Unconventional Construction Methods for Large-Scale Infrastructure Projects in Japan

The Second Keihan Expressway in Japan is located between Kyoto and Osaka and was constructed as a bypass of an existing national route. The project is one of the largest construction projects in Japan. Since the expressway runs through suburban residential areas, construction had to be carried out as quickly as possible. To meet these requirements, especially efficient construction methods were used for two viaducts located on the new expressway - the viaducts in Nasudukuri region and in Aoyama region.

During construction of the viaduct located in Nasu-dukuri, parts of the construction site were used as a casting yard to manufacture unique U-shaped precast girders.

In contrast to conventional projects, the precast segments did not consist of a multitude of small precast segments divided longitudinally. The U-shaped precast girders without top slabs were transported to the area below the viaduct. Then, the precast girders were lifted onto the pier near the supports of the erection girder. As a result, the bending moments acting on the erection girder were reduced by 1/6 in comparison to conventional by-span erection, allowing the weight of the erection girder to be significantly reduced.

The casting cycle for the four girders was set to be equal to their erection cycle so that no storage yard had to be built for the U-shaped girders. Four casting beds and two sets of lifting girders were used to achieve an erection cycle of only two weeks for four girders per span.

For the viaduct in Aoyama region, there was neither enough space for a casting yard, nor was it possible to use the area under the superstructures due to unfavorable topographical conditions. The segments were fabricated in a remote precast yard and transported to the site. The girder was longitudinally divided into several segments, and the completed deck surface of the bridge was used as an assembling point for the segments. The segments were lifted onto the deck and jointed to form girders.

Subsequently, the girders were transported on the deck to the span currently being constructed using the erection girder. The core segment carried the weight of the girder. Special transverse movement devices were used in order to reduce the number of erection girders needed and thus save costs. Similar to the viaduct in Nasu-dukuri, the construction cycle for four girders was two weeks and therefore only half the time needed compared to conventional methods.

For the construction of the two viaducts, Sumitomo supplied the 19x15.2mm Type MC, DYWIDAG Post-Tensioning System with epoxy coated and filled strands that were used for external tendons. Thanks to the unconventional construction methods used, a rate of construction of 2,400m² per month was achieved for both viaducts.