I live in a home which was built 1 year ago. The cement walkway from
the driveway to the front porch is intact. However, the soil next to
the sidewalk and extending under it right where the sidewalk hits the
brick porch is eroded. If you look under the sidewalk you can see
that there is a hole extending 2 feet toward the middle of the
sidewalk and even under the bricks of the porch steps.

Since picking up the actual sidewalk and putting in a better
foundation is presumably out of the question, what is the best way to
fill in this defect? What should I put there--gravel? Dirt? How
does one ensure that the entire space is filled?

Thanks!