Protecting Water Access with Trenchless Technology

As our infrastructure ages and access to water resources grows increasingly uncertain, we need innovative, cost-effective and minimally-disruptive methods to protect our water supplies. Trenchless technology allows us to upgrade aging infrastructure with minimal disruption.

Significant population growth and its concentration in major cities, combined with a better appreciation of environmental issues and protection, demand a better way to provide water and wastewater services. As our infrastructure ages and access to water resources grows increasingly uncertain, we need innovative, cost-effective and minimally-disruptive methods to protect our water supplies.

Water is one of our most important resources, and its transport and access is a major concern in both the developed and developing world. Water is the lifeblood of our cities and communities — but it relies entirely on a well-functioning circulatory system. Water conveyance systems move water and wastewater from points of collection to facilities for treatment, and finally for distribution or disposal. Water supply tunnels, aqueducts, intake and outfall structures, interceptors, trunk and drainage pipelines are major components of water distribution. Pumping stations and facilities for flow control, surge abatement, collection, storage, and disposal are also a necessary part of the system.

However, much of this critical infrastructure is not easily accessible for maintenance or repair. Aging infrastructure has become an increasingly crucial issue, because when this infrastructure is underground and needs to be replaced or rehabilitated, access can be a problem. Often times, in the intervening years since its initial construction, roads, utilities, and other infrastructure have been built above, restricting our options for underground access.

When this occurs, traditional open-cut construction may not be suitable for pipe replacement or rehabilitation for any number of factors:

  • The underground space in the public right-of-way is congested with pipelines and utilities
  • Traffic management in urban areas
  • Street pavement damage and the cost of surface restoration may be prohibitive
  • Located under runways or taxiways which prohibits road closure
  • Direct and indirect business losses
  • Large amounts of soil that could be contaminated

In these cases, trenchless technology is the solution. Trenchless technology minimizes the construction impacts associated with a project, and causes less surface disruption. There are significant benefits to using trenchless technology — and many different methods that can be used.

 

Tunnel Boring Machines (TBM)

One method of trenchless access is by using Tunnel Boring Machines (TBM). TBMs are used to excavate tunnels with minimal disturbance to the surrounding ground. Compared to the cut and cover approach, TBMs significantly reduce the disturbance of traffic and the associated environmental impacts in urban areas. They can be used to tunnel through anything from sand to hard and competent rock.

For deeper, longer tunnels in urban areas, or for a tunnel crossing major bodies of water, a pressurized-face tunnel boring machine is the best fit, because it is capable of handling the full range of expected ground conditions. A single-pass, precast concrete segmental lining forms the tunnel behind the TBM. The selection and design of the precast segmental liner is critical for successful application. The segments are equipped with waterproofing gaskets and act as the structural support system and water barrier.

There are two major TBMs used in soft-ground tunnelling: Earth Pressure Balanced (EPB) and Slurry Type Shield Machines. An EPB TBM will perform better where the ground is silty. A slurry TBM is ideal in loose water-bearing granular materials. However, with the application of appropriate ground conditioning agents, the range of ground conditions for each machine can be extended. TBM technology has advanced significantly in the last 15 years, allowing for the construction of larger, deeper, and longer tunnels in more difficult ground conditions.

This technique has been used in several WSP projects including the Twinning of West Trunk Sewer (Region of Peel) 3.0m & 2.7m diameter and Bathurst Langstaff Trunk Sanitary Sewer (York Region) 2.7m diameter.

img-Twinning of West Trunk Sewer TBM

Twinning of West Trunk Sewer TBM, 3.0m dia.

img-Bathurst Langstaff Segmental lined Sewer

Bathurst Langstaff Segmental lined Sewer 2.7m dia.

Micro-Tunnelling

Micro-tunnelling is a trenchless solution for constructing small diameter tunnels that is particularly useful for projects that require the tunnel to cross under dense traffic roads, railways, or rivers. This method minimizes disruptions on the surface during the tunnel construction, in comparison with the traditional open trench method, and there is no requirement for personnel to be inside the tunnel during construction operations.

This technique installs concrete pipes with a pushing or jacking frame installed in the launching shaft. A Micro-Tunnel Boring Machine (MTBM) is attached to the head of the pipe that follows the path of the tunnel as it is being bored. Micro-tunnelling can be used in varying ground conditions and the cutterhead is designed for the specific ground conditions at the site.

