7.5 Connecting elements
7.5.1 Connecting elements shall be dimensioned for all actions which can occur during handling, transportation and installation.
7.5.2 For couplers and nipples, the cross section which is reduced by a thread shall be calculated on the base of the nominal diameter (minimum section).
7.5.3 Joints between load bearing elements shall satisfy the required capacity in compression, tension and bending.
7.5.4 When reinforcement bars or cages are installed within a permanent casing, filled afterwards with grout, mortar or concrete, normal overlapping may be used in accordance with EN 1992–1–1.
7.6 Corrosion protection of steel elements
7.6.1 The protection against corrosion of steel elements placed in a micropile shall take into account:
- the aggressiveness of the environment (groundwater, soil, stray electric currents, etc.);
- the micropile type;
- the type of load (tension or compression);
- the type of steel; and
- required design working life.
7.6.2 A corrosion protection shall consist of:
- an efficient cover of appropriate grout, mortar or concrete or;
- a sacrificial thickness of steel for the corrosion;
- specific precautions.
NOTE 1 Guidance on the minimum cover of appropriate grout, mortar or concrete is given in Annex C.
NOTE 2 Guidance on the loss of steel thickness to consider is given in Annex D.
NOTE 3 Specific precautions for protection against corrosion may be specified and consist of:
- use of special cement;
- use of an adequate steel type;
- cathodic protection;
- use of permanent casings or linings;
- surface coating.
7.6.3 The selection of grout, mortar and concrete composition and properties shall take into account the environment exposure class given in EN 206–1.
NOTE 1 Guidance on the concrete composition and properties to consider is given in EN 206–1.
7.6.4 The class of exposure of the environment should be chosen with special care and the time dependent development of the aggressiveness should be taken into account.
7.6.5 Specific precautions shall not reduce other properties.
7.6.6 When steel components of prestressing steel are used corrosion protection shall be in accordance with EN 1537.
7.6.7 For connecting elements the same rules of corrosion protection shall be applied as for the other steel elements.
7.6.8 Particular care shall be given to the continuity of the corrosion protection at connecting elements.
7.7 Spacers and centralizers
7.7.1 The design of spacers and centralizers shall take into account the size of the hole, the weight of the reinforcement, the grout, mortar or concrete cover and the possible disturbance of soil during the insertion of the reinforcement.
7.7.2 Spacers and centralizers shall not impede grout, mortar or concrete flow.
7.8 Micropile enlargement
Where micropile enlargements are considered, the method of forming the enlargement and the bearing area and shaft perimeter to be used in the design shall be agreed before the commencement of the work. Typical examples of enlargements are shown in Figure 4.
7.9 Connections to the superstructure
7.9.1 Unless otherwise specified the connection between the micropile and the superstructure shall be designed for the micropile capacity.
7.9.2 For micropiles of reinforced mortar or concrete the connection shall be designed in accordance with EN 1992–1–1.
7.9.3 For micropiles with bearing elements the selected method of load transfer between the bearing element and the superstructure shall be designed in detail and/or proven by tests.
7.9.4 The overlength of the reinforcement or bearing element shall be specified in the project documentation (see Figure 5).
7.10 Spacing of micropiles
7.10.1 The spacing of micropiles shall be considered in relation to micropile type, micropile diameter, length of micropile, the ground conditions, and their group performance.
7.10.2 The possible interference of one micropile with another during installation should be considered when determining micropile spacing, orientation and installation sequence.
7.11 Special requirements for micropiles installed through very weak soils
7.11.1 In very weak soils it can be necessary to provide a sacrificial lining or permanent casing to contain the fresh grout, mortar or concrete.
7.11.2 For micropiles installed through soil layers with characteristic undrained shear strength of less than 10 kPa, a check for buckling is required taking into account the geometrical construction tolerances.
7.12 Micropile shoe
When a micropile shoe is used it shall be designed in accordance with 7.8.3 of EN 12699:2000.