Aquamine PVC Pipe - Thrust Block? 1

[Poe]

For those not familiar with it, aquamine pipe is a pvc piping system that is similiar to victualic for iron pipe. It has couplings that use o-rings and plastic splines that run between a groove in the pipe and a groove in the coupling, essentially locking it together. However, many of the factory fittings are standard spears schedule 80 pvc fittings with pre grooved aquamine stubbs socket welded in place. So, there is a combination of PVC socket weld joints and the aquamine spline/groove joint.

The line is 6" and operates up to 100psig

So, for a shallow, underground installation (just at 2' below grade) are thrust blocks recommmended at 45 sweeps? At 90 elbows? At Tees? At Wyes?

I have heard arguments both for thrust blocks and against thrust blocks. Some have said that thrust blocks will do more harm than good. Is this possible?

Any insight, rational or opinion is appreciated.

Thanks,

 

[stanier]

If the pipe was to be installed on the ground would it pull apart? If the answer is no then you dont need thrust blocks.

Civil engineers rarely can get their head around the fact that pipes with rubeer ring joints dont need thrust blocks. I put it down to their love of pouring concrete to solve the world 's solutions.

Mechanical engineers build weapons civil engineers build targets.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[civilperson]

What mechanism holds the pieces of pipe together with rubber ring joints? (I am one of the civil engineers who puts concrete thrust blocks or restrained joints at changes in alignment.)

 

[bimr]

Aquamine is a restrained joint. That means no thrust blocks are required. The spline holds the joints in place.

http://perma-eng.microsite.mtsyellowpages.com/rightside.php?lngPageID=311

 

[stoozo]

I am also one of those civil engineers who pours concrete to make thrust blocks for unrestrained rubber-ring jointed pipes.
Please explain how you can afford not to at change in direction of the fluid flow.

 

[BigInch]

In pipe with restrained joints, thrust is balanced by opposing axial forces set up in the pipe. The axial forces are usually be dissipated, given sufficient length of pipe, from the pipe into the soil by friction and cohesion between pipe's perimeter and surrounding soil. In such a case, and if there is no need to restrain expansion at a change of direction, thrust blocks add compressive stresses into the pipe, which may cause buckling or snaking of the pipe, if the pipe is not adequately laterally restrained by the soil above the pipe. That may be especially true when expansion is forced toward overbend locations, where at times burial depth must be increased to prevent liftoff. It is also possible that full encasement thrust blocks constructed on poorly compacted soil, may settle consequently pulling the pipe downwards at the joint. In other cases, thrust blocks constructed against pipe with high compressive loads may have adverse effects via a high point load on the joint, or damage a pipe's exterior coating. In a piping system with thermal or pressure expansive changes in length, any restraint will add stress into the pipe, so unless there is a reason to prevent expansive movements, pipes are better left free to move.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[cvg]

I agree with biginch - when in easement outside of paved areas - it probably is easier and better to allow some amount of movement.


However, when constructing underground pressure pipes in street right of ways - movement of any kind cannot be tolerated as this becomes an expensive proposition to continually replace damaged pavement because of settlement, leakage or other problems caused by pipe which is "moving". The trend in this area is to backfill with concrete enriched slurry, aka "lean concrete", CLSM or "flowable fill". This forms a complete concrete encasement of the entire pipeline, greatly reducing the chance of settlement or movement. Where thrust needs to be restrained, thrust blocks are being used less and less in favor of other types of thrust restraint on the pipe joints.

 

[stanier]

Of course if you use rubber ring joints there is a need for thrust block at a change in direction. However if chemical, solvent cement or butt fusion welded fittings are used in a thermoplastic pipe system then thrust bl;ocks are not used.

The Virginia Recycle Water Scheme has 200km of up to DN800 AS 3518 ABS pipe with chemically welded joints and no thrust blocks.

Again I say if a piping system can be installed above ground without thrust blocks then it is perfectly happy below ground.

As for failures below ground in road easements then perhaps a better pipe system should be used rather than PVC.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[cvg]

I believe there are good alternatives to using a thrust block at a change in direction (even if you do use rubber ring joints)which may be cheaper and more effective in the long run over massive amounts of concrete.

I certainly don't believe that pvc installed in roadways is not acceptable. Many agencies allow it. Although, at least in this area it is generally limited to private streets or low volume local streets, not arterials. But any type of pipe installation that exhibits movement as might be expected without thrust restraint may eventually cause failure of the overlying pavement.

 

[stoozo]

These days, there is a trend to use special restrained joints at change in direction in an otherwise rubber-ring jointed underground pipeline, to mobilise the friction between an adequate length of pipe and soil to counteract the thrust. I knew of a case where a twin 1800mm dia steel pipeline (rubber ring jointed) was provided with fully welded joints at bends. I was told the pipeline had passed the hydrostatic test albeit at a mere 25m head.
I am not aware of any study or research material that could provide me with enough confidence on the assumed parameters for friction factors for varying soil characteristics and pipeline material or coating (in particular on high pressure applications). And what is the appropriate safety factor (ignorance factor) that should be used.
Would appreciate if anyone could enlighted me on that.

cvg, any other cheaper and more effective method than concrete thrust blocks?

 

[cvg]

thrust blocks are not particularly cheap when you consider the all the costs and not always feasible considering a)large excavation required to construct the block properly b)need to have clearance from adjacent utilities c)when digging up to repair or modify the waterline or other utility nearby, the block will be in the way d)prevents installation of anything else near the water (both a good and bad thing) e)contractor can't backfill and test the line until the concrete has cured f)thrust blocks are not very effective in softer soils such as soft clays

do a search using restrained joint and you will find many methods and discussion of pros and cons

http://www.acipco.com/adip/pipe/restrained/lok-ring.cfm

http://www.acipco.com/adip/pipe/restrained/flex-ring.cfm

http://www.certainteed.com/NR/rdonlyres/2001D1AC-AC2C-43F4-8CA1-793B8D580461/0/407.pdf

http://www.uspipe.com/main/Default.asp?CategoryID=4&SubCategoryID=5&ContentID=29

http://www.ebaa.com/pdf/pdf/PD-1.pd

 

[BigInch]

There is a lot of soil friction and cohesion factor data out there. It doesn't have to be exact, just on the conservative side.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com