Can I Pour a Concrete Sidewalk Over Ground Level Stumps?

Subgrade Material and Preparation

• Movement in soil causes concrete to crack and settle or lift up. Soils with a high moisture content and poor drainage are avoided for concrete; organic matter in the soil must be removed as it creates an unstable base for construction. The best material for concrete subgrades is a gravel material, leveled to provide a uniform base for the sidewalk. The base is compacted to prevent settlement. The depth of the base for a sidewalk is typically about 6 inches.

Stumps and Roots

• Stumps and roots decay over time. Typically tree roots extend 3 to 4 feet into the ground, and lateral roots can run several feet beyond the tree canopy. As the root system decays, it leaves large voids in the subsurface from the stump and root channels. The sidewalk lacks consistent support in the subgrade and sinks into the gaps. Soil subsidence from decaying tree stumps needs to be monitored regularly in any part of the yard.

Stump Removal and Subgrade

• The best way to remove stumps is to cut them high enough to be pulled out or pushed over by a bobcat or backhoe. Often they can remove buried stumps as well. Stumps can also be dug out by hand. Stump extraction is disruptive to the site, but that can be remedied in the normal course of construction. A large depression will be left once the stump is gone, and organic material will also be present and has to be removed.

Sidewalk Repair

• There may be liability concerns when a sidewalk fails due to substandard site preparation; often the concrete has to removed and replaced. It might be repaired by jacking the sidewalk to the correct level and injecting cement or other material into the gaps. This is only advisable if the concrete is in good structural condition; and the more adjustment the sidewalk needs, the more likely it is to settle again.