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.
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level of depth, replacement of the drilling fluid by a (primary) grout injected through the injection conduit which is withdrawn as the borehole is filled with grout (simultaneous drill and grout).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
• Reinforcement of excavation pits, anchorage of retaining walls (withhold active earth pressure), slope protection and stabilization (loose soil or rock slope)
• Resist and absorb tensile forces (e.g. uplift of slabs below groundwater).
• 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).
• 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:
• 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).