Question
Grading Plan
I am attempting to build a dry laid limestone retaining wall in a new housing development that sits on an old sand pit. So, the soil is PURE sand for 40+ feet down. The max height of each wall will be 3 feet. The land use above the wall will be turf and/or mulched tree/shrub beds. So, there will be a 3 to 4" cap of clay over the sand followed by approximately one foot of soil (all trucked in).
-Is a subgrade needed (crushed compacted rock)?
-How far below grade does the limestone need to go (more than 6")?
-I'm looking at 2' deep block (is that enough, can I get buy with less)?
-any other ideas tips?
Thanks So Much!
-Ryan
AnswerYes generally you still should use a crushed aggregate footing probably 10-12" thick/deep and extending 10-12" beyond each face of the wall. If you live in an area subject to significant freezing and heaving of soil you may need a more substantial footer including concrete. Sand comes in many forms (some better than others when speaking of compaction)Consult a local structural engineer if you are planning to build several successive walls of 3 feet each. Your footing needs to be below the frost line and the bottom of the first course of stone should also be several inches below the frost line on top of the footing you construct. I have no idea where you are from this email so you'll have to look up your frost line.
I suggest a friendly call to a local wall builder, pretend to be considering a wall job and ask how they generally do their footings.
best of Luck
Sean J Murphy
www.amenityarchitects.com
www.seengineering.com
