The Structural Engineer's Corner

Eng. Onorio Francesco Salvatore

Strength of soils at Serviceability and Ultimate Limit States

Written By: Lexatus - Oct• 13•13

Soils type - ONORIO

In a previous post we discussed about the relations to use in order to evaluate the embedment depth of the utility services poles direct-planted. To whom could have missed it, the post is the following:

Embedment depth for utility services poles according to Australian Standard 4676

The relation discussed requires values for the foundation soil. The following can be used as a reference, as shown in the Australian Standard 4676 and Geotechnics books.

Class: very soft;

Soil description: silty clays and sands; loose dry sands.

Strength: fb < 60 kPa.

Class: soft;

Soil description: wet clays; silty loams; wet or loose sands.

Strength: 60 < fb ≤ 100 kPa.

Class: firm;

Soil description: damp clays; sandy clays; damp sands.

Strength: 100 < fb ≤ 150 kPa.


Class: very firm;

Soil description: dry clays; clayey sands; coarse sands; compact sands.

Strength: 150 < fb ≤ 240 kPa.


Class: hard;

Soil description: gravels; dry clays.

Strength: 240 < fb



Those values are based on foundation deformations of approximately 12 mm under serviceability loads.

In case of installations sensitive to displacements at their supporting points, such as the microwave antennas, this degree of deformation might be inappropriate and a suitable reduction has to be evaluated.

The Ultimate Limit State values, with the above in mind, can be taken as the serviceability value multiplied by 1.5.

For any issues or questions, you can contact the author at:

Eng. Onorio Francesco Salvatore

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