August 11, 2016

Soil Test


A variety of problems may arise in the construction of new homes, granny flats and extensions. Issues for many existing homes could have been avoided if a thorough site investigation and soil testing was conducted prior to construction. Since the mid 1990’s all new house developments have been required to have a site and soil test and site classification investigation conducted prior to building. The classification report is used by builders and engineers to plan building site preparation and provide site specific information to assist in appropriate foundation design. This service will be offered by a geological consultant, engineering consultant, environmental consultant or drilling contractor with sufficient skills and knowledge.

Potential Issues

There are a variety of issues to consider when planning to build on a specific site. Reduced bearing capacity may require specialised foundation design at considerable expense. Vegetation, tree roots, slope and local topography may effect on site drainage with roots required to be removed and any drainage issues addressed. Changing moisture conditions in the soil cause a change in soil volume. These factors will combine to effect local soils and the building structure above. The properties of the local site soil must be tested and measured. Soil testing requirements are outlined in Australian Standards  AS1684, AS2870 and AS3798.

Why Test Soils?

Inclusion of these requirements for building of residential homes has resulted in a great reduction in homes with defects such as dropped floors, cracked slabs, cracked brick work and binding doors. Water is commonly the greatest issue when it comes to building damage. Reactive soils absorb water and change in volume. Where foundation design is not appropriate to compensate for the amount of movement expected, damage to buildings will occur. Water can also cause erosion of some soils which may result in subsidence of foundations and building damage. For this reason anyone planning on constructing a dwelling must order a pre purchase inspection and site soil report. Where building or extensions are planned a soil test must be conducted to satisfy council requirements and ensure correct design.

What is a Site Classification Report?

A site classification report involves soil testing to define the soil reactivity. Below is a table taken from Australian Standards AS2870 outlining the soil classification code and description.


CLASS A Mostly sand and rock with little or no ground movement from moisture changes.
CLASS S Slightly reactive clay sites with only slight ground movement from moisture changes.
CLASS M Moderately reactive clay or silt sites, which can experience moderate ground movement from moisture changes.
CLASS H1 Highly reactive clay sites, which can experience high ground movement from moisture changes.
CLASS H2 Highly reactive clay sites, which can experience high ground movement from moisture changes.
CLASS E Extremely reactive sites, which can experience extreme ground movement from moisture changes.
CLASS P Sites which include soft soils, such as soft clay or silt or loose sands; landslip; mine subsidence; collapsing soils; soils subject to erosion; reactive sites subject to abnormal moisture conditions or sites which cannot be classified otherwise.

The Soil Test requires a site visit and costs $550.

Our 10 Steps:
Step 1 – Aerial Mapping
Step 2 – Preliminary Site Assessment
Step 3 – Soil Test
Step 4 – Quote (based on steps 1,2 & 3)
Step 5 – Finance (pre approval)
Step 6 – Plans Drawn
Step 7 – Fixed Price Contracts (signed)
Step 8 – Finance (formal approval)
Step 8 – Plans Certified & BA
Step 9 – Construction (commences)
Step 10 – Completion & Handover

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