What is Piling?
Piling is defined as being foundations that are driven or bored through the ground along a certain length of area to carry and transfer loads to soil considered to be weak in structure due to the soil conditions. Essentially this means that piles are generally used when the bearing capacity of the soil is considered to be inadequate for the structural load of heavy construction. The piles transfer the load to the solid ground located at a depth.
“The art lies in selecting the most suitable type of pile and method of installation for the ground conditions and the form of loading. Science enables the engineer to predict the behaviour of the piles once they are in the ground and subject to loading. This behaviour is influenced profoundly by the method used to install the piles and it cannot be predicted solely from the physical properties of the pile and of the undisturbed soil” – Burton-on-Stather, 1977
Pile foundations should be carefully designed in accordance with the soil and load conditions. The piles should be designed to carry axial, shear, and bending stresses that may develop by the relative horizontal movement of piles between the layers in the soil. Piles may be required to carry uplift loads when used to support tal structures subjected to overturning forces from winds or waves. Piles used in marine structures are subjected to lateral loads from the impact of berthing ships and from waves. Combinations of vertical and horizontal loads are carried where piles are used to support retaining walls, bridge piers and abutments, and machinery foundations.
Piles can be made from various materials, like steel, timber, in-situ or precast concrete, each possessing different characteristics that should be considered.
The Origins of Piling
The history of constructing buildings using piles dates back to the ancient times, when people used piles for constructing foundations on weak peat soils near rivers. Many villages and towns were located in the close vicinity of lakes and rivers due to the availability of water, and, also, to ensure proper protection of the area. Therefore, the weak bearing ground was reinforced by the use of timber piles that were either manually forced into the ground, or fixed in holes that were filled with stones and sand. In Britain, there are numerous examples of the Romans utilising timber piles in bridge works. In mediaeval times, piles of oak and alder were used in the foundations of the great monasteries constructed in the fenlands of East Anglia. Timber, because of its strength combined with lightness, durability and ease of cutting and handling, remained the only material used for piling until comparatively recent times.
Timber was replaced by steel and concrete only because these newer materials could be fabricated into units that were capable of sustaining compressive, bending and tensile forces far beyond the capacity of a timber pile of like dimensions.
Concrete, in particular, was adaptable to in-situ forms of construction which facilitated the installation of piled foundations in drilled holes in situations where noise, vibration and ground heave had to be avoided. Reinforced concrete, which was developed as a structural medium in the late nineteenth century and early twentieth centuries, largely replaced timber for high capacity piling for works on land. It could be precast in various structural forms to suit the imposed loading and ground conditions, and its durability was satisfactory for most soil and immersion conditions.
Steel has been used to an increasing extent for piling due to its ease of fabrication and handling and its ability to withstand hard driving. Problems of corrosion in marine structures have been overcome by the introduction of durable coatings and cathodic protection.
While materials for piles can be precisely specified, the calculation of their load-carrying capacity is a complex matter which at the present time is based partly on theoretical concepts derived from the sciences of soil and rock mechanics, but mainly on empirical methods based on experience. Practise in calculating the ultimate carrying capacity of piles based on the principles of soil mechanics differs greatly from the application of these principles to shallow spread foundations. In the latter case, the entire area of soil supporting the foundation is exposed and can be inspected and sampled to ensure that its bearing characteristics conform to those deduced from the results of exploratory boreholes and soil tests.
Types of Piles (Categories provided by the British Standard Code of Practice for Foundations)
Large Displacement Piles (Driven Types)
- Timber (round or square section, jointed or continuous)
- Precast concrete (solid or tubular section in continuous or jointed units)
- Prestressed concrete (solid or tubular section)
- Steel tube (driven with closed end)
- Steel box (driven with closed end)
- Fluted and tapered steel tube
- Jacked-down steel tube with closed end
- Jacked-down solid concrete cylinder
Large Displacement Piles (Driven and Cast-in-Place types)
- Steel tube driven and withdrawn after placing concrete
- Precast concrete shell filled with concrete
- Thin-walled steel shell driven by withdrawable mandrel and then filled with concrete
Small Displacement Piles
- Precast concrete (tubular section driven with open end)
- Prestressed concrete (tubular section driven with open end)
- Steel H-Section
- Steel tube section (driven with open end and soil removed as required)
- Steel box section (driven with open end and soil removed as required)
- 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
Aarsleff Ground Engineering is a leading piling contractor operating across the UK commercial, rail, residential, marine, energy and infrastructure commercial markets. We specialise in several pile types. We operate in Lincoln, Grimsby, Nottingham, Leicester, Warwick, Derby, Stafford, Shrewsbury, Birmingham, Coventry, Wolverhampton, Walsall, Swansea, Port Talbot, Cardiff, Chepstow, Worcester, Gloucester, Cheltenham, Oxford, Southampton, Bournemouth, Plymouth, Exeter, Northampton, Buckingham, Bedfordshire, Cambridge, Peterborough, Norwich, Great Yarmouth, Kings Lynn, Bury St Edmunds, Colchester and, Watford.
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