subsea locations.

[2] For example, the Horns Rev wind farm in the North Sea west of Denmark utilizes 80 large monopiles of 4 metres diameter sunk 25 meters deep into the seabed,[3] while the Lynn and Inner Dowsing Wind Farm off the coast of England went online in 2008 with over 100 turbines, each mounted on a 4.7-metre-diameter monopile foundation in ocean depths up to 18 metres.

[4] The typical construction process for a wind turbine subsea monopile foundation in sand includes driving a large hollow steel pile, of some 4 m in diameter with approximately 50mm thick walls, some 25 m deep into the seabed, through a 0.5 m layer of larger stone and gravel to minimize erosion around the pile.

An additional layer of even larger stone, up to 0.5 m diameter, is applied to the surface of the seabed for longer-term erosion protection.

Construction methods depend on the geology of the site; in particular, whether boring is to be undertaken in 'dry' ground conditions or through water-saturated strata.

These piles are suited for expansive soils which are often subjected to seasonal moisture variations, or for loose or soft strata.

Recent innovations in addition to stringent quality control allows reinforcing cages to be placed up to the full length of a pile when required.

Augercast piles are not generally suited for use in contaminated soils, because of expensive waste disposal costs.

This type of foundation results in a crawl space underneath the building in which wiring and duct work can be laid during construction or re-modelling.

[8] High pressure water cuts through soil with a high-pressure jet flow and allows the pile to be fitted.

Although unit costs are generally higher than with most other forms of piling,[citation needed] it has several advantages which have ensured its continued use through to the present day.

The tripod system is easy and inexpensive to bring to site, making it ideal for jobs with a small number of piles.

The main application of sheet piles is in retaining walls and cofferdams erected to enable permanent works to proceed.

[citation needed] Lagging can be constructed by timber, precast concrete, shotcrete and steel plates depending on spacing of the soldier piles and the type of soils.

[citation needed] Screw piles are galvanized iron pipe with helical fins that are turned into the ground by machines to the required depth.

Sand is difficult to penetrate but provides good holding capacity, so the height may be as short as half the diameter.

Clays and muds are easy to penetrate but provide poor holding capacity, so the height may be as much as eight times the diameter.

[citation needed] In high latitudes where the ground is continuously frozen, adfreeze piles are used as the primary structural foundation method.

[citation needed] Secant piled walls can either be true hard/hard, hard/intermediate (firm), or hard/soft, depending on design requirements.

[citation needed] All types of wall can be constructed as free standing cantilevers, or may be propped if space and sub-structure design permit.

A slurry wall is a barrier built under ground using a mix of bentonite and water to prevent the flow of groundwater.

These are essentially variations of in situ reinforcements in the form of piles (as mentioned above), blocks or larger volumes.

Cement, lime/quick lime, flyash, sludge and/or other binders (sometimes called stabilizer) are mixed into the soil to increase bearing capacity.

The normal method for splicing is by driving the leader pile first, driving a steel tube (normally 60–100 cm long, with an internal diameter no smaller than the minimum toe diameter) half its length onto the end of the leader pile.

If an empty pipe is required, a jet of water or an auger can be used to remove the soil inside following driving.

In some cases, pipe piles are filled with concrete to provide additional moment capacity or corrosion resistance.

It is common to allow for an amount of corrosion in design by simply over dimensioning the cross-sectional area of the steel pile.

[citation needed] Concrete piles are typically made with steel reinforcing and prestressing tendons to obtain the tensile strength required, to survive handling and driving, and to provide sufficient bending resistance.