The Credit Valley Trunk Sewer Sanitary Sewer extends from Highway 401 in Mississauga, Ontario to Queen Street in Brampton, Ontario. The tunnel is 3,100 meters (10,168 feet) long and follows existing road allowances and easements through a mixture of residential, commercial and industrial areas. The tunnel depth ranged from approximately 10 meters (33 feet) to 20 meters (66 feet) and was completed through a variety of soil and groundwater conditions.
A particularly sensitive area included a section of tunnel alignment that passed directly beneath residential homes and two schools. In this area the geology changed from shale bedrock to an unstable sand/silt/clay layer. Prior to proceeding through this section, the Project Stakeholders agreed that precautionary ground improvement treatment should be conducted to protect the existing homes.
Advanced Construction Techniques (ACT) was contracted to install a permeation and compensation grouting system across the entire right of way, and to perform settlement monitoring along the tunnel alignment in the influenced area. The grouting system consisted of a double-line, or two parallel rows of injection grout pipes, which were installed using an overburden rotary drilling rig. Tube-a-Manchettes (TAM) or sleeve port grout pipes were installed in the holes in order to inject grout as the tunnel advanced.
ACT installed ten multi-point borehole extensometers (MPBX) along the center of the tunnel alignment in order to monitor ground settlement. The MPBXs were automated in order to deliver real-time data to ACT’s IntelliGrout® monitoring station. Monitoring both the grouting operation and ground movements allowed adjustments to the grouting program to place in real-time.