No woodchips?

Is it me or does this sound like a seventh grade science project?

Excerpt from today's BBC article on the mechanics of underground nuclear testing:

"The nuclear device is placed into a drilled hole or tunnel usually between 200-800 metres below the surface, and several metres wide.

A lead-lined canister containing monitoring equipment is lowered into the shaft above the chamber. The hole is then plugged with gravel, sand, gypsum and other fine materials to contain the explosion and fallout underground."

More:

http://news.bbc.co.uk/2/hi/asia-pacific/6033893.stm