Grouted Hollow Bar Micropiles

Similar to cased micropiles, grouted hollow bar micropiles are small diameter drilled piles. Diameters typically range from 3 to 11 inches with capacities capable of exceeding 200 tons.  These piles develop their capacity through skin friction with the surrounding soil or through the socket into rock.  The steel reinforcing for this pile type consists of the hollow bar itself; a threaded high strength bar with a diameter of 1.2” to 4” and center hole the length of the bar.  Excellent tension capacities can be achieved as well as lateral when installed at a batter.  A high strength neat cement grout is pressure injected through the center of the hollow bar and up around the outside of bar.

Hollow bar micropiles are a versatile deep foundation element because of the wide range of drilling equipment available for installation.  The compact size of the drilling equipment along with the versatility of length and weight of the material is of particular importance where piling is required in confined or low-headroom areas.  Technical Foundations can even utilize electric installation equipment where diesel exhaust cannot be tolerated.  Hollow bar micropiles can be used for structural support in new construction as well as for underpinning existing foundations.


 Benefits of Hollow Bar Micropiles:

  • Small installation equipment footprint.
  • Great for limited access applications.
  • Can be installed with electric equipment, eliminating exhaust issues with interior applications.
  • Can achieve relatively high capacities.
  • Lower cost alternative to cased micropiles.

How it works:

  • The hollow bar, with a leading sacrificial bit, is advanced into the ground. A coupler and an additional piece of threaded hollow bar are added as the pile is advanced.  Note that one of benefits of hollow bar micropiles is that the added bars can be field cut to the length necessary based on the available headroom.
  • Additional couplers and bars are added until the tip elevation is reached.
  • If a rock socket is required, the drill hammer is engaged once rock is encountered to penetrate the rock and establish the bond zone.
  • Hollow bar micropiles can be advanced using air to clear the cuttings or a flushing grout.
  • Once the tip elevation is reached, the pile is grouted out with a high strength structural grout until the grout is observed at drill grade.
  • The pile is cut off at the proper elevation and a pile termination plate is added or an underpinning bracket is installed and attached to the structure.

Celebrating Over 30 Years of Quality Foundation Construction Services

Technical Foundations has designed and installed hollow bar micropiles across the Mid-Atlantic region.  We have numerous drill rigs to accommodate most any project and ground conditions.  Please contact us if we can help you with your next hollow bar micropile project!

Ready to Get Started?