47TH AVENUE TUNNEL CROSSINGS FOR THE STAPLETON NORTH DEVELOPMENT

Denver, Colorado

The project was part of a large scale redevelopment effort for the 1,500-acre Stapleton North parcel, a portion of the former Stapleton International Airport property. Development included planned residential, commercial, and retail facilities. The initial phase of development encompassed more that 200 acres of land, requiring significant storm drain and sanitary sewer improvements. These utilities required a crossing beneath I-270, requiring construction using tunneling or trenchless technology methods. The soft ground tunnels were constructed within CDOT right-of-way; therefore CDOT requirements such as using a steel casing were followed. One 84-in.-diameter storm sewer and one 42 in. sanitary sewer were constructed using tunneling methods .

Lyman Henn provided value engineering and cost estimating services to the project team so that the number and size of the proposed pipelines could be optimized with respect to ground conditions and project constraints. Once the project alignments were determined, Lyman Henn provided final design services, including preparation of a basis of design report, specifications, details, and estimate of probable construction costs. Construction phase services including tunnel inspection and observation began in early 2005, and were completed by summer 2005.

The storm sewer was excavated with a large-diameter microtunnel boring machine (MTBM), and the sanitary sewer was excavated with an auger boring machine in conjunction with a guided boring machine pilot rod. Ground conditions consisted of sand and clay below the water table, which required careful tunneling to reduce the potential for roadway settlement.