For the majority of the expanded Trans Mountain pipeline route, an open-cut construction method is being used, which involves the pipe being set down into a trench and buried.

But sometimes, digging a trench isn’t an option.

The focus on environmental protection and minimizing impacts has led to innovation and advances in pipeline construction techniques such as trenchless crossings, which involve drilling or tunnelling underground to install the pipe.

Trenchless methods are a key tool in the construction of major pipeline projects and allow us to safely cross underneath watercourse crossings, environmentally sensitive areas, archaeological sites, railways, highways, major roads and in places with restricted workspace, such as in some urban areas. They minimize or eliminate ground disturbance and greatly mitigate impact to normal daily activities and traffic circulation patterns.

Crews will conduct close to 75 major trenchless crossings and more than 400 minor trenchless crossings along the new pipeline route, which spans from Edmonton, AB to Burnaby, BC. Several different trenchless methods are being employed with the selected methodology based on geotechnical conditions, topography, available working space and length of the crossing.

Here’s a look at five trenchless techniques being used on the Expansion Project:

Major Trenchless Crossings

Horizontal Directional Drilling (HDD)

HDD is a trenchless methodology widely used to install pipelines, often under rivers, roadways or other surface features. This technique involves the setup of an HDD drill rig on one side of the crossing, completing a pilot hole and then successively enlarging the borehole utilizing reamers. The pipe is assembled and welded on the opposite side to the drill setup, and once the final borehole diameter is achieved, the product pipe is connected to the drill string and pulled into the borehole.

Microtunnelling (MT)

Microtunnelling is a technically advanced crossing technology that uses hydraulic jacks and a tunnel boring machine to push concrete casing segments through the soil. The pipeline is then safely pulled through the tunnel created by the concrete casing.

DirectPipe® Installation (DPI)

DPI is a hybrid of HDD and microtunnelling and combines the advantages of these technologies by utilizing a directionally steered microtunnel boring machine (MTBM) affixed to the lead edge of the product pipe or casing. This technique involves setup of a pipe thruster on the launch side of the crossing, which pushes the pipe and MTBM combination along a predetermined curved tunnel alignment. The pipe section is typically welded entirely beforehand, or split into long segments, depending on available workspace. Once complete, the MTBM is disconnected and the internal slurry and control equipment is removed, leaving the product pipe or casing in place.

Minor Trenchless Crossings

Horizontal Directional Bore (HDB)

Similarl to HDD, this method is typically used to drill under smaller obstacles, such as utility or surface infrastructure. It utilizes a small-to-medium size HDD rig, and the length of the bore usually ranges between 20 metres and 250 metres. This technique is similar to an HDD, in that there is a pilot hole and subsequent reaming passes prior to pulling the pipe. The product pipe is pulled between two excavated bell holes. The alignment of an HDB typically does not introduce a bend in the drill profile.

Auger Boring

One of the oldest forms of trenchless technology, auguer boring is predominantly used for crossing railways or areas without enough room for an HDD rig to set up.

This is a trenchless method where rotating auger flights within a steel casing are used to transport excavated material back to a jacking shaft for removal. Cutters at the leading edge of the auger flights can be matched for soil or rock conditions. Hydraulic jacks or track system located within the jacking pit/shaft are used to propel the augers and jacking pipe forward. While the cutting head excavates the hole, the pipe is pushed into the bore simultaneously.