Small Pilot Tunnel Advance and Step Reverse Expansion in Super-Large-Section Tunnel Excavation

Figure 3

Settlement cloud diagram caused by the key steps of the double-side pilot pit. (a) Completion of the left pilot tunnel. (b) Completion of the upstairs. (c) Completion of the intermediate step. (d) All construction completed.

(a)

(b)

(c)

(d)