8 Anchorages

8.1 General

8.1.1 Scope

(1)P This Section applies to the design of temporary and permanent anchorages used:

  • to support a retaining structure;
  • to provide the stability of slopes, cuts or tunnels;
  • to resist uplift forces on structures,

by transmitting a tensile force to a load bearing formation of soil or rock.

(2)P This Section is applicable to:

  • pre-stressed anchorages consisting of an anchor head, a tendon free length and a tendon bond length bonded to the ground by grout;
  • non pre-stressed anchorages consisting of an anchor head, a tendon free length and a restraint such as a fixed anchor length bonded to the ground by grout, a deadman anchorage, a screw anchor or a rock bolt.

(3) This Section should not be applied to soil nails.

(4)P Section 7 shall apply to the design of anchorages comprising tension piles.

8.1.2 Definitions

8.1.2.1

permanent anchorage

anchorage with a design life of more than two years

NOTE definition taken from EN 1537:1999

8.1.2.2

temporary anchorage

anchorage with a design life of less than two years

NOTE definition taken from EN 1537:1999

8.1.2.3

acceptance test

load test on site to confirm that each anchorage meets the design requirements

8.1.2.4

suitability test

load test on site to confirm that a particular anchor design will be adequate in particular ground conditions

NOTE definition taken from EN 1537:1999

8.1.2.5

investigation test

load test to establish the ultimate resistance of an anchor at the grout/ground interface and to determine the characteristics of the anchorage in the working load range

NOTE definition taken from EN 1537:1999

8.1.2.6

anchor bond length

length of the anchor that is bonded directly to the ground through a grout body

8.2.1.7

tendon free length

the length of the tendon between the anchor head and the proximal end of the tendon bond length

NOTE definition taken from EN 1537:1999

8.1.2.8

tendon bond length

length of the tendon that is bonded directly to the grout and capable of transmitting the applied tensile load

NOTE definition taken from EN 1537:1999

8.2 Limit states

(1)P The following limit states shall be considered for anchorages, both individually and in combination:

  • structural failure of the tendon or anchor head, caused by the applied stresses;
  • distortion or corrosion of the anchor head;
  • for grouted anchors, failure at the interface between the body of grout and the ground;
  • for grouted anchors, failure of the bond between the steel tendon and the grout;
  • for deadman anchorages, failure by insufficient resistance of the deadman;
  • loss of anchorage force by excessive displacements of the anchor head or by creep and relaxation;
  • failure or excessive deformation of parts of the structure due to the applied anchorage force;
  • loss of overall stability of the retained ground and the retaining structure;
  • interaction of groups of anchorages with the ground and adjoining structures.

8.3 Design situations and actions

(1)P When selecting the design situations, consideration shall be given to:

  • all circumstances during the construction of the structure;
  • all anticipated circumstances during the design life of the structure;
  • all pertinent limit states of the list compiled in 8.2, and their combinations;
  • the anticipated level of the ground-water and water pressures in confined aquifers;
  • the consequences of the failure of any anchorage;
  • the possibility that the forces applied to the anchorage during pre-stressing (anchorage load) may exceed the forces required for the design of the structure.

(2)P The anchorage load, P, shall be treated as an unfavourable action for the anchorage design.

Eurocode 7 Geotechnical design Part 1 : General rules