Another retaining wall question

I live on the side of a steep hill. All the gardens are terraced with retaining walls to support the various levels. One section of my terrace is supported by an old, sturdy, stone retaining wall (which looks to me as if it is in fine condition) topped by another, newer, stone wall which isn't. The top section goes about a foot below the soil level and the capping stones are about a foot above the soil so this top section is about two foot high in total. Several large cracks that go from top to bottom of this top section have appeared over the winter and spring.
There used to be a tree in the corner. It had been cut down before but the stump had sprung back into life again and I'm pretty sure that this is what has caused the damage. I've now cut the trunk and the new growth down again and the stump is still in the soil. My plan is to remove the stump, dig a trench behind this top section of wall to take off the pressure and then dismantle and rebuild this two foot upper section.
Having seen some other local gardens where the soil has pushed the retaining walls into gravity-defying distortions I suddenly wondered whether the soil and roots might actually be holding it all together? In which case I suppose the wall ought to be dismantled first - to avoid stones dropping down into the next level.
Any thoughts about which way to approach this? Is it within the scope of an amateur bricklayer like me or ought I call in someone with more experience?
Thanks,
Nick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Retaining walls like yours work by gravity. ie they rely on the weight of masonry to prevent overturing. A general rule is that the hieght needs to be three time thickness at the bottom. It can be battered and tapered. (ie thinner towars the top) And important point is to have drainage behind the wall and drain pipes through the wall to relieve hydrostatic pressure. If the wall is more then 6m long, it will have to be broken into panels with vertical movement joints between (with slip ties) to stop vertical cracks appearing. If there is a tree at the top of the wall, the rocking action in wind will evetually destroy the wall.
You can kill the stump by drilling vertically down behind the bark and pouring "Roundup" in the holes and covering to keep rain out. (Holes about 3" apart). It will eventually rot away.
You can do it but it will be a big job. Lots of digging and chucking earth about.
http://en.wikipedia.org/wiki/Retaining_wall#Gravity
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Nick - you know that old saying "a picture is worth a thousand words". Any chance of a picture?
BTW I know a really good semi-retired and trustworthy brickie out your way should you need him (ISTR you are in West Yorkshire)
--
Adam


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 6 Jun 2014 19:04:51 +0100, "harryagain"

That's the badger. The original retaining wall looks okay to me but the "parapet" (the newer top section) is the part that seems to be in trouble.
Nick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 8 Jun 2014 08:44:43 +0100, "ARW"

I know, I know - but it's not really been the kind of weather for climbing through next door's garden and taking photos. I'll try and take some soon and post links to this thread.

That could be very useful - I'm in Huddersfield.
Thanks,
Nick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote: >>Nick - you know that old saying "a picture is worth a thousand words". Any

I thought so. And so is he:-).
I'll email you his phone number if you need him. But be warned - as much as I trust him and like him (I have worked with him and for him lot's of times) always supply coffee or coffee making facilities. NEVER offer him tea:-).
--
Adam


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 8 Jun 2014 18:14:15 +0100, "ARW"

Well, I hope he's okay with the fresh-brewed stuff because I almost always have some on the go.
Thanks Adam - I'll get those pictures sorted out and see where we go from there.
Nick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 06 Jun 2014 18:06:41 +0100, Nick Odell

A couple of pictures, taken this morning.
http://tinypic.com/r/9ks85j/8
http://tinypic.com/r/209kf1l/8
I cut the stump back to the soil level because that's where the new growth sideshoots were coming from.
The back wall (bordered by the hedge) drops down about 2m into the garden behind and looks like a classic retaining wall made with large purposeful stones. AFAICT the drystone supporting the side wall and the parapet above parts that have been affected.
Nick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.