Direct Land Grading Design of Irrigation Plane Surfaces

Existing land grading design methods involve trial and error procedures to determine the plane that balances cut and fill volumes, considering the shrinkage of soil, to minimize earthwork. This paper presents simple formulas for direct land grading design that eliminates the need for trial and error procedures. The design formulas explicitly consider specifications which may include the two edge slopes of the plane, one edge slope and a control point, or two control points. The formulas are based on the assumption that the before and after‐grading volumes measured from a reference elevation are equal; the computed plane provides equal cut and fill volumes. Adjustment factors to account for the shrinkage of soil are then developed and can be applied to directly determine the position of the plane that satisfies the required cut/fill volume ratio. Application of the complete design procedure is illustrated by a numerical example.