The 3RPORT Project consists of approximately 25,000 feet of TBM-mined tunnel with minimum inside diameter of 16 feet and at a depth of 230 feet, constructed primarily through limestone. The project includes three shafts with finished inside diameters ranging from 26 to 64 feet in diameter. The TBM will be launched from a starter tunnel extending from a working shaft, with trailing gear extending back through a tail tunnel that connects to the pump station shaft. Construction of these shafts requires up to 170 feet of drill and blast shaft excavation. The starter and tail tunnels will have a combined length of approximately 250 feet and are also constructed using drill and blast methods, with several enlarged sections to accommodate the TBM launch and support equipment. This paper describes the drill and blast construction for these shaft and tunnel elements. This includes the design of the initial rock support consisting of rock dowels and shotcrete for both the shafts and starter and tail tunnels and development of alternative testing procedures for these elements. Procedures for the drill and blast excavation rounds are also presented, including the staging of the blast rounds between the adjacent shafts, details of the blasting including round lengths and perimeter controls, methods used for preventing fly-rock out of the shafts, and staging of the work in the starter and tail tunnels. Issues encountered in the field and resolutions for these operations are also presented.
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