Peel region’s Water and Wastewater Master Plan identi_ ed the need for a new feedermain in the southern portion of the existing Hanlan Feedermain from the Lakeview Water Treatment Plant (WTP) to Burnhamthorpe Road. The project includes the construction of a new 2,400mm diameter watermain, known as the Hanlan Feedermain (HFM), which will extend 14.5km from the connection point at Britannia Road and Tomken Road to the WTP at Lake Ontario.

Additionally the construction of a new 1,500mm diameter watermain, known as the Mississauga City Centre Watermain (MCC), is proposed to extend from the connection point at Britannia Road and Tomken Road along Tomken Road to Eastgate Parkway and Cawthra Road to its final destination with the existing distribution system located at Cawthra Road and Burnhamthorpe Road East.

Significant public and political consultation was undertaken during the design of the project. As a result a substantial portion of the overall project was selected to be tunnel construction to avoid traffic impacts and reduce the effect on the large business and industrial areas nearby. This was further confirmed by a multitude of existing utilities and transit corridors, which resulted in a deep tunnel alignment with some areas in excess of 50m.

The Britannia Road, Tomken Road and Eastgate Parkway route was selected and construction methods were evaluated to minimise overall construction impacts.

Considering the alignment six shafts were planned for the construction of the tunnelled sections. The shafts are used to launch and or retrieve the TBMs and provide access and space for construction of the tunnels and structures within the shafts, including valve chambers and complex hydro-mechanical systems.

What makes this project particularly challenging is the critical need for precise multitasking across six job sites and tunnel headings, all at different stages of construction. Consider a typical day: two TBMs are mining for breakthrough at one shaft, while preparation work is ongoing at another; there is a piling operation at a third site; while vertical excavation is halfway at a fourth; at the fifth site installation of steel liner and Concrete Pressure Pipe (CPP) has started in one of the completed drives and at the sixth shaft site, pouring the concrete slab and installation of sensitive mechanical systems are also progressing.

Geological Setting
The project is located within the physiographic region known as the Peel Plain. Most of the tableland within the Hanlan Water Project Contract 3 site consists of till, partly modified by the former presence of shallow glacial lakes and post-glacial erosion features, such as local existing streams and rivers.

The existing ground surface slopes downward from north to south between approximate elevations of 174m and 136m. One surface water course is present – the Little Etobicoke Creek located approximately 150m to 350m east of Tomken Road along the tunnelled section on Eastgate Parkway. Much of the surface topography has been modified in the project area due to recent residential, commercial and industrial development including the construction of roads, bridges and highways. The southerly limits of Contract 3 crossed an area of fine, noncohesive glacial till and granular material, which extended to a depth of in excess of 30m.

Tunnelling Operations
Two TBMs are being used to mine the main tunnelling sections for Contract 3. Both have been rebuilt to meet original manufacturer specifications and requirements for the contract.

The MCC boring machine is a 105in diameter TBM modified for rock tunnelling purposes and equipped with variable frequency drive or soft start controllers to minimise starting current surges. The cutting head is a 300hp, electrically-driven, bi-directional cutter head that consists of 23 12in-diameter front loaded roller cutters. There are also 28 spade teeth at the entrance to the cutting head cavity.

This machine is equipped with a unitised conveyor to provide efficient removal of excavated material. The conveyor is driven by a motorised pulley at the end of the conveyor mounted in a shock absorber. Lifetime sealed bearings ensure maximum efficiency and maintenance-free operation. The conveyor is made up of interchangeable sections and is hydraulically retractable from the cutting head opening to permit access to the wheel and face.

The HFM machine is a 128in (3.25m) diameter TBM with an electrically-driven cutting head with six, 100hp motors powered through gear boxes and a bearing/pinion assembly. The head is bidirectional – 0 to 4.6 r.p.m. at full torque of 672,500ft lb (93,000m/kg). The conveyor is driven by an electric motor that drives a separate hydraulic pump. The conveyor has a 24in wide belt and is up to 100ft (30.5m) long depending on the setup of the machine. The speed and direction of the conveyor is controlled by the operator through a hydraulic stick. As the material exits the cutting head it travels through a water curtain that keeps dust down.

