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.