pipe cover 1

[john88]

I have an existing 42" diameter prestressed concrete cylinder pipe (pccp)for a water transmission main. Per original design calculations, the minimum and maximum allowable load over the pipe is 4 feet and 11 feet respectively. Currently, the pipe is within this allowable 'cover zone'.

However, new grading design would exceed 11 feet of cover over the pipe. Is there a design criteria and/or method that I can use in order to exceed this maximum cover? Someone has suggested a cradle or soil arch over the pipe, but I cannot find any literature on it.

Thanks

 

[CarlB]

See if you can find calculations that determined the 11 feet max. Probably had plenty of conservatism built in-such as poor bedding conditions, heavy trucks simulataneous with backfill, large safety factor, etc. - maybe combined load in your case is okay. Don't know about cradle approach. But could make backfill lighter by using lightweight fill or thick layer of expanded polystyrene insulation within backfill (if not too extensive).

 

[civil21]

What is the purpose of the fill? If the fill is for something important like an approach for a bridge or other such structure, and it is possible, abandon the existing line and lay a new one with a pipe designed to handle the new cover. You have no idea how that line was installed regardless of the record drawings and design conditions. The consequences of a failure (could be pretty big with a 42" transmission main)are not worth the risk. From the hip, relaying the line would be much easier and less costly than installing any arch or cap over the pipe.