Settlement of Oil Pipeline due to Leakage of Water Pipeline.

[jonjose123]

Here we have an issue with recently oil pipeline.
pipeline 20" oil pipeline crosses water pipeline (1000mmx3 nos) corridor

Oil pipeline encounter settlement caused by leakage of water pipeline passing under 20" oil pipeline.

Water pipeline is 4 m below crude oil pipeline.

The ground subsidence of 190 mm align with water pipeline micro tunnel pit.

I would like to get your advice on feasible options to contain this settlement.

One option we suggested was to provide grouting the area underneath oil pipeline upto 1m above Water pipeline but which was rejected by authorities as grouting may create access issues to Water pipeline for maintenance.

And protect further settling due to any possible future leaks of water pipeline.

Looking forward to hear your advice on this matter.

 

[LittleInch]

Got a sketch with plan and cross section?

First thing is to remove the overburden on the oil pipeline ASAP to stop the pipe holding the ground up for probably 4 to 5m beyond the edge of where the washout is happening.

First stop the water leak eh?

Then you should be able to simply backfill in layers compacting as you go to re create what you had before.

 

[HTURKAK]

Here we have an issue with recently oil pipeline.
pipeline 20" oil pipeline crosses water pipeline (1000mmx3 nos) corridor

You did not provide alot of info .here. Please correct me if my guess is wrong,
- The 3x 1000mm waterlines are steel pipes closely spaced , installed under the existing 20 in oil pl with microtunnelling,
- The settlement/ subsidence 190mm is due to ovalization of the steel water lines rather than leakage . ( do you have any evidence for leakage ?)

If my guess is reasonable , I will suggest , excavate trench for the clashing portion ( say 6 m) + 3x 2 m= 12 m length with hand excavation, remove the soil above and below bedding soil 200 mm below the pl with supporting on sand bags , then align the pl then provide compacted sand pipezone backfill.

PS: If the country is QA , i know the country.

 

[jonjose123]

Got a sketch with plan and cross section?

First thing is to remove the overburden on the oil pipeline ASAP to stop the pipe holding the ground up for probably 4 to 5m beyond the edge of where the washout is happening.

First stop the water leak eh?

Then you should be able to simply backfill in layers compacting as you go to re create what you had before.

Thank you so much for the response.

Yes, I will upload the plan and cross section.

Overburden pressure - Oil pipeline is at a depth of 1.2 m from ground level and water pipeline is at a depth of 6 m from ground level and the leak is from Water pipeline which is 4.5 m approx below the oil pipeline.

Water pipeline leak has been arrested, however, in case of any future leak from Ductile iron water pipe, the oil pipeline needs to be protected.

The water pipeline (DI pipe) collar is where the leak happened and is right below the Oil pipeline.

Is re routing the oil line away from water pipeline collar is also suggested, however due to Hot tap requirement , this option also axed.

 

[jonjose123]

You did not provide alot of info .here. Please correct me if my guess is wrong,
- The 3x 1000mm waterlines are steel pipes closely spaced , installed under the existing 20 in oil pl with microtunnelling,
- The settlement/ subsidence 190mm is due to ovalization of the steel water lines rather than leakage . ( do you have any evidence for leakage ?)

If my guess is reasonable , I will suggest , excavate trench for the clashing portion ( say 6 m) + 3x 2 m= 12 m length with hand excavation, remove the soil above and below bedding soil 200 mm below the pl with supporting on sand bags , then align the pl then provide compacted sand pipezone backfill.

PS: If the country is QA , i know the country.

Thank you for your response.

-Water pipelines are DUctile iron pipes. and installed way prior to oil line installation. It was installed by Thrust boring technicque.
- Leakage is from collar of Ductile iron water pipe which is below CS oil pipeline.

- If the soil below the oil pipeline is removed after placing sand bags, chance of collapse of soil needs to be estimated.

Country is in India in the north west part of India.

 

[GD2]

Thank you so much for the response.

Yes, I will upload the plan and cross section.

Overburden pressure - Oil pipeline is at a depth of 1.2 m from ground level and water pipeline is at a depth of 6 m from ground level and the leak is from Water pipeline which is 4.5 m approx below the oil pipeline.

Water pipeline leak has been arrested, however, in case of any future leak from Ductile iron water pipe, the oil pipeline needs to be protected.

The water pipeline (DI pipe) collar is where the leak happened and is right below the Oil pipeline.

Is re routing the oil line away from water pipeline collar is also suggested, however due to Hot tap requirement , this option also axed.

How about the possibility of a clamp over the coupling, injecting with sealant, with tapping to a surface vault to monitor the joint pressure and inject with fresh sealant when required.

 

[Snickster]

Possibly install an underground spread footing support on each side of the crossing on the oil pipeline. I had a case once where underground gas transmission pipelines were supported on concrete slabs every 10 to 20 feet or so in very soft soil in swamp area.

 

[jonjose123]

Possibly install an underground spread footing support on each side of the crossing on the oil pipeline. I had a case once where underground gas transmission pipelines were supported on concrete slabs every 10 to 20 feet or so in very soft soil in swamp area.

Thanks for the response. With reference to concrete slabs, was it concrete saddles to counter balance buoyancy?. Can that be used in this situation as we have soil subsidence below the oil pipeline.

 

[LittleInch]

The risk here is that subsidence underneath your pipeline will result in high shear and bending loads on the pipeline due to the overburden. Adding concrete will just make that worse.

So for me now, you expose the pipe and let it span the area where the subsidence is occurring NOW.

Then you either back fill to regain the ground support or maybe even fit a sub terreanean structure to support the pipe from firm ground either side of the area where the washout might happen again. leave the pipe exposed or back fill with something like pea gravel or Leka which allows the ground to subside without stressing your pipe.

But a drawing / sketch / photo would hep a lot

 

[Snickster]

They were existing structures we found when we made a major modification to an Enron pipeline site in Southern Louisiana. My understanding they were to spread out the bearing load on the soil to prevent the pipeline from sinking. If you have general ground settlement then anything you put there will likely sink too, but you should consult a Civil Engineer. I was thinking that a large enough spread footing supports at the pipe crossing would support the pipe over the crossing even though the water lines are sinking underneath.