Grouted anchor
Anchoring systems for construction pits, slope stabilisation and civil engineering structures

The vibro-compaction method is used for subsoil improvement in soils with low bearing capacity. This involves creating compacted columns of mineral materials, such as gravel or crushed stone, within the subsoil. The work is carried out on a project-by-project basis, taking into account the geotechnical and structural requirements.

Encyclopedia: Grouted anchor

General Applications Advantages Basic facts Quality assurance Design variants References

Grouted anchors in accordance with DIN EN 1537
Anchoring systems for construction pits, changes in ground level and civil engineering structures

Grouted anchors are used as anchoring elements – usually as pre-stressed anchors – to stabilise construction pits, changes in ground level or transport routes.

Various drilling methods are available for creating the boreholes. The different design variants allow for adaptation to varying subsoil conditions and site circumstances. The selection of the anchor system and design is made in accordance with the technical and project-specific requirements.

Using our own drilling rigs, boreholes can be drilled even where working height is limited, space is restricted or special site conditions apply.

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Technical brochure
Grouted anchor

Technische Broschuere Verpressanker
Grouted anchor (only available in German)
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Applications

Grouted anchors are used to anchor construction pit walls such as diaphragm walls or bored pile walls. Underpinning elements can also be anchored back using grouted anchors. If anchoring is not possible for any reason, bracing can be used as an alternative.

Common uses for grouted anchors include:

  • Temporary construction pit systems
  • Embankment reinforcements
  • Anti-buoyancy control
  • Dam rehabilitation
  • Rope bracing
[Translate to English:] Auf dem Bild sieht man das Innere der Fertigungshalle Colbitz ; im Vordergrund liegen die Litzenanker
[Translate to English:]

Eigene Produktion in Deutschland: PORR Spezialtiefbau verfügt über eigene allgemeine Bauartgenehmigungen für Litzenanker in Boden und Fels. Die Verpressanker werden zentral in unserer Fertigungshalle in Colbitz zusammengesetzt.


© PORR

Benefits / Features

Thanks to a range of anchor systems and design variants, grouted anchors can be adapted to different subsoil conditions and project requirements. The anchor system is selected in accordance with the geological, technical and site-specific conditions.

  • Adaptability: Can be adapted to different subsoil and site conditions.
  • Construction pit design: Grouted anchors can be installed within the construction pit without the need for additional bracing elements.
  • Anchor forces: The permissible anchor forces are designed on a project-by-project basis, taking into account the geological and technical conditions.
  • Installation: Low-noise installation with minimal vibrations is possible.
  • Design variants: Can be supplied as removable anchors.
  • Operating conditions: Can also be used where working height is limited and space is restricted.
  • Type approvals: General type approvals for grouted anchors are available from the German Institute for Building Technology (DIBt).
  • Quality assurance: Installation carried out in accordance with defined quality and monitoring measures.
  • Drilling methods: Different drilling methods can be used depending on the subsoil conditions and project requirements.
  • Suspected presence of explosive ordnance: Can also be used in construction projects where the absence of explosive ordnance has not been confirmed; the relevant permit under Section 7 of the Explosives Act is in place.
  • Production: Grouted anchors are manufactured at our own production facilities in Germany.

Basic facts

Grouted anchors are dimensioned in accordance with:

  • DIN EN 1997-1: Eurocode 7 – Geotechnical design – Part 1: General rules
  • German version of EN 1997-1:2004 + AC:2009 + A1:2013 with DIN 1054: Subsoil – Safety analyses in earthworks and foundation engineering – Supplementary regulations to DIN EN 1997-1
  • Recommendations of the DGGT Construction Pits Working Group )
     

The following apply to the production of grouted anchors on the construction site:

  • DIN EN 1537 Execution of work in specialist civil engineering - Grouted anchors
  • German version of EN 1537:2013 in conjunction with DIN SPEC 18537 Title (German): Supplementary specifications for DIN EN 1537:2014-07, Execution of work in foundation engineering – Grouted anchors
     

Grouted anchors are tested in accordance with:

  • DIN EN 22477-5: Geotechnical investigation and testing – Testing of geotechnical structures and components – Part 5: Testing of grouted anchors
  • German version of EN ISO 22477-5:2018

Grouted anchors transfer an applied tensile force (prestressing force) to a load-bearing layer of subsoil. Each anchor consists of an anchor head, a tendon free length and a fixed anchor length. This is often also referred to as a grout body.

There are two types of anchors: composite anchors and pressure pipe anchors.

  • In the case of composite anchors, the prestressing force is dissipated into the subsoil from the beginning of the fixed anchor length and the grouted anchor is tension loaded.
  • In the case of pressure pipe anchors, the force is applied from the end of the fixed anchor length via the pressure pipe, so that the grout body is compression loaded.

