Large size dished end of pipe-buried design

We are designing a cooling water system for a power plant. The delivery manifold has a torispherical dished end at one end. the pipeline is buried in soil and filcrete (2100 kg/cum) to about 5 metres above it. I designed for the overburden/ buckling for the pipeline using Iowa's formula. but i am not able to get a reference for load over a dish. Remember the dish is vertically placed as it is welded to the pipe which is horizontally aligned, tending the dish to buckle elliptically. how do we calculate the stresses ?The stresses are likely to be critical at the knuckle. is there any example/reference? is there a permissible deflection for dish or is it the same as the main pipe? All books I referred consider dished ends welded to process vessels which are above ground and so this issue is absent.