Allan Block Retaining Wall

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Old 04-24-13, 07:33 PM
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Allan Block Retaining Wall

I need to lengthen my driveway to increase parking spots. To do this I am adding an Allan Block type retaining wall in a hill side that is about 30’ past the driveway.


Background and Detail:

Slope Below Wall: The grade drops ~5’ in a ~13’ run.

Slope Above Wall: The grade is the same as below. Wall height will be ~4’

Soil: Mid west. Heavy Clay. The soil is backfill from when the house was built 17yrs ago. It is fairly stable… a ~2’ dry stack stone landscape (retaining) wall has been in place at the foot of the hill for all 17 yrs with no movement.

Top Of Wall: Gravel backfill behind wall will be topped with pavers. Flatter area between existing driveway and new retaining wall will be excavated ~10.5” as necessary and topped with pavers (2.5” paver + 1” sand + ~7” compacted crushed limestone). Note, that I need to check manual for actual required depth of limestone. Cars will be occasionally parked near top of wall.


Questions:

1) What do I backfill behind the wall with? Compacted crushed limestone? Compacted wall rock? The Allan Block manual calls out wall stone behind the wall. However, compacted limestone should go under the pavers. Since the pavers will border the retaining wall, I am worried that using two different types of stone under the pavers may settle differently.

2) Should I worry about the slope below the wall? I plan to bury at least the first course of blocks.

3) When the plastic drainage pipe is placed in the compacted limestone base… are there any worries about collapsing the pipe with the compactor?
 
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Old 04-25-13, 12:14 AM
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Worry is wasted anxiety, so don't let it control your life. Don't worry--be happy.

You want a washed-rock type product behind the wall to promote water drainage and prevent excessive wall pressures building up. Few if any fines.

With flimsy pipe or an over-sized, heavy compactor, yes, you could crush or possibly just crack the pipe. Use a heavier walled pipe, Schedule 40 or so, as opposed to some of the really thin plastic stuff available. And don't use a D-10 for your compaction.
 
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