What types of tunnel shafts are there?
Shafts are vertical tunnels of varying diameters for supplying equipment, personnel, and support systems to the horizontal tunnel where the pipeline is installed. There are three types of shafts: construction or working shafts, retrieval shafts, and riser shafts. Working shaft – This is the main shaft on a tunnel alignment where all material from the tunnel boring operation is removed and where all pipeline materials are inserted. Once the shaft is fully excavated, sections of a tunnel boring machine (TBM) are lowered through the shaft and assembled. During tunnel excavation, the shaft is used for routing construction support utilities (such as electrical power and water), ventilation, access for construction employees, and removing excavated materials. A total disturbed area of two to three acres is required. Construction activity is nearly continuous throughout the construction period. Retrieval shafts – These are smaller than working shafts but are constructed the same way and are u
