When removing existing concrete structures in the roadbed, how many inches below the subgrade elevation should the removal occur?

The appropriate depth for the removal of existing concrete structures in the roadbed is typically specified as 36 inches below the subgrade elevation. This depth allows for sufficient removal of all existing concrete materials, ensuring that any deteriorated or compromised underlying layers are also addressed.

Removing concrete to this specified depth is crucial to prepare the roadbed for new construction or repairs, ensuring that the new work sits on stable, suitable material. Insufficient removal could lead to future settlement issues or structural failures, as remnants of the old concrete or unstable soils may still affect the integrity of the new pavement layer.

Thus, adhering to the guideline of removing material to 36 inches below the subgrade provides a foundation that meets engineering and safety standards in highway construction practices.