We just purchased a 1/2 rai lot (Koh Samui) and had the lot cleared and 125 truckloads of fill dirt laid down, graded, leveled. On two sides the dirt is exposed, not level with the existing ground (ranging in height of 1/2 meter to 1 meter higher). One of the construction crew suggested a retaining wall be installed as I will be letting the lot sit for awhile (maybe a year) before building on it. His design was 5-star; concrete footers 1.8m down, a very solid wall rising about a half meter above the fill dirt. Suitable for adding a wall on top later of 2-2.5m height. His price quote was 5-star as well :). I'm thinking this is more an attempt to get the foreigner to bite. Since the land is level, I believe whatever erosion occurs will be minimal and I can much more cheaply add some fill later, OR, simply make a makeshift temporary retaining wall (wood/plastic/metal) to minimize erosion. Thoughts on the need for a retaining wall in this situation?

I would say yes.. or the newly laid land will wash away in the rains..

Make sure he has drainage slits in the retaining wall...it has stella bar coming from the footings up thru the blocks on the wall..  filled with concrete to the top layer of blocks with at least 10 inches of har stuck out the top..

 

Good luck..

Plant grass around the exterior of the house and the grass roots will prevent the soil from eroding.  If you use the retaining wall, I would make sure they used full-sized block 8" thick, not that thin block that always seems to fall over and crack.

Here is his plan for the retaining wall

Below is his design plan for the retaining wall (the wall on top is only for reference). However, for the price of the 59 meter in length retaining wall I could build a small house or good sized swimming pool up north I think. I have asked a couple others for estimates but as I did not originally factor this cost in...I'm looking for other viable options as well. Planting along the edges might help a bit or possibly a temp wall.

I would say this, that if you are going to build a wall around the property at some stage, then why not do it now. I have alot of experience with land and enclosing it in the South and found that when the perimeter was secured that there were alot less invasions and encroahment. For this very reason I would define the border preferably with a wall, but not less than a decent fence. Locals do love to invade especially when a foreigner is involved. Another very good reason is that you've made your mark, as even with Chanote posts, things can happen (moved, removed and contested even after surveys for example) and it's better to be safe than sorry IMO............................