8.6 Grouted displacement piles

8.6.1 Grouting during driving An enlarged shoe can be used to create along a part or the full perimeter of the pile a space which is filled with grout during driving. The grouting can be carried out at the shoe level through a pipe fixed temporarily or permanently along the pile or through the drive tube. The rate of flow from the pump shall take into account the speed of driving and the size of space around the pile.

8.6.2 Grouting after driving For concrete piles, shaft grouting shall be carried out through permanent grouting pipes fixed to or incorporated in the pile. For steel piles, shaft and base grouting shall be carried out through grouting pipes attached permanently or temporarily to the pile. Grouting shall proceed at appropriate pressures and grouting rates:

  • to allow the spread of grout at the interface of the pile with the ground;
  • to avoid fracturing of the surrounding ground. After the initial grout has set, second stage post grouting may be carried out. Shaft and/or base grouting shall be carried out to cast in place piles only after the concrete has set and/or cured as speciefied.

8.7 Trimming of concrete piles

8.7.1 Cutting off and stripping of the pile head shall be done carefully to avoid damage to the rest of the pile.

8.7.2 Particular attention shall be paid to the quality of the concrete in the top of the pile. Any defective concrete in the head of the completed pile shall be cut down to sound concrete and made good with new concrete well bonded onto the old.

8.8 Additional methods for special cases

8.8.1 Driving assistance methods Auxiliary methods may be needed to facilitate the driving of piles. Methods include:

  • water jetting during driving;
  • predriving;
  • preboring;
  • preblasting;
  • enlargements on the drive tube or pile base. These methods shall not impair:

  • the performance of previously installed piles;
  • the stability of surrounding soil (sliding, liquefaction, heave, lateral movements );
  • the stability of adjacent structures. The water jetting shall be stopped immediately if the pile or drive tube tends to deviate from its position or inclination.

8.8.2 Ground movement limiting methods

When driving piles in a group and when the piles will cause unacceptable soil movement preboring or coring in accordance with the design, should be used to mitigate the effects.

8.8.3 Working from floating platform

Particular attention shall be paid to the guiding auxiliary structure to ensure the alignment of the piles during driving.

8.8.4 Cast in place base enlargements Methods of base enlargement shall be agreed before commencement of the work. See 7.8.5. Cast in place base enlargements may be formed by ramming compacted quantities of concrete into the ground below the bottom of the drive tube. The concrete consumption as well as the driving energy for the base fabrication shall be measured and recorded as required. For piles which are subject to tensile forces (e.g. by tensile actions from the superstructure or when heave is likely to occur), particular care shall be taken to provide sufficient anchoring of the reinforcement cage in the enlarged base.

EN 12699:2001 Execution of special geotechnical work – Displacement piles