Canadian Consulting Engineer
Gloucester Street Water Main Sliplining, OttawaEngineering
Robinson Consultants Inc.Category: Water Resources and SupplyIn 1997, the Region of Ottawa-Carleton decided that the existing water main in Gloucester Street in downtown Ottawa needed to be rehabilita...
Robinson Consultants Inc.
Category: Water Resources and Supply
In 1997, the Region of Ottawa-Carleton decided that the existing water main in Gloucester Street in downtown Ottawa needed to be rehabilitated. Constructed of cast iron in the First World War, the pipe is a critical link in the water distribution system of the city core. Within its pressure district are Parliament Hill, National Defence Headquarters and many corporate offices.
The 1.3 kilometre water main measuring 914 mm (360) in diameter was in poor structural condition and had failed twice in the last two decades. Investigations concluded that areas of the pipe wall had corroded to around one-third of their original thickness. The pipe also contained casting flaws.
Rehabilitating the water main posed many logistical challenges. It is below a road surface that is in good condition, and it crosses every major north-south arterial road into the city core. As well, a series of other large construction projects were taking place in the area as part of an infrastructure renewal program called “Restore the Core.” A method of rehabilitating the watermain had to be developed that would ensure the main gives reliable service over a reasonable design life, but could be done with minimum disruption to the road surface and traffic movement.
Robinson Consultants of Kanata, Ontario in association with Trenchless Design Engineering were retained to study the most appropriate trenchless method for rehabilitating the pipe. Several techniques were considered, taking into account factors such as life expectancy, reliability, operations, maintenance and capital costs. The researchers looked at various lining techniques as well as pipe bursting.
The method selected was sliplining using an 840-mm (330) (OD) DR 17 High Density Polyethylene Pipe (HDPE) liner inside the original 914-mm diameter cast iron pipe. The diameter gave sufficient annular space between the liner and the host pipe to ensure that the contractor could successfully pull the liner through and complete the grouting. Studies by the National Research Council’s Institute for Research in Construction with support from Robinson had recommended that the annular space should be grouted. IRC research had also investigated the thermal and mechanical interaction of the various materials. The institute will be monitoring the pipe’s actual performance for three years, providing the first research of this type in cold weather climates.
A closed circuit television (CCTV) inspection of the pipe interior had shown that sliplining around the bends was not possible, so the project team decided that construction at the bends should be by open cut methods using reinforced concrete pressure pipe. Connections between the HDPE and concrete pipe were complex. Special Aqua Grip fittings were imported from England that allowed flanged connections to be made to the concrete pressure pipe fittings in areas where a fusion welding machine could not be inserted into the excavations.
In calculating the inserted pipe lengths and the location of insertion and receiving pits, the engineers and contractor tried to minimize disruption to the roadway, and take into account the stresses and pulling forces on the pipe. The final operation involved six pulls with pipe sections ranging in length from 130 metres to 270 metres.
Robinson provided contract administration and technical support throughout construction, which took place between March and July 1999. Using open trench techniques to do such a project would take approximately two years due to having to relocate utilities and repair road surfaces.
The Region of Ottawa-Carleton’s budget including all capital costs, engineering and internal charges was $2.5 million. The capital cost is estimated to be $1 million less than with conventional techniques.CCE
Project name: Gloucester Street Feedermain Sliplining
Award winner: Robinson Consultants, Kanata, Ontario.
Project team: Derek Potvin, P.Eng., Hugh MacDonald, Andy Robinson, P.Eng.,
Client/owner: Region of Ottawa-Carleton, Mike Willmets, Dave McCartney, P.Eng., Jim Miller, P.Eng.,
Other key players: Trenchless Design Engineering Ltd./Ian Doherty, P.Eng.(trenchless consultant), Dufferin Construction Company (contractor), National Research Council/Institute for Research in Construction.
Gloucester Street Watermain