Driven pile foundations are mainly used in low-rise buildings and bridge structures. If the topsoil is not in good condition and does not have sufficient bearing capacity to withstand the load of the superstructure, a driven pile is used.
A driven pile is a type of pile driven into the hard layer of soil where it can provide the necessary ultimate support and surface friction.
Because construction costs are lower compared to cast-in-place bored piles, these types of pile foundations are more commonly used in bridge construction.
There are basically four categories based on the type of material.
Types of driven piles
- steel piles
- Precast concrete piles
- wooden posts
- Composite piles
Let's discuss each individually driven pile above.
Foundations with metal piles
There are different types of steel piles. Since steel is readily available, construction can be done quite easily.
Additionally, steel piles such as micropiles can be used to support heavy loads in bridges, and other types can be used to support medium loads.
The main problem with steel driven piles is corrosion. However, they are placed below the Earth's surface. Therefore, the presence of oxygen for corrosion is minimal.
Let's discuss the types of steel piles available.
Types of steel driven piles
- Micropiles
Micropiles are steel piles filled with concrete. Furthermore, the pile diameter can be increased depending on the load.
If necessary, a reinforcing cage can be inserted into the pile to increase the pile's bearing capacity.
Pile design can be done as described in the article Pile Foundations Design, Construction and Testing Guide.
- H Stakes
Hot-rolled profiles are used for construction, which are welded together to increase their length.
These types of pile foundations are not commonly used in construction.
However, in special cases, H piles can also be used.
- Steel Box Piles
The design may use four steel sheets welded together to form a box-shaped pile or sheet piles welded together to form a hollow box section.
The inner core can be filled with concrete to improve transverse rigidity, bending rigidity, torsional rigidity, etc.
- piles of screws
Cast iron helical piles are driven by rotary drilling and are not as popular a type of pile in construction.
Depending on the nature of the soil and the intended use, different diameters can be used during construction.
- Steel Railing Posts
Old rails were made like steel pilings. Three rails are welded at the top and bottom respectively.
Butt welding is used to join two sections together to increase the length of the pile.
As these batteries are made from abundant materials, the cost is lower.
Furthermore, it could be considered a green construction because we reuse materials.
Driven pile foundations made from prefabricated concrete parts
The most commonly used type of driven pile in construction. There are basically two types of prefabricated piles.
- Normally reinforced precast piles
- prestressed piles
The following important points are highlighted in relation to prefabricated piles.
- These piles can accommodate high axial and bending stresses.
- Piles constructed with adequate coverage and concrete quality are not subject to deterioration.
- Therefore, these stakes are more durable.
- However, the composition of the concrete, the porosity of the aggregates, the coverage of the reinforcement, etc. can lead to deterioration of the cuttings.
- As a result, durability issues can reduce the life of the piles.
- The use of solid and hard aggregates, proper mix design, proper placement, compaction of concrete, proper curing of concrete, etc. Concrete durability .
- Minimum coverage can be 50mm, Shelf life requirements .
- Furthermore, prestressing reduces concrete cracking.
- If costs are affordable, it is recommended to galvanize the reinforcement.
There are no major problems such as steel corrosion in prefabricated pile structures.
Additionally, it is easier to build than other types of pile foundations. Additionally, the time required to complete a single stack is also shorter.
Construction costs are also comparatively very low compared to site-cast bored piles.
Prefabricated piles are available in different dimensions such as 300, 350, 400, 500 mm etc. Additionally, they are available in a circular or rectangular shape .
wooden posts
Let's take a quick look at the basics of wooden posts.
- Wooden piles can have different dimensions and load capacities.
- Due to their low load capacity, they are not used frequently.
- A tree is used as a woodpile after the branches are removed
- The bottom diameter would be in the range of 300-500mm
- The top diameter can be in the range of 125 – 250 mm
- Generally, piles are available in lengths from 9,000 mm to 18,000 mm.
- The pile can withstand the applied loads and compaction forces. However, he is vulnerable when hit hard.
- Wooden posts are susceptible to damage
The following illustration from Bowels' book “Foundation Analysis and Design” shows the necessary care that must be taken when driving a wooden pile.
The design load of timber piles is in the range of 150 kN to 250 kN. The maximum permitted load is approximately 300 kN. However, tests carried out have shown that they can withstand a maximum load of around 400 kN.
Care must be taken when penetrating hard layers as this may damage the pin.
Composite piles
Composite piles were first used about 60 years ago. The main purpose of composite piles was to economically construct relatively long piles.
Different materials are used to construct composite piles. Furthermore, the material must be selected according to the conditions. The following combination can be expected.
- Wooden piles are embedded below the existing ground level and a concrete structure is constructed above the existing ground level (up to the top level).
- The lower part of the pile is filled with steel or iron H pipes filled with concrete, the upper part must be concrete.
