[kjander79]

Can someone explain to me why the brickwork in the picture in this example is just separated columns, using the cap to hold them together, rather than interlocking the bricks? I'm sure that's not the reason the structure collapsed, but once there's movement in the wall, it seems like that would contribute to loss of cohesion.

[hinkley]

He covered this type of construction in an earlier video, and I think this is the key line:

> Gravity walls and mechanically stabilized earth are effective retaining walls when you’re building up or out. In other words, they’re constructed from the ground up.

The soil behind this type of wall is supposed to have been stabilized by layering a tension material at intervals to keep it from moving. There's a demo of compacting sand with layers of cloth and then using the cube of 'sand' to support one wheel of a car. The material sags slightly and then holds.

My understanding is that those concrete puzzle pieces aren't predominantly load bearing. Mostly they are for erosion prevention and perhaps moisture control (not just keeping water out but keeping the hydration consistent over time and distance).

[hamburglar]

Yes, he goes into it in more detail on the video about mechanically stabilized soil, but the techniques used to stabilize the soil mean the wall is entirely stable without the concrete face, and the face is there to keep the soil from getting eroded away and to look nicer.