Weld steel shaft liner thickness for external pressures

[sbw]

I'm trying to design a steel shaft liner for a new pump station and I'm having difficulty finding design reference material on-line.

Here's the situation:

A 6' diameter hole is drilled through rock to the underground reservoir. The 54"x.375" steel liner is dropped in and the space between rock and liner is grouted (in 12' lifts to avoid buckling pipe).

One of the reviewers is suggesting that the lining should be design for a hydrostatic head of 66' and in doing so the liner thickness should be 0.5" instead of 0.375".

My questions are:
1. does it make sense to assume full hydraulic pressure when the liner is grouted in rock?
2. can I include the concrete grout ring (f'c 4000psi) as participating in the buckling capacity?
3. is there an on-line reference that provides design guides and equations for calculating the maximum allowable external pressure on the pipe wall?

Any help would be greatly appreciated. Thanks in advance.

 

[cvg]

the grout and the rock are both brittle materials and will crack, allowing full hydrostatic pressure at the face of the steel casing. I'm not sure you should count on the grout to help prevent buckling. 1/2 inch thick steel casing is not all that thick, especially when you consider the design life and the corrosion which will reduce the effective thickness of that plate (from both the inside and the outside.