A majority of this problem is caused by tree roots lifting the walkways. You can thank the former Boro Tree Commission for planting them decades ago. Some of us fought against the planting of these trees in front of our houses but were told "You have no choice, they're being planted." Now 40 years later, they're destroying all the sidewalks. I conveniently get a letter every so often saying the trees are the homeowners responsibility and homeowner is responsible for tree and sidewalk maintenance. To replace 15 -30 feet of sidewalk is not in most homeowner's budgets these days.