Guided boring systems have been used in North America since the late 1990s, and since then the pace for innovation, particularly in the upsizing tooling arena, has varied this application significantly and increased expectations of the average length of sewer, water and utility installations in harder geology. Initial guided boring capabilities were limited to up to a 12in (305mm) diameter final product pipe, but today’s technology is suitable for up to 48in (1.2m) and even larger when pilot tube systems are used for guided auger boring.

Compared to open-cut, a guided auger boring pipeline installation is desirable to project owners because of minimised construction impacts, a safer less disruptive construction environment for the public, and its ability to circumvent existing subsurface infrastructure and surface structures.

Trenchless contractors like using guided boring because of the system’s versatility for a range of pipe lengths and diameters, in varying geology at great depths. Additional benefits to the contractor include a quick set-up time, and ease of use with minimal crew training which can result in reduced operating costs and quick production rates.

Guided boring guidance systems utilise a digital monitor with affixed theodolite and LED-illuminated target to view the target in the lead pilot tube at great distances. With some guidance systems, alignment line and grade can be maintained to within a quarter of an inch (6.35mm) at distances up to 400ft (122m). Given ideal conditions, distances of well over 500ft (152m) are regularly achieved with the same level of accuracy to reduce project risk.

This paper will address guided auger boring, guided auger boring in non-displaceable geology as well as hybrid pilot tube methods including guided pipe ramming, guided pipe roofing and provide recent case studies of each method.

Description pilot tube installation

The first step for any pilot tube application is set up of the jacking frame and guidance system per the project specifications. First pilot tubes are installed to achieve accurate line and grade.

The lead pilot tube adapter features an affixed steering head or drill head to establish the bore path, selected by its compatibility with the project’s ground conditions to displace soil with an N-value of 50 or less. Visibility of the guidance system’s target is maintained through the hollow inner tube.

The theodolite with a camera on the telescope is positioned between the jacking frame cylinders to site- down the center of the pilot tubes, and the theodolite’s cross hairs are set to the drive’s line and grade. The guidance system monitor is mounted on the jacking frame for constant real-time assessment throughout the bore.

After the steering head and adapter are launched, pilot tube installation commences. As the operator advances each length of pilot tube, a new one is threaded onto the former and pushed forward by the jacking frame’s hydraulic cylinders. Some pilot tubes designs allow for lubrication on the exterior by flow through the pilot tube string to the steering head port.

While pilot tube advancement takes place, the operator assesses the target’s position on the monitor to keep the pilot tube string on line and grade. If a steering correction is necessary, the operator turns the pilot tube string in the appropriate direction. The forward advancement from the jacking frame gear box and rotation of the angled steering head displaces the ground until the correct alignment is achieved. While this sequence unfolds, operators make notes of changes in jacking forces to prepare for what to expect during casing installation.

Pilot tube installation is complete when the steering head reaches the reception shaft.

Description of guided Auger Boring method

Guided auger boring is the method of accurately installing pipelines using a guided boring system for the pilot tube installation and the final steel casing pipe installation is completed with conventional auger boring techniques.

To install pilot tubes, the jacking frame is placed at the front most position on the auger bore track using a frame adapter closest to the shaft wall bore entrance point, and the appropriate centerline and survey grade. The theodolite and camera are positioned in a manner to protect them from the effects of movement or vibration from the jacking frame or other nearby equipment or personnel, using a mounting stand to suspend the assembly between the jacking frames’ thrust cylinders (see Figure 1). The auger boring machine is secured on the track directly behind the jacking frame and serves as a backstop when the other unit is installing pilot tubes. Pilot tube installation commences as described previously.

With an established bore path for subsequent upsizing tooling, pipe is installed with the auger boring machine. A pilot tube adapter and increase tooling are directly connected to the last pilot tube to increase the diameter of the bore to match the steel casing diameter. The guidance system and jacking frame are then removed from the launch shaft and the auger boring machine is repositioned on the track to accommodate the steel casing and tooling lengths.

In soft, non-compacted ground, where casing can be easily advanced with the thrust of the auger boring machine, a reaming head in one or two stages is used to increase the steel casing diameter (see Figure 2). Reaming heads are welded between the last pilot tube and first casing. The arms are flush with the inside diameter of the steel casing to allow for correct positioning of the cutter bit and augers for soil removal from the pipeline. Reaming head arms cut the soil into chunks, which allows it to be enveloped into the casings for removal with the augers while concurrently transferring thrust from the casing to the smaller diameter pilot tube.

Guided Auger Boring case study

Ivy Testing Service completed a series of 30 gravity sewer bores for a total of 4,959ft (1,512m) with the guided auger boring method and reaming heads for six diameters of steel casing ranging from 16-42in (400-1,070mm) for the City of Shreveport, Louisiana. The Hearne Avenue and Hollywood Boulevard Trunk Main Project required the installation of the infrastructure in an obstacle-laden region of the city under several highways and roadways, making line and grade accuracy a necessity and open cut installations unfeasible. The bores ranged from 70-465ft (21-142m) in length in sandy clay and sandstone geology.

Guided Auger Boring in Non-Displaceable Geology

New tooling innovation has made it possible to tackle projects in non-displaceable geological profiles up to 12ksi unconfined compressive strength (UCS). Referred to as pilot tube rock drilling, the method has achieved success in rock conditions using a specialty adapter and commercially available drill bits for densely compacted soils and soft rock.

