Roads & Paving
Roadbuilders tackle Ottawa infrastructure challenges
September 10, 2008 By Administrator
Aggregates & Roadbuilding
recently visited Ottawa to see at first hand how contractors are
turning the capital’s ambitious infrastructure program into reality.
Aggregates & Roadbuilding recently visited Ottawa to see at first hand how contractors are turning the capital’s ambitious infrastructure program into reality. At different sites, roadbuilders have tackled the challenges of downtown street reconstruction, residential street resurfacing and difficult ground conditions.
In 2007, Ottawa City Council identified infrastructure renewal as a priority and approved a three-year levy to fund infrastructure projects in the city’s 2008 budget. Seventeen major projects are listed for this year, including the Wellington St. West Phase One reconstruction valued at $12 million.
Located in downtown Ottawa, the comprehensive Wellington St. West reconstruction includes watermains, sanitary, storm and combined sewers, lateral services to the property line, utilities, a traffic control signal system, road structure and pavement, street lighting and signage as well as transit facilities, cycling facilities and sidewalks. Work is being completed in three successive construction phases. Construction on Phase One covers a ten-block section between Parkdale Ave. and Western Ave. in 2008 under City of Ottawa contract ISB07-51777. Phase Two, between Parkdale Ave. and Bayswater Ave. will begin in 2009 while Phase Three on Somerset St. West, from Wellington St. to Champagne Ave. North, will begin in 2010.
The general contractor on the Phase One project is Ottawa Greenbelt Construction Co. Ltd., with R.W. Tomlinson Ltd. a principal subcontractor.
Sewer work by Greenbelt totals some $4 million, while Tomlinson’s scope of work includes excavation, granular base, curbs and paving with a tender value of $4.2 million.
Project engineering and design adds about another $4 million for a total project value of over $12 million.
Yves Bisson, project manager for Tomlinson, explains that the complete reconstruction of an existing street, including above-grade and below-grade infrastructure, results in a complex construction process. Within the construction zone, for example, work to remove or replace below-ground municipal services can take significantly longer than greenfield installation. In the case of some existing buried cable ducts, the existing protective tile surround has been replaced with concrete encasement, a labour intensive process involving extensive hand digging and the temporary slinging of cables prior to concrete placement. Elsewhere, water jetting has been used to expose underground services rather than risk damage by an excavator, however carefully operated. Activities are further complicated by the requirement to maintain pedestrian access to businesses within the construction area. That requirement has meant the frequent setting up and moving of temporary fencing to delineate the site as well as crossing guards to control pedestrian traffic at designated crossing points. The site is also challenging for equipment operators due to tight manoeuvring space and restricted access. In addition to being vigilant for the presence of construction personnel, operators are frequently working close to existing line poles, overhead phone cables and other objects.
Vehicle traffic management can be challenging in these congested locations, both outside and within the construction zone, and considerable effort goes into minimising traffic delays. Outside the fence line, police assistance is occasionally sought to direct traffic at busy project intersections, although some traffic delays inevitably occur from full detours or lane closures. For the site itself, vehicle access has to be maintained for large trucks delivering bulk construction materials as well as smaller vehicles. Bisson notes that bulk quantities are relatively high per kilometre of roadway, partly due to the decision to fully reconstruct the pavement. Principal material quantities include 16 0000 m3 of excavation, 17 000 tonnes of Granular B placement and 7 000 tonnes of Granular A. base material, 3 500 tonnes of SP19 level D asphalt with PGAC 58-34 as well as 1 500 tonnes of SP 12.5 FC1 level D surface asphalt. Significant street landscaping adds 7 000 m2 of interlocking brick, 130 trees and shrubs and 70 aluminum lighting poles to the materials list.
This somewhat daunting listing of challenges aside, Bisson is pleased to report good progress and a project on schedule.
Ottawa resurfacing program
Away from the downtown area, Aggregates & Roadbuilding’s visited a suburban residential street being resurfaced under Ottawa’s asset renewal program. Southvale Cres., located some five kilometres east of downtown Ottawa, is one of at least thirty five locations being resurfaced under an annual resurfacing program that is expected to total $11.34 million in 2008. City budget documents explain that the program is required to preserve and extend the life of the infrastructure and prevent roadway failures requiring more extensive reconstruction.
