Ontario Technologist Sept Oct : Page 18
Major SucceSS with Remote-controlled tunneling technique makes mighty impact with minimal public disruption by s te V e cONWA y, c . e . t ., rcsi, pmp Microtunneling T he community of Bolton, in the Region of Peel, has been inundated with major construction projects for several years, so when CIMA+ and GM BluePlan Engineering were awarded the assignment to design and administer the final phase of an extensive water systems upgrade project, we set out to do it as efficiently and with as little inconvenience to the community as possible. 18 The Ontario Technologist • www.oacett.org
Major Success With Microtunneling
Steve Conway, C.E.T., rcsi, PMP
Remote-controlled tunneling technique makes mighty impact with minimal public disruption
The community of Bolton, in the Region of Peel, has been inundated with major construction projects for several years, so when CIMA+ and GM BluePlan Engineering were awarded the assignment to design and administer the final phase of an extensive water systems upgrade project, we set out to do it as efficiently and with as little inconvenience to the community as possible.
The project was an effort to improve water supply to the north hill, north of the Humber River. The engineering assignment, involving the construction of a new water tower and extending a larger Zone 6 feedermain through the downtown and connecting the north and south sections, was split, with CIMA+ responsible for project management, design and construction administration of the elevated tank, twin 750 mm feedermains and connections, and GM BluePlan responsible for design and administration of the remaining 900 m section of Zone 6 watermain.
In the spring of 2012, GM BluePlan crews surveyed the route for the new 600 mm feedermain (a continuation of the watermain east along King Street and north on Ann Street and connecting to the existing watermain in an easement in a municipal parking lot) and commenced work on the base plans. Since numerous utilities existed along the route, Terra Discovery, in conjunction with GM BluePlan survey crews, completed a Level B Subsurface Utility Engineering (SUE) survey. The resulting information was added to the base plans and any major conflicts were further investigated by daylighting. It became apparent that construction by typical open cut methods would be difficult and very disruptive to the public.
The design team investigated alternative trenchless construction technologies for installing this section of watermain along King Street, and microtunneling emerged as the best-suited method. Microtunneling is used for small diameter tunneling applications (3 m diameter or less) and involves an unmanned micro tunnel boring machine (MTBM) that is remote-controlled from the surface. The MTBM is able to maintain face pressure by the use of a slurry, which is also the way excavated material is transported to the surface. The MTBM is guided using laser technology and is able to tunnel long lengths while staying on line and grade within tight tolerances. As the MTBM proceeds, tunnel liner sections are jacked in place behind the machine from the launch shaft. The jacking frame and hydraulic cylinders provide the forward thrust to push the MTBM along the tunnel alignment.
With microtunneling deemed the method of choice, the design team carefully selected four shaft locations. Shaft locations had to protect traffic movements with two lanes in service on this busy truck route. At most of the shaft locations, existing services, including watermains, gas mains, and hydro utilities, had to be temporarily relocated or temporarily removed and replaced. There were also vertical conflicts at two of the shaft sites and some overhead wires had to be removed or raised to allow construction to proceed safely. The design team met with all utility stakeholders early in the design stage to co-ordinate the utility relocations, which proved vital in keeping the project timelines in front of all stakeholders so that relocations did not delay construction.
With the work being very close to residences and businesses, tight noise restrictions were in place and there were additional requirements for noise walls around the shaft sites. The plan was for the contractor to occupy the various shaft sites for six months or more, and during tunneling they would be working 24 hours a day.
In order to minimize community frustration and maintain open lines of communication, the design team prePared a communication plan that outlined the expected construction impacts together with mitigation strategies for the proposed shaft site compounds. The design team reviewed this information with town councillors and business representatives to inform them of what to expect during construction and to solicit their input and support. These meetings during design proved very valuable during construction when issues arose and all parties worked together to resolve them.
With the watermain alignment and shaft compounds design complete, the project was tendered in the summer of 2013. The successful contractor was a joint venture between Dibco, a well-known traditional tunneling contractor, and CRS Microtuneling, a microtunneling specialist.
The project started with shop drawing reviews while the contractor set up the shaft site compounds and installed settlement monitoring points beside the shaft sites and along the proposed tunnel alignments. This included deep benchmarks set outside of the working area which would serve as vertical control. With settlement points in place, baseline readings were established prior to construction. Baseline vibration monitoring provided a comparison to active construction.
