Retaining wall strengthening

[R0ss]

I have a 1.2 metre concrete retaining wall in my back garden that I would like to strengthen to keep it good for the forseeable future, and also make it a bit nicer to look at. Water is starting to come through the wall and affect the rendering, the wall also leans forwards by around 7cm at the top.

My plan is to lay a 40cm concrete footing in front of it and then build a brick wall and connect it to the existing wall with brick ties.

I have a few concerns though:
- There is no obvious drainage system in the current wall
- There doesn't seem to be any foundations under the current wall, after doing a bit of digging I can only see soil, would putting in footings make drainage more of a problem? (as water can't travel under the wall as easily)

Any advice would be very welcome, thank you.

 

[KenGMac]

R0ss, good evening.

Can I suggest? you consider.

Proceed with the footings, consider reinforcing? then at a distance from the existing R/T wall erect another wall in front, how about blocks, laid flat, not one there edges.

But?

Before erecting the wall cut out several bricks / blocks from the existing wall to facilitate ground water escaping from behind the existing wall.

Now for the "gap" between the two walls, old and new?

How about filling the gap with gravel, this will allow any trapped ground water to be managed, the management could be as simple as plastic pipe off cuts built into the new wall, at low level?

Ken.

 

[R0ss]

Hi @KenGMac

Thanks for taking the time to reply to my post, really appreciated!

Drilling some holes into the existing wall is something I’ve been thinking about, to give the ground water somewhere to escape.

I hadn’t thought about putting pipe/gravel in the cavity between the walls - that sounds like a great idea!

I guess I’ll need to leave sone gaps in the blocks at the bottom of the new wall too.

 

[KenGMac]

R0ss, good evening, again.

What tends to happen is that when a R/T wall is built, a layer of "Geotextile" material is placed, down the earth side, across the base of the gap, and up the face of the new, being constructed R/T wall. at this point a perforated pipe is laid generally on a sloping layer of gravel, then the remaining gravel is piled in.

The geotextile is then wrapped over the top surface of the gravel, this in effect encapsulates the gravel, keeping it clear of mud and fine particulate material that will over time totally clog the gravel and negate the effect that is being attempted, to allow the removal of ground water from behind the T/Y wall and thus reduce the hydraulic pressure on the wall.

If possible the perforated drain can be led to a nearby storm drain.

If the gravel is kept below the top of the wall by [say] 300.mm. that area can be used as a planting border.

In a small wall such as yours, the perforated pipe is not really needed, But you can build in several plastic pipes into the wall over its length, they will allow the gravel to drain out.

As for the existing wall. Simply punch some holes through and that will allow any build up of water behind the old original wall to percolate away.

Ken.