In March 2015, Ward and Burke Microtunnelling Ltd (WBML) were awarded a contract to construct 5 No. concrete caissons and 740m of 1500mm OD microtunnel for the relocation of the West Don Sanitary Sewer. The microtunnels were constructed in extremely challenging soils ranging from dense boulder infested glacial tills to saturated sands and silts. Three microtunnels were driven from a centrally located shaft, which was 22m deep. The microtunnels ranged in length from 125m to 352m long. The longest microtunnel, 352m featured a 250m radius horizontal curve, making it the tightest 1200mm curved microtunnel ever constructed in North America.

Upon completion of the microtunnels:

  • WBML successfully carried out four live sewer tie-ins.
  • A combination of over-pumping and the use of pipe flumes, resulted in zero disruption to the sewer network during each of the tie-ins.