Why are you doing this?

where are you? .. are you in a significant storm area???? .. hurricanes.. tornadoes ... etc ????

what are the 4 x 4 structures around each tree??

some might suggests... that at every point you sever an existing root.. the tree will respond by putting out new feeder roots at that point ... if so .. would you not be encouraging massive roots growth.. right where you dont want it???

and if you bury wood.. isnt that just future compost ... which also will attract root growth??

also.. many of us.. might have suggested.. not planting a willow.. any closer than 30 to 40 feet from a structure ...

what is your foundation.. and basement if any .. how old is the structure.. is its structurally intact... or already failing??? ... trees USUALLY dont create problems.. but they are very good at taking advantage of pre existing problems ...

ken

How about I dig a 3 foot trench around all the problem area and fill it with cement?

In addition to being close enough to the house to grow over to it - both above and below the ground - your willows are too close to each other to allow for their normal development. Using only the photo posted here It can't be made out which specific variety they are but it can be seen that they are one of the large-growing kinds, reaching at least 60' high and across in time. So really the entire planting needs to be modified and reconsidered.

Generally, one weeping willow is considered excessive for a 'normal' sized suburban property. Big trees with a very aggressive root system. 8 planted in a similar sized backyard is overkill on a grand scale!!

btw, wood will not stop the roots for long and especally if you are irrigating enough to keep the trees happy. It will rot in just a couple of seasons (or less) and then all those far reaching roots will be seeking out water from your plumbing or water lines.

This is just not a good idea on many levels and would agree that the whole planting needs to reconsidered.