CDI Clears the Way for Bridge Reconstruction
November 22, 2022
This article originally appeard in the March/April 2008 issue of DEMOLITION magazine.
Bridge demolition offers both challenges and opportunities that are often best addressed through the application of explosives as a safe and effective option to conventional demolition. While bridge demolition projects are usually performed to remove an obsolete structure and/or to make way for new construction, the recent partial demolition of the Mudeirij Bridge in Lebanon was anything but usual.
At over 230 feet high and nearly 1,600 feet long, the parallel, twin span Mudeirij Bridge is the largest bridge in Lebanon and the tallest in the Middle East region according to the Lebanese government. With Damascus as its destination city, the bridge is the nation’s key connection for east-west commerce. During the 2006 Lebanon war, an Israeli air strike destroyed more than half of the south bridge span, resulting in a 6 foot shift in the remaining deck system, while the north bridge suffered significant damage to its center span and pier systems. As a result, the bridge was incapable of carrying traffic on either the north or south structures.
The U.S. Embassy Team for Lebanon Reconstruction retained Michael Baker Corporation of Moon Township, Pennsylvania, to assess the integrity of the structure and make recommendations for expedient repairs of the north structure and the long-term reconstructions of both bridges.
The Michael Baker Corporation determined that the damage to the north structure, concentrated at one span and the associated piers, was repairable, while the south bridge’s five remaining spans and much of its substructure support system could not be salvaged. Contrack International Inc. of Arlington, Virginia, was awarded the main contract for the reconstruction.
Faced with the challenge of providing for the precise explosive demolition of the south bridge in tandem with reconstruction efforts on the north span, the U.S. Agency for International Redevelopment (USAID) and its reconstruction contractor solicited Controlled Demolition Inc. (CDI) of Phoenix, Maryland, to assess the situation and recommend a comprehensive explosives demolition plan.
CDI’s long-standing relationship with the U.S. Army Corps of Engineers (USACE) encompasses hundreds of successful projects on or over navigable waterways and the co-authoring of a technical field manual on structural demolition. In 1995, the USACE presented CDI with their highest recognition of excellence, the Silver Castle Award, for demolition of a former Soviet radar facility in Latvia. In addition, CDI was already a familiar presence in Lebanon and this Middle East region, having successfully completed demolition of both the Sheraton Beach Hotel and the Hilton Hotel in Beirut as well as the Sheikh Abdullah Alakl Center in Jeddah, Saudi Arabia.
Based on these regional projects and a 60-year history of unparalleled global experience, they were the contractor of choice to address the current situation. As part of the $30 million reconstruction project and a $500,000 demolition contract, CDI’s $150,000 fee called for the safe felling of a 700 foot section comprising the south bridge’s five surviving spans and selected portions of its substructure. Each heavily reinforced span was comprised of three pre-stressed/pre-cast box girders that were post-tensioned together before being topped by a reinforced 10 inch thick, cast-in-place deck, all supported on 10-foot by 24-foot cast-in-situ pier stems.
Successful demolition would require the elimination of three heavily damaged piers while preserving two relatively undamaged piers closest to the west abutment, and three plinths to be reused in the new bridge. All demolition was to take place with primary consideration for protection of the north structure located just 3 feet away. The task would eventually require the drilling of 1,459 holes and the detonation of 1,001 pounds of explosives.
“Any project that includes the demolition of a structure that has been partially compromised is a special challenge,” explains Mark Loizeaux, CDI president. “You cannot be certain how the damaged components may react. The original collapse had resulted in cracks in the west stem faces of piers 4 and 5, creating a concern that the weakened stem walls might fail compressively as they rotated during the implosion sequence, causing the deck to hit the north structure as it fell.”
Subsequent challenges were to be confronted as the project progressed. Due to United Nations sanctions placed on Lebanon since the 2006 war, restrictions on importing explosives forced CDI to initially rely on local explosive supplies. Although they were assured in advance that the locally available electric and non-electric blasting caps specified were fresh and immediately available.
