Retaining wall made of masonry panels - how to properly backfill?

Hello everyone,

I have a question about the proper construction of a retaining wall made of wall panels 105 to 130 cm high. I am concerned about the permeability and frost resistance.

=>> What can happen if the retaining wall is backfilled not with frost-resistant, permeable sand-gravel mixture, but with existing sand (medium sand, partly fine sandy, silty)? Will the wall then have a shorter lifespan? Or are we being too cautious?

The commissioned landscape gardener has a robust view of proper work and wants to set the wall panels in concrete in one go. He also believes that, due to the existing sandy soil, no special gravel-sand mixture is needed to backfill the retaining wall in a permeable and frost-resistant way.

We are laymen and what we can do is google: Both manufacturer specifications and "internet experts" state that one should backfill with permeable, coarse-grained gravel or gravel-sand mixture. Furthermore, this layer should be separated from the soil so that the layers do not mix.

The landscape gardener wants to start right after the weekend on Monday. I would like to know from you what we should require from the landscape gardener and what I should discuss with him on Monday morning.

We are laymen and what we can do is google: Both manufacturer information and "internet experts" claim,

But you do realize that you also ended up on the internet here? What is this about anyway: L-stones - are the height specifications meant to indicate the dimension of the free height on the valley side of the height difference - is the "concrete" in which the wall panels are set supposed to be a foundation ... ... ... ?

You basically have several problems with poor drainage
- wet soil is heavy and exerts more pressure
- in wet soil the cohesion is worse, which also increases earth pressure
- water expands and exerts pressure when it freezes

How bad all this is depends mainly on your soil. As soon as waterlogging is to be expected, I definitely wouldn't skimp on the drainage

But you do realize that you have also ended up on the internet here, right?

Good point. ;)

What is it actually about: L-blocks – are the height specifications supposed to indicate the measure of the free height on the valley side of the height difference – is the "concrete" into which the wall panels are set supposed to be a foundation ... ... ... ?

1. The planned height difference between our property and the neighboring property is between 35 cm and 100 cm.
2. The top of the wall is to be at the same height along the entire length, the property slopes down at the front and back.
3. The L-blocks are set "with concrete C20/25". That is the description in the offer.
Is that explanation sufficient?

You basically have several problems with poor drainage - moist soil is heavy and exerts more pressure - in moist soil the cohesion is worse, which also increases earth pressure - water expands and pushes when it freezes How bad all this is mainly depends on your soil. As soon as waterlogging is to be expected, I would definitely not skimp on drainage

WilderSueden, first of all, many thanks for the late evening reply! The question is, from when exactly is it "poor drainage" and how do I know if the soil is good enough? Honestly, I had assumed that with sandy soil you don’t have to install a drain pipe at the base of the L-stones at all. Although this is regularly required for public projects, it is probably rather the exception in private projects, I suppose. I mainly wanted to know what quality the backfill soil should have.

We have 7 meters of L-shaped stones between 1.2m and 3m in height, they are even backfilled with mineral concrete and there is drainage inside. But here we have clay and forest soil.

I would say that with soil, drainage is always required, insist on it but be aware that you will also have to pay for it.