Geo-Drill Hollow Injection Bar

The Williams Geo-Drill Injection Anchor System is today’s solution for a fast and efficient anchoring system into virtually any type of soil.  The system has historically been known as a “self-drilling anchoring” because the hollow fully-threaded bar serves as both the drill string and the grouted anchor, thus installation is performed in a single operation.  The sacrificial drill bit is threaded onto the end of the Hollow Injection Bar and left in place following drilling.  The drilling fluid (air, water, or grout) is introduced through the hollow bar and allows the spoils to flush from the borehole.

The Geo-Drill System is particularly suitable for soils that do not allow for open-hole drilling (i.e. granular soils that are collapsible in nature).  In such cases, drilling with a grout fluid serves the purpose of flushing spoils from the borehole and prevents looser, surrounding material from collapsing due to the higher relative density of the grout.  Williams Geo-Drill Injection Anchor System should be considered on any project requiring fast production that would otherwise need to involve a casing system in order to maintain borehole stability.


Geo-drill injecting anchors


Advantages of the Williams Geo-Drill Injection Anchor System

  • Fast, single-step anchoring system with simple equipment.
  • Eliminates the need for a cased borehole in collapsing soils.
  • Efficient installation since drilling and grouting can be performed in a single operation, saving both time and money.
  • Continuously drilling and grouting under high pressure causes the grout to permeate into looser soils and creates a bulb-effect for increased bond capacity.
  • Suitable for working in limited space and areas of difficult access.
  • Multiple ranges of drill bits suitable for most soil conditions.
  • Installed with standard track drill (top hammer) or hand-held drilling equipment, eliminating the need for larger casing rigs.
  • Continuously threaded bar pattern can be cut and coupled anywhere along its length.
  • Domestic available in 10’ or 20’ lengths, non-domestic available in 3 meter lengths only.
  • Corrosion protection systems available upon request.
  • FHWA approved for use as a micropile or soil nail (Domestic Hollow Injection Bar only)


Thread Profile of Domestic Bar

The Domestic Hollow Injection Bar is a high strength, impact resistant heavy wall steel tubing continuously threaded over its entire length with a heavy duty left hand thread/deformation pattern.  The thread form (similar for all diameters) is a unique Williams feature that provides a lower thread pitch angle to provide easier coupling disengagement without “locking up”, versus conventional rope threads during drilling operations.  This thread form provides more surface area and thread/deformations per unit length for superior bond capabilities over that of competitive drill steel thread forms.  The Geo-Drill Injection Anchor system is available with enhanced corrosion protection with hot-dip galvanized/epoxy coated bars and components.   Installation adapters for the Geo-Drill Injection Anchors are available for all drill rigs.

Applications for Williams Geo-Drill Injection Anchor System

Soil Nails

Soil Nails are non-tensioned, in-situ reinforcement for the stability of excavations and embankments in top-down construction.  The Williams Geo-Drill Injection Anchor System is an ideal choice for soil nailing in difficult soils as it offers high installation rates.  Hollow bar soil nails have been used extensively on private and select DOT permanent soil nail walls for years.  With the 2015 edition of the FHWA Geotechnical Engineering Circular #7, hollow bar soil nails are specifically addressed and allowed for use in non-corrosive ground conditions.  Consult your Williams’ Technical Representative for more information.


Williams Hollow Injection Bar offer an excellent choice for micropiles in difficult ground conditions where open-hole drilling isn’t possible.  The continuously threaded bar profile lends itself perfectly for restricted headroom applications because the bar can be cut and coupled at any length.  The FHWA has approved hollow bar anchors for permanent use in micropile applications.

Prestressed Ground Anchors

Williams Geo-Drill Injection Anchors can be used as a choice for pre-tensioned anchors in loose or collapsing soils without the need for a casing.  A free length must be installed onto the anchor if the project specifications call for a pretension load to be applied from the bond length.  Please consult with a Williams specialist for suggestions to properly attach a free length sleeve.  Note to Designer:  Consult with Williams for an appropriate level of corrosion protection if prestressed ground anchors are intended to be used for a permanent application.

Tunnel Spiles and Forepoling

The Geo-Drill Injection Anchor System is often used for spiling in NATM tunneling.  Spiles are continuously drilled and grouted pre-support reinforcement to enable the heading of a tunnel to advance without the risk of falling debris.  The anchors can also be used as face stabilization of portals.

Limitations of System

In general, Williams recommends using the Geo-Drill Injection Anchor System in difficult soils that do not allow for open-hole drilling.  Ground conditions featuring large voids or the presence of an artesian water condition are generally not suitable for a drilled and grouted hollow bar.  In hard rock, conventional DTH (Down the Hole Hammers) in open-hole drilling offer a more efficient alternative.  In all such cases, Williams offers solutions in their complete line of solid bar anchor systems and multi-strand tendon systems.

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