Using the Cantilever Construction Method to Protect the Environment
At one of the junctions of the New Tomei Expressway, the Matoba Viaduct is being constructed over the Matoba River. This river is one of Japan’s most important biotopes for fireflies. In order to minimize the impact of construction work on this habitat, the cantilever erection method with precast segments was used for the construction of the Matoba Viaduct.
The New Tomei Expressway is a motorway located on the south-eastern coast of Honshu, Japan’s main island. The new expressway is being built parallel to the existing Tomei motorway.
Thanks to cantilever erection method, construction work that usually is done on site (such as the assembly of steel frames and the casting of concrete) could be carried out elsewhere so that work on site was kept to a minimum and the habitat was protected.
The segments were prefabricated in a casting yard in the earthwork area behind the bridge abutment using the match-cast method. In this method, the segment that has just been concreted is used as a bulkhead formwork for the next segment, which insures that the joints fit together precisely.
The short line match cast method facilitated the time and space saving production of the bridge superstructure elements in stationary formwork.
The core cross section of the main girder was used for the installation of the segments from the cantilever. Thus, weight can be reduced to approx. 80% of the weight that has to be supported when the entire cross section is used during cantilever erection.
Consequently, both installation costs related to the erection girders as well as the amount of material needed were minimized.
For post-tensioning the viaduct, Sumitomo supplied external 19S15.7 MC DYWIDAG Tendons with epoxy coated and filled ultra-high strength strands. The strands are coated with high quality epoxy in order to increase the corrosion resistance and durability of the tendons.
Tensile strength and yield strength of ultra-high strength strands are approximately 20% greater than those of conventional strands. As breaking loads and yield point loads are approx. 28% higher than those of conventional 19S15.2 Strand Tendons, fewer tendons were needed so that the segments of Matoba Viaduct are lighter than those of conventional bridges.
Construction of the Matoba Viaduct started in April 2009 and was successfully finished in August 2011.