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 As the concrete reaches the top of the hole, the tremie pipe is retrieved and the short temporary casing is being withdrawn.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