1.1 This document establishes general principles for the execution of micropiles.
They are for:
- drilled micropiles a shaft diameter not greater than 300 mm;
- driven micropiles a shaft diameter or a maximum shaft cross sectional extension not greater than 150 mm.
1.2 Micropiles are structural members to transfer actions to the ground and may contain bearing elements to transfer directly or indirectly loads and or to limit deformations. Their shaft and base resistance may be improved (mostly by grouting) and they may be constructed with (see Figure 1):
- uniform cross section (straight shaft); or
- telescopically changing shaft dimensions;
- shaft enlargements; and/or
- base enlargement.
1.3 Other than practical considerations, there are no limitations regarding, length, rake (definition of rake, see Figure 2), slenderness ratio or shaft and base enlargements.
1.4 The provisions of the document apply to (see Figure 3):
- single micropiles;
- micropile groups;
- reticulated micropiles;
- micropile walls.
1.5 The micropiles which are the subject of this document can be installed into the ground using drilling, driving or a combination of these methods.
1.6 The material of micropiles covered by this document can be:
- steel or other reinforcement materials;
- grout, mortar or concrete;
- a combination of above.
1.7 Micropiles may be used for:
- working under restricted access and/or headroom conditions;
- foundations of new structures (particularly in very heterogeneous soil or rock formations);
- reinforcing or strengthening of existing structures to increase the capacity to transfer load to depth with acceptable load settlement characteristics, e.g. underpinning works;
- reducing settlements and/or displacements;
- forming a retaining wall;
- reinforcing of soil to form a bearing and/or retaining structure;
- improving slope stability;
- securing against uplift;
- other applications where micropile techniques are appropriate.