- Build upper section with prefabricated piles
Composite piles are in the range of 18m-36m. However, the 54m length must also be compacted.
The ideal load range is approximately 300 kN – 800 kN and the maximum load limit is approximately 1,500 kN.
One of the main disadvantages of composite piles is creating a proper connection between two materials.
Prefabricated pile project (driven pile project)
When designing prefabricated piles, two aspects must be taken into consideration.
- The pile must be designed to support the superstructure loads.
- Piles must be designed and constructed so that they can withstand the thrust load during driving.
The structural and geotechnical design of driven piles for superstructure loads can be carried out using the same procedures described in the article. Pile foundations .
To absorb the forces generated during compaction, special detailing techniques must be used. There are special details for prefabricated piles.
The following illustration from Bowels’ book “Foundation Analysis and Design” shows the typical layout of a prefabricated stack.
As shown in the drawings above, the upper and lower areas of the pile are limited by reducing the distance between the links. This allows the layer to withstand higher loads.
As already mentioned, prestressed piles are also used in civil construction. The following drawings show the typical arrangement of a prestressed pile. Special attention is required when constructing a pile of this type.
Construction of driven piles
As prefabricated piles are widely used in construction, let us look at the important aspects of driven piles.
There are two main methods for driving piles.
- The conventional method ,
Apply a force to the post by placing a weight on it. The applied load is calculated based on the free fall height of the weight.
It must be ensured that the applied load does not exceed the bearing capacity of the driven pile.
- Hammer impact method .
There are three types of driving methods. They are
-
- Diesel hammer drive
- Pneumatic hammer drive
- Vibrating hammer lifting
Hammer impact methods are easier to use compared to traditional methods that require more time.
For transport reasons, prefabricated piles are generally erected with a length of 6 m. However, if necessary, they can also be built with a length of 12 m or more.
If driven piles 6 m long are used and the driving depth is more than 6 m, two piles must be combined. To increase the length, steel plates embedded on top of the piles are welded together.
Unnecessary pile length is demolished during block construction.
For more information on hammer impact methods, see the Wikipedia article hitting .
Completion and acceptance criteria for driven piles
- The pile is driven to the hard soil layer, which is determined as the final level according to the project. Final grade design and selection is based on information from the soil test report.
- Upon reaching the final level, the stack movement slows down.
- Criteria for pile termination and driving are based on pile wave equation analysis (WEAP). Any necessary modifications must be made on site as they may vary depending on actual terrain conditions.
- In addition, the number of blows during the movement of the pile must be recorded. This can be expressed as the number of hits to the post for a certain distance or as the penetration of the post for a certain number of hits. This can be done according to project specifications.
- There are restrictions on termination. The specification could specify the number of attacks for a specific penetration. If the number of blows for penetration of the specified distance is exceeded and the pile rests on the termination layer in accordance with the geotechnical data, the pile can be terminated.
Advantages of driven piles
- Unlike bored piles, driven piles can be prefabricated. This minimizes design errors and allows adequate quality control to be carried out.
- Additionally, any defects such as honeycombs can be repaired prior to installation.
- As the piles are driven against soil pressure, the bearing capacity of the soil improves through compaction at the tip of the pile.
- Less time and less use of labor and machinery until installation comparatively reduces costs.
- In the event of material failure such as concrete, the pile may be removed prior to installation. However, in the case of bored piles, this will only be known after installation.
- The pile can be installed at an angle to accommodate lateral loads. Commonly used in bridge construction.
- The use of technical personnel is lower.
- The development will not have any influence on groundwater levels.
- The time it takes to launch a single post is very short. Therefore, it is more suitable for quick constructions.
Disadvantages of driven piles
- Before construction begins, careful planning is required regarding equipment, location and transportation.
- They are generally unable to carry heavy loads. Therefore, bored piles are generally used when the load on the pile increases.
- Furthermore, there is a limitation in increasing the pile diameter. The larger the diameter, the more problematic it becomes to handle the batteries. Transport will be very difficult.
- The construction must be checked against transport loads. Special attention must be paid to prestressed concrete piles, as they can be damaged during lifting if they are not taken into account in the design.
- Because the depth or length of the pile varies from location to location, the length of the pile cannot be determined in advance. Therefore, the cuttings need to be connected and the excess cut off.
- When erecting piles in compacted ground, soil loss and reduced top load capacity may occur.
- Noise during the installation process must be controlled.
- Vibrations also need to be controlled.
- If the length of the available piles is not sufficient, they must be connected together to reach sufficient depth. This may result in part of the new pile being wasted.
- The construction and dimensioning of driven piles must be carried out in the sizes available at the time of purchase on the market. Otherwise, they must be made to the required size and length.
- Driven piles may not be suitable for soils with poor drainage properties. The suitability of driven piles must undergo appropriate geotechnical investigation.
