Pipeline Slip-Sleeves for Ground Movement due to Slope Instability 1

[auzie5]

Anyone know of a good slip-sleeve pipe wrap? Looking for two independent overlapping layers of geosynthetic material that we can use where we identify moderate risk of ground movement due to slope instability. This would be for cases where our pipeline is running parallel (i.e. in-line) with the slope. For areas along the ROW where we anticipate some slope instability (which cannot be avoided with pipe routing), a geo-hazard monitoring program will be in place; but this would be an additional pipeline design measure to hopefully limit pipe movement (and potentially a buckle) when slope instability leads to ground movement around the line.

 

[cvg]

wrapping the pipe will do very little. placing it on top of a smooth sheet would allow it to slide. it would also promote slope instability. Unless the sheet of material is very tough, it would likely be damaged if it moves. Doesn't sound like a good idea. Maybe a flexible pipe such as HDPE would be better.

 

[lilliput1]

Consider Victaulic piping.

 

[BigInch]

Slope instability should not be treated lightly. This can be a very serious problem that requires continuous maintenance for the life of the pipeline. It can easily result in high stress, deformation and line breakage, or at the least ... reduced operating pressure! Wrapping is likely to be of no use whatsoever, unless the soils are very poor, which leads to the question of why that route. Far better to avoid known areas of unstable slopes at all cost. That can be determined by a local geohazard analysis performed before final routing is decided.

A geohazard monitoring program might be useful after the fact to try to prevent further damage to the pipe or slope, if slope instability became a problem after the fact or to monitor stresses (such as at an unavoidable active fault crossing), but IMO it should not be used as an initial risk reduction method.

I would first try to eliminate the source of the slope instability, cut the slope down, catch and divert all upslope water, drain unstable soil layers with geotextile wrapped perforated drain pipes, excavate unstable soils, install gabion retaining walls, cribbing, trench breakers and the like. You might even make some kind of above ground crossing with sliding supports such as on the Alaska Pipeline did over the Denali Fault. You can see that extra costs quickly become insurmountable making it far more economical to avoid such areas in the first place.

If you absolutely cannot avoid an unstable slope and still want to take the risk of crossing it, increasing pipe flexibility is probably the best way to approach the problem. Add dog legs before and after (and within) the slope and possibly mechanical anchors to try to ensure the pipe will act like you think it will. You might also want to gently slope the sides of the trench and fill the trench to the brim with sand, so an easy separation of pipe from any sliding motion of the earth is possible. In extreme cases, very active faults and seismic zones, a break-away fitting and shut down valves on each side might reduce risk of even more severe damage after a semi-controlled rupture took place.

Best advice is to avoid it any which way you can.

 

[brimmer]

We use Nilex geotextile fabric for this, there are others. One thing I will say is make sure you have a good anti corrosion coating underneath that is low friction and will also allow the soil to slide by too (i.e. an epoxy is really the only coating that will work), any other coating the overlaps, or sleeves etc. will get dragged by the soil when it moves (should your geotextile fabric breakdown or slide off). I have seen tapes, sleeves, even extruded poly get damaged. Other options at these sites, assuming you are not going for full remediation (HDD or re-route) can include: shallow burial, bringing pipe to surface, and then different types of slope remediation they can try with berms, vertical/horizontal drains, etc.

 

[rconner]

I have not heard the terminology "slip-sleeves" applied to landslide application, so I'm not exactly sure what soil/structure interfaces etc you are referring to with that terminology. You also don't mention the specific service of the pipeline, but from the forum you have chosen I am suspecting welded steel energy piping. I have however heard of pipelines in general being encased in loose polyethylene or even double polyethylene encasement, or in more recent years even slick, rounded aggregate surrounds to simulate flowable ball bearings (all in attempts to lessen the drag of soil on pipes in some geologically hazardous areas). Such systems will reduce, but not eliminate the soil drag on pipe.
That being said, I agree however with the Big one that (while there may be some other options for services other than very high pressure, welded steel energy pipelines), it is best to avoid if at all possible as there can be many feet of long term creep displacement, and maybe many times that amount in the seismic events that occasionally seem to plague such significant landslide areas as well. Maybe another possibility not yet mentioned directly (but that brimmer may be alluding to) that could be introduced at least into a discussion would be drilling say below the basal shear plane, into deeper strata that does not slide, assuming there is dependable geotechnical info concerning same and practical access/means to do so?

 

[LittleInch]

A well written post by BI - made all the points I would have said as well.

The friction on wet modern pipeline coatings, e.g. PP or PE is already fairly low, but normally you do everything to stop the ground moving beneath your feet.

I'm not really sure what benefit you think you get from this approach, which seems highly unusual and has few, if any, precedents.

I've done, or rather tried to do, analysis of pipes subject to soil movement in mud and peat when across the slope, but there are many variables on how the "fluid" actually flows that the results don't mean much.

What we did find and has been shown in reality, is that anything large and solid, such as a boulder or a tree / tree stump can act as a significant point load which then buckles and breaks the pipe.

Rather than allowing the soil to "slip" past the pipeline, I think you really should do everything you can to stop the soil moving in the first place. There are many ground stabilization schemes and systems available - look up chad Cameroon pipeline for many of them.

In poor ground subject to ground movement, you may actually need to use something other than the original ground and install permanent gabions, piles or re-inforement grids etc and not use wholly back fill material. The environmental team might not like it too much, but in the long run it's much better than have the ground move and your pipe buckle or break

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