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| The construction of the new viaduct structure carried out prior to the replacement works uses steel pipe columns from the underground station continuing through to the viaduct columns. To do this, it was necessary to construct the foundation piles of the new viaduct simultaneously with the underground station steel pipe columns.
For this project a new construction method of steel pipe columns was developed. The main construction sequence of this method is described below (steel pipe column construction sequence)
| (1) | Mechanical hole drilling (reverse circulation method)
| | (2) | Prior installation of casings (t = 9mm), with diameters larger than steel pipe columns, into slurry water
| | (3) | Pour concrete infill (as water barrier) into base and around casing perimeter, and drain out water inside casing.
| | (4) | After inside the casing has dried out, welded steel pipe columns are installed and the casing then withdrawn during excavation of the underground station. For this project, by the adoption of this new construction method, it was possible to shorten the construction schedule for the continuing steel pipe columns and also to construct safely while preventing deformation of the existing structure |
| | (Presented by East Japan Railway Co.)
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| Case of metropolitan Expressway
From the results of comparison studies between open cut excavation and the pneumatic caisson method, from the certainty of ensuring the safety of the various adjacent facilities, the superiority of influencing the underground water level, and from cost and schedule aspects, the pneumatic caisson method was adopted.
By drafting the following measures relating to the pneumatic caisson method, construction was carried out. | (1) | To build the total 221.5m long structure, it was divided into 6 caissons, with a gap of 2.5 to 10m between each of the caissons.
| | (2) | To prevent the air penetration flow through phenomena occurring due to constructing 6 caisson simultaneously, the internal pressure in the work chambers was controlled by high accuracy automatic pressure adjustment devices, so that the sinking speed could be adjusted to prevent differences occurring in the depth of the caissons. | | (3) | ) To ensure the safety of the various adjacent facilities, a protection wall was built between the tunnel structure and the facilities, and by carrying out real-time monitoring of the displacements of the facilities | | (4) | To alleviate the works being carried out under high pressures, worker-less excavation was carried out using remote control from the ground surface, thus improving the labour conditions. | | (5) | After the sinking of the caissons, a slab was built above the caissons between the piers of the Saikyo line to carry out underpinning |
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| | (Presented by East Japan Railway Co.)
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