Demolition of ruined southern half of Lebanon bridge clears way for rebuilding.

More than a year after the end of the 2006 Lebanon war, a mid-December blast ripped away a 215-meter portion of the Mudeirej Bridge—a key link in the nation’s primary east-west route. It was not a renewal of hostilities, but a carefully choreographed demolition.

 

Controlled Demolition Inc. (CDI), Phoenix, Md., executed the $150,000 job as part of a $30-million reconstruction project funded by the U.S. Agency for International Development (USAID). It cleared the way for a complete rebuild of the bombed canyon crossing, which has parallel 11-span, 430-m bridges on concrete piers as high as 71.5 meters. 

Demolition of southern structure was done without damaging northern twin.

In 2006, Israeli bombs destroyed more than half of the south bridge and shifted its remaining deck system by nearly 2 m. The north bridge suffered damage to its center span and piers. Michael Baker Corp., Moon Township, Pa., engineer for the U.S. Embassy Team for Lebanon Reconstruction, found that the north bridge was repairable but the south bridge’s surviving five spans and most of its substructure were not.

The robust bridge was designed for an active seismic zone.  Each span had three precast, post-tensioned box girders topped by a reinforced 25-cm-thick cast-in-place deck, on 3-m x 7-m piers. CDI had to blow them up while preserving two relatively undamaged piers closest to the west abutment, three plinths for reuse in the new bridge, and the north structure, just one meter away.

Sturdy columns are pocked from air strike.

“You don’t know how the damaged components will react,” says Mark Loizeaux, CDI president. “Cracks from the original collapse in the west stem faces of Piers 4 and 5 were a concern because the weakened stem walls might fail compressively as they rotated during the implosion sequence, causing the deck to hit the north structure on its way down.”

Restrictions on importing explosives to Lebanon forced CDI to rely on local materials or find other means. “It took a lot of close work with the U.S. Embassy, USAID and the Corps of Engineers to arrange an emergency shipment of fresh non-electric blasting caps from Dyno Nobel in Sweden,” Loizeaux says. 

The locally manufactured explosive mix had ammonium nitrate, a compound that deteriorates when exposed to moisture. With the threat of rain on Dec. 17, the charges were wrapped in silicone-sealed plastic bags and placed inside into the deck and piers. Protective block walls and scaffolds were left in place.

The implosion was triggered at 2:14 p.m. The timed blasts in the deck diaphragms and anchor bars caused all five spans to drop vertically, with no damage to Piers 1 and 2.  The stems of Piers 3, 4, and 5 fell parallel to the deck line, leaving two plinths only minimally damaged, Loizeaux says. 

Arlington, Va.-based Contrack International Inc., is now overseeing the USAID-administered design-build contract for rebuilding the south structure. “The reconstruction is on schedule to be completed by May 30, 2009,” says Gene Lin, a USAID senior infrastructure engineer. “Restoring the Mudeirej Bridge will be an important step in Lebanon’s financial recovery.”