Why do we need to do a soil test

Why do we need to do a soil test?


You may have a completely flat block with little or no clay and high enough not to be flooded – so the question arises why do we need a soil test?

It has been mandatory for many years to have a soil test for every home site, and it must be carried out and any extra costs must be advised to the customer before a contract is signed.

A soil test will determine if your site conditions will create additional building costs, for example, if they find rock or deep fill. These costs can sometimes be significant, so best to be well prepared before you start building.

Getting a Site Investigation report will give you an indication of the expected amount of potential movement and reactivity in the soils across your building site.

On site features such as trees, creek beds, waterways, rocks and climatic conditions also need to be considered to receive a ‘Site Classification’.

Soil movement can occur as well when clay layers absorb moisture into their structure and expand, and shrink: when they lose moisture and contract. There is also the dreaded ‘floaters’ or large rocks that can create havoc when digging footings.

One person recalls “I remember our land was sandy loam, no clay for miles. But the test showed clay 1 metre (3.3ft) down. As the soil was ‘soupy’ we had to have deep footings, through to the clay 1.2m (4ft) down!! They also had to be 600mm (2ft) wide. Concrete footings in sandy soil really do require an engineer to design and certify.”

So before you start to build make sure you get a qualified person to do a soil test and an engineer to do the site classification.

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