Several problems may arise in the construction of new homes and extensions. The home builder should be aware of some issues that may affect 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 report conducted prior to building. The classification report is used by builders and engineers to plan building site preparation and provide site information to assist in appropriate foundation design.

Potential Issues

There are a variety of issues to consider when planning to build on a specific site.  To improve the bearing capacity of a foundation  it may require a specialised design which could come at a considerable expense. Vegetation, tree roots, slope and local features in the area, 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.

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.

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TABLE 2.1 GENERAL DEFINITIONS OF SITE CLASSES

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.

For a site 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. At Norm Wales Constructions we endeavour to undertake a full and complete site investigation addressing the issues mentioned here and also take note of other issues that may be effect the quality of your new building, house, extension or any other building project that requires a soil test and site classification.

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