How To Select The Pile Type On Civil Engineering Construction?

Selection of pile type
The selection of the appropriate type of pile from any of the above categories depends on the following three principal factors.

The location and type of structure.
The ground conditions.

Considering the first factor, some form of displacement pile is the first choice for a marine structure. A solid precast or prestressed concrete pile can be used in fairly shallow water, but in deep water a solid pile becomes too heavy to handle and either a steel tubular pile or a tubular precast concrete pile is used.

Steel tubular piles are preferred to H-sections for exposed marine conditions because of the smaller drag forces from waves and currents. Large-diameter steel tubes are also an economical solution to the problem of dealing with impact forces from waves and berthing ships. Timber piles are used for temporary works in fairly shallow water.

Bored and cast-in-place piles would not be considered for any marine or river structure unless used in a composite form of construction, say as a means of extending the penetration depth of a tubular pile driven through water and soft soil to a firm stratum.

Piling for a structure on land is open to a wide choice in any of the three categories. Bored and cast-in-place piles are the cheapest type where unlined or only partly-lined holes can be drilled by rotary auger. These piles can be drilled in very large diameters and provided with enlarged or grout-injected bases, and thus are suitable to withstand high working loads.

Augered piles are also suitable where it is desired to avoid ground heave, noise and vibration, i.e. for piling in urban areas, particularly where stringent noise regulations are enforced. Driven and cast-in-place piles are economical for land structures where light or moderate loads are to be carried, but the ground heave, noise and vibration associated with these types may make them unsuitable for some environments.

Timber piles are suitable for light to moderate loadings in countries where timber is easily obtainable. Steel or precast concrete driven piles are not as economical as driven or bored and cast-in-place piles for land structures.

Jacked-down steel tubes or concrete units are used for underpinning work. The second factor, ground conditions, influences both the material forming the pile and the method of installation.

Firm to stiff cohesive soils favour the augered bored pile, but augering without support of the borehole by a bentonite slurry, cannot be performed in very soft clays, or in loose or water-bearing granular soils, for which driven or driven-and-cast-in-place piles would be suitable.

Piles with enlarged bases formed by auger drilling can be installed only in firm to stiff or hard cohesive soils or in weak rocks. Driven and driven-and-cast-in-place piles cannot be used in ground containing boulders or other massive obstructions, nor can they be used in soils subject to ground heave, in situations where this phenomenon must be prevented.

Driven-and-cast-in-place piles which employ a withdrawable tube cannot be used for very deep penetrations because of the limitations of jointing and pulling out the driving tube. For such conditions either a driven pile or a mandrel-driven thinwalled shell pile would be suitable.

For hard driving conditions, e.g., boulder clays or gravelly soils, a thick-walled steel tubular pile or a steel H section can withstand heavier driving than a precast concrete pile of solid or tubular section. Thin steel shell piles are liable to tearing when being driven through soils containing boulders or similar obstructions.

Some form of drilled pile, such as a drilled-in steel tube, would be used for piles taken down into a rock for the purpose of mobilizing resistance to uplift or lateral loads. The factor of durability affects the choice of material for a pile.

Although timber piles are cheap in some countries they are liable to decay above ground-water level, and in marine structures they suffer damage by destructive mollusc-type organisms. Precast concrete piles do not suffer corrosion in saline water below the ‘splash zone’, and rich well-compacted concrete can withstand attack from quite high concentrations of sulphates in soils and ground waters.

Cast-in-place concrete piles are not so resistant to aggressive substances because of difficulties in ensuring complete compaction of the concrete, but protection can be provided against attack by placing the concrete in permanent linings of coated light-gauge metal or plastics.

Steel piles can have a long life in ordinary soil conditions if they are completely embedded in undisturbed soil but the portions of a pile exposed to sea water or to disturbed soil must be protected against corrosion by cathodic means if a long life is required.

Other factors influence the choice of one or another type of pile in each main classification, and these are discussed in the following pages, in which the various types of pile are described in detail. In UK practice specifications for pile materials, manufacturing requirements (including dimensional tolerances) and workmanship are given in a publication of the Institution of Civil Engineers(2.1).

Having selected a certain type or types of pile as being suitable for the location and type of structure, for the ground conditions at the site, and for the requirements of durability, the final choice is then made on the basis of cost. However, the total cost of a piled foundation is not simply the quoted price per metre run of piling or even the more accurate comparison of cost per pile per kN of working load carried.

The most important consideration is the overall cost of the foundation work including the main contractor’s costs and overheads. It has been noted  that a piling contractor is unlikely to quote a fixed price based on a predetermined length of pile.

Extra payment will be sought if the piles are required to depths greater than those predicted at the tendering stage. Thus a contractor’s previous experience of the ground conditions in a particular locality is important in assessing the likely pile length on which to base his tender.

Experience is also an important factor in determining the extent and cost of a preliminary test piling programme. This preliminary work can be omitted if a piling contractor can give an assurance from his knowledge of the site conditions that he can comply with the engineer’s requirements for load-settlement criteria.

The cost of test piling can then be limited to that of proof-loading selected working piles. If this experience is not available, preliminary test piling may be necessary to prove the feasibility of the contractor’s installation method and to determine the load-settlement relationship for a given pile diameter and penetration depth.

If a particular piling system is shown to be impracticable, or if the settlements are shown by the test loading to be excessive, then considerable time and money can be expended in changing to another piling system or adopting larger-diameter or longer piles.

During the period of this preliminary work the main contractor continues to incur the overhead costs of his site organization and he may well claim reimbursement of these costs if the test-piling work extends beyond the time allowed in his constructional programme. To avoid such claims it is often advantageous to conduct the preliminary test piling before the main contractor commences work on the site.

Finally, a piling contractor’s resources for supplying additional rigs and skilled operatives to make up time lost due to unforeseen difficulties, and his technical ability in overcoming these difficulties, are factors which may influence the choice of a particular piling system.

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Isabel Carr said...

Augered Pile Contractors:
AugerPiles are cast-in-place concrete piles installed by rotating a continuous-flight, hollow-shaft auger into the ground to the specified pile depth.

Isabel Carr said...

Driven Pile Contractors:
L.G. Barcus and Sons, Inc. has been in the construction industry for over 60 years, providing services of Bridge Construction, Retaining Walls, Concrete Structures, Cofferdams, and Deep Foundations (driven piles and AugerPile foundations).

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