I have a few questions about pumping grout into road crossings. What are the pitfalls? How far can you pump? What is a safe delay between loads? What's the safest way to release connection clamp? I've done a few but still feel like i'm rooting in the dark.

Hmm. I have no experience in pumping into road crossing, what you mean by that anyway?
But isn't grout a lot like shotcrete? Water, cement and sand, and steelfibre in shotcrete.
That stuff you can pump as far as there are hoses in the world.
Safe delay depends, but as always, just look in the hopper, are you unsure, unclamp, swing around, circulate and blow out your hoses.
Releasing clamps, just open them a little bit so the pressure releases, if you got some slack in your clamps leave the safety pin and open them so it hangs on the pin.

Road crossings, instead of opening a trench to lay a water/gas pipea large diameter steel pipe is pushed under from one side, utility pipe run trough, both ends sealed except for vent one side connection for pump the other. Grout pumped in to encase utility. You know its full when grout comes out vent. Problem is you've no idea what's happening inside. Is grout running along bottom of pipe or is it drying out and building up and being pushed along by pump. If its a long crossing and 75 cube+ is being pumped is first load gone off before your finished. How do you know how much pressure is is in line when your finished.

Been doing alot of these jobs, encasing big water pipes for hydropowerplants.
Just watch your pressure, and NEVER empty a load untill the next truck arrives if you are in doubt.
If it sets your in deep shit. Nowhere in hell you're gonna move the mud with your pump. If it sets you need air to blow it open and start over.
Steady pumping at about medium fast will do nicely, it will most of the time just push itself out.

I love these kind of jobs, don't think I'm like most pumpers. It just gives you a great feeling knowing your doing something good that most other can't or will. :D