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DDS (Drilled Displacement System) piles

DDS method 

DDS method (drilling displacement system or full displacement pile - FDP) is based on the principle of borehole loosening i.e. the pile is constructed without soil excavation with compaction of borehole walls using special displacement tool. It is a continuous process of cylindrical cavity formation in the soil by its deformation and compaction with loosening tool in the borehole walls. As a result, a compacted soil zone appears around the borehole. This technique has been successfully employed for more than 10 years at construction sites in Europe and is becoming more widely used in CIS countries (especially in Saint-Petersburg).

The use of special drilling tool, rigidly fixed on the rod,  enables construction of bored piles in clay soils and when an obstruction is encountered (e.g. a boulder) the rock cutting tools are replaced with a starter bit and the drilling is continued without any damage to the pile. The use of displacement tool ensures drilling of boreholes with hard and smooth walls with diameters 400 mm,  450 mm, 650 mm, 800 mm. (see photo 2) 

Construction Sequence

Formation of bored piles using the following steps (figure 1):

Fig.1.  Formation of bored piles by DDS method

  1. Borehole drilling using displacement tool without soil excavation
  2. Extraction of drilling tool with simultaneous injection  of pressurized  concrete
  3. Installation of reinforcement cage
  4. Completed bored pile  

 

Equipment and Tools

Compared to tools from other manufacturers, Soilmec and Bauer displacement tools mounted on Soilmec SR or Bauer BG drilling rig (see photos 1.1, 1.2)  assure high-quality concreting by using tremie pipe installed into drilling tool and increasing loading capacity through soil compaction while loosening and concrete pumping.

    

Photo 1.1- Soilmec drilling rig with a displacement tool                                Photo 1.2- Bauer drilling rig with a displacement tool

  

Photo 2-  Borehole formation through soil loosening

Displacement tools (photo 3,4) include a number of core rollers  installed one by one on a common shaft, the axes of which are displaced from the axis shaft in such a way that they slide on the helical line advancing the displacement tool. It allows drilling in soil thanks to the torque applied to the shaft of displacement tool.

 

  Photo 3 – Bauer displacement tool

Photo 4 – Soilmec displacement tool

Advantages of the Technique

  1. High capacity – up to 30 piles with depth up to 32 meters per shift.
  2. DDS technology is vibration- and noise free, which makes it especially suitable for work in restrained urban conditions.
  3. Absence of spoil reduces the cost of work by savings on soil removal.
  4. High accuracy of pile installation in terms of penetration verticality, depth of drilling tool advancement and concrete pressure during the borehole filling process are  controlled  by an on-board computer
  5. High quality concreting (smooth and solid walls after displacement, concrete feeding under pressure though hollow stem of the displacement tool).  

 

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