Building a short retaining wall

I have a semi-circular area inside of my semi-circular driveway, it has a tree in the middle. The perimeter of this area is about 40 feet. Currently I have pressure treated 4x4 used as a border around this area. After a few years in the hot and humid Miami sun, those are partially rotted and when I have severe rainstorms and the street is flooded, those 4x4 lumbers would float into the street. I anchored them with some rebars but still they move and shift.
So I am going to remove them and replace them with a stone wall. I am thinking of using something like this:
http://images.lowes.com/product/converted/742786/742786305220md.jpg
Because my driveway is not level, the top of the arch is higher then the "baseline" by about 14-16 inches. So I figured I need may be two layers of the stones on the high side, and four layers of the stones on the low side so that the border would be at an even elevation all the way around. I will set a couple of stakes and pull a string to guide me.
Now to the questions.
(1) I am going to dig down a few inches, and then fill and level with a layer of sand. Now would you start at the high side or the low side? My concern is that as I dig down in some spots I will hit a shallow tree root, and that would cause a problem as far as making everything level. I wonder which side I start would minimize any surprises. (2) I was told that I do not need mortar that these stones are heavy enough and my wall is short enough they would just stack. However, what if rain comes and wash out some sand below would the wall start to become uneven? If I don't use mortar between each piece of stone, would it be at least desirable to have a mortar footing (instead of sand)? or I should use sand below and put mortar between the stones? (3) What is the best way to stack the stones where there is a slope? I cannot create a sand base where it is sloping the steepest. Do I have to shape the ground there like a series of steps? I think I have to, but in that case, I would not be able to use a sand layer underneath.
Thanks in advance for any advise,
MC
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On Tue, 12 May 2009 12:50:05 -0700 (PDT), snipped-for-privacy@hotmail.com wrote:

MC
I think you have a wrong choice for material.
Nice video here:
How to Build a Curved Retaining Wall

http://www.youtube.com/watch?v=k37LTvLSUD8

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That's good video! Thanks.
The only difference is I am not doing a retaining wall, my wall would be free standing in that there is no difference in elevation between the inside and outside of the wall. I was thinking I would backfill the area inside but my tree is already there and I don't want to raise the soil level around the trunk.
So for my wall I need the finish to be on both sides instead of one side.
Thanks,
MC
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On May 12, 4:56 pm, snipped-for-privacy@hotmail.com wrote:

There is no rule that a planting bed has to be level. Contoured planting beds have a better appearance and let you focus attention on the plants you want.
You don't have to stack the brick you linked to. Install them vertically in a trench. I know of essentially nothing in construction where you start with an upper course and work your way down. That route is rife with problems.
R
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snipped-for-privacy@hotmail.com wrote:

It would help a lot to have a photo of the area. If I understand what you want to do, you will have a wall that is higher in places than the driveway, and level with the drive at the top of the arch? With the wall at different heights than the drive, will it be a hazard to people getting in/out of vehicles? Can you bank an area along the drive, rather than put in a wall - lay pavers or river rock along the bank and all should stay in place. We have corrected a lot of little problems areas around our condo, but nothing quite like yours. One of our problems was huge amounts of water from downspouts washing away soil from hedges nearby that are on a short slope. We replaced soil, put down landscape cloth and river rock where the water first hits - then planted liriope across the slope - that helps break up the force of the water but stays in place and allows water to disperse. It is pretty, no maintenance and holds soil very well. It is dark green, small blossoms, about 14" high. We also planted liriope around some light posts after we got tired of mower knocking them over. Great stuff.
Here is a link to info: http://edis.ifas.ufl.edu/document_ep016
Picture: http://classygroundcovers.com/item--Liriope-m -'Densiflora'-%7B50-Bare-Root-plants%7D-muscari--362
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snipped-for-privacy@hotmail.com wrote:

You should use commercially made pre-cast concrete retaining wall blocks. They lock together and have a built-in back slant to help hold up the dirt. Check locally as to which brands are available locally and chose the ones that you like for looks and ease of construction. The manufacturer will have details on how to construct the wall.
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I would not use sand as the base. I suggest road fill (DGA), a mixture of rock from 3/4" to dust which packs down nice and tight when tamped.
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