The report on the construction of large section tunnel by the MMST method

The Metropolitan Expressway Public Corporation is planning to construct a 4-lane two-directional highway tunnel of rectangular cross section at a shallow depth below an existing city street where no surplus width is available. A non cut-and-cover method is required. To achieve this, the MMST (Multi-Micro Shield Tunneling) Method has been developed. A large cross-section tunnel is first excavated as a shell using shield machines with small cross-sections, then the tunnel shell structure is completed by connecting these smaller excavations together, and finally the soil is excavated from within the shell to finish the work. Test construction by this method began in September 1997 for the ventilation tunnels along the Trans-Kawasaki Expressway Route. Because the MMST Method is previously untried, this test implementation is being used to establish rational methods for design and construction and to verify the technology. This paper presents an outline of the MMST Method, describes the test construction work, and gives partial results of this test construction.