Q. Formation of frost heave?

In the past, it was believed that formation of frost heave was related to volumetric expansion of soil water which changed from liquid state to solid state. Though the increase of volume of changes in states for water at zero degree Celsius is only about 9% and observed heaving is far more than this quantum. 

Actually the mechanism of frost heave is best explained by the formation of ice lenses. In cold weather ice lenses develop in the freezing zone in soils where there is an adequate supply of soil water.

Soil particles are surrounded by a film of water that separates the soil particles from ice lenses. Moisture adhered to soil particles gets absorbed to the ice lenses on top of soils and in turn water is attained from other soil pores to replenish the loss of water to ice lenses. This process continues as well as results in pushing up of soils on top of lenses and afterwards the formation of frost heave.