Design and Construction of the Magnolia Stormwater Project, El Paso, Texas

摘要

In 2006 a section of Interstate 10 (I-10) and a portion of the City of El Paso were subject to flooding. Analysis determined that the existing stormwater collection/conveyance system had insufficient capacity to handle the 100-year design flow. The solution was the Magnolia Stormwater Project which consists of an 84-inch-diameter stormwater gravity pipeline to convey stormwater to a retention/detention pond and pump station, which pumps the flow via a 60-inch-diameter stormwater force main to discharge into the Rio Grande, beyond the current US/Mexico border fence.The conveyance alignment crosses I-10, an active UPRR railyard, multiple canals, TXDOT Loop 375, the jurisdictional Rio Grande levee to end in the river. The ground conditions consisted of highly uniform clean sand. During planning, pre-design and design refinements, multiple trench and trenchless methods were considered including: open-face pipe jacking, conventional tunneling, microtunneling, pipe ramming, and auger boring. Various trench and trenchless methods were evaluated before two-pass tunneling and pilot-tube-guided pipe ramming were selected based on consideration of: environmental, easement, permitting, and other constraints: risks and potential consequences, schedule and estimated costs.The paper will describe the site conditions, issues and risks, and results from use of open-face, two-pass TBM tunneling with varied initial support systems to tunnel the alignment to the river discharge, and guided pipe ramming to install 98-inch steel casing for the railroad crossing.