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Re: Loads on culverts

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Bob Mahony wrote:
> 
> If a culvert is covered by many feet of fill can arching action of the
> fill over the culvert roof be taken into account when determining the
> load?
> 
> If the fill settles, does this mean that a wedge-shaped load of fil,l
> from finished ground level to culvert roof, is now supported on the
> culvert?
> 
> Will the fill over the roof not transmit a component of thrust on to
> the adjacent fill as it settles?
> 
> I would welcome any comments,
> 
> ==
> 
> Bob Mahony
> 
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> 


In practice, design of culverts is usually done neglecting any arching
action that could occur. Therefore, you do not have to consider the
weight of a triangular wedge of soil on the roof. You consider the earth
pressure and the live load pressure. Impact should be zero if the fill
is large enough. Please note that the live load pressure reduces with
increased height of fill due to live load distribution.

If you are interested in the behaviour of culverts you must
differentiate between flexible culverts such as Corrugated Steel Pipes
or rigid culverts such as concrete box.

In a rigid culvert, there should not be much arching action because the
top slab is stiff enough to carry the weight of the soil and the traffic
without deforming so not much arching action can develop. Since the box
is stiff, there isn't really any significant lateral thrust from the
vertical loads.

In a flexible culvert, it is debatable how much arching would exist.
However, it is not considered in the design. The lateral thrust you are
referring to exists in flexible culverts. What maintains the structural
integrity of a flexible culvert is the ability of the surrounding soil
to resist this lateral thrust without deforming. This is why compaction
is so important for flexible culverts. If the soil is not properly
compacted around the culvert, it will become oval and might eventually
fail. 

Bruno Côté
BOCTE(--nospam--at)ibm.net