Bore Casing Design

[soniam]

I have a project that has a bore under an irrigation ditch. The original design had a 54" steel casing pipe for a 36" carrier pipe. The casing pipe was specified to have a minimum thickness of 3/4". Due to the amount of construction activity happening these days, the cost and availability of the steel has made the original spec almost infeasible. The casing under the ditch will only have about 4' of cover to the bottom of the flowline, so I don't see an issue with a smaller casing thickness during winter. In the summer, however, the ditch runs full and will have the added pressure from the water. Does anyone know where I might find a chart that shows the minimum casing thicknesses that can be allowed for certain pressures?
Thank you,

 

[bimr]

A smaller casing will probably not work. Check with the manufacturer of the spacing devices.

http://www.sdwas.com/Documents/Vol2/Section2/Division15/15125.pdf

 

[cvg]

reducing the thickness of the pipe will do little to reduce cost, the majority of the cost will be installation which I assume is either jack and bore or open cut during dry up. if you are open cutting this, then encasement with CLSM can greatly reduce the time and labor required to backfill and also reduce the soil load on the pipe which might allow you to reduce the thickness a bit. for design, you will have to fall back to traditional Marston / Spangler method and check ring compression in the pipe. then factor in a corrosion allowance.