Abstract:

The stateofart of tunneling by TBM/shield in China, including underwater tunneling by shield, Metro tunneling by shield and mountaincrossing tunneling by TBM, is analyzed briefly. The problems in the tunneling by TBM/shield in China are analyzed on basis of typical case histories: 1) The diameter of the shields for underwater highway tunnels is too large; 2) The durability of the single segment lining shell is inadequate; 3) Shield TBM has many limitations; 4) EPB shield is not applicable for all cases; 5) The elevation of the route of some tunnels is irrational; 6) Some projects suffer from irrational construction schedule, irrational construction cost, irrational construction contract and irrational construction scheme. Regarding the aforementioned problems, the following proposals are made: 1) In general cases, the diameter of the shields for underwater highway tunnels should not be more than 12 m; 2) Castinsitu secondary lining should be added to form composite lining structure; 3) Shield TBM should be cancelled, while open TBM should be promoted; 4) Slurry shield, EPB shield and open shield should be considered in shield type selection; 5) The tunneling route should not be placed along the interface between different strata; 6) The concept of scientific development must be held in project construction. The following new solutions are proposed for tunneling by TBM/shield in China: 1) Open grid shields should be applied; 2) Extruded concrete lining should be applied; 3) The method of “TBM bore + enlarging by drill and blast” should be applied; 4) Shield can be launched from ventilation shaft in congested area. Finally it is stated that: 1) Large diameter shield is not the development trend; In the case of longdistance boring (longer than 2 km), deep shield tunneling is the development trend; 2) Shield tunneling method should be adopted for Qiongzhou strait crossing tunnel (the deep shield tunneling proposal is better than the shallow shield tunneling proposal); 3) The proposal of “10 mm TBM+drill and blast” method should be adopted for Bohai strait crossing tunnel; 4) Deep tunneling proposal consisting of “TBM bore + enlarging by drill and blast” should be adopted for Taiwan strait crossing tunnel.

Key words: TBM/shield, underwater shieldbored tunnel, shieldbored urban Metro tunnel, mountaincrossing tunnel, shield TBM, EPB shield, open shield, extruded concrete lining, shield launching from ventilation shaft, “pilot bore + enlarging by drill and blast”