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Emergency Bridge Underpinning: Choosing Micropiles

Posted by on May 18, 2016

Unusually high rainfall left the town of Murphy, NC without running water, a damaged sewer, and devastated roadways.  The North Carolina Department of Transportation contacted URETEK MA to design and build micropiles to support the bridge.  Bridge #245 in Cherokee County, NC suffered structural damage from the rainfall, as the soil under the bridge abutment was washed away by the rising river.  This rushing water exposed the piles supporting the bridge, and eventually washed out about 30 feet of sewer, and portions of surrounding roadway.

Some members of the town of Murphy were experiencing loss of their sewer, and running water.  Including eight restaurants, four hotels, and a handful of key shopping centers.  Daycare centers, as well as public schools were able to re-open with assistance of port-a-johns, bottled water, and packed lunches provided by unaffected neighboring schools.

Partnering with the NC DOT, URETEK MA worked to revise the original plan to save valuable time for the community of Murphy, NC.  Working quickly, URETEK MA re-designed to include micropile casing that was currently on hand.  From the date of contact the repair was re-designed, submitted, and URETEK MA arrived onsite in 10 days.  In addition to the urgency of repair, the site featured low overhead clearances, and would require a limited access drill.  URETEK MA worked closely with the NC DOT from start to finish.

The construction of the micropile foundation was a 3 stage process:

  • Step 1: Load Test one pre-production micropile (ASTM D1143)
  • Step 2: Placement of micropiles adjacent to the existing wood piles
  • Step 3: Connect/transfer loads to from existing piles to new micropiles

The micropiles used ranged from 10 to 15 feet, as what was on the ground was not enough to sufficiently support the bridge.  URETEK MA installed the micropiles, and worked with the NC DOT to layout and pour concrete pile caps.  The repair ran eight to ten days, and was successful on all levels.

Micropiles were the best choice for this emergency repair because of low overhead clearances, low mobilization cost, ideal soil conditions, and it allowed existing piles to be protected from damage, or disturbance.  Micropiles also lended to a speedy installation with a total repair time, including re-design, of 20 days.  URETEK MA’s design-build solution allowed for a quick, successful bridge underpinning for the town of Murphy, NC in their time of need.

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