What principle explains that a cubic yard of earth will typically differ in volume before and after excavation?

The principle of swell and shrinkage accounts for the changes in volume that occur when soil is excavated. When earth is removed from its original position, it often experiences a change in density and structure.

During excavation, the soil particles move from a compacted state to a looser arrangement, which typically increases the volume of the material due to the air spaces that form between the particles. This phenomenon, known as "swell," means that a cubic yard of excavated earth can occupy a greater volume than it did when it was in situ. Conversely, when the soil is compacted back, it may settle down, causing "shrinkage," where the volume decreases.

Understanding swell and shrinkage is crucial for surveyors and engineers when estimating the amount of earthwork needed for construction projects, as it significantly affects calculations related to material quantity and site planning.