Muck generated by the machine is transported out of the cutter head by a screw auger. The screw auger will drop the muck onto a belt conveyor at the machine center. The conveyor then inclines upward and passes over the equipment sleds to discharge the cuttings into muck cars. The muck train consists of four six-cubic yard muck cars and an eight tonne locomotive. Four muck cars will hold excavated material from one mining cycle. While the muck cars in the heading are being filled, another muck train is being unloaded in the shaft area. When the loaded train comes out of the shaft it will pass the other waiting train at the switch allowing the empty train to pass and advance into the heading for the next push, which minimises train delays.

TBM Launching and Receiving
For each section of tunnel the TBM is lowered into the shaft and connected together at the bottom. Once the whole TBM is lowered and assembled, the power is connected and excavation starts. Since the tunnel profile has been lowered into the shale, the TBM launch became less complicated. Once the shaft is excavated to the appropriate depth, the launch pad is installed at the proper line and grade and concreted in place. The launch pad is equipped with a movable thrust block at one end allowing the TBM to thrust forward until it is fully buried in the shale.

As with the launching, punching through into the receiving shaft is straightforward due to the lowering of the tunnel profile. Once the TBMs have holed through at the reception shaft, the individual parts of the machine, such as the cutter head, forward shell, etc., are disassembled. Once they have been detached from each another, they are hoisted by a crane to the site surface. There they will be cleaned and inspected before being shipped to the next location, either another launch site or on completion of mining, back to storage.

Tunnel Support
The design of the temporary tunnel support was based on the GDR. Since the tunnel profile has been lowered and not all boreholes from the GDR reach the new tunnel depth, Southland Technicore Mole Joint Venture (STM JV) started a geotechnical investigation and drilled additional boreholes to assess the unknown geology.

The TBMs have the capability to install rock bolts as the tunnel advances. Rock bolts and mesh are installed through the fingers at the back of the TBM and jacklegs are used to drill the holes.

The trailing gear is attached to hydraulic cylinders at the back of the TBM allowing the trailing gear to remain in place while the mesh is being installed. Where specified, ribs and lagging are installed manually in the tunnel under the tail fingers. The ribs are expanded to the tunnel wall using a jacking cylinder.

Pipe Installation
As specified for the project, CPP is being delivered by trucks and unloaded at designated locations on site. These pipes will be stored and inspected in accordance with contract documents during their temporary storage on the surface to ensure that they are not altered or damaged. At more congested sites, pipes will be unloaded and lowered down the shaft immediately. Once pipes are inspected they are lowered down the shaft by a crane and set carefully on the rail. The pipe carrier then travels through the pipe to the lifting position and prepares it for transport into the tunnel.

The pipe carrier is capable of running on both rail and tunnel invert. Prior to the pipe being transported into the tunnel, the carrier, pipe and portal will be inspected to verify that there are no interfering issues.

Before setting the pipe in place, the bell and spigot end of both pipes are thoroughly inspected, cleaned and lubricated and the pipe is then ready to be installed. Pipe laser is used to check alignment and a grade of pipe installed in a straightaway. The entire liner is temporary secured and all joints are welded and tested as required.

After 1,500mm and 2,400mm CPP pipes are installed in the MCC and HFM tunnels respectively, temporary bulkheads are installed at the ends of the liner and the entire liner annulus is grouted. A 3in pipe is used to pump the grout and grouting is completed in one lift. The annulus grout mix is produced at the batch plant comprising of 1,200kg/m3 cementitious and 625kg/m3 of water. Materials are batched and mixed before the transfer to the grout container. A generator provides the foam, which is added to the cement slurry before pumped into the tunnels.

