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Advanced TBM Tunnel Enlargement Method
Features of the Enlargement
Features
In LTM, whole enlargement process can be completed in the shortest period by using the bench cut. The upper and the lower half section of tunnel are blasted at once. However, different process of enlargement can be carried out respectively on the upper and the lower half section of tunnel, to reduce the cycle time of enlargement. By applying this concept to the enlargement process, stability of tunnel can be increased considerably, comparing this method with conventional drill and blast method. Thereby, the advance length of a blasting can be maximized without losing the stability of final tunnel.
Drilling and Blasting
⊙ Difference of blasting mechasnism
▣ Existing method
▣ New method
ㆍIn existing methods, the loosened area around a face increases during blasting since charge holes are drilled longitudinally
ㆍIn LTM, major direction of crack propagation due to blasting is changed to the front of the face.
▣ Benefits
ㆍThe loosened area around a face can be reduced considerably.-> Rock supporting materials such as shotcrete and rock bolts are minimized
ㆍThe vibration and noise at ground surface can be reduced significantly.
ㆍThe quantities of explosives are reduced
⊙ Blasting pattern
Muck Removal
⊙ Arrangement of the cables and the muck cars
Others
⊙ Ventilation to prevent dust from flowing into the pilot tunnel after blasting
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