concrete pipe encasement
concrete pipe encasement
(OP)
I am designing a reach of large diameter, reinforced concrete storm drain pipe which is quite deep. Pipe ranges from Class IV to Class V. About a 1/4 mile is too deep for Class V and required D-load goes as high as 4,062 (0.01" crack). I am thinking of giving the contractor an option to encase the pipe (Class IV or V) in concrete to provide the necessary extra strength instead of providing the special D-Load pipe. Has anybody done this before and will it reduce the contractor's bid? I would expect the contractor to provide calcs / shop drawings for any proposed encasement.





RE: concrete pipe encasement
RE: concrete pipe encasement
RE: concrete pipe encasement
Pipe encasements have been used extensively by USBR (United States Bureau of Reclamation) usually thru dams. They have a design guide for culverts under dams - I think that it uses the Beggs deformeter method of analysis. It gives the compressive, tensile & shear coeficients for a variety of conduit configurations. It may be still available on their web site - I think in the area of old monographs that they still make available on the web site.
Failing that, I usually (for small jobs) just assume that the lower half of the encasement will remain in compression & the top half becomes a simple arch. In the design, you usually ignore the pipe & just use it for a form for the encasement.
In most cases, reinforcement may not be necessary to carry the load but I usually use about 0.5% reinf for half the conc thickness (or 250 mm whichever is the smallest).
What is your pipe dia & how deep is it?
RE: concrete pipe encasement
Couldn't resist quoting this:
" About a 1/4 mile is too deep ..."
RE: concrete pipe encasement
A Type 4 Standard installation (Lowest Bedding class)has a minimum bedding factor of 1.5 for a trench installation. If you use a Type 1 Standard installation (Highest Bedding Class) a minimum bedding factor of 2.3 can be used for a trench installation.
RE: concrete pipe encasement
RE: concrete pipe encasement
D=(weight of soil/bedding factor)X(Safety Factor/Inside Pipe Diameter)
Based on a safety factor of 1.5(Conservative, you can use 1) and a 72 inch pipe I get a D load of approximately 2,700. Class 5 pipe has a D Load of 3000 with 0.01 inch crack. If you use a saftey factor of 1 you can use class 4 pipe.
RE: concrete pipe encasement