QUOTE: Originally posted by davekelly Just a gut resonse here. Given that the speed of the engine over such a pit would be slow, the depth of the pit relatively shallow, I would think that there would be very minimal forces acting on the pit walls other than the normal force (straight down). Thus, there is great force trying to pu***he rails (and it's support) down, but little trying to push it inwards. It is the strength of the material making up the rail support and pit walls that will determine whether the inspection pit collapses or not. While I am no expert on inspection pits, all the one's I have seen have the rails attached to and supported by some sort of masonary. Think of the weights that are supported by concrete columns. As long as the forces are directed downwards, such structures can support massive objects without "blowing out" to the sides. Sorry for the terribly worded answer . . . this is one of those "I know what I am thinking, but can't seem to put it in words." Dave