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Micropiles

in accordance with DIN EN 14199

Micropiles are used as foundation and anchoring elements in all soil types and rock where the load-bearing capacity of the subsoil is low, or where anchoring is possible without prestressing. The permissible pile forces and the length of the load-bearing elements depend on the geological and site-specific boundary conditions. They are calculated individually for each construction scheme.

Various drilling methods are available for producing the boreholes for installing the load-bearing elements, and our experienced employees are proficient in all of them. The wide variety of available design variants allows us to adapt to the most diverse subsoil conditions and construction site scenarios in order to achieve high load-bearing capacities.

We have our own drilling equipment which helps us meet your requirements. It allows our team to drill boreholes in confined spaces with limited working heights or at high altitudes. Micropiles are sometimes also referred to as small bore grouted piles, micro bored piles or composite piles.

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Micropiles (only available in German)
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Applications

Micropiles are used as precisely fitting foundation and anchoring elements.

Common uses include:

  • Deep foundations
  • Replacing the foundations of existing buildings
  • Bracing
  • Anti-buoyancy control
  • Embankment reinforcements
  • Anchoring
     

Advantages

  • Can be individually adapted to a wide range of subsoil conditions.
  • Very high pile loads can be achieved.
  • Production is vibration-free and low-noise.
  • Micropiles are made from segments that can be coupled together, which also allows them to be produced at limited working heights.
  • They are produced in a tried and tested high-precision method carried out with the General Type Approval of the German Institute for Building Technology (Deutsches Institut für Bautechnik, DIBt).
  • Safety during execution is monitored by applying high quality assurance standards.
  • The flush drilling method enables the particularly economical installation of micropiles with a high daily output.
  • Pressure-sensitive drilling using the flush drilling method means that micropiles can be used on sites that lack explosive ordnance clearance. We are licensed in accordance with section 7 of the German Explosives Act (Sprengstoffgesetz).
  • The micropiles are produced in Stump-Franki’s own facilities.
     

Basic facts

Standards and regulations

Micropiles are dimensioned in accordance with:

  • DIN EN 1997-1: Eurocode 7
  • Recommendations of the DGGT “Piles” working group (EA-Pfähle)


The following apply to the production of micropiles on the construction site:

  • DIN EN 14199 Execution of work in specialist civil engineering – Micropiles
  • DIN SPEC 18539 Supplementary specifications to DIN EN 14199


Micropile testing is performed in accordance with:

  • DIN EN 1997-1: Eurocode 7
  • Recommendations of the DGGT “Piles” working group (EA-Pfähle)


Further details are defined in the DIBt general type approvals.

How do micropiles work?

Micropiles transfer an applied force (pressure and/or tension) via skin friction into a load-bearing layer of the subsoil. They consist of a continuous load-bearing element, which can also be formed from segment pieces that have been coupled together. The load-bearing element is encased in cement blocks along its entire length. Additional injections can be applied to suitable soil types in order to increase the load-bearing capacity.

Rods with rolled-on or rolled-up threads can be used as load-bearing elements. Another alternative is to use load-bearing elements that also serve as drill rods. Reinforced in-situ concrete piles with a pile diameter of up to 300mm are also referred to as micropiles or micro bored piles.

Anti-corrosion protection is provided by the cement block coating with crack width restriction or by means of factory-made extruded coating made from PE piping.

Dimensioning

Dimensioning micropiles involves defining both the length of the micropile and the necessary pile force. An estimate is also made of the length of the force application section. Lower pile forces can be applied in cohesive soil types such as clay and silt than in non-cohesive soil types such as gravel/sand or rock.

Manufacturing stages

Each stage has a particular significance for the load-bearing capacity and durability of a micropile.

1. Drilling and replacing the drilling water

The drilling method used can have a strong influence on the load-bearing capacity of a micropile. This is why it is important to choose the right drilling method. Our many years of experience have equipped us to work with a wide variety of soil types, so that we can always use the best possible method. 

2. Installing and grouting the load-bearing element

Care must be taken during storage, transport and installation of the load-bearing element in the borehole to ensure that the protective anti-corrosion casing is not damaged. Our construction teams are specially trained in these processes.

