Analysis parameters

Owned by Iain Whyte
Last updated: Apr 11, 2023
2 min read

Include tree effects and/or tree removal/dying

If this box is ticked, then you enter Yt after entering Ys. This affects the calculation for mound height in the CENTRE OR EDGE HEAVE case. It also prompts the program to display 1.5 times the cracking moment in CENTRE AND EDGE HEAVE, as opposed to the 1.2 factor that is standard in non-tree cases.

Ys

The characteristic soil movement for the site, which is used to calculate mound height for centre heave and edge heave cases.

Yt

Soil movement for the tree affected case.
Potential surface movement due to the tree – induced suction change in addition to the normal design suction change. In tree design, Yt is calculated from the borelogs using the maximum design drying depth (Ht) (usually greater than Hs).

Hs

The depth of soil suction for the site, as given in Table 2.5 of AS2870-2011. Hs varies, from:

1.5m in climatic zone 1

1.8m in climatic zone 2

2.3m in climatic zone 3

3.0m in climatic zone 4

4.0m in climatic zone 5

>4.0m in climatic zone 6

The Hs can be inputed suitable for the zone where footing is being designed for the site.

Auto Ym centre and Ym edge

If this box is checked, then Ym (centre) will be calculated as 0.7 x Ys

Ym (edge) will be calculated as 0.5 x Ys. If the box is not checked then you may enter alternative values.

 

If Yt is checked, auto Ym tree (centre) will be calculated as (0.7Ys + Yt)

Ym (edge) will be calculated as (0.5 x Ys).

Auto edge distance

If this box is checked then edge distance is calculated in accordance with AS2870-2011, Appendix F2(b):

For centre Heave, in metres:

where Ym is in millimeters and Hs is in metres

For edge Heave:

where Ym is in in millimetres

If the box is unchecked then a custom value can be entered, however it is recommended that the

automatic value be used.

 

Auto soil mound stiffness (k)

If this box is checked, then soil stiffness will be taken as the larger value of 1000 kPa or 100q (where q is the total load expressed as a uniformly distributed load over the design rectangle).

For Melbourne basaltic clays a soil stiffness of 400kPa/m minimum or 50q may be used. Refer to AS2870-2011, Appendix F2(c).