Horizontal Directional Drilling
As part of the contract enabling works, STM JV had to install two temporary, thermally-fused High Density Polyethylene (HDPE) water discharge lines (installed within a single bore) between the Shaft S1 site compound located at the southwest corner of Tomken Road and Eastgate Parkway and an existing sanitary line approximately 400m to the east. The method of installation for the water discharge lines was done by horizontal directional drilling with a single drilling fluid supported bore followed by installation of two HDPE casings and finally the installation of HDPE water discharge conduit within each casing.

Open cut excavation
At the south section of the project, an open cut method has been chosen for construction of the watermain tunnels. A trench box with steel plates or hydraulic shoring is used to excavate the soil to the specific plan elevation. Polyethylene compressible foam boards are placed and supported in trenches located within the shale zone to avoid movement during placement of bedding and unshrinkable fill. Groundwater, if encountered, is removed by submersible pump and treated in accordance with an environmental management and water treatment plan. The open cut operation has a sensitive and complex traffic management plan that is updated frequently. The key to safe and successful production is close and effective communication with Region of Peel, residents and local businesses.

Instrumentation and Monitoring Due to environmentally sensitive nature of the project and six operating sites in close vicinity of residential areas, a strict and thorough instrumentation and monitoring plan was developed to ensure public safety and convenience. In addition there are tunnels under Highway 401, the largest highway in the country, and there are 10 post tensioned bridges adjacent to the highway 401/410 interchange along Tomken Road. As a result any ground movement needs to be closely checked and scrutinised. The Region employed several methods to track movement including real-time micro-strain gauges on all bridge structures.

The geotechnical monitoring comprises surface monitoring points along the tunnel alignment, inclinometers around each of the six shafts, and tunnel convergence points to measure any deformation in the tunnel. Monitoring points within 100m radius of the TBMs are being read daily and will continue on with reduced frequency until end of the project. This data is uploaded to an online system that visualises it and gives notifications if review or alert levels are reached.

Monitoring systems for bridges
STM JV employed experts to monitor the instantaneous and cumulative strain of the precast pre-stressed concrete beams of the Bus Rapid Transit (BRT) overpass at Tomken Road using the OSMOS monitoring system. The purpose of monitoring is to confirm that no damaging permanent movement occurs during the project. As required by contract, four fiber optic strain gauges were installed horizontally on three beams of the BRT overpass structure. In addition an OSMOS monitoring cabinet complete with one signal processing and communication unit, one data acquisition unit, one 3G broadcast modem and one temperature probe was installed on the west support of the structure.

Environmental measures
STM JV has also implemented a 24/7 in-house monitoring system for noise and vibration at all sites. Information extracted from these systems will ensure a minimal effect on public due to construction. For dewatering tunnels and shafts a range of pre-treatment and monitoring systems have been employed to prepare the water for discharge to the sanitary sewer system according to Region’s sanitary wastewater bylaw requirements.

STM JV uses a pre-treatment system with a two-stage process. The first stage includes a tank that distributes the water over flocculation blocks into a sedimentation tank. The flocculation process charges the suspended particles causing them to coagulate and eventually settle to the bottom of the tank. The second stage includes the water draining into sand filters to further remove particles.

The water is then discharged into the local sanitary system. Carbon filters and or absorbent pads are used to address hydrocarbons levels.

Current Status
Mining of both tunnels was completed in mid-May for north sections beneath Highway 401 (Shaft S5 to S7). Tunnelling was also finished for a shorter section between S8 and S7. At the time of writing this article, the smaller TBM (105in) has been launched at Shaft S1 to excavate the 3.1km MCC drive from Eastgate Parkway to S5 at the 401 highway. The larger TBM (130 in) is being refurbished and will be launched shortly to bore the parallel HFM tunnel.

Excavation of four of the six shafts is now completed with piling and excavation operations going forward for the two remaining shafts.