AS2870:2011 Design of Footings for Trees

[ShawThing]

Hi Everyone
I was wondering if anyone has had much experience with adjusting the ys value to reflect the potential influence of trees in accordance with Appendix H of AS2870:2011.
Also how you might take into account the presence of trees that might have been cleared and no longer exist but could still be having a impact on the moisture content of the soil by the fact that they are no longer withdrawing moisture out of the ground. Experiencing a lot of sites being classified as a 'P' as a result of this.
Cheers.

 

[GB1000]

Mate - I deal with this a lot.

Two things.

1. You can design slab taking by adding the soil surface and effects from trees (I can't remember the formula but I believe its 0.7ys+yt.
2. Or you use piles down to rock. We generally use method 1.

next item. I've asked the same question regarding trees. This is such an issue in the residential sector. I couldn't quite find anything on it in terms of litrature and I asked our geotechnical engineers, and their response was, the previous trees would at least have to go through a mositure varying season. i.e. I took this as a year. I fairly sure when site classifiers are giving movement this is not taking into account.

I'm sure if you asked an arborist there might be some answer and its specific to tree types etc

 

[ShawThing]

Thanks for the reply.

Yes, I think we have the centre and edge heave calculation under control but the other issue in respect to pre-existing trees is still a bit of an unknown.

We have been told (by a representative of a government authority) that trees could have an influence of up to five years which seems a bit extreme. Based on this site classifiers are looking at aerial photography and nominating sites with trees within five years as P sites. Some are doing an adjustment of the ys assuming a worst case scenario however others are not. I believe the five years has been tenuously linked to the five year reference in clause 2.3.2 Part (B). Your right though that this issue is probably not being addressed by site classifiers generally. I haven't been able to find too much information on this issue. Maybe in the next code update there might be further clarity?

 

[Tomfh]

It would be great if they clarified this. Always depressing seeing the dreaded "Class P" due to trees.