Rotary Bored Piling

Rotary bored piles are installed using specially designed digging tools to install bored piles of large diameter in highly variable and challenging ground conditions to excessive depths. They are suitable for carrying high structural loads on complex structures and are sometimes referred to as large diameter piles (LDP).

What is rotary bored piling used for?

Rotary Bored Piles are used across all sectors of the construction industry from large commercial and industrial developments to infrastructure projects like HS2 to residential developments, large basements, retaining walls to marine projects.

Bored piles are often larger in diameter than conventional continuous flight auger (CFA) piles and are used to support greater loads, overcome underground obstructions, penetrate ground too hard to bore using a continuous flight auger or create piles with a cut-off level beneath the platform level.

Using support fluids in unstable ground conditions

In locations where the ground remains unstable beyond a depth practical to use temporary casing, support fluids such as bentonite or vinyl polymers can be added to support the bore during excavation.

When the concrete is poured to form the pile, the less dense support fluid is displaced and pumped into a containment unit where it is filtered and cleaned so that it may be reused.

In majority of cases in the UK, support fluids are not necessary.

Using a super-latch cage splicing system

When prefabricated cages are required to be greater that 12m in length and need splicing together, Van Elle utilises the RCL Super-Latch splicing system.

This enables site teams to work safely and efficiently avoiding the need to place their hands inside the cage to align the bands and tighten up bolts.

Key capabilities:

  • Rig loadings: 35–100 tonnes
  • Pile diameter: 600–2100mm
  • Maximum depth: 70m
  • Working load: 400–25,000kN

What are the advantages of Rotary Bored Piling?

  • Piles can be installed across a wide range of ground conditions
  • Often used in ground conditions which is too hard or deep for the CFA technique to be used efficiently
  • Pile diameters of up to 2,100mm enables much greater loads to be carried than other techniques without increasing pile number
  • The telescopic Kelly bar facilitates the installation of piles up to 70m in depth
  • Specialist drilling tools including buckets, augers and core barrels are deployed to penetrate manmade obstructions and create rock sockets
  • Minimal ground disturbance
  • Reinforcement cage depths are limited only by length of pile and suited to full length installation
  • Delivers significantly greater tolerances than CFA solution, providing increased flexibility in retaining wall design

Common Uses

  • Large complex structures and foundations
  • Suitable for all soil types, ability to create rock sockets enhancing pile capacity
  • Secant and contiguous piled retaining walls and can be used in conjunction with temporary props and permanent anchors
  • Slope stabilisation and retention to prevent slip and landslides
  • Retention for deep excavations and basements close to adjacent structures
  • Ability to achieve tight drilling tolerances adjacent to site boundaries
  • Ability to drill through both natural and manmade obstructions
  • The use of temporary casing facilitates the installation of large diameter piles to depth
  • Ability to include complex pile instrumentation and load cells
  • Used across infrastructure projects including tunnelling, road or bridge construction

Rotary bored piles are constructed using powerful hydraulic piling rigs and a variety of interchangeable digging tools.  A temporary cased is firstly installed through unstable upper strata, the soil is then removed using a variety of digging accessories such as augers, cleaning buckets and core barrels depending on the ground conditions.

On reaching the required design depth, the base of the pile is cleaned using a cleaning bucket, the reinforcement is added, and the concrete tremmied from the pile base to a predetermined level above cut-off level.  The temporary casing is then removed using the piling rig and reused on the following pile position.

The temporary casing provides support during the boring and concrete process through unstable ground and safe working condition above piling platform level. Single length thin-walled casing are used where the depth of unstable ground is known and relatively shallow.  Doubled walled sectional segmental casing is used where ground conditions are variable, and the temporary casing is required to depth.