Hammersmith Flyover Closures?

[TJMurphy]

Anyone know what's going on with these? Signs being put up say it's going to be closed from 1 August to 22 August and you should use alternative routes. What alternative routes for crying out loud - both the M3 and the M4 traffic heads that way, it's going to be chaos!
I can't find anything on Google about them though so don't know what they're doing.