8.5 Driving Driving shall be performed in accordance with EN 12699:2000. The driving method shall be chosen taking into account all requirements of soil, foundation conditions and site environment. When impact or vibrating driving methods are applied for underpinning works, their feasibility shall be proven (e.g. with comparable experience taking into account the soil type and the condition of the structures to be underpinned).

8.6 Enlargements

8.6.1 Micropile enlargements may be formed:

  • by excavation;
  • by driving compacted quantities of concrete below the bottom of the drive tube or permanent casing;
  • by installing an expanded body.

8.6.2 The proper formation of an enlargement executed by excavation requires a stable excavation and complete filling with grout,mortar or concrete.

8.6.3 The excavation of enlargements should be done using mechanical tools which allow the control of their operation from the surface.

8.6.4 The proper formation of an enlargement constructed by driving out of concrete requires:

  • special measures to prevent the segregation or washing out of the concrete of the base enlargement;
  • the construction of the base enlargement without significant interruptions;
  • the use of an appropriate hammer.

8.6.5 The concrete consumption as well as driving energy for the base fabrication shall be measured and recorded.

8.6.6 For micropiles which are subjected to tensile forces, particular care shall be taken to provide sufficient anchoring of the reinforcement cage in the enlarged base.

8.7 Reinforcement and load bearing elements

8.7.1 Handling and storing Reinforcement cages shall be constructed in such a way they can be handled and lowered into the borehole or casing without damage or permanent distortion. Steel reinforcement shall be stored under controlled conditions and shall be clean and free from loose rust and loose mill scale at the time of installation and filling, grouting or concreting.

8.7.2 Joints Joints in reinforcement bars shall be made so that there is no detrimental displacement of the reinforcement during the installation and the withdrawal of the casing. Joints shall be fastened and checked properly before lowering into the ground. Welding and cutting of steel elements shall be done in accordance with subclause of EN 12063:2000. When bearing elements of a micropile are welded on site the welding shall be carried out in appropriate installations or with appropriate protection. Welding of galvanized or coated reinforcement bars or bearing elements shall only be done when a procedure for repair of the corrosion protection is agreed before the commencement of the work.

8.7.3 Spacers and centralizers The concentric position of the reinforcement in the borehole and the necessary grout, mortar or concrete cover shall be maintained by spacers and centralizers unless the position and cover are otherwise provided. Spacers and centralizers shall be provided at intervals of not more than 3 m and at least for every element. For inclined micropiles the intervals shall be chosen in such a way that the required cover is provided after placing taking into account the weight and stiffness of the reinforcement and bearing elements.

8.7.4 Installation Reinforcement cages or load bearing elements shall be suspended or supported so as to maintain their correct position and level during filling, grouting or concreting. The sequence of reinforcement or load bearing element installation and the borehole filling shall take into account:

  • the execution method (drilling, driving);
  • the filling material (grout, mortar or concrete);
  • the type of reinforcement (cage, tube, bar);
  • the condition of filling (dry or submerged condition). The installation of the reinforcement or bearing element shall assure its alignment with the micropile axis and maintain the correct grout, mortar or concrete cover over its full length. When reinforcements or load bearing elements have to be installed in raking micropiles, suitable means of support shall be employed for the installation and the direction control of the reinforcement or load bearing element. The temperature of the reinforcement or bearing element shall be high enough to avoid formation of ice on the surface when installed.

EN 14199:2005 Execution of special geotechnical works — Micropiles