I realize that this is a bit late in the game, but one company I worked for found out the hard way that pulling big wire through sharp 90's underground can be problematic. It is better to use sweeps of larger radius bends.
That's good; in the OP you called them "90 degree ells". In the example I cited, digging up the conduit and replacing the sharp bends with sweeps was the only solution. Ouch.
