Tunneling Minimized Disruption Caused by Water Main Installation
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The Regional Municipality of Peel, located on the north shore of Lake Ontario and west of the Canadian city of Toronto, is expecting a prosperous future and is planning ahead to accommodate new home construction and development. Water supply is a major part of the plan, and in the late 1980's a design project was approved for a pipeline from Lake Ontario to the northern part of the Region. This pipeline follows the same route as an existing 60-in. (1500-mm) diameter concrete main installed 20 years ago.
Called the Hanlan Feedermain, the new pipe will provide a backup water supply and also allow shutting down and inspecting the lines now in place. When it is placed in service, its owner, The Ontario Clean Water Agency (OCWA), expects to be ready to meet the water supply needs of the Region of Peel well into the next century. The OCWA supplies treated water to 350,000 people in Peel through two 36-in. (900-mm) diameter and one 60-in. (1500-mm) pre-stressed concrete cylinder pipe (PCCP) mains. The new Hanlan pipeline will extend 26,900 ft (8200m) from the Lake View Water Purification Plant on the Lake Ontario shore to Burnhamthorpe Road in Mississauga. An 84-in. (2100-mm) diameter pipe with working pressures between 200 psi (1400 kPa) at the lake to 175 psi (1200 kPa) at the distant north end of the installation, was specified by the design engineers. A request by the owner called for the tender documents to specify two options for the pipe materials: AWWA C301 PCCP, or reinforced concrete-encased and mortar-lined steel pipe. The job was tendered as six separate projects. One of the most challenging of these involved installing the pipeline through a rock formation. When the design engineer, KMK Consultants Ltd., of nearby Brampton, was asked to investigate this portion of the project, a major consideration had to be resolved. The pipeline's route was planned to run through an existing subdivision, and the anticipated disruption to the public was a major concern.A study suggested the most cost-effective way to deal with this problem and minimize the high cost of property acquisition was to install the pipeline through a tunnel. Contract No. 4, tendered on December 1, 1994, involved 3000 ft (914m) of tunnel and 1200 ft (365m) of open cut trench. The successful bidder was local construction firm C&M McNally Ltd., of Mississauga, which selected PCCP for this contract, all of it supplied by Lafarge Pressure Pipe of Stoufville, Ontario. To facilitate installation of 150 sections of pipe which each weighed 47,000 lb (21,000 kg), the contractor designed and built a pipe carrier to transport the pipe from the access shaft to the construction face. The pipe carrier was fitted with a hydraulic system that allowed the contractor to push the pipe home into the previously placed pipe section. On average, the contractor installed 15 or more pipe sections per day. The difficult task of boring the 10-ft (3.0-m) diameter tunnel was complicated by the need to navigate the underground route around a 2950-ft (900-m) horizontal radius curve. However, the self-propelled boring machine and its crew actually finished the tunnel on time, achieving a perfect line and grade. As soon as the tunnel excavation phase was completed, installation of the PCCP sections began. The standard deflection allowance of the pipe's bell and spigot joint system enabled the contractor to follow the horizontal curve. Approximately 10 in. (254mm) of annular space between the pipeline and the wall of the tunnel was filled with light weight grout. The contractor was somewhat concerned about the final hydrostatic pressure test required for pipeline acceptance. Contract documents specified a test pressure of 132 psi (911 kPa) based on the elevation at the lowest point in the tunnel. But at 66 ft (20m) deep in a rock tunnel, locating a problem, if the pipeline did not pass the pressure test, would be difficult. Consequently the contractor investigated different methods for testing each joint after the pipe was installed, and double gasket joints and the Cherne Large Diameter Joint Tester were evaluated. The joint tester was demonstrated at the pipe manufacturer's plant for members of the consulting engineer's team, and accepted by them for use on the project. This is a rugged unit that is light in weight, and with its retractable wheels was easily transported inside the pipe. To operate the tester it had to be centered inside the pipe over the installed joint being examined. A control panel on the unit initiated inflation of bladders which seal on each side of the joint. Water was introduced into the actual joint area under pressure and monitored through the control panel. After a joint was tested the device was pushed to the next one in line. No disassembly of equipment was necessary and each joint was tested in a matter of minutes. In all the tester was used to check every one of the 150 bell and spigot joints installed in the tunnel. That extra procedure turned out to be worth the contractor's effort because the pipeline passed the hydrostatic pressure test with no difficulties. The contractor decided to select PCCP for a number of reasons that were important since the installation work was to be carried out in the confined space of a tunnel. Characteristics considered necessary for this job were: the long pipe section lengths; the bell and spigot joints; the sturdiness of the concrete material; the inherent strength of the pipe; and the watertight joints and barrel. Beyond that the contractor perceived that this type of pipe would result in high productivity during the installation phase, as well as good economics.
Manufactured in 20-ft (6.1m) standard lengths, the pipe sections had a joint system that used a zinc-metallized steel bell and spigot with an rubber 0-ring gasket. All pipe was manufactured and designed to the American Water Works Association standards (AWWA C301-92 and C30492) approved for pre-stressed concrete cylinder pipe. The pipe was manufactured with a 16 gauge cylinder encased in a concrete core. After curing, core and cylinder were wrapped with high tensile strength wire which was then covered with a dense mortar coating to complete the process.
Editor's note: This article, which first appeared in the Spring 1996 issue of Concrete Pressure Pipe Digest, a quarterly publication of the <%=company%>, has been edited for use in Water Online. Edited by Ian Lisk |