Soil Testing

Australian Standards and Site Soil Classification.

Introduction

A variety of problems may arise in the construction of new homes and extensions. The home builder should be aware of potential issues that may effect their investment. 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. Currently in Queensland a soil testing service may be offered by professionals licensed by the Queensland Building Construction Commission. Usually 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. 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. 

TABLE 2.1 GENERAL DEFINITIONS OF SITE CLASSES  

CLASS AMostly sand and rock with little or no ground movement from moisture changes.
CLASS SSlightly reactive clay sites with only slight ground movement from moisture changes.
CLASS MModerately reactive clay or silt sites, which can experience moderate ground movement from moisture changes.
CLASS H1Highly reactive clay sites, which can experience high ground movement from moisture changes.
CLASS H2Highly reactive clay sites, which can experience high ground movement from moisture changes.
CLASS EExtremely reactive sites, which can experience extreme ground movement from moisture changes.
CLASS PSites 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.

For a site investigation classification report the following features should be investigated:

 • Soil classification.

• Soil condition.

• Watertable.

• Ground slope.

• Trees, shrubs and organic material.

• Service trenches.

• Water run-off

Summary

Site Classification including soil testing and investigation is compulsory across all areas of South East Queensland including Brisbane, the Gold Coast, the Sunshine Coast, Toowoomba and surrounds. At Express Soil Testing we endeavour to undertake a full and complete site investigation addressing the issues outline here and also take note of other issues that may be effect the integrity of your new building, house, extension or any other building project that requires a soil test and site classification. 

  • Soil Testing Service, Brisbane, QLD
  • Soil Testing Service, Gold Coast, QLD
  • Soil Testing Service, Sunshine Coast, QLD
  • Soil Testing Service, Toowoomba, QLD