Thrust block and surge

[Camell]

I am busy with the design of a pumped main. Regarding the design of thrust blocks: What is the accepted practice with respect to the pressure considered. I see three alternatives:
1) Normal duty point and flow
2) Pump maximum pressure (potentially zero flow, but not nessarily)
3) Surge pressure.....what flow?

I am sure no 3 will govern, but may be excessive!

Also the restriant factors involved in the resistance will be different: if soil resistance, the surge pressures will invoke passive resistance which will be significantly larger, whereas under normal operation a bearing capacity calculations is more appropriate.

My specific situation is the flanged steel bends leading upto the approach of a steel pipe bridge ( VJ expansion joints on steel pipe on bridge and PVC leading upto it, so non continuous piping.) I am not able to make much use of soil resistance and must provide a mass of concrete on these bends. The question of surge pressure now becomes much more important

Any comments?

 

[mflam]

Camell
I think you've answered your question.
You have to design for the worst case. That is a surge produced by an event such as pumps starting against closed valves or the like.
I think a mass of concrete and mechanical joints in the critical areas will be needed.
Alternatively, surge supression, like a surge tank may be applicable, but I'm not an expert on those systems.