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Pressing business

Piling Hodogaya bypass

Tubular steel piles are being installed with minimal noise and vibration as part of a complex road widening scheme in Yokohama, Japan.

Spectacular stadiums are not the only fruit of Japan and South Korea's joint hosting of this year's football World Cup. Both nations have been improving their infrastructure to enable teams and fans to reach their destinations quickly and easily.

At the Hodogaya bypass, on the National Road Route 16 in Yokohama near the port of Tokyo, traffic volumes are already high - an average of 130,000 cars a day - in the residential area.

In constructing the major new Shinskuragaoka interchange, two permanent retaining walls were built within existing sloped embankments, which were then removed, forming a 40m wide cut for the road improvements.

Clients for the project were Yokohama National Road Construction Office, Kanto Regional Construction Bureau, and the Ministry of Land Infrastructure and Transport.

The site itself was long and narrow, and traffic flow could not be affected at any time during construction. This meant equipment or materials were not allowed on to the highway and the close proximity of housing meant noise and vibration were also important considerations.

The ground investigation identified four main layers: a 7m to 8m thick layer of fill, with concrete and rock fragments in the top 0.5m; 2m to 3m of soft loam;

5m of hard clay; and hard clay/mudstone below 13m.

Engineer Dainichi Consultant assessed four installation methods for the retaining walls, based on environmental impact, safety, speed of installation, economy and aesthetics. These were a contiguous bored pile wall of 1m diameter piles; a Chicago caisson wall consisting of 2m diameter steel tube piles installed every 3m separated by concrete lagging; a 500mm square prestressed concrete pile wall, and a pressed-in steel tubular sheet pile wall of 900mm diameter, 12mm thick piles from Japanese piling equipment manufacturer Giken.

The pressed-in pile method was chosen because, unlike all of the other methods, it does not need temporary working platforms. Instead the compact equipment moves along the wall as installation progresses, using the top of the piles as the working platform.

Eliminating temporary works speeds up piling and reduces the installation costs. And, because the machine, the Super Crush Tubular Piler, is based on Giken's established silent piling system, the method is very quiet and its vibrations are generally below levels that disturb people.

The press-in system works by deriving reaction force from the negative skin friction and interlock resistance from previously installed piles to provide the press-in force to hydraulically jack-in subsequent piles.

The first stage is to build a piled 'reaction stand'. The silent piler then begins work, pressing in three piles. Once these are in place it moves on to them and is clamped in.

As the piles are installed, they are checked for alignment and verticality using Giken's Pile Laser, which the firm says means piles can be kept to tolerances of 3mm and below.

The rig is followed by a pile pitching clamp crane, which walks along behind and also clamps on to the piles. New piles are carried to the clamp crane by a powered transporter or 'pile runner', which is mounted on a trackway formed from inverted piles on top of the pile wall.

At Hodogaya, the piles are linked by a unique joint which comprises a T-shape section welded on to one side of the piles and a pipe with a slot cut down it welded on the other side. As a pile is installed, the T-shaped section is pushed down the slot of the pipe on the side of the previous pile.

The interlocking junction forms a permeable joint, preventing water pressure build-up behind the wall.

Hodogaya's hard mudstone layer meant piles had to be augered before being pressed in using the firm's integral augering system fitted to a SCP260 Super Crush Tubular Piler.

Once the tubular pile reached the top of the mudstone, an auger was lowered inside and driven down through the pile to about 500mm below its toe.

The tubular pile was then pressed in as the auger broke the rock up, forcing the spoil inside the pile. When the pile reached the required depth the auger was extracted by reversing it, which minimised the amount of spoil brought to the surface.

A total of 376 piles were installed on the Hodogaya project to depths between 12m and 20m. Piles were made up of two sections, welded together on site.

Once each wall was finished, the tubular piler and clamp crane made their way back, removing the trackway.

The embankment slopes were excavated, leaving the 'Giken wall' to retain the new cut and act as a cantilever structure, with a typical retained height of 5m. Noise barrier panels were fixed to the wall.

The five month US-3.5M piling contract was part of the yearlong widening scheme which cost US-20M.

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