Determination of demands over buried pipe or box type culvert structures
utilizes theories attributed to Anson Mars ton back in the early 1900s. I
haven't designed any since 1981, but I recall there are many variables such
as type of bedding material at the bottom of the structure, width of
trench, type of soil above, shape of the structure, type of construction
material etc. California Division of Transportation (Cal Trans) and NAVAC
DM-7 from the Navy has some design criteria.
Michael Krakower SE