The Central Freeway Viaduct in downtown San Francisco suffered major structural damage during the 1989 Loma Prieta earthquake and recently had to be safely demolished. The task was complicated because the bilevel, multispan bridge passed within six feet of heavily populated buildings, ran in the vicinity of both overhead and underground utilities(gas, water, electric and sewer lines), and crossed both commercial and residential areas with strict vibration and sound level restriction. Thus, managing the demolition while ensuring the safety of both the on-going population and existing facilities was a major challenge.
The primary tools for conducting such a delicate, but dangerous operation were detailed planning and through communications with all related parties. An extensive Demolition plan was required and included:
- A Code of Safe Practice describing personal protective equipment for the workers, as well as maintenance plan for the equipment;
- A demolition sequence plan (sequence of work, staging, equipment location, restraints, safety structures, traffic control)
- A dust control plan
- Work-hour schedule
- Noise-level monitoring
- Load determination and structural analyses
Most of the demolition was accomplished using a breaker on the upper deck of the bridge and a pulverizer on the lower deck. First the roadway slab was demolished, then the girders were pulverized and all the debris pushed down to the ground. Then the cap, columns and restrainers were demolished. This process continued along the length of the bridge until the entire distance was conducted for noise, vibration, safety, and procedures throughout the project. Continuous communications was made with utility companies and other concerned with a particular segment being demolished. In this fashion, the entire viaduct was demolished with no major accidents or injuries.
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