distribution of wheel loads

huangyhg

distribution of wheel loads
can anyone please suggest me a good reference or a book to find out factors for distributing wheel loads/point loads through earth fills??
i am designing a large underground sediment tank, which is covered by 3' soil at top (ground level). i need to know what loads will de distributed to the top of the tank (roof)if a moving load is considered. how the wheel load will be transfered through the 3' earth/soil.
please help!
check out our whitepaper library.
the aashto bridge manual has a section on box culverts where they provide design guidance for wheel loads through earth.
bowles 4th  edition has som basic stuff on using westergaard or boussinesq equations.  
i agree with the other responses and wish to add that most department of transportation agencies also have guidelines for vertical load distribution thru fills due to wheel loads in thier manuals.  many of these are now on-line.
as i recall, most use a 1:1 relationship for stress distribution.
also check out aashto on this, chapters 3 (loads) and 6 or 7.  either chapter 6 is for culverts and the other is substructure or vice versa but i can't re  
when designing wheels load on underground structure, use the wheel load for the heaviest piece of construction equipment on site. the traffic loads are always lighter than the equipment used to build it. also take into consideration that the cover on the newly constructed structure is less than final design.