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| Mature neighbourhood required jacking pit. |
By Frank Mazza, Munro Concrete Products Ltd.
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| Mature neighbourhood required jacking pit. |
A chronic flooding problem for residents along Chilton Road in East York, Toronto, has been corrected with a 1,200 mm diameter reinforced concrete storm sewer, installed by the jacking method. The new sewer is one of many ongoing projects by the City of Toronto to reduce surface and basement flooding in various neighbourhoods of the city. Residents in some old neighbourhoods in the Borough of East York have endured periodic flooding for decades.
The City of Toronto has been phasing in corrective measures for several years to mitigate the flooding. Historically, during wet weather conditions, stormwater was discharged along with sanitary sewage into combined sewers. Many of these old combined sewers were constructed over eighty years ago, and now have insufficient capacity to convey flows. Water that once was absorbed in open fields is now carried from rooftops of buildings then overland by paved surfaces. The combined stormwater and sewage causes flooding and overcharging of Toronto's wastewater treatment plants. In some instances, the combined stormwater and wastewater flows directly into Lake Ontario causing beach closures and increased levels of pollution.
In East York, part of the solution to flooding is construction of trunk storm sewers to collect flows from local storm sewers and discharge effluent to East York's existing Leaside trunk storm sewer. The Chilton Road trunk storm sewer is part of Toronto's CSO management strategy.
Chilton Road services an environmentally sensitive, and mature residential neighborhood. Installation of the trunk sewer by open cut method would have been extremely disruptive to the daily routines of the residents, and to the built and natural environments. Residents and their local elected representative expressed concerns about any construction activity that would cause traffic delays and road closures. The decision was taken by the City's Works and Emergency Technical Services Division to install the sewer by jacking reinforced concrete pipe below the road allowance.
Alsi Contracting Ltd., of Maple, Ontario, was awarded the contract to install 440 metres of 1,200 mm diameter jacking pipe. Because of the concerns of the residents, they were given only ninety working days to complete this project. To meet the tight construction schedule, Alsi decided to tunnel from two locations, using two tunneling subcontractors.
The jacking operation was complicated because of an existing sanitary sewer located three to four metres above the crown of the new storm sewer, and silty soil that resulted in wet jacking conditions. The soil in the area is saturated below three to five metres, to a depth of 6.5 metres. The invert of the new trunk sewer is at 9 metres.
Munro Concrete Products of Barrie, supplied the 1,200 mm diameter (100 D) jacking pipe. All pipes were manufactured with Swift Lift lifting devices and steel bands around the bells. Every 6th pipe was manufactured with 2-inch diameter grout holes at 10 o'clock and at 2 o'clock positions on the barrel. These grout holes were required to feed bentonite around the barrel to lubricate the pipe as it was being jacked.
The two tunneling contractors were Peran Tunnelling Ltd. and Jimmy Mack. Jimmy Mack was assigned two pushes that started from a shaft at O'Connor Drive and Chilton Road, running north for 129 metres and south for 129 metres. Peran was assigned a section that began at a shaft at Donlands Avenue and Chilton Road, pushing south for 182 metres. This construction technique, supervised by Lou Di Sarra of Alsi, was quickly initiated despite encountering poor soil conditions when sinking one of the access shafts to install the jacking equipment.
As the pipe was being jacked through the silty soil, water was pumped back to the shafts, along with the spoil, and removed. The two subcontractors managed to install an average of four pipes per day. The line and grade of the trunk sewer was guided by laser instrumentation, and a City survey crew checked the accuracy of the pushes every second day. The City took responsibility for the geodetic control and line of the sewer.
With the new stormwater trunk sewer running the length of Chilton Road, residents now have the flooding relief they have been seeking for many years.
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