The biggest unknown about any piece of land is the condition of the soil beneath the ground. It’s why a soil test is needed to ensure that the soil composition is suitable for building sturdy foundations to support any new property.

But besides being a construction requirement, soil testing can potentially save you thousands of dollars, either from negotiating down the purchase price of the land due to soil issues or through preventative measures and adjustments built into the construction design.


As such, any offer you make on the land should be subject to a satisfactory soil test as a risk management precaution. As they say, trust, but verify.


What Is a Soil Test?

A soil test is conducted by geotechnical engineers drilling into the ground with special equipment to extract soil samples at various depths. This allows them to classify the site and establish the soil conditions at different levels, as well as provide necessary recommendations in their soil report.


What Does a Soil Test Tell You?

Besides classifying the site based on how ‘reactive’ the soil is (i.e. how stable it is), a soil test will also determine its bearing capacity (i.e. how much weight it can support), and enable builders to provide fill/scrape recommendations for the construction work (more on this below).


What you’ll want to avoid are problem sites with potentially very severe ground movement, as they will cost considerably more to build on. Soil tests might not be 100% conclusive, but they do ensure more accurate pricing and optimal design of foundations, which will save you time and money in the long run.

  • Soil Reactivity

Soil reactivity refers to the likelihood of the soil moving, expanding, and contracting, usually due to changing moisture content in the soil, and is graded by class. The soil test will also reveal chemical or physical abnormalities on the site that might cause damage to the property later on.


Soil Classifications


  • Class A: Stable, non-reactive, possibly very little or no ground movement (usually sand and rock sites)
  • Class S: Possibly slight ground movement (usually clay sites)
  • Class M: Possibly moderate ground movement (usually clay or silt sites)
  • Class H: Possibly high ground movement (usually clay sites)
  • Class E: Possibly extreme ground movement
  • Class P: Problem sites, potentially very severe ground movement

For Class A and S, a basic foundation is the standard requirement, but all the other classes will probably require additional reinforcement. Being particularly prone to ground movement, Class P sites will require consulting a structural engineer for options before any construction work can be done.

  • Bearing Capacity

The bearing capacity of the ground determines how much weight the soil can support per unit area and the kind of footings or foundation needed for your new house. The more unstable or ‘reactive’ the land is, the deeper the footing may need to be placed into the ground, which will be recommended in accordance with the established guidelines for foundations and footings.


A soil test showing the site’s bearing capacity will help builders quote more accurately instead of issuing the standard foundation quote, as the information will tell them what kind of foundation or footing is required and the recommended specifications. This will save you the stress of unexpected footing issues down the line, the costs of which can be prohibitive.

  • Fill/Scrape Recommendations

A site might need to be ‘filled’ to ensure that the house is built level. If the fill exceeds the recommendation or isn’t compacted as recommended, you might face problems in the future.


The same applies to the amount of topsoil that can be scraped from your site. A soil test will provide the pertinent information for a builder to make more accurate fill and scrape recommendations to prevent avoidable construction issues down the line.


A professional soil test is crucial in order to determine your soil conditions and classification, which are key to ensuring the best possible construction design for your new home. A small added expense for your peace of mind.


Why Choose Smolders Geotechnical for Your Soil Testing?

Smolders Geotechnical specialises in the highest quality soil testing and geotechnical investigations throughout Victoria for both the commercial and residential sectors. In addition to providing soil tests and reports for houses, subdivisions, unit developments, extensions, pools and decks, we also do small tests for home renovators and high-volume builders.


Smolders Geotechnical is fully insured with Professional Indemnity and Public Liability insurance, and comply with all relevant Australian Standards for your protection and peace of mind. We are also members of the Foundations and Footing Society Victoria, Australian Geomechanics Society, and the Australian Institute of Geoscientists.


Our team of fully qualified and highly experienced engineering geologists and geotechnical engineers deliver top-notch professional services that are fast, responsive, and comprehensive.


Get in touch for a free quote today!