This technique has been used in several WSP projects including the West Don Sanitary Trunk Sewer project (City of Toronto), the Courtice Trunk Sanitary Sewer Phase 2 (Region of Durham), the North Don Sanitary Relief Sewer (York Region), and the Douglas Trunk Sewer (Metro Vancouver).

img-West Don Sanitary Trunk Sewer MTBM

West Don Sanitary Trunk Sewer MTBM

img-Courtice Trunk Sanitary Sewer Phase 2 MTBM

Courtice Trunk Sanitary Sewer Phase 2 MTBM

Trenchless Pipeline Rehabilitation

Trenchless technologies for watermain and sewer rehabilitation typically includes the installation of a manufactured liner pipe within the host main and/or in-situ spray application of a liner material. This can provide a no-dig solution, in which the new liner seals any leaks or flaws in the existing pipeline. The rehabilitation is often done by cured-in- place-pipe (CIPP) lining, slip-lining, swagelining, or carbon fibre reinforced polymer.

In selecting the preferred method for rehabilitation, the following considerations need to be taken into account:

  • Pipe material, internal corrosion and tuberculation, joint failure, and external corrosion
  • Operation factors, including hydraulic conveyance limitations and water quality
  • Condition of the pipeline foundation and depth of the pipeline and water table
  • Hydraulic operating pressure and transient pressure requirements
  • Number and type of fittings, including branch and service line connections, valves, fire hydrants, and repair sleeves
  • Duration and level of service interruptions, and the provision of temporary service
  • Site conditions and factors, including local utilities
  • Traffic conditions

This technique has been used in several WSP projects including the Watermain Rehabilitation Program (City of Toronto), Rehabilitation of High Level Interceptor at King-Strachan Area (City of Toronto), and the West Thornhill Sanitary Sewer and Lateral Relining (City of Markham).

img-Toronto Watermain Rehabilitation Program

Toronto Watermain Rehabilitation Program

img-Rehabilitation of High Level Interceptor

Rehabilitation of High Level Interceptor

Shaft Construction

Generally, shafts are constructed from the ground surface down, using conventional shaft sinking methods. However, in rock tunnelling projects, shafts not used for primary construction access can be constructed using raise boring. In raise boring, a small-diameter pilot hole is drilled from the ground surface to tunnel depth. A reaming bit is then used to excavate the shaft to final dimensions.

A number of methods are used to support shafts excavated in soil during construction. Some forms of support are installed prior to the start of excavation, including steel sheet pile, slurry walls, jet grout walls, secant pile walls, and ground freezing. Other segmental lining support systems are installed concurrently with excavation, including steel liner plate, ductile iron segments, and precast concrete segments.

A hybrid type of excavation support would be soldier piles and lagging. In this method, the soldier piles are installed prior to the start of excavation and then timber or concrete lagging is installed concurrently with excavation. Dewatering is often required when segmental lining or soldier pile and lagging construction is used.

For certain shaft applications, ductile iron segments and precast concrete segments can be used as the final lining. When the other excavation support methods are used, a cast-in- place concrete final lining generally is required. In some cases, a shotcrete (sprayed concrete) lining can be substituted for the cast-in- place concrete lining.

These techniques has been used in several WSP projects including the Twinning of West Trunk Sewer (Region of Peel), West Whitby Trunk Sanitary Sewer (Region of Durham), Bathurst Langstaff Trunk Sanitary Sewer (York Region).

img-West Whitby Trunk Sanitary Sewer

West Whitby Trunk Sanitary Sewer

img-Twinning of West Trunk Sewer

Twinning of West Trunk Sewer

Conclusions

Trenchless technologies are a critical tool for ensuring water access in a future that’s uncertain. They allow for decreased surface disruption and improved installation accuracy — a particularly important factor in heavily-populated urban centres where disruption and traffic congestion have significant impacts. Local businesses, roadways, trains and walkways can generally remain open during trenchless operations. Trenchless technology also allows much shorter rehabilitation time for affected areas. With minimal environmental disruption and impact, trenchless technology can mitigate many of the unintended side-effects as we protect our infrastructure and water supplies from the changes to come.