Soil Investigation for Building Foundations

Specifically related to the subsoil beneath the site under investigation and could be part of or separate from the site investigation.

Purpose of Soil Investigation:

  1. Determine the suitability of the site for the proposed project.
  2. Determine an adequate and economic foundation design.
  3. Determine the difficulties which may arise during the construction process and period.
  4. Determine the occurrence and/or cause of all changes in subsoil conditions.

The above purposes can usually be assessed by establishing the physical, chemical and general characteristics of the subsoil by obtaining subsoil samples which should be taken from positions on the site which are truly representative of the area but are not taken from the actual position of the proposed foundations. A series of samples extracted at the intersection points of a 20000 square grid pattern should be adequate for most cases.

Soil Samples

These can be obtained as disturbed or as undisturbed samples.

Disturbed Soil Samples

These are soil samples obtained from boreholes and trial pits. The method of extraction disturbs the natural structure of the subsoil but such samples are suitable for visual grading, establishing the moisture content and some laboratory tests. Disturbed soil samples should be stored in labelled air tight jars.

Undisturbed Soil Samples

These are soil samples obtained using coring tools which preserve the natural structure and properties of the subsoil. The extracted undisturbed soil samples are labelled and laid in wooden boxes for dispatch to a laboratory for testing. This method of obtaining soil samples is suitable for rock and clay subsoils but difficulties can be experienced in trying to obtain undisturbed soil samples in other types of subsoil.


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