Ground Anchors in Construction

A ground anchor can be mentioned as a type of deep foundation system that is capable of transmitting a tensile load into a component stratum, by drawing support from the structure to be anchored. It is a support structure that is used in geotechnical and construction applications.

It is also called a ground anchor, percussion-driven earth anchor, or mechanical anchor. These anchors are either impact-driven or run spirally into the ground. Ground anchors can be either used for permanent or temporary applications in civil engineering and other structures.

Applications of Ground Anchors

The main applications of ground anchors are:
  1. It is used to prevent the deformation of a retaining wall after excavation.
  2. Stabilization of slopes and landslides
  3. Anchoring of slabs below the water table
  4. Anchoring narrow structures
  5. Transmission of tension for rigging lines ( suspension bridges, pylons, etc)

Components of Ground Anchors

Ground anchors are installed in grout-filled drilled holes in soil or rock and transmit applied tensile load into the ground. The main components of a ground anchor are:

  1. Anchorage and anchorage head
  2. Unbonded length
  3. Bond Length

Ground Anchors in Construction

1. Anchorage

The anchorage in the ground anchor system is a combined system of anchor head, bearing plate, and trumpet. These components are capable of transferring the prestressing force from the prestressing steel bar of the strand to the ground surface or the supporting structure. 

2. Unbonded Length

The unbonded length is the portion of the prestressing steel that is free to elongate elastically and transfer the resisting force from the bond length to the structure. 

A bond breaker is a smooth plastic sleeve placed over the tendon in the unbonded length to prevent the prestressing steel from bonding to the surrounding grout. A bond breaker also enables the unbonded length to elongate without obstruction during the testing and stressing. It leaves the prestressed steel unbonded after the lock-off.

3. Bonded Length

The tendon bond length is the length of the prestressing steel that is bonded to the grout and is capable of transmitting the applied tensile load into the ground. The anchor bond length is located behind the critical failure surface. 

Grout anchors are tension elements that are made of high-grade steel. The anchor's tensile force comes from the shear stress between the grouted anchor body and the surrounding soil. 

Performance of Grout Anchors

The performance of the ground anchor is dependent on the:

  1. The shear angle of the soil
  2. The size of the anchor
  3. The depth of the installation
  4. The load applied to the anchor
Anchors are found to work best in granular soil, stiff, cohesive soil. For soft alluvial soils, larger anchor size and deep driven depth are required. 

Also Read: Sheet Piles

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