Courtesy of CDI
After seven days of preparations, the implosion, which went off without a hitch and left adjacent structures undamaged, took only seven seconds.
Courtesy of CDI
Completed in 1986, the Radio Network House posed a challenge because its concrete structure was heavily reinforced to accommodate seismic loads.
Controlled Demolition Inc. demolishes the Radio Network House in Christchurch, New Zealand.

Despite many challenges, Controlled Demolition Inc. successfully led the razing, using explosives, of the 14-story Radio Network House in Christchurch, which was damaged in the 2011 New Zealand earthquake. The  Aug. 5 implosion may open the door to other controlled demolitions in New Zealand, says CDI.   

“The structure did exactly what CDI said it would, in spite of the extraordinarily heavy rebar in the 1986 [structure] that was built to what was already a rigorous seismic code,” says J. Mark Loizeaux, CDI president.

The concrete structure's reinforcing steel, the area's poor soil conditions and the limited selection of low-energy and low-velocity explosives available in New Zealand were the job's greatest challenges, Loizeaux adds.

The building came down in seven seconds after a week of preparation. Workers placed 47 kilograms  of explosives into 141 holes drilled on different levels of the building.

No debris flew outside of the at-source protection placed within and around the structure, says CDI. Also, there was no damage to the adjacent structures, including a two-story building located less than 35 ft away.

Further, CDI and its team managed to avoid damaging any underground utilities, which was a major concern to government authorities. “Vibration generated was very low," says Loizeaux.

The key remaining task is to compare the actual vibration readings, taken from soil that has been called “the worst in Christchurch,” to see if CDI’s computers were able to accurately predict vibration at the variously located adjacent properties. The models are based on CDI’s implosion database of similar structures and soil conditions.

If the real data lines up with the models, it is likely the Canterbury Earthquake Recovery Authority will accept requests to use controlled demolition on other damaged properties, rather than razing using slower, more conventional methods, says Loizeaux.