How are they done?

A discussion about the people, tools and process of doing soil tests, who does what and when, what is produced and why/how and where the results are used.

One of the essential steps is conducting a soil test. This test is crucial as it determines the soil’s characteristics on your property, which influences the type of foundation and construction methods required.

Here’s a guide on how soil tests are conducted for residential houses in Australia.

1. Importance of Soil Testing

Soil tests are critical for:

  • Determining soil composition and properties.
  • Identifying potential problems like soil movement or poor drainage.
  • Ensuring the foundation is suitable and stable.
  • Complying with Australian building standards and regulations.

2. Preliminary Steps

Before conducting a soil test, the following preliminary steps are usually taken:

  • Site Inspection: A visual inspection of the site to identify any visible issues such as erosion, vegetation type, and general topography.
  • Site Plan Review: Reviewing the site plan to understand the layout, proposed structure locations, and any previous land use.

3. The Soil Testing Process

a. Drilling Boreholes

  • Borehole Drilling: Qualified geotechnical engineers drill boreholes at various locations on the site. The number of boreholes depends on the size of the property and the complexity of the proposed structure.
  • Depth of Boreholes: Typically, boreholes are drilled to a depth of 1.5 to 3 meters, but this can vary based on local soil conditions and the requirements of the building.

b. Soil Sampling

  • Sample Collection: Soil samples are extracted from different depths within each borehole. These samples are carefully labeled and stored for analysis.
  • On-Site Testing: Some basic tests, such as penetrometer tests to measure soil strength, may be conducted on-site.

c. Laboratory Analysis

  • Soil Classification: In the lab, soil samples are classified according to their composition (clay, silt, sand, gravel) and properties.
  • Moisture Content: Determining the natural moisture content of the soil.
  • Atterberg Limits: Testing the plasticity and liquid limits of the soil, which indicate how much the soil can expand and contract.
  • Compaction Tests: Assessing the soil’s ability to compact, which affects its load-bearing capacity.

4. Reporting and Recommendations

Once the soil tests are completed, the geotechnical engineer compiles a detailed report that includes:

  • Soil Profile: Description of soil layers encountered in the boreholes.
  • Test Results: Data from laboratory analysis and on-site testing.
  • Site Classification: The site is classified according to the Australian Standard AS 2870, which provides guidelines for residential slabs and footings.
  • Foundation Recommendations: Based on the test results, recommendations for the type of foundation (e.g., slab, pier, or strip footing) and any necessary soil treatments or drainage solutions.

5. Compliance and Building Approval

The soil test report is a critical component of the building approval process. It ensures that the foundation design complies with local building codes and standards, helping to prevent future structural issues and costly repairs.

We also wrote a blog post discussion soil tests which you can read HERE