That's standard. The trench that they dig is only 4-6" deep, and it
won't affect the foundation. Basically, they are building a little
gutter just inside of your foundation walls. I had this done on a
house I renovated once, and it worked great in conjunction with some
1)Be sure your gutters are clean and that water isn't rolling off of
your roof and sinking into the ground near the foundation walls.
2)Be sure you have a proper drainage slope for the grade near the
exterior of the foundation walls.
3)Use retaining walls if necessary to keep water from rolling downhill
towards your foundation.
4)Use a dehumidifier in the crawl/basement, and feed the accumulated
water into the trench that the foundation company is digging.
You can get more info at my website.
Hope this helps,
Builder/Instructor at Emory University
Author of www.renovation101.com