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00The two construction shafts with finished diameters of approximately 30 feet were constructed down to the tunnel elevation. The Elizabeth Lane Construction Shaft is approximately 230 feet deep and the Circle 75 Parkway Construction Shaft is approximately 190 feet deep. Both construction shafts required use of concrete diaphragm walls socketed into rock to support the overburden section. For the Elizabeth Lane Construction Shaft, pre-excavation grouting of the rock was performed to limit groundwater drawdown, followed immediately by concrete lining. For the Circle 75 Parkway Construction Shaft, pre-excavation grouting of the rock was performed in the transition zone to limit groundwater drawdown.
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