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Twinning the South Surrey Interceptor – Metro Vancouver

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The South Surrey Interceptor (SSI) was originally constructed in the 1970s to convey sewage from the Fraser Valley to the Annacis Island Wastewater Treatment Plant. The existing sewer is a cast-in-place box structure measuring 1.4 m wide x 1.7 m tall.

Due to growth in the Municipalities of Delta, Surrey, White Rock, and both Langley City and the Township, Metro Vancouver, responsible for managing the region’s wastewater, identified the need to twin (a.k.a. South Surrey Interceptor No. 2) approximately 10.5 kilometres of the sewer interceptor to increase capacity to meet existing and future demand. The twinning project began in 1999, and highlights the versatility and innovation of precast infrastructure products from open cut pipe installation to the minimal disturbance seen with trenchless installation.

Metro Vancouver has historically tendered material supply contracts out in advance of the installation contracts to reduce the supply lead time for custom materials, and ensure the materials are ready when the contractor is ready to mobilize onsite.

RELATED: Benefits of Precast Concrete Box Standards

Research and development for the project began in 1998, when Metro Vancouver let out a tender for corrosion resistant sewer pipe for the New Westminster Interceptor replacement project.

This sewer pipe required a liner material, and The Langley Concrete Group (LCG) successfully tendered the project, supplying 1200mm and 1500mm diameter PVC T-Lock lined reinforced concrete pipe. This is the first time a lined concrete pipe was used in British Columbia.

Construction of the SSI twinning project began in 1999 with a section of corrosion resistant sewer pipe along Highway 91 heading north towards the treatment plant. LCG supplied 2480 metres of 2438mm PVC lined reinforced concrete pipe. 2438mm diameter concrete pipe was not a common size in B.C., therefore a significant investment was made in the manufacturing equipment to fulfill the contract by LCG in their Langley City plant facility. Due to the presence of compressible soils, the pipe was designed as a simply supported beam between pile supported concrete pile caps, also supplied by LCG.

The 2438mm installation continued in 2005, with a 1.9 km section of sewer adjacent to Colebrook Road. The ground conditions began to improve which required 40% of the sewer to be installed as simply supported beams between pile supported caps, and the remainder, standard open cut grade installation.

In 2010, Metro Vancouver began construction on the Trites Road section between Peacock Brook and King George Highway. This section required 3 km of 3048mm lined reinforced concrete pipe which had never been made in B.C. before.

Upon award of the pipe supply contract, LCG procured the equipment required to manufacture this diameter of pipe at their new precast manufacturing facility in Chilliwack. The manufacturing equipment included a new automated steel reinforcement welding MBK machine, internally vibrated pipe core customized for making lined pipe, outside jacket, pallets, and a pipe tipper to turn the pipe from the vertical manufactured orientation to the horizontal installation orientation as well as a 100,000 lbs. capacity forklift truck to facilitate yarding and loading of the finished pipes.

The 3048mm diameter lined concrete pipe was designed as an ASTM C76 CL III pipe for HS20 /BCL625 live loads with a depth of pipe bury that varied from 0.6m to 5.50m of earth cover. The pipe normally is designed to act as a gravity sewer but had to be designed to withstand a surcharge pressure of 5.0m above the pipe crown.

Quality assurance during sewer production was important to Metro Vancouver during all phases of the pipe supply contracts. Generally,the following tests were completed:

  • Three-edge bearing test on non-lined test sample to ensure design strength of pipe.
  • Permeability testing on non-lined 3EB sample.
  • Joint shear test to ensure adequate strength of joint.
  • In-line and off centre hydrostatic joint tests to ensure the gasket design.
  • Squareness and pipe dimensional tolerance measurements.
  • Liner spark test to ensure no voids or deficiencies in the liner.

QA procedures by Metro Vancouver included on-site inspection of the manufacturing process and complete pipe inspection and sign-off at the manufacturers yard prior to delivery.

The Trites Road section was completed over two years, with the contractor installing 1250m in 2010 and 1670m in 2011. The contractor employed a unique installation methodology where the access road for the sewer line was integrated into the bedding structure. The entire access road was completed prior to installing any pipe. The contractor then efficiently installed the pipe with an excavator attachment that excavated the radius of the pipe 4-o’clock to 8-o’clock to provide the required support, with the pipe being mobilized and installed with a large forklift into this cradle of bedding material.

In 2015, a 500 m section of 3048mm lined reinforced concrete pipe was completed at 14933 Colebrook Road. The pipe was designed and manufactured in accordance with the Direct Design Method, rather than the D-Load Method generally used for previous concrete pipe supply contracts. In 2016, the final pipe supply tender was let out by Metro Vancouver to complete the open cut portion of the SSI. This tender included the supply of 1080m of 3048mm lined reinforced concrete pipe, 190 m of 2438 lined reinforced concrete pipe and 220 m of 1829mm lined reinforced concrete pipe. The installation of the 3048mm pipe from King George Boulevard to
Panorama Drive was completed in 2017. Again, the pipe was designed with the Direct Design Method for up to 7.5 m of earth cover.

The trenchless portion of the Johnston Section of the SSI began in June of 2018, and was complete in the summer of 2019. The project was featured in the Spring 2019 Issue of the Concrete Pipe Journal. The Langley Concrete Group worked to supply 800m of 3000mm diameter Microtunneling (MT) Pipe for the installation contractor, Ward & Burke. Due to the installation tolerances required for the tunnel boring machine, the 3000mm MT pipes were cast using Self Consolidating Concrete in wet cast forms. The wet cast manufacturing method limited pipe production to four (x4) pipes per day, where typically up to ten (x10) pipes could be manufactured using conventional dry cast production.

The pipe was designed as a Class V reinforced concrete pipe in accordance with ASTM C76, ASTM C655, ASCE 27-00 and ASTM C361. The pipe was lined with a 2.0mm thick GSE Studliner as the corrosion resistant liner. A steel tail skin was cast into the bell end of the pipe to provide the flexibility of a curved alignment, whilemaintaining a hydrostatic seal preventing the pressurized bentonite slurry and grout from infiltrating into the pipe.

The contract required a joint seal pressure of only 15 p.s.i. but during the testing process it was decided to prove the maximum pressure that could be achieved which ultimately was 85 p.s.i.

The supply contract included precast fittings to reinstate five tunneling shafts. These fittings included a combination of mitre bends, riser manholes, and short pipes to accommodate the pipe angles intersecting in the shaft.

Metro Vancouver aims to complete twinning of the South Surrey Interceptor by 2023. The sewer line will connect to the trenchless segment on 153A Street and along 56 Avenue, where the sewer will tie into a junction chamber. The construction of the South Surrey Interceptor over No. 2 the past 20 years has demonstrated the design flexibility of using reinforced concrete pipe and the structural advantages of precast. The composite pipe with corrosion resistant liner will provide the long-term sewage conveyance solutions for the extensive growth in the region.

By: Joel Shimozawa, P.Eng., Technical Marketing Engineer Langley Concrete Group. Percy Yu, P.Eng.Senior Project Enginee Collection Systems Project Delivery Metro Vancouver.

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