Dimensioning grouted anchors involves defining both the necessary anchor force and the length of the grouted anchor. Care must be taken to ensure that the fixed anchor length comes to rest in a uniform soil layer. An estimate is also made of the length of the grouted body. Only low anchor forces can be applied in non-cohesive soil types such as clay and silt than in as gravel/sand or rock.

The production of grouted anchors on the construction site comprises four basic work stages. Each phase has a special significance for the load-bearing capacity and durability of the grouted anchor.

  1. Drilling the anchor borehole
    The selected drilling method can have a strong influence on the load-bearing capacity of the grouted anchor. 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. Installation and grouting
    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. The construction teams are specially trained for this work stage. After the anchor has been installed, the grout body 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. Testing and prestressing
    The testing and prestressing stage, which usually takes place about a week after the installation of the grouted anchors, must be carried out carefully and adapted to the soil type. The acceptance tests verify that each anchor is fully functional.
     
  4. Applying anti-corrosion protection to the anchor head
    Anti-corrosion protection measures must be implemented comprehensively and to a high standard of quality if the anchor is to be durable. This is especially the case for permanent anchors. This is only achieved if the seals are in good working order and the anchor head area is completely filled with certified anti-corrosion protection. For this reason, special attention is paid to this point and only specially trained tensioning professionals are assigned to this task.

Specific subsoil conditions may make it necessary to equip the structure with anchor load cells or deformation measuring devices and monitor them over the long term.

Quality assurance

We ensure high execution quality with:

  • Individually coordinated instructions
  • Our own DIBt general type approval for grouted anchors
  • Compliance with the requirements of execution standard DIN EN 1537
  • In-house production of the grouted anchors in Germany
  • In-house and third-party production monitoring
  • Clear processes via our quality management system in accordance with DIN EN 9001:2015
  • Suitability and acceptance tests in accordance with DIN EN 1537

Design variants

Grouted anchors are available as strand anchors or bar anchors. Different design variants are available depending on the service life, corrosion protection, load requirements and ground conditions.

  • Temporary anchors / short-term anchors
    Service life of up to two years

Short-term anchors with a service life of up to two years, as specified in DIN EN 1537, are used, amongst other things, for construction pits. Corrosion protection is specified in the standard. Both single-bar anchors and strand anchors are used for short-term anchors.

Extended service life

If the intended service life is exceeded, project-specific measures must be defined. This may include, for example, adjustments to the corrosion protection on the anchor head or the use of suitable strand designs.

  • Permanent anchors
    Anchoring systems for long-term applications

Permanent anchors are used, amongst other things, for slopes, terrain steps and other permanent anchoring tasks.

In this context, requirements relating to corrosion protection, transport, installation and the durability of the load-bearing member are taken into account. The design is carried out in accordance with the applicable standards as well as project-specific specifications.

Anchor forces

Permanent anchors can be designed for typical anchor forces of up to 7,500 kN. They are manufactured on the basis of defined production, testing and monitoring processes.

  • Flush drilling method
    Drilling methods for different subsoil conditions

In the flush drilling method, cuttings are removed via an external flushing system. The method is adapted to the respective subsoil conditions and project requirements.

Compact equipment and a range of site set-ups enable deployment across projects of varying sizes and under different boundary conditions.

  • Pressure-sensitive drilling 
    Drilling in areas where explosive ordnance is suspected

Pressure-sensitive drilling can be used in areas where the absence of explosive ordnance has not been confirmed.

The work is carried out under the supervision of suitably qualified experts in accordance with the applicable legal requirements. PORR special civil engineering holds the necessary permits for these services in accordance with the Explosives Act.

  • Staggered anchors
    Anchoring systems in soils with low bearing capacity

Staggered anchors can be used in ground conditions where force transmission is limited.

Principle of the staggered anchor

In staggered anchors, the load-bearing lengths of individual strands are arranged at different depths and converge in a common anchor head.

By distributing the load over different depths, different soil layers can be utilised in load transfer.

  • Removable anchors
    Systems for planned demolition works

In construction projects in inner-city areas or near existing infrastructure, there may be requirements for the partial or complete dismantling of grouted anchors.

Various dismantling systems are available for these applications. The selection is based on the ground conditions, the anchor lengths and the project requirements.

  • Drilling entry points below the water table
    Grouted anchors under special boundary conditions

Where the groundwater level is high or the construction pits are deep, grouted anchors with insertion points below the water table may be required.

Planning and installation are carried out taking into account the geotechnical, hydrogeological and project-specific requirements. This may necessitate preparatory measures as early as the construction of the construction pits.

Selected projects
Grouted anchor