You could potentially shotcrete (spray it with concrete to reinforce) the wall after the robotic excavator is done if you’re concerned about stability. I can’t speak to whether you can highly automate this as well, but it seems possible with current state robotics with human operators.
The ability of a dry stack retaining wall to shift and breathe is a feature, not a bug. For stone walls that require added reinforcement against lateral loads, look into tiebacks or geogrid reinforcement.
This would be discussed in an introduction to soil mechanics and foundation design (Braja Das's textbooks used to be the standard reference in the US when I was a student 15+ years ago) but I'm afraid they're too dry for anyone outside the profession. I'm not aware of an author who can animate civ eng subjects for the adult with the talent of David Macaulay. But I can point you to a few "engineering gems" that might pique your interest if you like this sort of stuff: prestressed and post-tensioned concrete (the work of Freyssinet, see Billington's books), readings from John Ochsendorf's class on historic structures in https://ocw.mit.edu/courses/4-448-analysis-of-historic-struc..., bicycle wheel as prestressed structure (the same principle used in some tension-compression stadium roof structures): http://www-civ.eng.cam.ac.uk/cjb/papers/p20.pdf
There are Civil Engineers here (I only studied it at Uni - I ended up in IT!)
When you deploy a structure like a retaining wall you want to try and ensure that the materials you use will retain their properties as long as possible and if part of it fails, it should not case the whole structure to fail. Add additional design requirements as you like eg colour and texture but always think about function first or you will regret it later!
In a garden setting, you will want to consider: gabions, drystone walling and "sleepers" (large lumps of wood - like railway sleepers).
Some quick material thoughts: Wood is prone to rotting, so ensure it is treated and well drained. Drystone walling can be prone to collapse unless it is allowed to drain properly and plants/weeds should be removed. It should be slanted at around 5 degrees from vertical to resist collapse. Gabions made of galvanized steel wire are extremely strong and resistant to pretty much anything. Devon Popples are an ideal filling for gabions and make a phenomenal structure.
I built a deck part way down in my garden. It is about 5m wide and sticks out about 1.8m. Behind it is a sleeper retaining wall which is about 1.8m high. I angled it back by about 2 degrees from vertical. I laid it on a concrete strip to spread the load and gravel base and back filled with quite a lot of scrap brick and rubbish for drainage. I used some 2m x 10mm stainless steel threaded rods embedded into the conc base to ensure horizontal stability (horizontal shear). I used 180mm, No. 10 passivated screws to keep the wall together whilst I built it and back filled.
"Where can we read more on this engineering"
It's everywhere but you will have to deal with local conditions. I am not convinced you are what you claim.
Knowing where to look without colleagues or steeping in the field is difficult. When teaching people to code, I often run into the same issue: assuming people are good at googling, or know what Stack Overflow is.
I am very good at googling and other online resource discovery, but that is no replacement for a knowledgable practitioner pointing you towards known good, high quality online resources. You don’t know what you don’t know. "Unknown unknowns."
I will even pay subject matter experts when necessary to bootstrap the research and autodidact process. There is no speed limit when learning, but rails and direction have value until you have enough foundation in a domain. I will absolutely let someone teach if they’re willing to set me on the right path, one of the reasons this forum is so valuable: highly knowledgeable people willing to bestow knowledge for free. And asking is mostly free (assuming you are polite and receptive).
Another quick tip: resist the urge to stack your stones long-ways parallel to the course of wall. Instead, put the longest dimension perpendicular to the wall.
This makes it much harder for the wall to fall outward as it shifts.
Perhaps, and there are lots of different types of stone and how to stack them.
My garden walls are of blue lias which is a bit like slate (https://en.wikipedia.org/wiki/Blue_Lias) it lends itself to flat 1-6" thick blocks that lay into quite neat horizontal rows whilst still being disjoint and allowing water to flow out. Weeds do grow in the cracks and the woody ones at least should be removed.
As you say a thicker wall will be more stable. Water and soil pressure will be most intense at the base, so make the base thicker and thin out as you move up. A slight deviation from vertical will allow for the soil expanding. For example my walls were rebuilt after a dry spell so a few degrees off vertical allows for the clay to absorb water and expand.
Look at the Dry Stone Wall Association of Great Britain, or The Stone Trust in the United States. These organizations still teach traditional methods of dry stone walling which cover a lot of these techniques.
You could stop water draining through the retaining wall and turn it into a dam, which will not end well.
My back garden/yard has a 40m drop to a lawn. The levels are managed by dry stone walls. Soil here is heavy clay with really heavy clay sub soil, so efficient drainage is imperative.
As well as drystone walls, consider gabions which can form phenomenally tough retaining walls. You can plant on them too rather than having to weed drystone walls. Gabions are much more resistant to plants forcing joints apart than drystone walls.
A 'sealed' retaining wall where the stones are interlocked or even glued/mortared together would probably have a higher load capacity than one made dry/unadhered. Or someone could simply like the aesthetic of a more 'filled in' wall, regardless of practical considerations.
Eh, the perforated pipe technique can efficiently collect the water and move it somewhere else entirely. It's nice that dry stone can just let water fall through, but then it just runs out at the base. Which might be fine, but you might still want a french drain anyway.
You would still need humans to erect the gabions though, no? Trying to understand the best optimization use case for this product and best fit final results. Please excuse my knowledge gaps! I’m am trying to fill those gaps.
You can fill gabions that have been pre-made by using a mini excavator. Or you can do it by hand but that's pretty labor intensive, unless you like wheelbarrows and buckets I would advise against it. Personal experience and all that ;)
The important thing with gabion is to realize that they still need careful planning, anchoring, leveling and possibly a foundation to ensure that they aren't going to shift over time.
Reduction in human labor for building these types of structures. The world is getting old fast, but infrastructure is still required, both new and maintenance of what exists today. Also, job assistance that reduces the toll on humans in this industry. This prevents treating the human as a consumable when the automation can be human driven, increasing quality of life and potential career longevity (if desired).
Not replacing humans, to be clear, but helping them build better with less effort. Thank you for indulging me. I hope to eventually leave tech to build things that are needed that are built to last (I too am getting old fast).
This defeats the purpose a little bit though because the environmental benefit is to _not_ use concrete, as producing it has very high CO2 output.
They use shotcrete a lot here in BC where cliffs are close to the road, but usually when it's soil or more loose material. Any rock structures (natural or man made) are typically left bare.
Shotcrete is regularly applied via robot in mining. The problem with shotcrete in open cell designs such as this is overspray and plugging of the large voids.
Gabion baskets are likely a better idea if you have stability problems and want to do a similar kind of automation.
One of the ideas of this project is, to NOT use concrete, to not have CO2 emmisions.
And depending on the "skill" of the robot and its algorithms, it could be very stable. I know that quite some ancient buildings in south america are put together just with stones put together(with precision and shaping of stones). They survived earthquakes and are still standing. So if enough stones of various shapes are avaiable - you won't need concrete. The weight and friction will hold them together.
The shotcrete I have been around was sprayed onto hogwire (already on the rock) and then bolted. It was not just coated onto existing rock as if it was a cake icing.
Not to mention the shotcrete | granite rock binding will shred itself after a year or two of daily heat|cool cycling in the sun - the expansion rates of the two materials don't match.
https://en.wikipedia.org/wiki/Shotcrete
https://www.geostabilization.com/technology/shotcrete-robot/
https://dawinvehicles.en.made-in-china.com/product/jBMnaOKdL...