Sand vs Clay Foundations

Is a house only as good as the foundation it sits on?   Many people don’t consider the type of soil when purchasing real estate or building a new house on land. In Victoria there are several types of soil classifications, particularly around the Melbourne suburbs, the Mornington Peninsula and Bass Coast.  Below are 2 main types including a brief description and general characteristics to the main soil types encountered in Melbourne’s Southern suburbs, Mornington Peninsula and the Bass Coast.

  

Sandy Soils: Sandy soils generally tend to have very good building characteristics.  Generally, a sand foundation will settle immediately but requires good density, and not be exposed to water inundation which can cause cementation weakening and soil collapse.   Sands don’t tend to suffer from reactive soil movements meaning that there is very little to no seasonal foundation movement.  On the other hand, sands derived from dune deposits can sometimes be loose due to the way they have formed by wind-blown (aeolian) particle deposits and the void spaces between the sand particles can be quite large which can facilitate large settlement problems or foundation differentiation.  We generally test for sand density in order to inform structural engineers of the potential bearing capacity so engineers can mitigate and design accordingly. 

Clay Soils:  Like sandy soils, there are many different types and mixtures that make up a characteristic soil.  In general clays are reactive meaning they react to moisture content.  When a clay is inundated with too much moisture, it absorbs the moisture and will tend to swell causing foundation heave, cracking and foundation differentiation.  Inversely, when a clay dries out too much, the soils tend to shrink also causing foundation movement, settlement and cracking.  The key with clay foundations is to keep a constant moisture from season to season.  With a constant moisture, clays stay the same volume and therefore minimising the reactivity from too much or to little moisture in the soils.  

Engineers are familiar with both types of soils and mitigate the problematic issues using design principles with the site-specific foundations which are applicable.  Unfortunately, reactive clay soils will move, and the effects are minimised but not completely eliminated.  The cost to engineer foundations to the point where reactive movements are virtually eliminated generally proves to be cost prohibitive for most people.  If you had a choice, solid foundations with no to very minimal foundation movement is preferred, so suitable sands or rock foundations would be the most ideal foundations.   For independent advice call Chris on 0400 372 763 or contact our friendly staff by email: Office@4spheres.com.au