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

Along most of the right-of-way, the pipe will be set down into a trench and buried.

However, at about 50 locations, trenchless (underground) crossing technologies such as horizontal directional drilling (HDD), microtunneling, augur boring and Direct Pipe are required as alternatives to an open-cut trench.

Trenchless methods allow for underground crossings that minimize disturbance to highways, railways, major rivers and other watercourses, sensitive environmental areas and urban areas.

Each trenchless method has individual advantages, depending on factors such as soil condition and length of crossing. TMEP has carried out engineering feasibility assessments to determine the most suitable trenchless crossing techniques based on subsurface conditions at each specific location.

For example, TMEP is employing trenchless methods for eight Lower Mainland crossings of proposed or final critical habitat for Nooksack Dace and Salish Sucker in order to minimize construction impacts.

Other considerations for trenchless crossing include:

  • Watercourses that have high fish and fish habitat sensitivity and too much water flow to allow a temporary diversion supporting conventional open-cut construction
  • Wide, deep rivers with very high flow such as the Fraser River near the Port Mann Bridge
  • Urban areas where surface construction would be difficult and would create significant impacts for homeowners, businesses and traffic
  • Railway and highway locations intersected by the TMEP right-of-way
  • Underground utility infrastructure
  • Boring under both a dike and adjacent large river such as the Fraser

In addition to trenchless crossings, Trans Mountain is building an underground tunnel to connect Burnaby Terminal and Westridge Marine Terminal, avoiding impact on residents and infrastructure. For this project, TMEP is using a tunnel-boring machine to construct a 2.6-km tunnel through Burnaby Mountain.

The new tunnel, at least four metres in diameter, will be large enough to contain three delivery pipes for Westridge. This is the only location along the right-of-way where this method will be used.