DIY Doctor

Retaining wall and drain channel on clay soil

Postby daiku » Wed Jun 10, 2020 3:23 pm

Hi all

I am building a low retaining wall and installing a drain channel on clay soil in front of the house.

There is an existing concrete path (1m w x 7m h x 100-150mm d) next to the house.
The drain channel and the wall go next to this path. There is a sloped lawn next to the path.

Drain channel:
The plastic drain channel is 130mm w x 80mm d.
I have dug a trench (200mm d x 330mm w) and filled with gravel (50mm d).
As I walk on the gravel it still moves.
I will suspend the channel and pour concrete in the form. So the channel will be supported by concrete (100mm both sides and 70mm below). Concrete will be 150mm deep on both sides of the channel.

Retaining wall (300mm h x 215 d):
The wall goes next to the drain channel and retain the sloping lawn.
I have dug a trench (300mm d x 400mm w). it gets filled with water overnight even when it’s not raining. So I dug 100mm deeper than the drain channel section.
I am intending to fill gravel (10mm d) and concrete (200mm) on top to create a footing.
The wall will be 300mm h x 215 d x 7m long, with two rows of concrete blocks laid on the flat side and one row of sleeper on top.
There is a gas pipe running 90degrees to the drain and the wall at 270mm deep.
The wall needs to bend at a 45-degree angle in the middle, and the corner sits exactly where the pipe is.

I will fill the back of the wall with gravel wrapped with geo fabric. Also create weep holes on the walls so the water behind the wall can move through and goes to the channel drain.

Questions:

1. Is the channel depth needs to be the same for the wall and the drain?

2. Is gravel enough? 50mm deep for drain and 100mm for the wall.

3. Are concrete slabs deep enough? 80mm under the drain but the sides are 150mm, and 200mm for the wall.

4. Can I concrete over the gas pipe (yellow plastic one) if I cover it with sand (100mm on both sides and 30-50mm on top)?
Or should I not concrete around the pipe and bridge the slabs with concrete blocks (retaining wall) on top (of course surrounding the pipe with sand)? If so, will it sink unevenly and cause a crack on the wall or concrete?

Thank you
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daiku
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