The Trans Mountain Expansion Project includes 980 kilometres of new pipeline and travels across an exceptional variety of terrain.

For the majority of the pipeline route, conventional construction will be used. This is often referred to as open-cut construction and is the style most people think of when they imagine pipeline installation. This method involves the pipe being set down into a trench and buried.

The focus on environmental protection has led to innovation and advances in pipeline construction techniques such as trenchless crossings. Trenchless methods are a key tool in the construction of major pipeline projects in urban and environmentally sensitive areas. They greatly mitigate impact to normal daily activities and traffic circulation patterns, and minimize or eliminate ground disturbance.

Trenchless construction allows us to safely cross underneath watercourse crossings, railways, highways, major roads, sensitive environmental areas, and in places with restricted workspace, such as in some urban areas. Several different trenchless methods can be employed with the selected methodology based on geotechnical conditions, topography, available working space and length of the crossing.

Trans Mountain has approximately 40 major trenchless crossings planned for the Expansion Project, with the majority being horizontal directional drilling (HDD). These major crossings range between 400 metres and 1,600 metres in length and are located throughout the route of the pipeline. We have carried out engineering feasibility assessments to determine the most suitable trenchless crossing techniques based on subsurface conditions at each specific location.

HDD and DirectPipe® (DP) crossing methods are used to construct pipelines under rivers and other environmentally sensitive areas, such as wetlands and ravines, as well as major transportation corridors, such as railways and highways, to minimize or avoid environmental and socio-economical impacts associated with open-cut construction. The HDD technique involves setting up a drill rig on one side of the crossing. Following the drilling of a pilot bore, the borehole diameter is enlarged using a series of consecutively larger reams. Next, the pipe is assembled and welded on the opposite side of the crossing, with the pipe string connected to the drill assembly and pulled back through the drill path to the HDD rig. 

Several of the crossings will be completed using the DirectPipe® (directional microtunnelling) trenchless crossing method. This is relatively recent addition to the trenchless industry and is a hybrid of HDD and microtunnelling, combining the advantages from these trenchless technologies to create another unique trenchless alternative.  

The prefabricated/welded pipeline is laid out on the surface and placed on rollers. A microtunnel boring machine (MTBM) is mounted on the surface or in a shallow launch pit in front of the pipeline and is welded on.

A pipe thruster, located at the launch area, clamps to the outside of the pipeline and pushes the pipe column and MTBM machine into the ground, while simultaneously excavating the soil/bedrock by slowly rotating the cutterhead at the face of the MTBM machine.

In addition to the major trenchless crossings to be completed using HDD and DP, we are planning several hundred shorter trenchless crossings that use many construction methods to minimize and mitigate potential impacts of construction activities on the natural and urban environments traversed by the pipeline alignment.