Walkway, Driveway, and Hardscape Settling
Settling is caused by brick or concrete or other hardscape surfaces applied over soil that was disturbed during the construction process and not fully recompacted before the weight of the hardscape was applied. Disturbed soil can expand up to 30%, and eventually, this expansion re-compacts causing settling. Over the years, as the ground that was disturbed from construction compacts, it causes the concrete or other hardscape surfaces to settle and crack, and the brick to migrate and settle.
Is This Settlement a Concern?
Hardscape cracking is a common occurrence and is not necessarily an indication of structural problems with the foundation of the house as house foundations should be built over undisturbed soil and with a deeper and more reliable footing system. More significant cracks – over 3/4″ – can be considered a tripping hazard and patching or grinding down the high spots is recommended for safety.
Can I Repair My Settled Driveway or Walkway with Slab jacking?
Sometimes, for concrete sidewalks, patios, and slabs, slab-jacking is useful. Slab-jacking involves inserting a cement slurry, under pressure, into the area under the settled material, lifting/floating the hardscape back into place. Many companies who specialize in lifting slabs are now using foam as a means of lifting settled slabs. In general newer concrete can often be successfully jacked back into place. Older concrete is more brittle and often thin and may not withstand the forces of being push back into place. Older concrete may simply require replacement. Where settlement is minor to moderate, often the proud edge of the concrete can be ground down with a grinding tool. While this does not level the concrete it can at least eliminate a trip hazard and make the walkway or driveway safer.
What About Tree Roots?
Where tree roots are causing cracking and lifting of hardscape, more complex repairs may be needed as the roots need to be removed prior to repairing the cracked hardscape surface. In cases like this, I would expect the need to possibly even remove the tree in question and then remove the roots and re-compact the soils prior to patching. Hardscape surfaces with extensive lifting from tree roots can be complex and expensive to repair reliably.
Cracking in hardscape surfaces is common and usually a sign of poor site work preparation for the hardscape surfaces during construction. This type of cracking is seldom an indication of structural problems with the foundation, though it is possible. Many cracks can be tolerated for years without a problem and moderate cracking can often be improved by patching or grinding down without necessitating a full replacement. Tree root problems can be more complex and extensive to repair.