The driven piles or also known as displacement piles are a type of construction foundation that is used with great frequency.
This is responsible for providing the structures with the support they need, They do this by transferring their loads through the layers of the soil that do not have the bearing capacity to the layers of soil or rock that do have a considerable bearing capacity.
In general, driven piles are used to support tanks, buildings, bridges and walls, this type of piles is a great solution when making a deep foundation. They can also be used in embankment application, in retaining walls, bulkheads, sheet piles and anchor structures.
Bases are described as stacked when their depth is more than three times their width.
Powered stacks are long, thin columns made of preformed materials and of predetermined shapes and sizes that are installed using percussion, vibration, or pressure to push them into the ground until they reach the strength or depth stipulated in the design.
If the soil is characterized by being dense, it may be necessary to pre-drill in order for the pile to reach the depth stipulated in the design.
The driven piles are very adaptable and can be installed to adapt to compression, lateral loads or tension, with the specifications that are established according to the needs of the structure, the budget available and the conditions of the ground where the project is carried out.
Types of Driven Piles
There are several types of piles that can be driven among these are steel piles, precast concrete piles, wooden piles and the composite pile. Next, we will explain each of them.
Standard steel piles can be used to form the pile section box. These piles are driven using percussion and are used primarily to connect marine structures. They generally have a load range of 300 – 1,700 kN and are capable of reaching up to 36 m in length.
Steel screw piles feature a cast iron propeller, are rotary driven, and are typically used for shallow foundations in soft sand and silt. They have a load range of 400 – 3,000 kN and are capable of reaching up to 24 m in length.
Steel tube piles are generally used in the construction of marine structures and in foundations that are made in soft subsoil on layers of suitable bearings. Most often they are driven to the bottom using an internal drop hammer.
Precast concrete piles
This type of pile is characterized by having different shapes such as square, cylindrical, octagonal or laminated. They are percussion driven piles that are used where boring piles are not suitable due to the current of water or the presence of very loose soil. They have a load range of 300 – 1,200 kN and can reach 30 m.
The wooden piles are generally square but can also have circular, sharp, tared and untreated and are driven using percussion. They are typically used for small projects in locations with shallow alluvial deposits that line a suitable bearing layer, such as riverbanks and estuaries.
The load range of wooden piles is 50 – 350 kN. They can be up to 12 m long without splicing.
This type of pile is characterized by using a combination, that is, a precast concrete pile with a steel point extension.
Quality of driven piles
Driven piles are built to precise tolerances thanks to the materials used that are high strength and need good quality control. The consistency of the quality of the pile materials is achieved taking into account those stipulated by BS 8004: 2015 as well as the standards established by the CE, and due inspection before the pile is installed in order to verify its integrity. It is important that the driven piles maintain their shape during the installation process and it must be verified that they will not suffer any damage when later installing other piles.
Driven pile tests
The dynamic or static tests, which are carried out on the piles, are used in order to verify the capacity of the pile, this means the maximum load that a pile can support without excessive settlements or failures in the ground . The capacity of the pile depends on three main factors that we are going to tell you about below.
- The method used to install the pile
- The dimensions of the pile, that is, the cross section and its length
- The type of soil on which the pile is to be driven
The soil axis force generally increases after the pile is installed, providing an additional load to the capacity it has. When the foundation design is done, it can allow the installation of shorter piles which provides savings in labor, materials and time used to perform the task.
Installation of driven piles
The installation of the driven piles is carried out by means of a hammer that is responsible for driving the piles into the ground, this compacts the ground around it and leads to the densification of the mass and increases its load capacity. Despite this, with saturated silty or cohesive soil types, compared to granular soil types, poor drainage quality does not facilitate the same densification. The presence of water in the soil generates a decrease in the general load capacity and for this reason the design of the pile must correct these factors.
What is the hit count?
The hit count means the number of times the pile must be hit before it can go down to the required depth. In places where variations in subsurface conditions are evident, the lengths of the piles may have to be cut or spliced in order to adapt them to the terrain.
Because driven piles do not require special coatings or delays that are related to concrete curing, this type of pile is suitable for the difficult conditions that a project presents. They can be used immediately when driving through water, can be installed to create temporary working platforms, and can be used in large diameter form in regions that are prone to earthquakes.
Driven Piles Advantages and Disadvantages
Driven piles have certain advantages and disadvantages, we are going to tell you about them below.
Main advantages of driven piles
- The driven piles can be manufactured outside the site where the project is going to be carried out, this makes an efficient installation possible once it is at the construction site.
- These piles compact and displace the soil, this increases the load-bearing capacity of the pile. While other types of deep foundations tend to require soil removal, which could lead to subsidence and other possible structural problems.
- Driven piles are cost effective, this is because they can be easily manufactured in a variety of shapes and materials, they can also have specific dimensions. Which can mean fewer piles are needed in construction.
- In general, these piles have a higher structural strength compared to other types of foundations. Their great lateral and bending resistance makes them ideal for various difficult conditions such as wind, water, seismic load, among others.
- Their installation generally produces little waste for disposal.
Main disadvantages of driven piles
- They need advance planning for their handling and driving, it is also necessary to use a large team in the construction to drive them.
- In order to withstand handling stresses during the transportation and installation process, precast concrete or prestressed piles must be adequately reinforced.
- The exact length required may not be able to be determined exactly, and for this reason splicing and cutting techniques may be required, resulting in higher cost and longer installation time.
- Driven piles are sometimes not suitable when the soil has poor drainage quality.
- Powered piles may not be suitable in compact locations, where the foundations of surrounding structures can be affected by vibrations generated by the installation process.
- Driven piles can generate a lot of noise when installed.