Execution methods of micropiles
A.1 Drilled micropiles
|Drilling method||Reinforcement type||Filling/Grouting method||Grout type||Options|
|Rotary / flush drilling
Grab, chisel or bailer boring
|Reinforcement cage||Filling, concreting||Grout mortar or concrete||Casing|
|Single step grouting through temporary casing||Grout or mortar|
|Bearing element||Filling, concreting||Grout, mortar or concrete||Casing|
|Single step grouting through:
|Multi–step grouting through:
|Grouting during drilling||Grout||Multi–stage grouting
|Permanent casing (with or without reinforcement cage)||Filling or concreting||Grout, mortar or concrete||Enlarged base|
|Continuous flight auger drilling||Reinforcement cage
|Grouting/Concreting through the hollow stem of the auger||Grout mortar or concrete|
A.2 Displacement micropiles
|Driving method||Material (casing)||Cross section / Reinforcement||Options / Grouting|
|A.2.1 Prefabricated||Reinforced concrete
Steel or cast iron
|Open end tube||Shaft grouting|
|Closed end tube||Filling with grout ,mortar or concrete, with or without shaft grouting|
|A.2.2 Cast in place||Temporary casing||Reinforced cage||Filling, concreting|
|Single step grouting through casing|
|Bearing element||Filling, concreting:
Single step grouting through
|Permanent casing||Reinforcement cage||Concreting, with or without base enlargements|
Guidance on geometrical construction tolerances
The following geometrical construction tolerances should be considered for the design and execution:
- plan location of vertical and raking micropiles (measured at the working level): ≤ 0,05 m;
- deviation from the theoretical axis:
- for vertical micropiles: max 2 % of the length;
- for subvertical micropiles (n > 4): max 4 % of the length (see Figure 2);
- for inclined micropiles (n < 4): max 6 % of the length (see Figure 2);
- radius of curvature ≤ = 200 m depending on buckling conditions;
max angle deviation in a micropile joint = 1/150 radian.
Minimum cover (in mm) for reinforcement and bearing element of low strength steel for cast in place micropiles taking into account exposure classes related to environmental actions as defined in EN 206–1
|Exposure class||Chemical aggressiveness||Bearing element with grout cover||Mortar||Reinforced concrete|
|Compression||Tension||Compression||Tension||Compression and tension|
|XC1 – XC4||Not existing||20||30||35||40||50|
|XD1, XD2, XD3*||Chloride, except salt water||***||***||***||***||***|
|XS1 – XS3||Chloride from salt water||***||***||***||***||***|
|* For XD3 special measures for the corrosion protection may be required in particular cases.
** HS cement shall be used for sulfate aggressive conditions.
*** Empty fields to be specified.
Guidance on corrosion rates
Loss of steel thichness (mm) due to corrosion for piles and sheet piles in soils, with or without groundwater (= Table 4–1 of EN 1993–5)
|Required design working life||5 years||25 years||50 years||75 years||100 years|
|Undisturbed natural soils (sand, silt, clay, schist, …,)||0,00||0,30||0,60||0,90||1,20|
|Polluted natural soils and industrial grounds||0,15||0,75||1,50||2,25||3,00|
|Aggressive natural soils (swamp, marsh, peat, …,)||0,20||1,00||1,75||2,50||3,25|
|Non–compacted and non–aggressive fills (clay, schist, sand, silt, …,)||0,18||0,70||1,20||1,70||2,20|
|Non–compacted and aggressive fills (ashes, slag, …,)||0,50||2,00||3,25||4,50||5,75|
|NOTE 1 The values given are only for guidance. Local conditions should be considered and suitable values taking into account local conditions should be given in the national annex.
NOTE 2 Corrosion rates in compacted fills are lower than those in non–compacted ones, In compacted fills the figures in the table shoud be divided by two.
NOTE 3 The values given for 5 and 25 years are based on measurements, whereas the other values are extraplated.