plastic pipe

[johnhan76]

Our client wants to use plastic pipe instead of RCP. The groundwater is within 2' of surface. I am worried about buoyancy forces lifting the pipe up. Does anyone know a quick formula to use to see if it will work or how much cover we need. Thanks

 

[cvg]

no quick formula, just sum up the forces
draw your free-body diagram and add up the vectors

downward
weight of pipe
weight of soil over the top

upward
bouyant force

use a safety factor and make sure the resultant is pointing downward

 

[johnhan76]

ok
safety factor of 1.5 good enough?

 

[cvg]

1.5 should be adequate

check out technical note 2.107 at the following site:

http://www.ads-pipe.com/us/en/technical/technotes/index.shtml

 

[lsp01]

Just a note....

Don't forget about structures, inlets, catch basins and end sections that will act to secure the pipe. I work in an area with very shallow water tables (Florida) and there is seldom a problem if the structures are not too far apart. Just be careful during construction.

Laura P, P.E.