Settlement of a culvert supporting railway

I am looking at the settlement design associated with a railway passing over 4 box culverts (which allows a river to pass beneath), the box culverts are precast concrete lifted in to position.

The ground make up is both granular and cohesive therefore I have looked at both the immediate settlements and long term consolidation for dead load - this is fine.

As for live load when a train passes over the structure, I was going to consider the live load component with an immediate response of the ground only.
The client has confirmed it is very low likelihood that a train would sit for any length of time on the culvert and thus long term consolidation would be too conservative.

Looking for confirmation on this approach but also the theory behind settlement analysis of dynamic loading (railway load) here in the UK, or abroad for comparison?
This load is being determined by a Structural Engineer consultant who have given me an applied stress at base of culvert of 400 kPa!!(albeit this appears to be contained to the location of the walls rather than the entire culvert base due to their current assumptions on the stiffness of the system).

any hints/tips much appreciated.

Thanks,