Mineral grains, water and air can be disposed  in many ways forming that kind of material as we know as soil. Notion, in geomechanics as we call structure or more correct microstructure is used to describe geometry and relation of set grains and pores between them. So, we could  difference three groups of soil:

1. Large granular microstructure
2. Tiny granular microstructure
3. Cemented microstructure

We must mention something about these three groups:

1. large microstructure is made of  compact grains and they can be presented as squares or geometry correct shape similar form. In the dependence of  relative  position of grains a high interval of  porosity is possible.
   Index which is called relative compactness Dr shows dependence between state of porosity of soil and  crossing  porosity. The formula is
   Dr = emax – e / (emax – emin) * 100%
   But more correct form which is used nowadays is index of compactness Id = γd – γdmin/ (γdmax – γdmin)
   Mechanical conduct of large granular structure soil, in considerable measure is depending of relative compactness.
2. Tiny granular microstructure of soil contains a high level of clay. And because of that this microstructure could be present as many tile grains. Also, the building on the clay could be very difficult , because clay becomes soft after certain work of  building machines.
3. Cemented microstructure can appear with accumulation of calcite, iron oxide and other inorganic and organic matter.