I.down1[美 daʊn, 英 daʊn]副down often appears as the second element of certain verb structures in English (back down, clamp down, tone down, etc). For translations, see the relevant verb entry (back, clamp, tone, etc).
He suggests that businesses bolt down their machines and put a large concrete barrier in front of any doors to prevent vehicles from being able to ram through.
The rising water leaches inside the hollow barriers and from there it gets through holes drilled into the steel support structure to bolt down the barriers.