Roads & Paving
By Ontario Ministry of Transportation
Highway 11 Culvert replacement using innovative contract delivery and installation.
By Ontario Ministry of Transportation
March 10, 2016 – The Ontario Ministry of Transportation (MTO) replaces or rehabilitates many culverts each year. During a regular culvert maintenance inspection in 2010, it was determined that an existing corrugated steel pipe culvert under Highway 11, a major north-south corridor, had deteriorated, displaying excessive deformations. The ministry replaced the culvert in 2012 using an innovative new contract delivery model and a state-of-the art installation method.
MTO identified the Highway 11 centerline culvert replacement project as a candidate for the design-build (DB) method for delivering construction projects. The ministry implemented the Design Build Type B Minor model due to project complexity, the opportunity for innovation and the need to reduce the time for project completion.
Highway 11 project site and preliminary field investigations
Installed in 1975, the original 215m long, 1.8m diameter corrugated steel culvert crossed both the southbound lane (SBL) and northbound lane (NBL) highway embankments. The embankments are 17m high; the slopes are covered with sparse vegetation, cobbles and large boulders.
The depth of the embankment fills along the existing culvert alignment ranged from 1.4m along the east toe of the NBL embankment, to 16.8m over the SBL. The new culvert was to be installed between the embankment fill and the underlying native deposits.
In May 2011 and February 2012, two separate foundation investigations at the site identified subsurface soils consisting of a superficial layer of sand and gravel fill underlain by silty sand. Borehole samples taken on the embankment crest showed groundwater levels approximately 1.0m to 2.0m above the existing culvert invert. Subsurface conditions at the site would require a tunnelling operation below groundwater level to replace the culvert.
Accessing the launch site
In order to accommodate the tunnel-boring machine, access roads were cut into the southeastern slope of the adjacent creek valley with a 25- to 30- per cent slope down to the
In September 2012, the DB team began construction of the entrance pit with the installation of sheet-pile walls to hold back soil in the excavation. The necessary dimensions for the entrance pit were 8 m in length by 4.9 m wide and 485 mm below the invert level of the concrete pipe. Once the entrance road was complete and all sheet piles were installed, the backstop area for the boring machine was constructed. Concrete was placed between the steel components and inserted in the eight friction tube piles installed creating a massive support system for the jack station.
A 250-mm concrete slab was placed on the native subgrade. To provide extra support for the south sheet-pile wall of the entrance pit, five-metre long H-Piles were installed in one row, three metres away from the pit, and anchored with steel cables passing through the braced walls. The installed system combined steel H-Piles and steel cables to minimize deformations on the braced sheet-pile wall.
Tunnel boring machine
Marathon Drilling Co. Ltd., tunnelling contractors, a DB team member, and experts in trenchless installation technology, installed a 1.5m diameter concrete jacking pipe Class 140-D culvert using an 1,800 tunnel boring machine (TBM).
The Earth Pressure Balance tunnel boring machine, operated and owned by Marathon Drilling, is state-of-the art equipment, manufactured by the Palmieri Group in Italy, and is the only one available in Ontario.
The TBM consists of a cutting head connected to an enclosed pressure chamber where, spoils are passed into the TBM by a screw conveyor. The 18-080 mm cutting head is equipped with rock cutters. This mechanized Earth Pressure Balance machine allows different deposits to be tunnelled safely, including wet, soft deposits and unstable ground.
Since the tunnelling site consisted of fine granular soil in the presence of an elevated ground water table, the use of the Earth Pressure Balance tunnelling machine maintained a balance between the TBM face pressures and the earth pressures and eliminated the need for dewatering along the tunnel alignment. Bentonite slurry was used as a lubricant for the cutting head and to fill the possible spaces and any remaining voids outside of the pipes.
Many aspects of this experience were successful and the ministry acquired valuable learning experiences for reducing construction difficulties. Since this project, the ministry has begun conducting more detailed preliminary foundation investigations to detect organic material deposits underneath existing embankments.
The ministry will consider trenchless technologies for the replacement of culverts situated in deep fill embankments and encourage its use where technically applicable for its foundations component.
For more information, please contact: Márcia Mora, P.Eng., Head of Corridor Management, at (705) 497-5530, or at Marcia.Mora@ontario.ca
Reprinted with permission from Road Talk-Ontario’s Transportation Technology Transfer Journal, originally published by the Ontario Ministry of Transportation, Fall 2015.