Bored piles

Bored piles are used as foundation elements where high loads must be transferred to deep, load-bearing soil layers. Soil is loosened and extracted during the pile manufacture. An entire pile volume’s worth of soil may be extracted during the process, or just part of it.

A well-known method used in specialist civil engineering is the bored pile, also known as the large bored pile. Bored piles are fabricated using rotary drilling rigs, hydraulic casing machines and specialist drilling equipment.

Our DIN EN 1536 compliant pile systems include:

• Bored piles
• Partial displacement bored piles (PDP)
• Continuous flight auger piles (CFA piles)
   

We use bored piles as deep foundation elements for all kinds of constructions.

Suitable projects include:

• Bridges
• Industrial buildings
• Residential and commercial structures
• Office buildings and hotels
• Construction projects near sensitive areas or structures

These piles can be used in limited height conditions.

We can also arrange multiple bored piles in a line to create bored pile walls as a form of temporary construction pit system.

Owing to the many possible variants, these piles can provide economically optimised solutions for every construction site situation and soil type.

The advantages of bored piles

• Bored piles can be fabricated with little noise and no vibration. This pile system is particularly suitable for foundation works in built-up areas and where neighbouring buildings are vulnerable to the effects of vibration.
• Bored pile dimensions can be tailored to suit high tensile and compressive loads. Moreover, large-diameter bored piles are resistant to bending and very well suited to taking horizontal strain.
• Gripper boring procedures with casing machines enable bored piles to be used in limited height conditions.
• Perpendicular piles and raking piles can be used at angles of up to 4:1.
• Piles can be bored straight through obstructions and hard soil layers.
• Equipment can be used flexibly for pile fabrication, enabling a variety of construction types including bored pile walls.
• They can even be used as energy piles, with the bored piles conducting geothermic energy.

The advantages of partial displacement bored piles (PDP)

• Small-diameter partial displacement bored piles can be quickly and economically installed with limited material consumption.
• In addition, the displacement effect ensures higher load bearing capacities than conventional bored piles.
• As the soil is partially displaced, this also reduces transport and disposal costs for the extracted cuttings.
• The reinforcement cage is constructed within the protection of the large hollow stem before concreting.
• This method can even be used for energy piles, with the PDP piles conducting geothermic energy.
• Perpendicular piles and raking piles can be used at angles of up to 4:1.
• These piles can be installed with no vibration and little noise.

The advantages of continuous flight auger piles (CFA piles)

• High drilling capacity makes these piles an economical choice.
• They are also suitable for pre-drilling through hard soil layers.
• These piles can be installed with no vibration and little noise.
   

Standards and regulations

The design and manufacture of bored piles are governed by Eurocode 7 and DIN EN 1536 and subject to the recommendations of the “Pfähle” working group (EA Piles). Possible diameters range between 0.3m and 3m. Piles usually measure between 10m and 50m in length. 

Fabrication

Current fabrication methods include:

• Standard pile procedures using kelly rotary drills with cased boring
• Uncased boring with suspension support
• Gripper boring procedures with casing machines
• Partial displacement bored piles (PDP)
• Continuous flight auger piles (CFA piles)

The following foundation types are available:

• Single-pile foundations with one-dimensional load distribution
• Pile group foundations with two-dimensional load distribution
• Special cases: combined pile raft foundations

The variety of design variants allows for individual adaptation to a wide variety of subsoil conditions and site scenarios. This ensures high load bearing capacities can be achieved. 

We can also use bored piles to create bored pile walls, used to secure structures such as construction pits. Bored pile walls can be manufactured in contiguous, tangential or secant designs. 

Quality assurance in construction work requires the observation of both European and national standards. The design and manufacture of bored piles are governed by Eurocode 7 and DIN EN 1536 and subject to the recommendations of the “Pfähle” working group (EA Piles). The self-monitoring and documentation of construction execution are also regulated by manufacturing standards.

Bored pile fabrication procedures must be individually tailored to the requirements of the specific method used. This requires specialist knowledge and experience in the field, together with sound instincts on the part of the machine operator. Large specialist machinery must be handled with sensitivity and due attention to the optimum adjustment of manufacturing parameters if the desired pile resistance is to be achieved.

We ensure high execution quality with:

• Individually tailored procedures
• Adherence to the requirements of DIN EN 1536, Eurocode 7 and EA Piles
• Clear processes overseen by our quality management system in accordance with DIN EN 9001:2005
• Static and dynamic pile loading tests
• Pile integrity tests
   

We offer the following design variants:

Cased bored piles (kelly boring)

These bored piles are fabricated using a supporting casing, which is initially drilled into the soil. Soil material is then extracted from inside this tubing using an auger drill or drilling bucket. This method requires a kelly rotary drill and leader. When working in groundwater areas, a hydrostatic force of ≥1m is required to create excess pressure against the assumed water level. The drill cuttings generated during bored pile fabrication must be used or disposed of legally according to test results. Once drilling works are complete, a reinforcement cage is inserted. The tremie method is used to pump concrete into the borehole through tremie pipes from the bottom up. A pile protocol compliant with DIN EN 1536 is generated to record important data during the pile manufacturing process.

Gripper boring procedures with casing machines

Bored piles can also be fabricated in limited height conditions. Height restrictions can arise in works on existing buildings, under bridges or while working near power lines. Gripper boring procedures with casing machines can be used to fabricate bored piles in working height conditions from approx. 5m.

Bored piles with suspension support

As a general rule, the borehole is supported by casing until the concrete is introduced. Where piles are particularly long, however, there is a risk that casing may become stuck in the subsoil or may even break off.

In this scenario, boreholes may be supported with casing at the top, while deeper layers are instead supported by a pressurised liquid. This prevents the bore wall from breaking up or sagging. The soil is loosened and extracted using a kelly drill or, with particularly long bored piles, a cable dredger and gripper drill.

The supporting liquid, which will later be displaced by fresh concrete, generally consists of a suspension of bentonite clay. This clay can also be used to manufacture cast in situ concrete diaphragm walls. Where groundwater or supporting liquid is present, underwater concrete must be made and inserted.

Continuous flight auger piles (CFA piles)

Bored piles using a continuous auger drill with a small hollow stem are also referred to as continuous flight auger piles (CFA piles). With this method, the soil is not laterally displaced. Instead, as the auger drill is extracted, the soil is completely removed. The reinforcement cage is inserted or vibrated into the fresh concrete after pouring. CFA piles are an extremely economical solution for relatively low pile loads and pile lengths, and comparatively quick to manufacture. The vibration-free and low-noise fabrication process makes this option particularly well suited to inner-city projects.