Design of the Underground Structures Constructed by the MMST Method

Increasingly, large-scale structures are being constructed underground in order to maximize effective use of limited land area. Use of conventional cut & cover or TBM methods in such cases poses problems in terms of detrimental impact on above-ground transport, the securing of boundaries between public and private sectors, and the disposal of excavated soil and other environmental matters. A construction method that can efficiently resolve these problems is needed. The Multi-Micro Shield Tunneling (MMST) method, a non-open cut tunneling method for constructing underground structures with large cross-sections, was developed to resolve these problems. The world's first application of the MMST method was for the construction of the ventilation tunnels connecting the Trans-Kawasaki Expressway tunnel and the ventilating station within the Daishi Junction. Implemented as a test construction, the work was completed in 1999, and various data were collected. This paper describes the unique structural problems involved in constructing the tunnel structure for the main Trans-Kawasaki Expressway using the MMST method, compiled based on the knowledge gained from the test construction. It also covers the results of confirmation tests and the MMST design techniques reflecting the results of these tests.