This method is similar to a standard pilot tube installation, but a drill bit is used instead of a steering head, a specialty adapter houses the guidance system’s target (see Figure 3) and steering control is managed with much lower thrust pressures.

The first pilot tube rock drilling project took place in September 2015 on a guided auger boring project in Darwin, Australia for an 83ft (25m) bore. Since then thousands of feet have been achieved. The longest installation to date is 400ft (122m) on a project in Bakersfield, California.

Urban Contractors switched to pilot tube rock drilling after the pilot tube string became unmovable at 60ft (18m) into a 180ft (55m) run in red shale ground conditions. The Utility Extension Project took place on a college campus in Stillwater, Oklahoma and required the installation of parallel chilled water lines, just below sanitary sewer lines and perpendicular to concrete electrical duct banks with one foot of clearance. Avoidance of these utilities and minimal disruption during campus activities were important factors. The contractor completed a second installation of equal length and both resulted within a quarter of an inch of the target and were finished with 12in (300mm) steel casing in September 2017.

Ingenieria En Tuneles Y Redes S.A. DE C.V. used pilot tube rock drilling to install 197ft (60m) of 36in steel casing under a taxiway at the Monterrey International Airport in Monterrey, Nuevo Leon, Mexico. Project challenges included ground conditions containing weathered rock, minimal cover above the alignment and construction below an active taxiway. The alignment was completed using a combined swivel and cutter head assembly.

Swivels are also available on the non-displaceable tooling market and are used between the pilot tube adapter and cutter bit to reduce rotational forces on the auger string and prevent rotation of the pilot tubes while the cutter bit excavates for the final diameter pipe. Certain swivels designed with a cutter assembly can withstand high levels of continuous thrust to excavate difficult and non- displaceable ground conditions.

Hybrid methods of Guided Boring

Contractor ingenuity has brought several unique guided auger boring methods including guided pipe ramming and guided pipe roofing installations.

Guided pipe ramming

Guided pipe ramming was first conducted by Claude H. Nix Construction in 2006 to rescue an auger bore project in Farmington, Utah, installing a 24in (600mm) irrigation line and 36in (900mm) storm drain in 200ft (61m) runs under several rail lines (TT Technologies 2007). The method has since become a standard service offering for several contractors for up to 144in (3.7m) steel casing installations and is ideal for railway and highway crossing and culvert installations in difficult ground conditions. Guided pipe ramming uses pilot tube technology to establish line and grade which are followed by a pneumatic pipe hammer powered by an air compressor which is attached to the rear of the steel casing pipe. The hammer transfers force to the open-ended pipe to advance it with repeated blows. Contractors like this method because it can be an economical application, and the pneumatic hammer ensures ground control at the face of the excavation because advancement happens so quickly, the potential for settlement is minimal.

Claude H. Nix Construction completed a guided pipe ramming project for the Utah Transit Authority to install a 20in (500mm) gravity sewer and 30in (760mm) storm drain in a densely populated private development in Draper, Utah. The new utilities ran under active commuter train tracks, within a few inches of the fiber optic network of utilities that control the train’s signals. The project required construction ordinances for a four-hour per day window and a total of 20 hours allotted for completion.

The two 80ft (24m) alignments were simultaneously installed, on line and grade to successfully meet all project restrictions.

Guided pipe roofing

The Guided Pipe Roofing or sometimes called Piped Canopies method is used for short , culverts or crossing for extra reinforcement in heavily traversed regions for stress distribution and to mitigate ground settlement. Interconnected lengths of steel casing provide an arch above a support structure, culvert or tunnel. Pilot tubes are first successively installed to form the arch on line and grade. The guided boring jacking frame is positioned on an adjustable platform to relocate the point of entry for each pilot tube pass. Sometimes the pilot tubes complete a full pass or they can be are pulled back. The passes are usually finished with steel casing that remains in place, the casing arch is filled with concrete and rebar and soil improvement is inserted around the outside of the structure. The steel casing installation is completed by an auger boring machine or a guided boring system dependent on the pipe diameter and ground conditions.

Tunnelling Solutions of Melbourne, Australia recently incorporated the piped canopy approach into their service portfolio. Their solution includes using a guided boring jacking frame on a custom adjustable platform and have installed 20ft (6m) length, 12.75in (350mm) diameter steel casing canopy tubes totalling 45 pilot tube to canopy pipe bores with an average 131ft (40m) length in up to 50MPa and sticky ground conditions.

This method was successfully used on three projects in Sydney; the Castle Hill Pedestrian Underpass for the Northwest Rapid Transit Infrastructure Joint Venture (NRTIJV), the Norwest Pedestrian Underpass for the NRTIJV and the Darebin Rail Underpass for the North Eastern Program Alliance.


Guided boring technology has positively changed the small diameter trenchless market, allowing contractors to bid new projects and enter the trenchless realm. The guided boring equipment sector has seen some of the most significant developments of any trenchless market in a short period of time. Contractors, engineers and municipalities can expect that future guided boring innovation will continue to increase length of bores and expand the range of tooling for even harder rock and larger diameters.