Demolition of piers 5 and 4 were planned as part of the final blast sequence. Initial loading began with pier 5, then pier 4, followed by series wiring of the charges in both piers. It was during the wiring stage that excessive and differential resistance in the blasting circuitry was discovered.
As an investigative measure, CDI began testing the electrical resistance of individual caps in each delay period and found unacceptable variances. With approval from the site safety director, detonation of selected unloaded caps revealed further problems. The caps had a failure-to-detonate rate of 29.9% to 52% over three tests. Although labor intensive and not without risk, all of these charges had to be unloaded and removed until the resistance problem could be determined.
Upon further questioning of the local explosives supplier, it was revealed that the caps had been stored well past the manufacturer’s mandatory disposal date. Some caps were manufactured in 1999 and should have been destroyed three years following the date of manufacture, while others of Indian manufacture were only one to one-and-a-half years old but were corroded due to improper transport and storage. All had been offered to CDI during the bid phase without provision of technical sheets or manufacturer’s dates of production requested by CDI.
“When you are working in a foreign country, you cannot assume that business practices and standards found in the U.S. are going to prevail,” Loizeaux says. “With the assistance of the U.S. Embassy, USAID and the USACE, however, we arranged for an emergency shipment of fresh, non-electric blasting caps from Dyno Nobel in Sweden.”
A second explosives-related challenge had to be addressed when it was found that the locally manufactured explosives compound provided contained a percentage of ammonium nitrate, a compound that deteriorates when exposed to water. In anticipation of heavy rain leading up to the scheduled blast day, each charge was placed in a plastic bag and sealed with silicone before being loaded into holes in the decks and piers.
Additional weather precautions included the construction of block barrier walls around holes cut into the deck to provide access into the box girders at five transverse sections of the span. This prevented the rain from flooding across the deck and running into the holes where the explosives would have been neutralized by the water. In addition, scaffolding with plastic tenting was constructed over these deck openings, allowing work to continue without delay to the schedule due to the persistent rain.
“Although these were isolated incidents, you can be certain that international work can be very demanding and is not as ‘exotic’ as it may, at first, seem,” Loizeaux says. “Even though this project was paid in American dollars from the USAID, State Department and administered by the USACE with support by Michael Baker Corporation, there were few Americans on-site. Only a handful of key personnel spoke English, and absolutely none of the laborers did.
“Issues as simple as verbal communication and as routine as inclement weather can become problematic on projects in truly Westernized countries … in countries like Lebanon, they become serious performance barriers if you are not prepared to address them in a timely fashion, with an alternate plan of action. Our depth of experience and comprehensive working knowledge of the industry, has prepared us to make critical, in-place, operational changes a necessary, regardless of local culture, work ethics or practices.”
While protection of adjacent property is always a priority, it becomes a critical issue when blasting in close proximity to retained construction. In anticipation of the sizeable debris fall, 6 feet of soil was placed over the temporary access road from the Beirut highway, which passed under the west end of span 2 and alongside the east face of pier 1.
To the east of this road, an additional 10 feet of soil were added to create a berm cushion where CDI could fell span 2. An explosives notch was created in the box girders above the peak of the berm so that the falling span would “lock” over the soil berm and reduce the velocity of downhill slide into pier 2. With concern for the west face of pier 2, 10 feet of soil and another 10-foot wall of tires were placed against the west face of the pier for added protection against damaging impact of debris.
On Dec. 17, 2007, at 2:14 p.m., months of planning were compressed into 30 seconds of reality as timed blasts in the deck diaphragms and anchor bars between adjacent spans allowed all five bridge spans to drop vertically with no damage to piers 1 and 2. The stems of piers 3, 4 and 5 fell as planned, parallel to the deck line, leaving two plinths only minimally damaged. And, the protective precautions worked as anticipated, as the fall of span 2 was slowed by them berm of soil and gradually slipped down the steep grade, coming to rest on the protective barrier against pier 2 with no visual damage.
CDI’s primary goals of safety to personnel and removal of risk to the north span had been accomplished on schedule and within budget. Timely reconstruction of both bridges could now move forward without further delay to Lebanon’s economic recovery.