Skip to main content

In with the New and Out with the Old

The bubble curtain is part of the blast attenuation system that creates a barrier of bubbles to lessen the shock of implosion, helping protect marine wildlife.

When the eastern span of the San Francisco-Oakland Bay Bridge began showing wear, tear, and ultimately unsafe conditions, the California Department of Transportation (Caltrans) decided it was time for a replacement. Dubbed the Old Bay Bridge by Caltrans, its capacity was also in question, and it was in dire need of seismic updates. While the new bridge was constructed, the Old Bay Bridge awaited its fate. The day of 14 November 2015 marked the beginning of the end as Pier E3, the largest support pier of the bridge’s east span at 80- by 140 feet, was demolished—with a bang.

As part of an ongoing effort to disassemble the Old Bay Bridge east span, Pier E3 was dismantled with a 6-second, underwater, controlled implosion. A blast attenuation system was used that decreases the impact of an implosion and lessens environmental damage and the potential harm to marine wildlife. This attenuation system includes a “bubble curtain” that encircles the pier underwater and, upon implosion, creates a curtain of bubbles that decreases the implosion’s shock by 80 percent. BergerABAM and Wood Harbinger, who designed the mechanical system, were instrumental in the production of the bubble curtain ensuring it met all specifications and requirements for a safe and successful implosion.

Although it sounds simple, the process is complex. The attenuation system is carried to sea by barge, and the bubble curtain is subsequently put in the water 55 feet below the surface where it sits on the seafloor. For the Pier E3 implosion, the cores were made in the concrete pier from above the waterline to a couple of feet below the mudline and were filled with explosives that were then set off sequentially at different elevations. To contain the approximately 20 million pounds of debris from the blast, a wooden and steel mat was placed on top of the pier. The 22,000 pounds of dynamite caused water to shoot about 100 feet above the surface, but the implosion was mainly underwater. Spectators watched the 6-second show from nearby at safe distances, and the new Bay Bridge was shut down for only about 5 to 7 minutes and resumed soon after the implosion. The event was smooth and without incident, which instills confidence the future, planned implosions of the remaining bridge span will be successful.