Trenchless Tunnelling Technology

Aging infrastructure has become an increasingly crucial issue for both developed and developing countries. When this infrastructure is underground and needs to be replaced or rehabilitated, however, access can be a problem: in the intervening years since initial construction, roads, utilities, and other infrastructure have been built above, restricting our options. 

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

• Under runways or taxiways which prohibits their closures

• Direct and indirect business losses

• Large amounts of spoil that could be contaminated

In these cases, trenchless technology is the solution.

Putting Our Experience to Work for You

WSP has a long track record of successful work with trenchless methods, and we have developed expertise and advanced the state of the art with various trenchless technologies. Using these techniques, we can assess, rehabilitate, or install underground infrastructure with little to no excavation, minimizing the disruption and environmental impact of the project, and reducing the impact on adjoining buildings, structures, utilities, and the public.

Some of our main areas of expertise include:

• Condition assessment of existing pipes and utilities

• Feasibility, conceptual, and preliminary studies

• Design, specifications, and contract administration for trenchless projects

• Design, specifications, and contract administration for pipeline rehabilitation projects

In the United Kingdom, we used HDD to construct the 132kV New Cross to Finsbury Market Cable Tunnel. The project was 6km long, between 20m and 30m below the surface, and bored through London’s basin geology.

The tools used to assess the condition of underground infrastructure, such as underground water or sewer networks include destructive and non-destructive methods, such as acoustic leak detection, closed circuit television (CCTV) for visual inspection, and electromagnetic inspection for wall thickness measurement.

We qualify which method is the best fit for a specific project by reviewing the data collected from the condition assessment and recommend a plan of action that maximizes rehabilitation of the pipeline in question, taking into consideration time lines, budget, and our findings.

Feasibility and Conceptual Studies

WSP conducts feasibility studies, as well as design and specifications for various trenchless technologies, including:

• Microtunelling

• Horizontal directional drilling (HDD)

• Pipe ramming

• Cured-in- place-pipe (CIPP) lining

• Slip-lining

• Swage-lining

• Carbon fibre reinforced polymer

• Pipe bursting

• Spray-on liners

This has led to several new technologies for new pipes to be installed, or for existing pipes to be rehabilitated using trenchless technologies.

Micro-Tunnelling

Micro-Tunnelling is a trenchless solution for constructing small diameter tunnels that is used especially 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 traditional open trench method, and there is no requirement for personnel to be inside the tunnel during construction operations.

This technique installs concrete pipes, by 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. Microtunelling can be used in varying ground conditions and the cutterhead is designed for the specific ground conditions at the site.

Horizontal directional drilling (HDD) is a trenchless construction method for installing subsurface piping or conduits by using a surface mounted rig, first to drill a guided hole along a bore path consisting of a shallow arc and then to pull a string of pipe into the hole. In the United Kingdom, we were commissioned to provide geotechnical services for the undergrounding of 33kV overhead lines using HDD techniques under the M4, Junction 19 (with M32) Motorway.

Trenchless Rehabilitation of Pipelines

Trenchless technologies for water main 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.

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

• 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

The rehabilitation is often done by cured-in- place-pipe (CIPP) lining, slip-lining, swage-lining, or carbon fibre reinforced polymer.