This informal CPD article on Let’s Talk About Piling was provided by Aarsleff Ground Engineering, a leading provider of Ground Engineering, Sheet Piling, Piling and Geotechnical solutions.
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 in soil considered to be weak in structure due to the 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 depth below the poor ground conditions.
The history 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 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. And in medieval times, piles of oak and alder were used in the foundations of the great monasteries constructed in the fenlands of East Anglia.
The materials used for piling and how they’ve changed
Timber has been commonly used for piling because of its strength combined with lightness, durability and ease of cutting and handling, leading it to remain 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 with similar 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 also 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.
Pile design
Pile foundations should be carefully designed in accordance with the soil and load conditions. 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 also be required to carry uplift loads when used to support tall 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 as well as waves.
Combinations of vertical and horizontal loads are carried where piles are used to support retaining walls, bridge piers and abutments, and machinery foundations.
“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
Why would a site need piling?
Traditional shallow foundation can be enough when the ground is suitable and the load it has to support is moderate. However, when the ground is not favourable for this type of foundation, a piling alternative may be better suited. Piling is ideal when:
- The water table is high.
- The soil is of a type whose stability will be affected by water.
- Deep trench foundations from a previous building would be too expensive to remove.
- Existing foundation trenches are unstable.
- The ground is unsuitable for more than two metres.
- The nature of the load requiring support.
Why use driven piling?
The advantages of driven piling are clear to see – and the UK construction market must start to embrace it. Driven piles have a multitude of advantages which make it ideal and effective for sites across the UK.
- Piles can be precast to the required specifications.
- Piles of various size, length, and shape can be made in advance and used at the site. As a result, the progress of the work is rapid.
- A pile driven into granular soil compacts the adjacent soil mass and as a result, the bearing capacity of the pile is increased.
- The work is neat, clean and creates no spoil arisings. The supervision of work at the site can be reduced to a minimum. The storage space required is very much less.
- Driven piles may conveniently be used in places where it is advisable not to drill holes for fear of meeting groundwater under pressure.
- Driven piles are the most favoured for works over water such as piles in wharf structures or jetties.
- Driven piles maintain their shape during installation. They do not bulge in soft ground conditions and are typically not susceptible to damage from the installation of subsequent piles.
- Driven piles require no curing time and can be driven in natural sequence rather than skipping alternate piles, thus minimising the moving of the equipment and speeding up installation time.
- The equipment and installation methods are time-tested and well proven. Advances in materials, equipment, methods, and testing continually combine to improve the efficiency of driven piles.
- Fewer traffic movements are required to and from a site when compared to alternate piling methods.
We hope this article was helpful. For more information from Aarsleff Ground Engineering, please visit their CPD Member Directory page. Alternatively please visit the CPD Industry Hubs for more CPD articles, courses and events relevant to your Continuing Professional Development requirements.
