MICROPILES

A Micropile is a small diameter, typically less than 300mm, drilled and grouted non-displacement pile which is heavily reinforced and carries most of its loading on the high capacity steel reinforcement.  The four methods of grouting micropiles are:

  • Grout placed under gravity conditions
  • Pressure grouting through the casing
  • Post grouting using single or multiple stages
  • Grouting during drilling using high capacity steel threaded hollow-bar members

Positive Features

  • Micropiles can be installed in limited access and headroom conditions
  • Micropiles can be installed with minimum disturbance to adjacent structures with the appropriate installation methodology
  • Micropiles can be installed through existing foundations and are ideally suited to under-pinning and as load enhancement of existing foundations
  • Due to the high capacity steel reinforcing elements, micropiles have high uplift load capacity and can be effectively used for tension structures
  • Due to the wide range of installation methods available and the relevant ease of penetrating boulders or hard rock formations, micropiles can be economically installed in difficult ground conditions, e.g. Karstic formations
  • Micropiles can be utilised as soil reinforcing elements providing significant economies in suitable soil conditions where the applied load is shared between the base and the piles
  • Micropiles can be installed as steeply raking piles providing significant horizontal load capacity for a pile group
  • Micropiles generally provide a high degree of redundancy

Pile Details

There are a wide variety of installation methods available and the method of reinforcement can be in the form of:

  • Steel casing
  • Steel casing supplemented by internal reinforcement
  • Heavy reinforcement without casing
  • High capacity threaded hollow-bar members installed and grouted during drilling

Micropile maximum axial load capacities of up to 2000kN can be achieved.

Franki have developed and implemented the drilled-in high capacity hollow-bar solution in co-operation with Ishebeck Titan, and typical details of this system are tabulated below.

MICROPILE TECHNICAL SPECIFICATIONS PDF