The contractor started at shaft compound 4, with construction of an oval concrete secant pile launch shaft in the municipal parking lot. Shaft compound 3 was located within the parking lane on King Street at the intersection with Ann Street. Once utilities were relocated at compound 3, construction of the 8 m deep shaft commenced. While shaft 3 was being constructed, CRS started to mobilize the microtunneling equipment to the first launch shaft site. The contractor spent considerable effort protecting the microtunneling separation plant from the extreme cold and icy precipitation of December 2013, and ultimately started the first tunnel drive in late January 2014. They tunneled 152 m from shaft 4 to shaft 3, breaking through in early February.
As soon as shaft 3 was completed, the contractor began construction of the shaft 2 site compound. The westerly intersection of Connaught Crescent and King Street was closed for eight months in order to allow the contractor to construct an oval secant pile shaft. Shaft 2 was used to launch both an east tunnel towards shaft 3 and a west tunnel to the shaft 1 site compound. The construction of shaft 2 proved difficult due to the limited compound access and the attention required for the numerous utilities. With houses close by, and the need to minimize noise and vibrations, arrangements were made with the local hydro utility to provide a 600V hydro service which avoided operating generators 24/7.
Construction of shaft 1, on King Street just west of Deer Valley Drive, followed shaft 2 with the installation of a 5 m diameter secant pile shaft. The shaft 1 site required relocation of a 150 mm watermain.
While work was going on at shaft 2, the contractor’s second crew was working diligently to install the watermain within the first tunnel run. The new 600 mm CPP was jacked into the 152 m long tunnel piece by piece until it reached shaft 3. Crews then continued with the installation of a drain chamber and the open cut work towards the northerly connection point.
Enduring the harsh winter weather, the contractor was ready to commence the second tunnel drive by March 2014. The tunnel drive from shaft 2 to shaft 3 along King Street was 373 m long and downhill. The contractor tunneled continuously from March 24 to April 3, breaking into shaft 3 on line and grade in 11 days with an advance rate of 40m± per 24 hours. Once the annulus for the second tunnel drive was grouted, the contractor removed the jacking frame and repositioned it westward towards the Deer Valley shaft. The third, 316 m tunnel drive was completed on April 30. It was a similar advance rate of 40m± per 24 hours, breaking through at shaft 1 in nine days.
With the third tunnel drive complete, Dibco/CRS dismantled and demobilized the microtunneling equipment to make room in the tight compound site for the installation of the watermain within the tunnels. At the same time, reconstruction of Ann Street and Sterne Street had commenced, making for a very busy construction site. While the road reconstruction work was plagued with utility conflicts, the open communication fostered at the start of the watermain design phase meant these conflicts were resolved relatively quickly.
August’s successful watermain pressure test results allowed the contractor to proceed to commissioning, and the new watermain was connected and operational by mid-September. During the testing phase, the contractor reinstated watermains and sewers that were removed to permit shaft construction, and co-ordinated with the gas company to reinstall a section of gas main before starting final restoration. Shaft sites were restored to original conditions by October 2014, and today there are no signs that we were ever there except for the new watermain chambers at either end of the project and some asphalt patching.
Choosing microtunneling significantly reduced the impacts on construction in the community. Had this project used open cut construction, numerous complaints from residents regarding dust, noise, access and traffic delays, along with possible service interruptions from broken services or cut utilities, would have ensued. Using microtunneling avoided removal of over 1400 truckloads of material and importing of 1400 truckloads of granular material, plus the repaving of 900m of roadway. The minimal construction footprint saved literally tonnes of material resources and lowered the overall social and environmental impact of this project.
We learned a number of things on this project, but two main things stick out in my mind. First, the SUE work gave us a high level of confidence in the accuracy of the location of underground utilities, permitting us to design safely around them. In the areas that required utilities to be relocated, we were able to work with utility stakeholders to design permanent or temporary relocations so construction could proceed. Second, microtunneling technology allowed the Region of Peel to install a critical piece of watermain infrastructure within their municipal right of way by going below existing infrastructure from just a few access points, minimizing construction impacts to the local residents and traveling public.
This successful project was a great example of truly open communication between the Region’s project manager and operations staff, town staff, councillors and local business leaders, the utilities, the contractor and the consultant design and construction inspection team. Using microtunneling enabled us to participate in a big win for this community.
Steve Conway C.E.T., rcsi, PMP is a senior project manager in the Guelph office of consulting engineering firm GM BluePlan Engineering.