6 Materials and products
Anchor systems shall be used for which successful experience with respect to performance and durability has been documented.
All anchor systems shall have been subjected to at least one system test to verify the competence of the system. The results of all tests shall be documented in detail.
The documented system test shall be approved by the Client's Technical Representative in accordance with principles stated in this standard.
All materials used shall be mutually compatible. This applies in particular to adjacent materials with a common interface. Material properties shall not change during the design life of the ground anchor in such a way that the anchor loses its serviceability.
Anchors involving the use of newly developed materials or methods of execution are permitted subject to the performance of the anchor and durability of the materials used being proven by system tests and approved by the Client's Technical Representative to ensure that the serviceability of the anchor system is maintained for the design life of the anchored structure.
All steel tendons shall comply with the following European Standards:
Construction steel - ENV 1993-1: Eurocode 3: Design of steel structures - Part 1: General rules;
Steel reinforcement - ENV 1992-1-1: Eurocode 2: Design of concrete structures - Part 1: General rules;
Prestressing steel - prEN 10138: Design of prestressing steel;
prENV 1992-1-5: Eurocode 2 Part 1-5: The use of unbonded and external prestressing tendons.
Other tendon materials may only be used if their suitability as anchor components has been proven and they are approved by the Client's Technical Representative.
6.3 Anchor head
The anchor head shall allow the tendon to be stressed, proof loaded and locked-off and, if required, released, destressed and restressed. It shall be able to carry the characteristic tensile load of the tendon of 100 % Ptk
The anchor head shall comply with ENV 1992-1: Eurocode 2 unless the required deviation is justified. The anchor head shall be designed to tolerate angular deviations of the tendon from the direction normal to the head, up to a maximum of 3° at 97 % Ptk of the tendon.
The anchor head shall distribute the tendon load to the main structure or to the ground in accordance with the overall design of the structure through designed or tested components.
The anchor head (i.e. the connection between the anchor tendon and the structure) shall be able to adjust to deformations which may be expected during the design life of the structure.
Couplers shall comply with ENV 1992-1-1: Eurocode 2, and shall not compromise the required tensile strength of the tendon.
The tendon should not be coupled inside the bond length.
The free extension of a steel tendon shall not be compromised by restraint of the coupler.
The corrosion protection of the coupler shall be compatible with the corrosion protection provided to the tendon.
6.5 Tendon bond length
In order to anchor the tendon in the bond length, profiled or ribbed tendons, strands or compression tubes shall be used in this section.
As a guide the following types of steel tendon may be anchored by bond action:
- cold drawn wires profiled after drawing;
- quenched and tempered wires ribbed during hot rolling;
- ribbed bars;
- seven wire strands.
The relative area, fr, of the ribs of ribbed or profiled wires and bars shall be in accordance with ENV 1992-1: Eurocode 2.
Prestressing steels with a smooth surface with or without special proven anchoring devices may only be used with temporary anchors when approved by the Client's Technical Representative.
6.6 Spacer and other components in the borehole
All installed tendons and encapsulations shall be provided with a minimum of 10 mm grout cover to the borehole wall. This may be achieved by the use of spacers or centralizers.
Any component installed and remaining in the borehole should be spaced and located so that it does not reduce the bond capacity of the anchor. To ensure correct positioning of the tendon(s), the tendon components, the corrosion protection components and any other component in the borehole, spacers should be located such that minimum grout cover requirements and complete filling of open volume by grout are provided.
Spacers and centralizers shall not impede grout flow.
When used outside an encapsulation in a permanent anchor spacers should be manufactured from corrosion resistant materials.
The design of centralizers shall take into account the shape of the hole, e.g. the presence of underreamed bells, the weight of the tendon and the susceptibility of the ground to disturbance during insertion of the tendon.
6.7 Cement grout and admixtures
Cement grouts used in the encapsulation and in contact with prestressing steel tendons shall conform in general with prEN 445, prEN 446 and prEN 447. Where there is conflict between the provisions of this standard and prEN 445, prEN 446 and prEN 447, the provisions of this standard shall be adopted.
For cement grout used to encase a tendon within an encapsulation or to protect steel tubes, the properties should be controlled to prevent bleed and shrinkage. Water/cement ratios for anchor grouts outside the encapsulation but within the borehole should be chosen appropriate to the ground conditions.
High sulphide content cements shall not be used in contact with prestressing steel.
When selecting the type of cement for grout placed in contact with the surrounding ground, account shall be taken of the presence of aggressive substances in the environment, e.g. carbonic acid and sulphates, of the permeability of the ground and of the design life of the anchor. The aggressivity of the environment shall be defined in accordance with ENV 206.
Admixtures may be used for improving workability or durability, for reducing bleed or shrinkage, or for increasing rate of strength development. The use of admixtures with prestressing steel shall be approved by the Client's Technical Representative. Admixtures shall be free from any product liable to damage prestressing steel or the grout itself. No admixture that contains more than 0,1 % (by mass) of chlorides, sulphides or nitrates shall be used.
Where appropriate, inert fillers (i.e. sand) may be incorporated within the grout mix to reduce leakage away from the borehole.
Laboratory and field tests should be undertaken to verify mixture, mixing efficiency, setting times and performance. These tests should be undertaken in accordance with prEN 445 where applicable.