WCW Conference & Trade Show Calgary September 21 – 24 2010
UTILIDOR REPLACEMENT IN INUVIK, NWT Ken Johnson, AECOM
ABSTRACT The Town of Inuvik is Canada’s largest community north of the Arctic Circle, and has a unique history as the first completely "engineered" northern community. According to some, there has never been a Canadian town so “pondered, proposed, projected, planned, prepared and plotted” as East-3, which was its original site identification back in the 1950’s. The notable aspects of Inuvik’s townsite that continue to challenge engineers include long, very cold winters, permafrost, and great distance from sources of supply. The built environment of Inuvik must cope with the permafrost, and the extreme cold for buildings, water, sewer, roads and drainage; each of these elements requires unique design and construction considerations. The water and sewer mains that service each building are aligned along the back of each lot; the cost of these services is about $50,000 per lot or about $5,000 per metre. The service connections exit above ground from each building and resemble a large “metal centipede” as they connect to the water and sewer mains. Much of the water and sewer infrastructure is now almost 50 years old, and is at the end of its design life. A program to replace the water and sewer has been ongoing for the past 15 years, and will continue for many years into the future. BACKGROUND The Town of Inuvik is Canada’s largest community north of the Arctic Circle, (68° 22' N latitude, and 133° 44' W longitude) and has a unique history as the first completely "engineered" northern community. According to some, there has never been a Canadian town so “pondered, proposed, projected, planned, prepared and plotted” as East-3, which was its original site identification back in the 1950’s. Inuvik was planned and engineered by the Canadian government in the late 1950’s to replace the flood-prone Aklavik, 50 kilometres to the west, as the region’s administrative centre. Canadian Prime Minister John G. Diefenbaker dedicated Inuvik as "The first community north of the Arctic Circle built to provide the facilities of a southern Canadian town. It was designed not only as a base for development and administration, but as a centre to bring education, medical care and new opportunity to the people of the western Arctic." The site for Inuvik was chosen for its elevation above the Mackenzie River flood zone, abundant gravel deposits, ample space for an airport, freshwater lakes and navigable waters. The community sits on a broad terrace between the East Channel of the
WCW Conference & Trade Show Calgary September 21 – 24 2010
Mackenzie River, and the upland that forms the present-day Mackenzie Delta’s eastern boundary. The Mackenzie Delta is the largest delta in Canada; it is 210 kilometres long and an average width of 62 kilometres, occupying 13,000 square kilometres. The July mean high and low temperatures in Inuvik are 19.7°C and 8.2°C. The January mean high and low temperatures are -26.1°C and -35.7°C. The average yearly temperature is -9.6°C. The total yearly precipitation average is 276 mm with 110 mm of this occurring as rainfall. Inuvik originally developed with a reasonably compact and efficient downtown business core just east of the East Channel. Primary and secondary schools were located on large blocks of land between the downtown core and surrounding residential areas. A large regional hospital was sited at the south end of the townsite. The residential areas radiate outward from the central core area, and there is a considerable amount of undeveloped space between the current margins of developed residential districts and the perimeter collector road. Inuvik acts as its own developer of serviced land for townsite expansion, undertaking both financing and administrative work itself in order to supply serviced lots at the lowest cost reasonably achievable. Inuvik grew steadily in the period of 1961 to 1986, from 1,200 people to 3,570 people. The population increased significantly in the mid-seventies along with the gas and oil exploration at the time. When the exploration activity declined in the late seventies, the population also declined a bit from about 3,100 people to 2,900 people. In the period of 1986 to 2004, the population of Inuvik dipped to around 3,400, with minor fluctuations until returning to the 1986 population of near 3,600.
Figure 1: Original Metal Box Utilidor System in Inuvik
WCW Conference & Trade Show Calgary September 21 – 24 2010
The original water and sewer servicing scheme used an above ground metal “box” or “utilidor” which housed water, sewer and a high temperature hot water heating system. The utilidor was supported on timber piles. THE ENGINEERING AND DEVELOPMENT CHALLENGES The notable aspects of Inuvik’s townsite that continue to challenge engineers include long, very cold winters, permafrost, and great distance from sources of supply. Inuvik depends on southern sources for materials of all sorts, with the exception of drinking water. The built environment of Inuvik must cope with the permafrost, and the extreme cold for buildings, water, sewer, roads and drainage; each of these elements requires unique design and construction considerations. The problem with permafrost is that it never completely melts, however in the summer the top metre or “active layer” may melt with the warm temperatures. The permafrost ground below Inuvik also “ice rich”, which means that when it melts, the ground may settle by hundreds of millimetres to fill the voids left by the melting ice. This magnitude of settlement can cause major structural damage to buildings and pipes. The heat from houses and water and sewer pipes may also melt permafrost, therefore all of the buildings and pipes in Inuvik are built on piles to provide a “thermal break” between the building and the ground. The water and sewer mains, and power poles that service each building run along the back of each of the development sites. In most cases the utilidor is positioned in a dedicated right-of-way, but in some cases no right-of-way exists. The cost of these services is about $50,000 per lot. The service connections exit above ground from each building, and resemble a large “metal centipede” as they connect to the water and sewer mains. Road crossings of the utilidor create another challenge because the road must literally bridge the utilidor, at a cost of nearly $50,000. Inuvik’s methods of development access and site preparation have also adapted to the extreme conditions. Roads are built above the natural grade, with embankments thick enough to provide an insulating layer to minimize permafrost melting. Road grades and building lots are never excavated for pre-grading purposes, to avoid the effects of continuing thaw settlement, which can continue for several years in the developed or disturbed areas. Building lots are often filled, to provide grading for drainage, and a drivable access to construction vehicles, as well as to reduce thaw settlement. Drainage runs on the surface, in ditches, except where it passes through culverts under roads.
