Chelsea the Chomper is a Tunnel Boring Machine, or TBM. In mid-February 2014, Chelsea began her journey beneath Saint Louis to dig the Lemay Redundant Force Main, which will allow the Lemay Wastewater Treatment Plant to accept a higher volume of wastewater, and allow MSD to inspect the original Force Main for the first time since its construction in the 1960s. Chelsea will dig until the middle of May, traveling over 3,000 feet through primarily limestone.

You can follow Chelsea here on the MSD Project Clear website, or on Facebook or Twitter @ChompingChelsea.

Latest updates

May 19, 2014: After nearly 3,200 feet, Chelsea broke through today, May 19, after nearly 60 working days! Once complete, in 2015, this tunnel will allow the Lemay Redundant Force Main to accept a higher volume of wastewater, reducing the likelihood of a wet weather-related system problem.

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February 6, 2014: Lemay Redundant Force Main: Chelsea the Chomper Arrives

Fun facts about Chelsea

  • Every TBM is given a name for each project she (or he) is used for. These names hold significance for the project teams, and are thought to bring good luck to the project. Chelsea is named for the granddaughter of a principal at SAK, the contractor managing the Tunnel Boring Machine.
  • Chelsea is bilingual! Chelsea returns to Saint Louis from Central America, where she most recently dug El Encanto HEP, a 8,202 ft Main Power Tunnel in Miramar, Costa Rica in 2009. She has also dug tunnels in Guatemala and the Dominican Republic. Chelsea previously constructed an outfall tunnel for the MSD.
  • Chelsea weighs 300,000 lbs, with the heaviest single component weighing 142,000 pounds.
  • One of the most important pieces of the TBM is the cutting head. Chelsea’s cutting head is 11 ¼ feet in diameter.
  • Fully assembled, Chelsea will be 250 feet long from cutting head to end of trailing gear. Trailing gear includes a conveyor system and tracks which cart material back through the tunnel and out the starter shaft.
  • The Redundant Force Main will be 3,028 feet long, 11 ¼ feet in diameter, and is cut primarily through Limestone.
  • Two shafts provide access to the tunnel – one at the south end, where Chelsea will start, and one at the north, where she will break through.
    • The south shaft is 175 feet deep.
    • The north shaft will be 128 feet deep.
  • At least 23 workers are on site at any given time, and workers operate the cutting head of the TBM two shifts, totaling 16 hours a day.

Photos

Chelsea's cutter head is lowered into the 175-foot-deep starter shaft on February 6, 2014.
Chelsea’s cutter head is lowered into the 175-foot-deep starter shaft on February 6, 2014.
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The Starter Tunnel of Chelsea the TBM, following the first week of blasting in January 2014.
Chelsea the TBM, fully assembled at an offsite location in November 2013.
Chelsea the TBM, fully assembled at an offsite location in November 2013.