Highway 50 Sanitary Trunk Sewer
Role: General Contractor
Project Delivery: Design-Bid-Build
Tunnel Equipment: 1.8m EPB MTBM
Primary Support: Microtunnelling Pipe
Ground Conditions: Soft, wet & mixed face, with cobbles and & boulders
The sanitary trunk sewer was installed in variable soft ground and mixed face conditions under significant groundwater pressures and with high content of cobbles and boulders.
Technicore designed and manufactured a unique EPB MTBM with pipe jacking capabilities in order to provide continuous support to the tunnel face while maintaining provisions for access to the cutter head from inside the tunnel if required for maintenance, cutter replacement, or emergency repairs. Technicore elected to use the EPB method, in lieu of a slurry spoil removal system, to allow for pressures to be controlled without affecting the rate and efficiency of soil removal from the cutting chamber. The TBM was equipped with a sealed variable speed auger which could control the rate of spoil removal and aid in maintaining target face pressures. The design of the EPB TBM allowed for use in low cover applications or projects where frac-outs are of concern. The ability to change between EPB and open face excavation mode, combined with the cutter head design and tooling, provided the TBM with additional capabilities to tunnel under nearly all soils conditions which can be encountered in the local geology. This is an additional advantage which could prove extremely valuable to the Project and Client in the event that unforeseen ground conditions were encountered and can be offered at no additional premium as compared to some other risk aversion methods.
Owner: Regional Municipality of Peel
Drive Length: 1500 meters
Consultants: Hatch Mott MacDonald
Contract Amount: $12,365,752
The subsurface conditions along the tunnel alignment generally consisted of a thin layer of fill overlying a layer of plastic till which in turn overlies a thicker layer of non-plastic till. Pockets of silt and sand were encountered in many locations along the alignment. Nearing the end of the tunnel, a layer of silty clay was found within the non-plastic till layer.
The tunnel excavation also encountered significant amounts of water bearing sand, cobbles, and several large boulders.