WCW Conference & Trade Show Calgary September 21 – 24 2010
Figure 2: Modern Utilidor System in Inuvik The utilidor creates unique development and planning challenges because it is above ground. The minimum floor level in a building must be high enough to drain by gravity to the sewer utilidor. Road crossings of the utilidor create unique humps in the streets. “Open” back yards are not very common in Inuvik because the utilidor service connections usually fill a portion of the yard. UTILIDOR DESIGN Inuvik’s ground is thaw sensitive (warm) permafrost, which means that the temperature of the permafrost is only a few degrees below zero, therefore small variations in the ground temperature caused by excavation will cause the permafrost to melt. In addition, the ground is also "ice rich", which means there are significant pockets of ice that may thaw causing significant slumping in the ground. The thaw sensitive soil is the primary reason for the above ground utilidor system. The first generation of the utilidor was built with timber piles. It was expected that the timber piles would last indefinitely because of the cold air and ground conditions. However, timber will eventually deteriorate if exposed to warm temperatures even for brief periods
WCW Conference & Trade Show Calgary September 21 – 24 2010
of time in the north. Steel piles have been used for the past 20 years to replace the deteriorating timber pipes.
Figure 3: Pipe Support for Modern Utilidor System in Inuvik Piles support the utilidor, and thermal stability is maximized by placing the piles to a minimum of 6 metres into the ground. The piles are coated with heavy grease and wrapped with polyethylene to maintain a non-bonding surface between the ground and the pile for inevitable shifting of the ground. The piles are backfilled with a sand slurry which helps the bottom section of the pile freeze into the existing permafrost regime. The pipe used for the sewer and water system of the utilidor is an insulated steel pipe with a metal jacket covering the insulation. For the steel pile utilidor, the water and sewer pipes are structural beams which carry the gravity loads of water, cement mortar lining, the pipes themselves insulation, jacket, fittings and snow and ice. A standard space of 7 metres has been chosen as a reasonable balance between pile capacity, beam capacity and pile frequency. The pipes are specified Schedule 80 (12 mm wall thickness) to provide corrosion resistance, in addition to the cement mortar lining. In addition to the thermal concerns in the vertical direction, thermal movement is also a concern in the horizontal direction. With an operating temperature range from minus 50°C to plus 30°C expansion, and contraction and expansion of the pipe is significant. The thermal considerations for horizontal pipe movement include either a bend, or an expansion joint every 25 to 30 metres along the pipe. Each pipe support at the piles is a roller system to accommodate the horizontal movements. The movement of the pipe is also controlled with line anchors every 60 to 80 metres.
WCW Conference & Trade Show Calgary September 21 – 24 2010
The ultimate objective of the utilidor system is to provide water and sewer connections to individual buildings. To accomplish this, a service box is attached to the utilidor near each building, and water and sewer services run into the box and ultimately into the building through a common carrier pipe. The service box provides easy access to the service connection or "utilidette", and also provides a common space where heat from the system may provide additional freeze protection. The common carrier pipe for the water and sewer services accomplishes the same freeze protection objective.
Figure 4: Water and Sewer Service Connection to Utilidor System A similar configuration is used for hydrant servicing along the utilidor with hydrant boxes placed at intervals along the utilidor. The hydrant boxes are painted red for easy identification. UTILIDOR CONSTRUCTION Initial site work for the utilidor projects for both extension of the system or replacement of the system includes: clearing and brushing of the utilidor alignment, temporary removal and replacement of private installations (replacement only), excavation to the subgrade of the utilidor, preparation work pad and drainage related work. The minimum width of clear working area needed for a utilidor project is about 5 to 6 metres. About 4 metres is needed along one side of the pipe centerline for vehicle movement as well as the utilidor installation. Where the pre-existing ground is to be graded down by more than 250 mm, the standard practice is to sub-excavate by a further 200 mm, and install 100 mm of rigid close cell insulation and bring the ground elevation back up to grade. The width of the insulated area depends on the grading cross-section but typically would be at least 4 m.
WCW Conference & Trade Show Calgary September 21 – 24 2010
The potential thaw of permafrost is always an issue with any excavation, but it is less of a problem in the built up areas of the community. The excavation in built up areas is not likely to cause any significant lowering of the permafrost table and the accompanying ground subsidence because the thermally protective organic cover material was removed long ago and the permafrost has established a new equilibrium. However, deeper excavation has the potential to cause subsidence problems even in built up areas. The utilidor system (water and sewer mains, pile system, service connections, hydrants, etc.) have historically cost about $50,000 per lot or about $5,000 per metre. This compares to a buried “utilidor” system, such as the one in Iqaluit, Nunavut, which costs about $1,500 per metre. These costs were based upon a local contractor in Inuvik with a long standing success at capturing utilidor work. This contractor retired several years ago and the most recent costs for the utilidor (2010 construction season) are $7,500 per metre.
Figure 5: Temporary Sewer Service for Utilidor Replacement Some of the individual cost components are: Piles Water main Sewer main Hydrant box Expansion joint
$3,000 each $1,000 per metre $1,000 per metre $6,000 each $7,000 each
WCW Conference & Trade Show Calgary September 21 – 24 2010
Figure 6: Completed Pile Construction for Utilidor and Marking of Sewer Invert CONTINUING UTILIDOR CONSTRUCTION Utilidor replacement in Inuvik is a continuing project which ultimately depends upon the available capital funding. It is a very specialized system, and the only similar infrastructure occurs in Norman Wells, NWT, which is serviced in a portion of the community by an above ground utilidor. The complete replacement of the original utilidor system in Inuvik may take decades to complete, with a price tag of over a hundred million dollars.