The 2025 Japan International Expo (Osaka Kansai Expo) will take place on the artificial island of Dream Island in Osaka Bay. Plans include extending the subway, which will serve as the primary transportation route to the venue. Odaiba Corporation, responsible for constructing the port railway and the Kitakita Port Technology Line, will be tasked with building stations and tunnels, addressing issues such as soft soil foundations and underground obstacles on the reclaimed land. 重试    设置更换其他翻译服务。若您是会员，可以选择使用更为稳定的 DeepL, OpenAI, Claude 或 Gemini 翻译服务（点此免费体验）。 另外，您也可能需要检查您的网络或代理设置。

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▍ Make the railway pass through the highway tunnel

In 2000, the transportation project linking Sakan Island and Mihama Island, including the extension of the railway, began. The ——Mihama-Sakan Tunnel, which connected the two islands, was completed in 2009. At that time, the railway expansion plan was aimed at the Osaka Olympics; however, due to factors such as the cancellation of the Olympics, the project was abandoned. Only the road section of the tunnel was utilized.

However, in 2017, Osaka Prefecture, Osaka City, and the business community launched the "Miyajima Town Development Plan," which reactivated the railway development plan to prepare for the 2018 Osaka Kansai Expo and the IR (Integrated Resort) project. The North Port Science Harbor Line, extended through this construction, will serve as a major transportation route, transporting approximately 55% of the planned visitors to the Osaka Kansai Expo (126,000 people per day). 重试    设置更换其他翻译服务。若您是会员，可以选择使用更为稳定的 DeepL, OpenAI, Claude 或 Gemini 翻译服务（点此免费体验）。 另外，您也可能需要检查您的网络或代理设置。

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The project is characterized by the simultaneous excavation of the station area, the construction of the shield tunnel from the station area to Mengqi Tunnel, and the railway track engineering, with a very short construction period (3 years and 9 months). Due to the special difficult conditions of the reclaimed land, the construction period is usually doubled, so the ECI (Early Contractor Involvement) method is adopted for ordering.

In the ECI method, specifications are determined through technical cooperation with the construction party during the design phase, so that work can start early and reduce the risk of rework. In April 2020, the railway extension plan was restarted to prepare for the Osaka Kansai Expo. 重试    设置更换其他翻译服务。若您是会员，可以选择使用更为稳定的 DeepL, OpenAI, Claude 或 Gemini 翻译服务（点此免费体验）。 另外，您也可能需要检查您的网络或代理设置。

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he North Coast Technology Port Line will be a new railway line that starts at Universe Square Station, passes through other artificial islands such as Dream Island and Dance Island, and ends at New Sakura Island Station.

The upper and lower lines are constructed by shield, and the station area and special track area are constructed by excavation.

▍ The construction of the dream Island by land reclamation

Improvement of soft soil foundation

The construction area's ground primarily consists of earth from excavation and dredging operations at Osaka Port and rivers. Over the past 20 years, the consolidation of the subsidence has made significant progress, and the underground drainage system is largely complete. However, it remains an artificial surface, which is much softer compared to naturally deposited ground. To address this, we have implemented specific measures for treating the soft soil foundation characteristic of reclaimed land.

First, there is concern that a bulge (the phenomenon of soil behind the retaining wall wrapping inward, causing the bottom of the foundation pit to bulge and the surrounding ground to sink) will occur. To restrain the deformation of the retaining wall, it was decided to ensure that the depth of the retaining wall is below the level of the old seabed of the submerged alluvial clay.

In addition, in order to reinforce the bottom of the foundation pit surrounded by the retaining wall, the ground was improved by mixing and stirring cement slurry and excavated soil. By improving the entire surface of the bottom of the foundation pit, it prepared for safe construction even on soft ground.

A section of an open-cut backfill structure. Increase the depth to prevent soil from moving inward from the outside of the retaining wall in the direction of the arrow.

After the construction of underground retaining continuous wall, foundation improvement was carried out.

▍ Remove underground obstacles

When building retaining walls, scrape off (open excavation construction)

The TRD equipment is low in height, and the chainsaw is placed underground to move laterally, cut and mix to form a continuous wall of equal thickness of cement soil.

The TRD (Trench cutting Re-mixing Deep wall) method is used to build walls during excavation to prevent soil collapse. The advantages of TRD are continuous walls with equal thickness and high water stop performance.

Shape of the underground continuous wall constructed by TRD method

Many PBDs (Plastic Board Drains, vertically installed deep underground) are buried in landfills for drainage purposes. The primary concern is the management of these PBDs that remain underground. These PBDs are spaced 1.3 to 1.8 meters apart underground. Therefore, removing the PBDs that obstruct construction has become a major challenge for both open-cut and shield tunneling projects.

In the earth retention project, the chain saws of the TRD machine installed underground are first moved laterally to excavate trenches. The trench is then filled with a solidifying liquid, which mixes and stirs with the soil to form an underground continuous wall. A special claw-like component is attached to the cutter head of the TRD machine, which helps scrape up and expel PBD (Polymethyl methacrylate) during the construction of the underground continuous wall. Although PBD is rarely used on a large scale in landfills, it can be effectively removed as expected.

PBD (post-construction) left in the landfill

A claw is mounted on the knife post and is deeply inserted into the ground. The soil is excavated while the remaining PBD is scooped up and discharged.

PBD is scraped off and discharged 

The retaining wall constructed by TRD construction method is the open excavation part of the station area