Large rectangular cross-section tunneling by the multi-micro shield tunneling (MMST) method

The Metropolitan Expressway Public Corporation is planning to construct a 4-lane highway tunnel of rectangular cross-section with a shallow depth below an existing city street which width is approximately equal to the one of tunnel to be newly constructed. A non-cut-and-cover method is required. To achieve this, the multi-micro shield tunneling (MMST) method has been developed. To construct a large cross-section as a whole section of tunnel, first, smaller cross-sections, as units of tunnel, which are located at the circumference of a whole section of tunnel are excavated by shield machines and lined with segments. Secondary, these smaller units are connected and, finally, a tunnel by the MMST method is completed by excavating soil inside connected smaller units which function as a lining of whole section of tunnel (a large cross-section). This paper describes the MMST method and the outline of the shield machine developed to be applied to the MMST method, the construction results of the tunnels and the test implementation.