HomeTechniquesPilesLarge diameter bored pilesLarge diameter bored pile under support fluid

Large diameter bored pile under support fluid

The large diameter bored pile under thixotropic fluid is a cast-in-place circular cross-section concrete pile. For the construction of this non-displacement pile a borehole is made using purpose designed drill tools, with removal of soil. Where boreholes are required to penetrate considerable depths of unstable soil a support fluid, e.g. bentonite mud or polymer and a temporary recoverable top casing assist in stabilizing the bore and allow the perfect insertion of heavily reinforcement steel cages.

Construction sequence

Installation process in accordance with the requirements of standard NBN EN1536:1999

1.Implantation, set up, installation and centering of the top casing on the centre of the pile – pre-drilling

2.Drilling of first casing segment, subsequently filled with support fluid (bentonite mud or polymer).

3.The boring continues through filling with thixotropic fluid upon reaching the required depth.

A positive head of support fluid above the groundwater table of at least 2 m is required in order to maintain the required counter pressure.

4.Clean-up of the borehole front at the design depth, removal and recycling of the support fluid (bentonite mud is returned to the surface for sedimentation and desanding). Lowering of the reinforcement.

5. Concrete displaces the support fluid. Concreting is usually carried out by the tremie method.

6. As the concrete reaches the top of the hole, the tremie pipe is retrieved and the short temporary casing is being withdrawn.

7. Complete extraction of the temporary casing and control of the final concrete level

Fields of application

• Executed as single pile, contiguous (tangent) or - less often - secant pile wall

• Suitable for high point loads, important horizontal loads and bending moments

• Bearing or embedment in firm strata or hard rock possible

• Obstacle drilling (when other techniques cannot be implemented)

• Important installation depths (up to > 50 m)

• Create piles with a cut-off level beneath the working platform level possible ("contrebas")

• Infrastructure works, important industrial projects, large buildings.

Environmental impact

• Vibration-free

• Pile with soil extraction: removal of spoil from the job site is required

• Provision should be made to handle the thixotropic fluid

• A stable, dry and flat work platform is required.

Technical specifications

• Diameters from 620 to 1.980 mm

• Stable boring by overpressure of supporting liquid (water, bentonite, polymers, ...)

• The completed pile is reinforced

• Concreting is carried out by means of the tremie pipe technique to avoid segregation of the concrete.

• Create piles with a cut off level beneath the working platform level (non-concreted length possible)

• Allowable bearing capacity up to 24.050kN

• Execution possible with enlarged base.