I had an idea recently, how to rapidly and relatively cheaply make sewer pipes for simplified sewer systems (or vacuum sewers, I guess). Not sure if it has been done before:
Basically I think you can take a flexible pressure hose with a rubberized surface (commonly available for firefighters and such with diameters DN100/10cm for example) as an inner cast for a long concrete pipe created on site (even in the trench).
Just dig a small and shallow trench, add here and there some small pre-made concrete elements/rings to hold the hose and to add junctions, sharp corners, inspection holes etc. then apply water-pressure to the hose, add if needed some arcs of chickenwire as "rebar" on top. Once this is done fill the trench with concrete until the hose is covered completely.
Then you just wait a few hours until the concrete has hardend somewhat and depressureize the hose to pull it out... afterwards run some water though the new pipe for curing during the following days.
Steep slopes will be a bit harder to make, but can be made some with "steps" also.
The inner surface should be quite smooth due to the rubberized pipe and wide arcs are automatically nicely done as the pressureized hose can only be laid like that.
Probably not worth the effort where cheap PVC pipes are readily available, but even there it might be more duable and easier to repair.
Any comments or further related ideas?
Probably this isn't a new idea at all
Edit: Would probably work for low pressure drinking water pipes also.
Edit: At a much larger diameter a similar system seems to be a standard (but with air pressure). Probably also needs to have some sort of flexible joints at some points to avoid cracking... not quite sure how to do them yet.