Tunneling Through the K-T Boundary for the Southern Delivery System South 1 Pipeline - Pueblo, Colorado

摘要

The Southern Delivery System (SDS) is being developed by Colorado Springs Utilities as a regional water delivery system that will serve the City of Colorado Springs, the city of Fountain, Security Water District, and Pueblo West Metropolitan District (collectively, the project participants). SDS consists of multiple proposed components to convey and/or store, treat, and deliver water. One of these components is the 66-inch-diameter South 1 (S1) raw water pipeline that connects to the future Juniper Pump Station at the existing Pueblo Reservoir in Pueblo, Colorado. The S1 pipeline must rise approximately 150 feet vertically from the Juniper Pump Station onto an existing bluff, while passing beneath an existing Union Pacific Rail Road (UPRR) rail line rock cut that runs parallel to the bluff. The bluff in question is located only a few hundred yards laterally from one of the globally recognized type sections for the K-T (Cretaceous-Tertiary) boundary. The K-T boundary is the marker bed of the geologic period approximately 65.5 million years ago, which included a large-scale mass extinction of animal and plant species, most notably dinosaurs. It is also known as the K-T extinction event. The paper will describe the process by which the designers elected to design the tunneled rail crossing and bluff riser in a geologically important region using conventional tunneling techniques to install a 10-foot-diameter, initial lining system through the shale and limestone bedrock. Also presented will be a discussion of the permitting, operational, geologic/geotechnical, and non-engineering factors that went into the decision. Finally the paper will present construction observations and lessons-learned from the design and construction, including the use of baselines in tunneled construction.