Mega TBMs begin Tokyo ring road drives 17 May 2017

Four TBMs of more than 16m in diameter are preparing to excavate a major section of an outer ring road around the capital city Tokyo of Japan. The Tokyo Outer Ring Road is one of the three ring roads around the city’s metropolitan centre and was designed an arterial high-standard highway of about 85km long at about 15km from the metropolitan center (Fig 1).

Fig 1. Missing west segment of Outer Ring Road now in construction
Credit: Images courtesy of Tokyo Ring Project

The 34km elevated expressway segment to the north was built in subsequent segments with the Oizumi Expressway interchange to Bijyogi interchange section opened in 1994; the Bijyogi junction to Misato section opened in 1992; and the last Misato to Misato-Minami opened in 2005). The segment on the west, between the Kan-etsu Expressway and the Tomei Expressway and at about 16.2km in total length, was to be built next and also as an elevated highway structure of the original urban plan of the 1960s. The plan however was met with fierce opposition due to concerns over the potential environmental impact, and construction of the expressway extension was frozen in time.

Eventually, in 1999, the Governor of Tokyo announced that this section of the project should be constructed underground and in 2001, the Ministry of Land, Infrastructure, Transport and Tourism (MLlT) and the Tokyo Metropolitan Government published a draft of the underground alternative for the highway.

In the following years, studies continued to incorporate various opinions from local communities and in 2007 a decision was made to change the original elevated plan into a deep level, bored TBM underground route at up to 40m deep and more (Fig 2). The deep-level twin-tube highway will host three lanes in each direction and will require TBMs of more than 16m diameter to provide the necessary clearance within the segmentally lined bored tunnels.

Factory test for the mega 16.1m JIM TBM in Sept 2016

When completed, the project will be the largest shield-driven road tunnel in Japan, larger in diameter than the eight TBM bored tunnel drives of the Tokyo Bay Aqua Line highway, which required TBMs of 14.14m diameter when excavated in the early 1990s.

The budget estimate for the new expressway project is an expected total of about ¥1.6 trillion or about US$15.6 billion.

In planning for construction of the project, the authorities considered the risks of meeting the requirements of large diameter, long distance and high speed construction, and fixed on a solution of procuring four TBMs and a contractual strategy for making it possible to continue tunnel boring from either of the four tunnel portals, should any one excavation heading run into construction difficulty.

In the strategy, the two TBMs from the Tomei Expressway junction working shafts will start first and progress for about 9km each. The second two machines will launch subsequently from the Oizumi working shaft at the Kan-etsu Expressway junction north end and advance for about 7km towards in-tunnel breakthroughs for each pair.

Fig 2. Four EPBMs will operate at more than 40m beneath the streets of Tokyo and at of up to 7 bar maximum

Also considered in the feasibility and risk analysis studies were the needs for settlement monitoring and auxiliary technique required to meet additional project challenges. At the Oizumi working shaft at the junction with the Kan-etsu Expressway, where a complex crossover of the two TBM bores is required for aligning with the existing elevated section of the orbital expressway (Fig 2), the more shallow alignment of the headings as they transition to the deep level alignment, are known to interfere with the reinforced concrete foundation piles of the existing elevated highway and techniques to cope with the situation are being studied and verified.

Assembly of the JIM TBM at the Tomei working shaft

Construction of the orbital expressway must also allow for on- and off-ramps for connections and exits to the main radial routes (Fig 2). At these junctions, the main TBM bored tunnels must be enlarged to create the junctions and this must be achieved within the bored tunnel and without using cut-and-cover techniques. According to correspondence with and information provided to TunnelTalk by the Japan Tunnelling Association, a special committee has been established to study the feasibility for these underground enlargement operations and various methods and techniques publically solicited from the construction industry in Japan are being studied.

Scale of the 16m-plus diamter cutterhead as it prepares for assembly on the Kawasaki TBM at the Tomei launch site

For excavation of the main highway tunnels, four TBMs have been procured, one Kawasaki and three from JIM, the collaboration between Japanese TBM manufacturers Mitsubishi and IHI, and the country’s steel manufacturer JFE Engineering. One JIM machine and the Kawasaki TBM were the first manufactured and were launched in February of this year (2017) from the Tomei working shaft. Construction of the Oizumi shaft, from where the second two JIM TBMs will launch, is to start shortly. With the two machines from the Tomei shaft now into their 9km drives, excavation of the main tunnels, with four TBMs in operation simultaneously and heading towards their in-tunnel junctions, is expected to take 30 months and be complete in 2019.

News of the new TBMs of more than 16m diameter for the Tokyo Ring Project, adds to the TunnelTalk table of mega-TBMs of the world, which is updated also with new mega TBM drives in Shanghai since last the table was updated in September 2016.

Operation and success of the Tomei - Kan-Estu west section of the new expressway will also influence construction plans for the planned 20km extension southwest from Tomei Expressway to Bayshore section and the missing 16km section of the orbital expressway from Misato-Minami IC to Koya JCT (Fig 1). A success of the deep level TBM drives and the control of the junction ramp enlargements may well provide a repeat of the concepts to construct these remaining parts of the expressway project.