CONSTRUCTION METHODS & TECHNOLOGY CIVL462

Types of Pile

Function of piles Piles are columnar elements in a foundation which have the function of transferring load from the superstructure through weak compressible strata or through water, onto stiffer or more compact and less compressible soils or onto rock.

Historical The driving of bearing piles to support structures is one of the earliest examples of the art and science of a civil engineer. In Britain, there are numerous examples of timber piling in bridge works and riverside settlements constructed by the Romans. In China, timber piling was used by the bridge builders of the Han Dynasty (200 BC to AD 200).

The carrying capacity of timber piles is limited by the girth of the natural timbers and the ability of the material to withstand driving by hammer without suffering damage due to splitting or splintering. Thus primitive rules must have been established in the earliest days of piling by which the allowable load on a pile was determined from its resistance to driving by a hammer of known weight and with a known height of drop. Knowledge was also accumulated regarding the durability of piles of different species of wood, and measures taken to prevent decay by charring the timber or by building masonry rafts on pile heads cut off below water level.

Types of pile according to the construction method Classification of piles The British Standard Code of Practice for Foundations (BS 8004: 1986) places piles in three categories. These are as follows: Large displacement piles comprise solid-section piles or hollow-section piles with a closed end, which are driven or jacked into the ground and thus displace the soil. All types of driven and cast-in-place piles come into this category. Large diameter screw piles and rotary displacement auger piles are increasingly used for piling in contaminated land and soft soils.

Driven Piles Cast In Place How it is done A thick-walled steel casing is made watertight with a steel baseplate, including a seal. This casing is driven into the ground with a pile hammer, completely displacing the ground. Once the driving criteria or the required driven depth is achieved, the reinforcing cage is installed and the casing is filled with concrete. Following placement of the concrete, the casing is withdrawn.

Screw Pile A screw piling is a circular hollow steel pipe section (shaft) with one or more tapered steel plates (helixes) welded to the shaft.

Rotary displacement auger Pile

Small displacement piles are also driven or jacked into the ground but have a relatively small cross-sectional area. They include rolled steel H- or I-sections and pipe or box sections driven with an open end such that the soil enters the hollow section. Where these pile types plug with soil during driving they become large displacement types.

Replacement piles are formed by first removing the soil by boring using a wide range of drilling techniques. Concrete may be placed into an unlined or lined hole, or the lining may be withdrawn as the concrete is placed. Preformed elements of timber, concrete or steel may be placed in drilled holes. Continuous flight auger (CFA) piles have become the dominant type of pile in the UK for structures on land.

Large displacement piles (driven types) Types of piles in each of the BS 8004 categories can be listed as follows: Large displacement piles (driven types) (1) Timber (round or square section, jointed or continuous) (2) Precast concrete (solid or tubular section in continuous or jointed units) (3) Prestressed concrete (solid or tubular section) (4) Steel tube (driven with closed end) (5) Steel box (driven with closed end) (6) Fluted and tapered steel tube (7) Jacked-down steel tube with closed end (8) Jacked-down solid concrete cylinder.

Precast concrete Piles Prestressed Concrete Piles

Large displacement piles (driven and cast-in-place types) (1) Steel tube driven and withdrawn after placing concrete (2) Steel tube driven with closed end, left in place and filled with reinforced concrete (3) Precast concrete shell filled with concrete (4) Thin-walled steel shell driven by withdrawable mandrel and then filled with concrete (5) Rotary displacement auger and screw piles (6) Expander body.

Small displacement piles (1) Precast concrete (tubular section driven with open end) (2) Prestressed concrete (tubular section driven with open end) (3) Steel H-section (4) Steel tube section (driven with open end and soil removed as required) (5) Steel box section (driven with open end and soil removed as required).

Replacement piles Concrete placed in hole drilled by rotary auger, baling, grabbing, airlift or reverse circulation methods (bored and cast-in-place) Tubes placed in hole drilled as above and filled with concrete as necessary Precast concrete units placed in drilled hole Cement mortar or concrete injected into drilled hole Steel sections placed in drilled hole Steel tube drilled down.

Composite piles Numerous types of piles of composite construction may be formed by combining units in each of the above categories or by adopting combinations of piles in more than one category. Thus composite piles of a displacement type can be formed by jointing a timber section to a precast concrete section, or a precast concrete pile can have an H-section jointed to its lower extremity. Composite piles consisting of more than one type can be formed by driving a steel or precast concrete unit at the base of a drilled hole or by driving a tube and then drilling out the soil and extending the drill hole to form a bored and cast-in-place pile.

Composite piles

Ductile Iron Pile + Additional compressive strength is provided by the concreting or grouting of the bore, to form a composite pile.

Function of piles As with other types of foundations, the purpose of a pile foundations is to transmit a foundation load to a solid ground to resist vertical, lateral and uplift load . A structure can be founded on piles if the soil immediately beneath its base does not have adequate bearing capacity. If the results of site investigation show that the shallow soil is unstable and weak or if the magnitude of the estimated settlement is not acceptable a pile foundation may become considered. Further, a cost estimate may indicate that a pile foundation may be cheaper than any other compared ground improvement costs. In the cases of heavy constructions, it is likely that the bearing capacity of the shallow soil will not be satisfactory, and the construction should be built on pile foundations. Piles can also be used in normal ground conditions to resist horizontal loads. Piles are a convenient method of foundation for works over water, such as jetties or bridge piers.