I am in the process of digging a rubble trench foundation for a greenhouse which will have an earthbag stemwall and north wall to act as thermal mass.
I will be digging the trench 18" deep, lining it with fabric to prevent silting, filling it with 1" scoria, and starting my first row of earthbags below ground. I have clay soil, and I am digging a ditch from the foundation to lower ground to aid drainage.
I just bought a roll of 3" perforated drain pipe to run along the bottom, because that's what my research on rubble trench foundations has indicated that I should do. But I'm looking at this stuff and have two concerns: 1) won't this get crushed with the weight sitting on top of it? and 2) why do I need to do this if I'm already filling the trench with rock and am sloping it to ensure water drainage? What additional purpose does the drain pipe serve?
The shape of the pipe will prevent it from being crushed as it is firmly packed in place by the other drain material. Most of the weight will disperse around the pipe.
The pipe serves to add an easy path for lots of water to drain fast--it also helps direct water in the drainage if your trench doesn't go all the way to daylight. You could have the pipe be the only thing that leads away from the foundation, thus reducing the amount of drainage material you need.
So no to your title question, you don't have to have the drain pipe.
I've always been told that the layer around the drain pipe should be sand, and you should make the extra effort to ensure that the sand is down tightly around the pipe. The sand supports it from being crushed or punctured, whereas rock applies uneven pressures and can puncture or crush the pipe as it is filled in.
I understand the skepticism ... a lot of the "should" and "must" do's seem to be tied directly to "buy this product - and stop asking questions!"
That said, I would advocate for a drain line still. You are doing everything else right (maybe it could be "better", but it ain't wrong), but there is still a good argument to be made for a pipe here. As Daniel mentions, the pipe allows for rapid removal of water - but it also also as redundant system so there are TWO ways for the water to escape. Given that your trench is in clay, and thus is essentially a water trough, you really don't want to allow water to accumulate in there at all.
At a previous house we discovered that the prior idiot-owner had made a little land bridge over the exit from a large french drain (~ish). The first big rain created a pond that backed into the basement. I added a drain pipe, problem solved.
So I now make sure that I use infiltration pipe and then transition to solid so that collected water isn't just redistributed but moved away. The solid pipe is also much more resistant to the accidental shovel/backhoe contact - and under the driveway - is better protected from the crushing weight of gravel trucks. I think a gravel trench running to daylight is also a fine idea, but over time is more likely to have its effectiveness curtailed as it fills with silt, etc. The other benefit of a pipe is that its much easier to see if its actually working!
I don't mean to hijack your thread, however, I'm in a similar situation with my house, only that I already filled the rubble trench without adding a pipe. What are my options besides waiting until I construct an extension through which the pipe would go?
I got this tall by not having enough crisco in my diet as a kid. This ad looks like it had plenty of shortening: