Re: Tree Root Power??? -- GEOFORUM

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Date Posted: 20:02:57 08/05/99 Thu
Author: Dr. Chatterjea
Subject: Re: Tree Root Power???
In reply to: NSW Long (Sylvester Cat) 's message, "Tree Root Power???" on 08:11:22 08/04/99 Wed

> I quote from the notes which we received today which
> are based on Dr Chatterjea's transparencies. "FELLING
> OF TREES -> rotten roots decreases (c) cohesive
> strength, removal of trees reduce normal stress
> (load)." That point was presumably raised to aid in
> understanding slackening of soil particle
> cohesiveness. However, from what I have heard from Dr
> Chatterjea today and now from reading her notes,
> discrepancies surface, apparently.
>
> My understanding is that tree roots (living) have some
> kind of holding power on the soil such that the tree
> roots prevent the soil from becoming less cohesive,
> unconsolidated. In this respect, my understanding
> needs to be reinforced from readers and from Dr
> Chatterjea as to how the roots have such special
> holding power. Therefore, it makes sense to me, at
> least at this stage that dead roots from felled trees
> can no longer hold the soil together and so the soil
> becomes unconsolidated.
>
> So, how is it that the point of "removal of trees
> reduce normal stress (load) comes in?" The question is
> which of the component actually reduces soil
> consolidation (1) or (2) or (3), which is both?
> Point(1) being the removal of trees which leads to
> reduction of surface stress leading to soil becoming
> loose and that results in unconsolidation of soil and
> therefore is a prime candidate for water action to act
> as a trigger for gravity to lead to landslides.
> Point(2) being the loss of tree roots as the factor in
> soil unconsolidation. How exactly, I still do not
> know. Point (3) being both points working in synthesis
> to result in soil unconsolidation.
>
> Any answers for this little small query???
I would prefer you all to discuss this first. But just to mention that removal of trees should lead to reduction of Normal stress (load) as the weight exerted per unit area will be reduced. That is one point. Secondly, you know (I hope) that roots when they are living, will hold soil together within the root mesh - (try doing some gardening!!) this is what provides some shear strength. But when that is removed, that much shear strength is reduced. Added to this is the fact that rotten tree roots would leave some passage ways for water to enter the system - which causes extra pore water pressure etc. etc. So it's a combination of both. Rest can be sorted out by all of you. Do keep posting your comments. I like your nick name!!

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Replies:

Re: Tree Root Power??? -- Sylvestercat, 22:09:35 08/05/99 Thu