On April 18, NEXCO Central Japan opened to the public the site of the Tomei Tamagawa Bridge, a renewal work being conducted between the Tokyo IC and the Tomei Kawasaki IC on the Tomei Expressway.
The Tomei Expressway, which has been in operation for more than 50 years, is deteriorating, and large-scale renewal work is underway in many areas. In order to minimize traffic congestion and other impacts on traffic and the economy, we looked at the innovations and state-of-the-art technology used in construction without reducing the number of lanes as much as possible.
The Tomei Tama River Bridge, which was opened to the public, is a heavily trafficked section connecting to the Metropolitan Expressway Route 3, with a daily traffic volume of 100,000 vehicles. The bridge consists of an I-shaped steel girder spanning over a bridge girder, on top of which a reinforced concrete floor called a “slab” is laid. The floor slabs have deteriorated over time, exposing rebar and peeling concrete, and will be completely replaced in this large-scale construction project.
In the conventional method, one lane was restricted and a large crane was introduced to perform the replacement work, but traffic congestion due to the reduced number of lanes was inevitable. The “split construction” method was introduced to solve this problem.
The bridge, which has a width of 31 m (6 lanes), will be divided into 5 zones to limit the construction area, and work will be carried out in 6 different processes. The key point is that during construction, the median strip is demolished and the original lane width of 3.6m is restricted to 3.5m and 3.25m, thus securing six lanes.
The “Highway Strider,” a mobile gantry-type slab erector, replaces large cranes in slab installation. The slab can be lifted from a trailer and installed by adjusting its position back and forth, left and right in detail. The slabs are 7.5 m long, 2.5 m wide, 22 cm thick, and weigh approximately 10 tons. 1,000 slabs are available, and 800 have already been installed.
In order to ensure a reliable construction period, the concrete products are manufactured in a factory. The floor slab is made of “Slim Top,” a composite structure of UFC (Ultra High Strength Fiber Reinforced Concrete: Slimcrete) and concrete. It is waterproof, eliminating the need for waterproofing work on site. It also contributes to lower life cycle costs (LCC), as it has a service life of 100 years.
The protective railings also employ the precast “EMC Wall Railings” for speedy construction. Special bolts are used to fasten the wall railings to the floor slabs and to connect the members together, and they can be removed and replaced if any part of them is damaged.
Visualization” technology is indispensable for improving work efficiency and preventing industrial accidents at construction sites. In this renewal project, the construction simulator “GEN-VIR,” which is being jointly developed by Toyota Motor Corporation’s Future Creation Center and Obayashi Corporation, is being introduced.
GEN-VIR is a system that can analyze and display 3D records of worker behavior and the operation of each machine, vehicle, etc., and can also propose the optimal construction cycle and suggest risk points during work. The background of the introduction of this system was the issue of securing a waiting area for large vehicles and other equipment in a limited work yard, and the time required for workers to wait when vehicles enter and exit the yard.
Initially, construction began with four teams of 200 workers (daytime and nighttime sections), requiring 19 hours and 20 minutes of construction time per day, 32 vehicle entries and exits, and 185 minutes of waiting time associated with vehicle entries and exits.
In order to make improvements, it was determined that it would be appropriate to expand the area per construction area and switch to a three-team system that would provide a waiting area for multiple construction vehicles. As a result, the construction time per day was reduced to 16 hours (3 hours and 20 minutes less), the number of vehicle entries and exits was reduced to 12 (20 less), and the waiting time associated with vehicle entries and exits was reduced to 15 minutes (170 minutes less).
The risk visualization function visualizes risks by worker, such as “the person doing this work is close to the opening, so there is a risk of falling,” or “be careful of protruding objects and splashing mortar,” which the on-site workers found “easy to understand,” he said. In fact, he explained that such risk management has been successful, resulting in zero accidents resulting in injuries at the site.
He also introduced the introduction of a dashboard for monitoring the job site. The dashboard is a system that allows real-time images from a fixed-point camera, process charts, drawing data, precast product management, weather conditions, and other information to be displayed on a single screen, allowing for an accurate grasp of the site situation and greatly reducing the time and effort required to view data.
To speed up entry and exit from the site, a new type of temporary barricade is also being installed at the entrance and exit of the work zone. Conventional water barricades were difficult to move manually and required time and labor to set up. The new type used at this site is a mobile barrier equipped with casters (Vulcan Barrier), which can be moved in a short period of time by two people.
One last tidbit of information. The current process (STEP 5) is open to the public, and you can see the process described in this article live.
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