For the 100mpw, I think I've put an 18 miler, then a 10 miler, then a 20 miler on consecutive days, but I'm only able to do that because I'm not working that week.
Other weeks building up to that mileage I've got 2 doubles every week(which I do already) peaking at 3 doubles just to get the extra miles in.
I'm not actually planning to do 2 long runs back to back, as Saturday I have chosen as a rest day, this is the most difficult day for me to find time to run, but if I need to play catch-up I could probably get out to do 5 or 6 miles. Despite the BT I think on this sort of mileage I will need a rest day.
this week is going to be about 70ish miles, just because I have 2 marathons in 7 days.