After the pile has been installed in the slurry-filled borehole, the shaft of the pile is formed by applying grouting pressure. It is important to choose the right type of cement and the correct amount of grouting pressure. Targeted follow-up injections, which can be carried out several times, if necessary, can significantly increase the load-bearing capacity in non-cohesive soil types. 

3. Load test

Some of the micropiles must be tested under trial loads. The specifications of the type approvals and the relevant provisions must be observed. Where tension micropiles are used for anchoring breaks in the terrain, it is important to bear in mind that the piles undergoing testing must be produced so that the load is applied to the load transmission section that has been defined for the final state. This means that additional measures must be taken to exclude skin friction above the load transmission section in the test piles.

4. Installing the pile head

The final stage of producing a pile is installing the pile head. A range of different variants are available here. An anchor plate with a counter plate is generally used.

Quality assurance

We ensure high execution quality with:

  • Individually coordinated instructions
  • Our own DIBt general type approval for micropiles
  • Compliance with the requirements of execution standard DIN EN 14199
  • In-house production of the micropiles in Germany
  • In-house and third-party production monitoring
  • Clear processes governed by our quality management system in accordance with DIN EN 9001:2015
     

Professional pile test loading in accordance with DIN EN 1997-1 and DIN EN 14199

Design variants

Micropiles are highly flexible, which means that they can offer a solution for every foundation problem. Cost-effective and safe construction of foundations can be achieved even under difficult structural boundary conditions by adapting the equipment technology. We produce micropiles in a wide variety of design variants.

These include piles with:

  • Compressive, tensile or alternating loads
  • For permanent or temporary use
  • Single or double anti-corrosion protection
  • Steel protective anti-buckling pipe or PE pipe for load decoupling
  • Plate anchoring or adhesive anchoring

 

Anti-buoyancy control

Durable, economical and secure

Modern structures with several basement floors, hydraulic structures, and wastewater treatment plants can be permanently and very economically secured against uplift with micropiles. This yields considerable savings in excavation and underwater concrete. Drilling crews can place piles precisely – even over long empty drilling distances, ensuring that the pile heads bond with the structural concrete or jet-grouted floor slabs.

Constructing new buildings in existing structures

Individually adjustable even at low working heights

Changes in the groundwater table can impair the viability of old timber pile foundations under existing buildings. In these cases, micropiles are used as a rehabilitation element. The design, which allows several segments to be linked together, means that long micropiles can be produced – even at low working heights, provided that suitable equipment is used.

The conversion of existing commercial buildings and industrial facilities presents similar challenges. A wide pool of equipment is available for these applications. At our building yard in Colbitz, equipment is individually adapted and prepared for the demanding construction tasks.

Anchoring

The best system for every subsoil

If no active prestressing is required to secure breaks in the terrain, micropiles are used as an anchoring element. We also anchor foundations, underpinnings and abutments securely. High retaining forces can be transferred into the ground by selecting the appropriate micropile systems in combination with an adapted grouting technique. Our specialist engineers have developed special procedures for this purpose, in some cases involving the use of jet grouting technology.

Flush drilling

Rapid construction progress

The external flushing system enables us to extract the drilling cuttings as efficiently as possible. The grouting section is produced cleanly with an uneven surface (root effect). This helps us to achieve rapid construction progress and thus work at a low cost, thanks to the high daily output. Transportation, assembly and dismantling can all be carried out quickly thanks to the compact equipment and minimal site facilities. In this way, even small projects can be implemented economically and flexibly throughout the country.

Pressure sensitive drilling

For sites lacking explosive ordnance clearance

Sites that have not been proved to be free of explosive ordnance pose a particular challenge.  In cases such as these, we use our drilling rig for pressure-sensitive drilling. Sample drillings are conducted across the suspected areas in the company of an expert, as defined in section 20 of the Explosives Act, in order to obtain a drilling permit. Stump-Franki has a special permit for this in accordance with section 7 of the German Explosives Act (Sprengstoffgesetz). This means that we can implement your project, even in areas that are difficult to investigate, safely, straightforwardly, and in compliance with the regulations of the respective federal state regarding the handling of explosive ordnance.

Selected reference projects

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Tunnel trough repair, Mönkedamm . Hamburg
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Slope stabilisation and retaining wall . Rogätz
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WDR Filmhaus renovation . Köln
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Fifth sluice chamber construction . Brunsbüttel
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