The Southvale Cres. Resurfacing project called for the milling of 12 000 m2 of old surface asphalt to a depth of 50 mm in preparation for a new surface lift. Work was being done on a regular weekday morning, necessitating traffic control to handle the typical busy traffic flow of commuters, schools buses and delivery vehicles. The centrepiece of the milling train was a Roadtec RX-900 cold planer, supported by a water tanker, clean up clean equipment and a truck fleet. Gilbert Dupont, milling foreman for R.W. Tomlinson Ltd., explains that this three-track RX-900 is moved frequently and tackles a variety of milling jobs. Like other urban or suburban work sites, the presence of numerous utilities on this jobsite required close attention by the planer’s operators. Unlike highway or main line work where there are rarely any utilities in the roadway, the planer has to make frequent stops to avoid manhole covers and other utilities in the road surface. The cutter drum is raised ahead of any obstruction and lowered after it to allow milling to resume. Any unmilled areas are removed later with a small cold planer, backhoe bucket or by hand.
On this job, the RX-900 was working well within its capabilities, making a shallow cut in relatively unabrasive asphalt, while at other locations the planer has been used to mill at its maximum rated cutting depth of 355 mm. Component wear rate on the RX-900, like other milling machines, is a function of both the cutting depth and the physical properties of the aggregates in the asphalt being milled. In this case, the asphalt’s limestone aggregates wear cutter teeth more slowly than asphalt in the capital region containing dolomitic sandstone or granite aggregates.
Dupont adds that it is important to clean up milled material soon after the milling pass, for a number of reasons. Where milling is taking place close to live traffic, rapid clean up avoids material scatter by vehicles and also avoids any debates over body or windshield damage, particularly on a job such as this where paving was not scheduled to take place until the following day. On all sites, the milled surface has to be clear of loose material prior to tack coat application and paving so quick clean up is good site practice in any case. Tomlinson’s crew certainly wasted no time in picking up milled material here, utilising a multi stage clean up system. During milling, most of the material generated by the cutter was conveyed directly by the RX-900’s 1067 mm wide front load out conveyor to a supporting truck. Immediately behind the planer, a Schwarze Industries M5000 street sweeper travelling gathered millings for periodic discharge into another waiting truck. As a further measure, a Case 570MXT backhoe loader equipped with side and rear sweeper brushes was positioned at the back of the train to pick up any remaining material. With another job completed, the asphalt recycling cycle process continued. The RX-900 was moved to its next site while, back at Tomlinson’s hot mix asphalt plant, the millings from Southvale Cres. were stockpiled for use in the next recycle mix.
In addition to renewing existing infrastructure, Ottawa’s program for the future includes significant investment in new infrastructure. One of the major current projects is the Transitway, described as the largest project in the City’s transportation history. The West Transitway Extension from Bayshore Transit Station to Pinecrest Rd. is dedicated to buses only and runs along the north side of Highway 417, with a barrier separating buses and highway traffic. The completed project will include the Bayshore Transit Station, a Transitway underpass bridge on Richmond Rd. and a Transitway underpass bridge on each of the two Highway 417 interchange ramps at Richmond Rd. on the north side of Highway 417. Construction of the transitway will also include associated storm sewers, retaining walls and an upgraded sound barrier wall. A new transit stop including shelters and pedestrian access to Dumaurier Ave. will be constructed on a new bus access ramp intersecting Pinecrest Rd. at the existing westbound Highway 417 off ramp intersection. The existing 417 westbound on ramp at Pinecrest Rd. will be relocated closer to Highway 417. Site work on the three year, $27 million project began in June 2007 with an August 2009 scheduled completion date.
R.W. Tomlinson Ltd. is the general contractor on the $27 million project with Ottawa Greenbelt Construction Co. Ltd. as subcontractor. For Ottawa Greenbelt, one of the principal challenges of the job has been the installation of about one kilometre of 900 mm diameter storm sewer through variable site conditions, including running sand, hard pan and rock. Sewer pipe installation in the latter conditions, rock, proved to be the most difficult. Drilling and blasting would have probably meant relatively fast progress, but blasting was not allowed in this case due the close proximity of traffic on Highway 417. The contractor’s solution here was to break rock along the sewer line with an excavator mounted breaker in a progressive excavate and backfill cycle. On one open section, a Caterpillar 345C excavator was breaking rock down to the required sewer line elevation, just ahead of a trench box containing an exposed sewer pipe section. Once sufficient rock had been broken, the breaker was replaced with the regular machine bucket. Terex TA30 ADTs loaded with rock then made the short run of some 20 m from the front to the back of the trench box, where dumped material was levelled by a Caterpillar 963 track loader. As rock breakage progressed, the trench box was progressively pulled forward to allow the installation.
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