Sieving granular materials

My husband was watching a tv program the other day that tackles building construction.Some men were assessing the granular materials such as soil,sand,rocks and some other grading particles.I asked my husband why do they do that,he told me that they were using test sieves.It's really important to have a good test sieves when constructing a building.It helps to ensure the accurate specification of particles and also to attain a solid and durable construction.

So now I understand why they were sifting the granular materials.Just like the importance of sifting powdered ingredients when I am baking ckes.