Hydro-testing thrust block

[RustyChip]

Hi,
I was relocated to a new job site “Pipeline Project Site”, and the first task to handle is” Please check the design of this thrust block!!”
This thrust block is a temporary thrust block that will be used during the hydro-testing of 1600mm Dia DIP, with a pressure of 18.75 BAR. It will be laid against undisturbed trench wall, at depth approx. 3m.
We have the soil factual report and a lot of boreholes & trail pits have been done ( it is a 46km pipeline!yeah!)
MY PROBLEM:
Well, as far as I know, I can ONLY, and ONLY use the criteria of lateral earth pressure (Active & passive) to calculate the needed area of the thrust block. Of course with the addition n of the frictional forces between the pipe/surrounding and the thrust block base along the tested segment of the pipeline.
Is there any other criteria I can follow? Because the size of the thrust block produced from the lateral earth pressure criteria is very large and may not fit in the trench, since is there a lot of neighbor pipes already there.
Can I use the values of the uniaxial compression strength test? I mean divide the thrust force by the area of the thrust block if it is smaller than the UCS value then am in a good shape?
or can use the value of the vertical bearing capacity to calculate the needed thrust block area?

thanks

 

[SlideRuleEra]

You can use the bearing capacity of all soil that a thrust block bears on, both horizontally and vertically... assuming that the block if sufficiently far enough below the surface. See the design guidelines, including how far below the surface is satisfactory, in the Ductile Iron Pipe Research Association's (free) .pdf booklet "Thrust Restraint Design for Ductile Iron Pipe". The link is given below. Don't discount this booklet's info if you are not using ductile iron pipe. The design principles are the same for concrete, steel, polyethylene and other pipe materials.

If you don't have space for an adequate thrust block, the booklet also mentions the use of restrained pipe joints as an alternative. What I suggest that you do NOT do is combine restraints such as an undersized thrust block with pipe / soil friction, etc. to reach a theoretical cumulative total restraint that appears to be adequate. That is a recipe for trouble. If the thrust block cannot be sized appropriately, with a satisfactory safety factor, then go with suitable restrained joints to resist all the load.

http://www.dipra.org/app/uploads/Design-Thrust-Restraint.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[rconner]

Maybe pretty challenging "first project"! If there are e.g. many close parallel pipelines this doesn't seem like a real good place to locate a hydro testing location on a "46 km" pipeline, for at least unrestrained joint pipes. The bulkhead thrust force you will be dealing with is of course quite large (i.e. more than four million newtons, or near a million pounds). This force must be tranferred to the soil mass in some fashion. Is there any chance a conventional block, or maybe even better, sort of saddle/bag beam arrangement could be moved one way or other down the present or existing line, where there is more room? If not, you may have to consider going DOWN , with a specially designed sort of cantilevered pier structure or batter piling arrangement, the latter that would likely involve some strucural design, reinforcement etc. If steel beams are used directly behind the bulkhead (and the design is such that they can't be picked up and moved to another testing location etc) , there may be a cost associated with leaving the rest in place, but beams could of course be locally cut out of the way with a torch for continuing the line.
More information concerning soils, and what/where exactly you are dealing with as far as other utilities alongside the pipeline, might help to get better suggestions.