Try to avoid rocks touching the pipes. Soil movement and water hammer against rocks can wear a hole over time.

You need to flush out dirt after the pipes are glued up and the heads are installed (without nozzles). So fill the trenches halfway with dirt and flush each head for a couple minutes. This fills the trenches with water and make a muddy mess, but it also settles the dirt. After flushing, use a stick or something to move the dirt under and around the pipes. Once all the heads are flushed, fill the trenches with the remaining soil and soak them down with a hose until they're soupy. Use a stick to get all the air out of the soil.

No matter what you do, there will be more settling over time. If you want the trenches to disappear totally, you must level with sand in a year or two.

 

Not sure there is a real answer here. I would just fill the trench back up with the dirt that came out of it. After several inches of dirt is on top of the pipes, carefully step on it to flatten it, kind of at an angle to the sides so the pressure is on the dirt not the pipes, that pushes the dirt under the pipes. Do that from each side, get it nice and firm. Then fill in the rest. At that point you can then walk right on the trenched soil and try and flatten it down the best you can. Worked for me, but then again my soil is pretty sandy to begin with, may make a big difference. You can't get all the soil back in that you took out, just not really all that possible. I had extra dirt from the valve box digs that I spread around the low spots in the trenches. I'm sure OP will be seeding in the fall, right? I would compact it the best I could now and add topsoil to level it before seeding. Maybe make it a tad 'proud,' add soil so it is just a little higher than the surrounding soil, so when it settles down it's flat. Can always repeat that just prior to any seeding event. I'd rather have the seeds sitting on soil rather than sand.

 

Did my own irrigation this spring. I used an edger to cut the sod and then used my trenching shovel to try to not disturb the roots and then rolled it back. I normally had 4 to 6 inches of dirt attached to the grass, rocky heavy clay in Middle TN. I then excavated the rest and then added the soil back on top. I used poly for my runs and pvc for my main lines but used the same process. I tamped my soil down with a sledge hammer. Holding it by the handle and just using gravity to tamp down the soil until there was no more compaction. I then rolled the sod back in place.

This kept the yard feeling level and firm under foot. When I did my backyard last fall I didn't tamp the soil down just used my foot and you can still see where the trenches where. I'm going to bring in sand this fall to level. But because I tamped down the rest of the lawn it feels very level.

 

I just did my own and had some major issues because my clay soil trenches up as thousands of clods. Rain helped as I was able to use my lawnmower to drive over the wet clods and mush them to a solid mud state. Still, I have spots that are rock hard and too high and others that are too soft and sink several inches under any weight. So the answer may depend on your particular soil, but I like your idea of filling with sand first. Filling as much space as you can is a good idea, but everyone I know with irrigation says the lines sink forever. Just don't use any rock would be my suggestion. Even tiny smooth rocks will leave space that wet soil will move into over time, on top of the issue already mentioned about damaging the pipe.

That said, I bet enough sand to fill those trenches will be pretty pricey, so just having some sand available to level off the lines as they sink over time may be the best option.

Edit: if you have harder soil like mine you can fill in partially, soak with a hose, mush down, fill more, mush again. Not sure what tool to use for that other than a mud boot, but I'm sure there's something smarter!

 

This thread makes me think soil type really makes a big difference. My soil is mostly sand, so not great for water retention, but on this thread's topic perhaps I have found a benefit...

 

This thread makes me think soil type really makes a big difference. My soil is mostly sand, so not great for water retention, but on this thread's topic perhaps I have found a benefit...

I was surprised how hard it was just to trench. I rented a decent trencher and it still struggled with the clay. Then the clods starting filling the trench in for me. Just made life hard for a weekend, where if I had sandy soil I think I would have done a better job at a faster pace.

 

I was surprised how hard it was just to trench. I rented a decent trencher and it still struggled with the clay. Then the clods starting filling the trench in for me. Just made life hard for a weekend, where if I had sandy soil I think I would have done a better job at a faster pace.

It's interesting, the trencher just plowed through the sand like it was nothing. It just scoops it right out. However, b/c it's so sandy it doesn't hold the trench shape very well. I should have trenched deeper in a lot of spots, some sand moved back in (trenched one time but took weeks to actually lay all the pipe out since I was doing it a section at a time, did around 10 zones, and worked only one or two weekend days per week), and I ended up hand trenching prior to laying pipe in a lot of places. Unfortunately one side of my yard had so many roots, the trencher couldn't handle it. That was tough. Ended up cutting some with a handsaw, and hand digging a tunnel under a bunch to get the pipe through. It's amazing how far some significant roots will be from the closest tree.

 

Thanks for the information. It is on the clay side so I will have to adapt to that. I am strongly considering of shifting to a ditch witch and using PEX instead of PVC in hopes that it helps with the how level it all turns out. Even if it costs more to do due to the size difference, I am debating if it is cheaper in the long run due to the time required.

 

Why PEX? Polypipe is more cost effective than PEX.