Well, I'm happy to report that 2 full days and 5 afternoons later, the dirt is no more! I transported it all with a wheelbarrow to a container and it was taken away by a truck.
Right after that I bought all the wood that was needed for the missing layout frame modules. And it was of course immediately painted with a wood protector.
Once dry, the work on building the next set of walls has started. One challenge I had here was that the planks I bought were rarely really straight. I had to use a set of transport belts to force them into the correct position.
When the module walls were ready, they were painted the second time.
The next part was surprisingly easy. The wooden walls were connected using cross planks and immediately became my layout modules. They're not perfectly rectangular, but they fit pretty well. And it all actually looks pretty good, too (especially from a distance).
The trickiest part of the frame was the "soft corner". I really regret coming up with this idea. It took me over half a day to build and it was the moment when my lack of experience in working with wood really showed. The result is far from perfect but it feels sturdy and will have to do...
I also took an extra care about the modules' connections. Each module is supposed to be independent and be able to hold the filling by itself. But I really wanted to make sure that they don't shift and that the entire frame stays as one. Hence the extra support at the points of contact:
The remaining elements were installed and painted. The entire frame for my elevated layout is now ready. It's waiting for the stones to be filled with.
Unfortunately the days are becoming shorter and colder. The weather is often rainy, too. There's no way I can finish this project before winter. I guess I'll have to cover the structure for now to protect it and restart my activities in spring. So that might be the last update on my elevated layout this year...