What approaches are there for demolishing a structure and how is an approach chosen?

Question

From my office on the 21st floor of a building in Vancouver, BC two parking garages in the process of being demolished are visible. A third is just out of view a few more blocks away.

One of these structures is being taken down by a team consisting of an excavator with a jackhammer, an excavator with a claw and a man holding a hose. The jackhammer punches holes in the cement, and the claw breaks it up and allows it to fall to the floor below.

A couple of blocks away a different approach has been taken where it seems they are cutting the concrete into chunks and then lowering it down with a crane.

We've all seen the news clips and YouTube videos of demolition via pyrotechnics.

Are there other approaches?

Presumably, demolition by explosion requires a large amount of upfront time, effort and engineering skill as detailed in this answer. All of this culminates in one significant event, the detonation, and then substantial cleanup.

The jackhammer and claw approach seems like it is at the opposite end of the spectrum and requires relatively little skill and lots of labor to proceed at an excruciatingly slow and noisy pace.

Cutting and lowering seems to be in the middle with more expensive machinery to cut and skilled operators required. It also seems to move very slowly but anecdotally seems to have none of the noise associated with jackhammering.

What does the decision tree/matrix look like for picking an approach? Surely cost plays heavily into it but watching these sites move forward day by day I'm curious as to how two very similar sites in the same city (so permitting is presumably similar) chose different approaches and neither chose to use explosives.

Answer 1

According to university of Wolverhampton demolition masters degree literature, explosives are used where the shock is not likely to have detrimental effects on surrounding structures. Consideration of dust is important due to silicosis. The cost is high but relatively speaking not much different than other methods. Material from this method is usually a large mound which requires removal by the other two methods and also requires professionally qualified personnel to employ but they are very scarce and extremely well paid.

Cut and remove requires machine tools of higher rental costs but less expertise. Material may be removed to a specific site for disposal or reuse. There may be some hazardous material residue that should be dealt with outside the demolition area.

The crush and shift method is similar but dust and debris is less of a consideration than what lies underneath the foundations. With explosives there is need to consider the ground impact on subterranean services such as gas, water electricity and transportation tunnels. The other methods avoid this issue.