Vibrated combi piles - Vroom Funderingstechnieken
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Vibrated combi piles

Used in underground construction, such as tunnels, underground car parks and other such projects, in which the pile caps have to be installed under ground level. The features of vibrated combi piles are the same as those of vibrated HBF-type piles, where appropriate. Vibrated combi piles have the same geotechnical bearing capacity.

Vibro combo piles have the same relevant features compared to the HBF cast-in-situ vibro pile. The pile system offers additional advantages and has specific application options.  Vibrated combi piles have all the relevant properties of vibrated HBF-type piles. The pile system offers extra advantages and has several specific potential applications.

Features

  • They can be used for infrastructure works, including tunnel construction, underground car parks, and buildings and structures in which the pile cap has to be installed to a depth beneath ground level. 
  • Where there are tough intermediate strata or, for instance, obstacles, the pre-fab core of high-quality concrete remains undamaged, regardless of the conditions. 
  • They can be formed from a level above ground down to a specific depth below ground. In the case of tunnel construction, say 8 metres under ground level, this can have substantial benefits. On the one hand, excavation of the tunnel section can proceed unhindered. While on the other, excess pile length does not have to be cut off. The piles can be cast from traverse girders. 
  • When subjected to tensile strain they move slightly due to the pre-tensioning in the pre-fabricated concrete element.
  • When subjected to tensile strain they move slightly due to the pre-tensioning in the pre-fabricated concrete element.
  • These specific features are particularly useful for tunnel construction and cellar floors in underground car parks.

Features of vibrated combi piles

  • Vibrated combi piles have all relevant properties of vibrated piles, but have specific advantages and fields of application. 
  • The pile cap can be fitted below working level. 
  • A vibrated combi pile can absorb high tensile strain.
  • Once the tube has been driven in, a pre-fab element of reinforced concrete is placed in the casing. 
  • The starting point for determining the forming and diameter of the concrete element is that it satisfies the intended use, and is sufficiently strong in its own right during transportation and placing in the tube.
  • Extra features that can be fitted ex-works are available to connect the pile cap to the structure resting on it. This may be the creation of profiling for an underwater concrete floor, or the pouring of bar anchors.
  • The grout mixture is applied to part of the pre-fab concrete element. 
  • In addition they have the same features as those of vibrated HBF-type piles. 
  • Raking shores: 
    • Leaning backward up to a maximum of 3:1 - 4:1
    • Leaning forward up to a maximum of 4:1 - 10:1. 
  • The piles can absorb not just compressive force, but also tensile strain. 
  • The pile system displaces earth and has the same soil-mechanics bearing capacity as vibrated HBF-type piles. 
  • No soil comes to the surface. 
  • Pile systems and the load-bearing coefficients that apply to them are as per applicable building standards.
  • The foundation system is respected and well-known to designers and the Netherlands Building Control Committee alike.

Special aspects

  • Rough driving is used on sites where the upper layer may conceal obstacles.
  • Pre-drilling before installing vibrated HBF-type piles can substantially reduce the vibrations caused by conventional pile driving.
  • And a noise-reducing jacket can be used during installation to reduce the noise of pile driving. Accordingly, Vroom Funderingstechnieken (Vroom Foundation Technology) developed such a noise-reducing jacket in collaboration with parties including IHC Hydrohammer and TNO Delft.

Quality control

Vroom Funderingstechnieken produces vibrated combi piles as part of internal quality control and in line with nationally-applicable standards. It is possible to check their geotechnical bearing capacity by counting the number of blows per 25 cm, which can be automatically logged by the IHC hammers. It is not necessary to test the vibro combi piles acoustically, as the piles are inserted into the tube with little friction. If required, however, it is possible to have these piles acoustically monitored. The pre-fab concrete elements are supplied with KOMO certification. The grout for the vibrated combi piles is obtained from certified mixing plants. Vroom Funderingstechnieken can perform additional checks on the grout quality by casting cubes in-situ and having these tested. 

Allow us to advise you 

We at Vroom Funderingstechnieken prepare our leaflets and website with the greatest possible care and attention. However, no rights can be derived from such content. If you use information from our leaflets or our website without verification or further advice, this is at your own risk.

Vroom Funderingstechnieken accepts no liability for the correctness and/or suitability of the information for the purpose you envisage. Should you have any questions about the use of our products for actual projects we advise you to contact our sales department.

Technical specifications Vibrated combi piles

Concrete grade

Grout mixture

Strength 25 to 35 N/mm2.

Concrete element (pre-fab concrete core) 

Concrete grade C35/45, C45/55 or C55/65: dimensioning of reinforcement in pre-fab concrete element depends on tensioning/stressing information.


Bearing capacity

Ground-mechanical bearing capacity according to Eurocode 7 (NEN 6743) gives the following parameters:

Pile base coefficient

αp = 1.0.

Bearing pile shaft friction

αs = 0.014 (withdrawn by jolting)
αs = 0.012 (for tension piles)

Dimensions

Diameter of casing/tube (area of pre-fab concrete core)
Dimensions in mm
457 (290)
508 (320)
559 (350) 610 (380 / 400)
The foot dimensions as for HBF-type vibrated piles, relative to the diameter of the tube.

Process

Production process vibro combo piles  

  1. Steel tube, with foot, at working level.
  2. Steel tube driven in to required level with appropriate ram.
  3. Inspection to check that tube is dry and free from contamination.
  4. Installation of pre-tensioned pre-fab concrete element.
  5. Space around core partially filled with grout, followed by insertion of water column to apply sufficient pressure to grout column.
  6. Tube removed by jolting.
    Vibrated combi piles below ground level.

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