You wish to establish the depth of excavation to prepare a bridge footing for placement. Blueprints show the base of the footing at 2`-6″ below the benchmark elevation of 98.60`. Use a builders level with a surveyors rod to establish the depth of excavation. 2 readings are taken. A backsight to the benchmark with a rod reading of 5`-8″. Foresight to existing grade at the footing location of 3`-4″. To prepare the footing for placement, the existing grade must be excavated to a total of:

You wish to establish the depth of excavation to prepare a bridge footing for placement. Blueprints show the base of the footing at 2`-6″ below the benchmark elevation of 98.60`. Use a builders level with a surveyors rod to establish the depth of excavation. 2 readings are taken. A backsight to the benchmark with a rod reading of 5`-8″. Foresight to existing grade at the footing location of 3`-4″. To prepare the footing for placement, the existing grade must be excavated to a total of: