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1.2 DOT method
The DOT shield method was developed from 1987 with the concept of "Effective use of underground space". The outline of the method is as follows. (Ref. Figure-3)
Utilizing the characteristics of DK shield especially its spoke type of cutter.
Muddy soil pressure shield machine with Multi numbers of cutter arranged at equi-plane faces which make easier control of machine posture.
The method constructing a compound circular shape tunnel using DOT segments which consists of V-shape joint segments and panel segments.
Multiple circular sections can be arranged at vertical or horizontal orientation, and furthermore, both can be combined. (Ref. Figure-4)
In the case of a vertical orientation of tunnel, Right Of Way required can be smaller than what would have been required with 2 tunnels.
In the case of a horizontal orientation of tunnel, excavation can avoid other infrastructure or pipes.
The DOT tunneling method has been adopted for 18 projects so far. (including 4 projects oversea).
Figure-3 DOT machine
Figure-4 Vertical and Horizontal type
The 1st Project was New Traffic System in Hiroshima 1989 and The 1st Project in overseas was City Subway in Shanghai China in 2002.
(Ref. Figure-5)
Figure-5 DOT machine for Hiroshima and Shanghai Projects
One remarkable project utilizing DOT method is introduced as follows.
Project Name: High speed rail No.4 line Chayagasaka Park (Ref.Figure-6)
                        (DOT was applied for the other 6 sections)
Client: Nagoya city Traffic bureau
Diameter : Diameter 6.52m x W11.12m
Boring Distance : 1,007m
Over burden : 11 - 32m
Soil Type : Adhesive soil (N=10), Sandy soil (N=10 - 30)
Figure-6 DOT machine and Tunnel section with the special segments