Ground anchors and nails

Ground anchors and soil nails are soil mass retaining devices constructed to transmitting an applied tensile load to a load bearing stratum. Anchors and nails are normally pre-stressed, composed of steel bars that are introduced into a small diameter pre-drilled hole of limited diameter and covered with borehole grout.

Construction chart

Construction sequence

Installation process of ground anchors: in accordance with the requirements of standard NBN EN 1537 : Ground anchors

1. & 2. Drilling of a borehole at a defined angle using an external protection (tubes / casing crown), under drilling fluid

3. At the required level of depth, replacement of the drilling fluid by a (primary) grout injected through the injection conduit which is withdrawn as the borehole is filled with grout (simultaneous drill and grout). 

4. Insertion of the reinforcement (bar tendons, strand tendons,…) over a fixed bond length (anchor length) and a possible free tendon length (free anchor length), according to the design.

5. Cement grout under pressure (borehole grout) is injected as the external protection tube is progressively removed: formation of the (bond length) grout body (or ‘core’)

6. The completed ground anchor

7. Active anchor : pre-stressed to reduce structural movement. Transfer their load over a fixed length. Performance at least seven days after injection with classic grout cement.

Passive anchor or nail : un-pre-stressed, cemented in the stabilized mass over their whole length thus performing solely during deformations of the soil

Different construction processes anchor (active) VS nail (passive)

Fields of application

• Reinforcement of excavation pits, anchorage of retaining walls (withhold active earth pressure), slope protection and stabilization (loose soil or rock slope)

• Nailing

• Resist and absorb tensile forces (e.g. uplift of slabs below groundwater).

Environmental impact

• Vibration-free

• Removal of excavated soil and drilling spoil from the job site is required

• A stable, dry and flat work platform is required

• Execution with electrical machines possible (no emission of waste combustion gases).

Technical specifications

• The anchor allows for resisting tensile loads along its axis. Anchors transfer forces acting on a supporting structure either into the soil behind the structure or into the underlying soil layers.

• The anchor consists of:

  • pre-stressed strands (free length and bond or anchor length)
  • steel tubes, with couplers or single length
  • steel bars or rods of standard quality or high-resistance quality (pre-stressed bars)
  • fiber glass rods
  • self-drilling hollow steel bars (bars drilled into soil without the need for a casing to support the borehole)

• The anchor head transmits the anchor force to the structure through the anchor bearing plate

• Depending on the duration of use, two types are distinguished: temporary and permanent anchors (the latter ones provided with a corrosion inhibiting compound)

• Borehole diameter: 100 up to 250 mm

• Possibility to realize inclined anchors

• Anchors are prestressed (active), nails are not prestressed (passive anchors).

Related projects for this technique

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