Answer:
The five (5) mile long portion of the tunnel will be approximately 180 to 220 feet deep and will be dug using an underground tunnel boring machine or TBM. The machine will be put in place through a large opening at one end of the tunnel, called a working shaft, and will travel underground to the other end. After the tunnel is dug, concrete walls will be put in place. The TBM will dig the tunnel with a diameter of approximately 18 feet. The lined concrete "pipe" will have and inside diameter of 16 feet.
There will be two (2) miles of relief sewer at the south end of the tunnel that will be shallower and smaller in diameter and will be constructed using traditional "open cut" methods (surface digging and construction). A trench will be dug at the depth needed for the pipe. Pipe will be laid at the bottom of the trench. The trench will be refilled using stone around and above the pipe with soil added on top of that. Any above ground disturbance will be restored as it was prior to the construction. So, for example, a portion of the pipe will be located under the Foster Park golf course. Nevertheless, when construction is complete, the golf course will be restored as a golf course for future use by the public.
Deep drop shafts will be constructed to direct combined sewage collected from the near surface consolidation sewers into the tunnel. These drop shafts will be constructed from the ground surface to the depth of the tunnel by digging through the soft soils using a traditional excavator but the specialized drilling and/or blasting methods will need to be used to get through the rock to the final depth. The consolidation sewers that will connect to the drop shafts will be constructed using traditional "open cut" methods or trenchless technologies such as jack and bore and/or microtunneling.
Here you see a picture of a TBM digging through rock, soil, etc.