Railroads have long been important to theeconomy of Wichita, Kansas, USA. Itscitizens applauded the merger of the UnionPacific and Southern Pacific Railroads in 1996.However, when the Union Pacific proposed doublingits movements of mile-long coal trains through theheart of the city, local leaders began searching for analternative solution. With assistance from state and federal agencies and the railways themselves, theybegan planning a major construction project-one thatwould alleviate traffic congestion at dozens of city-centercrossings and improve the quality of life for residents.Construction on the Central Rail Corridor GradeSeparation project began in February 2006. Anamalgamation of federal, state, and local grants andprivate railroad financing funded the $98 millionendeavor. Its objective was to elevate a pair of side-by-side railroad tracks along the Burlington NorthernSanta Fe right-of-way through the downtown trafficcorridor. When completed, the project would create new grade separations connecting five new bridgesand one rehabilitated bridge along a 2.9 K.M. strip,allowing both trains and vehicles to flow unimpededthrough eight major thoroughfares.

Project
Central Rail Corridor Grade Separation,Wichita, Kansas.

Design/engineering
Soil Reinforcement Design, Inc.,Woodstock, Ga.HNTB, Overland Park, Kan.

Product application
Geogrid reinforcement supports a temporaryretaining wall and keeps trains running in two-stageconstruction of a rail grade separation

Temporary solution
HNTB's design concept required a temporaryreinforced wall as part of the comprehensive plan forerecting permanent, back-to-back T-Wall retainingwalls on the east and west sides of the 21 Mtrs.-wideright-of-way. Kansas Department of Transportationspecifications called for a design/build temporarystructure to support the combined seismic anddynamic loading of two fully loaded freight trainspassing side by side.

The necessity of maintaining active rail serviceon the track adjacent to the construction site as wellas vehicle crossings between bridge abutmentsdictated that the project be completed in two stages.First, one rail line would be closed and raised-supported by the west T-Wall and a temporary,geogrid-reinforced wall. Once train service wasreestablished along the newly elevated track, theEast T-Wall would be erected, the temporary rein-forced wall between the two T-Walls buried, and thelower track elevated.

Strata System, Inc.'s StrataSlope system, includ-ing Stratagrid temporary wire forms and Microgridfacing, was specified for the project. Strata engineersworked directly with designers from Soil Reinforce-ment Design, Inc. (SRDI), and project managersfrom Wildcat Construction, the wall installer.Demolition of the first track began in March 2006.

"This was a single-source, design/build project forus-with no up-front design details provided by theowner," said Strata Systems Vice President DavidButchart. "Strata's sales and engineering team, inconjunction with SRDI, immediately took the lead,coordinating preliminary structural designs andproviding on-site management services, includinginstallation training for Wildcat Construction crews,as well as ongoing technical support.

"The project required coordinated delivery andstaging of materials along the 2.9 K.M.-long job sitewithout impacting train schedules and vehiculartraffic. The Wichita Central R ail Corridor project'ssheer magnitude and the volume of materialsconsumed attests to its complexity:

• 2.9 K.M.-long by 21 Mtrs.-wide right-of way;
• 8.5 M maximum height;
• 260,000 Sq. Mtrs. of high-tenacity, knittedStratagrid reinforcement material;
• More than 12,000 temporary wire form baskets;
• 87,000 Sq. Mtrs. of Microgrid facing wrap;
• 688,000 Cu. Mtrs. of 100-percent compacted pitsand back fill.

SRDI, HNTB, Strata, Wildcat Construction,general contractor Dondlinger & Sons, and railwaysrepresentatives worked closely together on sitemanagement throughout the project's lifecycle.

Designed for heavy loads
Supporting the dynamic and seismic loads ofheavy coal trains with a temporary, reinforced wallis challenging under normal circumstances. But thedemands of the Wichita Central R ail Corridorproject proved exceptional. Averaging loads of 36.36MTs per axel, the heavyweight E. Cooper 80 enginesused by the Union Pacific Railroad along its Wichitaline far surpasses the typical 15.5 MTs-per-axleloading produced by commuter and light railengines. Consideration of a single engine load issignificant; however, the city and the railroadmandated contingency plans requiring the temporarystructure to be able to withstand the potential forboth rail liness to be loaded simultaneously, howeverremote the possibility.

With Wildcat Construction crews installingStratagrid and turning lengths of Microgrid wrapback into the wall for facing stability, theStrataSlope system demonstrated that it couldsupport the heavy rail loads. Integrated with 100-percent compacted pit sand backfill, the system metdesign specifications for supporting loads of 43 kPa,compared with 12 kPa loads commonly required forhighway/roadway traffic.

"It may be that reinforced walls supportingstatic buildings are heavier from time to time,but the Central Rail Corridor in Wichita is theheaviest dynamic loading we have everdesigned," said Thomas Rainey, SRDI seniorgeotechnical engineer.Unique designSince the temporary reinforced wall would beburied between two permanent T-Wall retainingwalls in a relatively short time, soil erosion was nota serious concern, so no thought was given tovegetating the temporary structure. Mechanicalsupport for the heavy loading was achieved byinstalling horizontal layers of Stratagrid at 0.45 Mintervals (one layer per wire basket) all the way tothe top of the wall. Additional structural stabilitywas provided by a facing of temporary wire baskets.These were backfilled with pit sand and wrapped in ablanket of Microgrid face wrap.

"The wire baskets serve as a construction andcompaction form, enabling installers to hold the fillin place while wrapping Microgrid back into the wall,encapsulating the sand-filled baskets. It further allowscompaction of the fill to the face of the structure,which means less settlement," said Butchart.

Tracking the outcome
After a regular train schedule began runningalong the top of the completed grade separation inNovember 2007, Wildcat Construction monitoredthe site for several months. Using 80, well-placedmonitoring pins, they looked for any possiblemovement in the track bed. The extensive surveil-lance validated the fact that even with heavy loading(E. Cooper 80 rail engines), the structure nevermoved more than 12.7 mm in any direction, including vertical settlement.
(Strata can be reached at info@strataindia.com)