NEW MEXICO'S RAIL RUNNER EXPRESS PHASE II:GEOLOGIC OVERVIEW AND GEOTECHNICAL EVALUATION OF THE MANCOS SHALE

摘要

New Mexico's Rail Runner Express is a commuter rail line that after completion of Phase II will connect the city of Belen, Albuquerque, and the state capital-Santa Fe. To make the connection from Bernalillo to Santa Fe a notable distance of 17 miles of new track is currently under construction. To meet the project completion target of December 2008 a design-build delivery method is being utilized.rnThe Rail Runner project resides in North-Central New Mexico, an active and diverse geologic setting with a rich mining history. The project site is in the Rio Grande Rift, passes through the Cerros del Rio volcanic field, and immediately adjacent to Cerrillos Hills, a mined out laccolithic intrusion. The preliminary geotechnical investigation encountered geologic units that include Cretaceous shales, basalt lava flows, Quaternary basin fills, and recent alluvium.rnThe new track alignment requires 7 new bridges, 5 concrete boxes over/under pass structures, and numerous retaining walls to be constructed. Two of the concrete box structures bring the rail in and out of the 1-25 highway median. A noteworthy portion of the alignment is where the new track will climb the La Bajada escarpment through Waldo Canyon, this area was avoided by historic rail alignments and requires construction of deep cuts and fills. In this area the Mancos Shale is prevalent and is known to be a highly degradable. Due to concerns with the quality of the Mancos Shale as a "soil" or "rock" material preliminary design considerations disallowed its use as a fill material.