Construction Vibratory Hammer effects on Buried Pipeline

[Claudia_C]

Hello,
I work for a pipeline company near La Porte, TX and I received and encroachment request to place an electrical tower near our 8in nitrogen pipeline. To complete the placement of the foundation of the tower, the contractor plans to drill 5ft to 10ft in depth and then insert a 30ft long casing. Then begin driving this casing straight down. The casing will be installed by a vibratory hammer attached to the top of the casing. After the casing is installed and held off at the surface, they will drill using a drill rig and slurry to finish drilling to a total depth of 55ft.
The casing is being driven in to protect our pipeline.
My concern is the effects of the vibration on the pipeline. We only have 1.5ft clearance from the edge of the casing to the edge of the pipeline.
I used the PPV vibratory pile driving equation of 0.65(25/R)^m to get a PPV of 14.34 in/sec.
This seems awfully high.
Could anyone provide any thoughts on this situation?
Reply

 

[geotechguy1]

I guess my first thought is, is there an alternative - could they just shift the electrical tower? Is there an alternative foundation methodology that avoids all this? Personally I'd want to see a better explanation for how the steel casing is meant to protect the pipeline. What depth is the pipeline? I guess the initial 10 foot bore allows you somewhat confidence the casing will go in relatively straight.

If the pipeline is shallow, surely a better way would be to definitively locate the pipeline with hydrovac. Maybe even hydrovac the pipeline location so you have 100% certainty where it is and what depth next to the pile, then hydrovac the hole for the bored pile down to below the elevation of the pipeline, then loosely place a casing and install a bored pile through it (casing to allow formation of a concrete pile). That's one idea but I'm sure there are other approaches as well.

 

[Claudia_C]

The pipeline is at a 14ft depth. I forgot to include that detail and the pipeline is in a casing also. They have also potholed our pipeline so we sre certainit is at 14ft deep and the clearances face to face will be 1.5ft.
What they told me is the casing is being installed so that while they drill the hole for the foundation it will be done inside the casing and it won't have a possibility to steer near the pipeline, is my best guess.

My concern really is not that the drill will hit the pipeline. I am more concerned with the vibrations induced on the pipeline due to the vibration of the hammer while it drives this casing in the ground.

Perhaps I should ask them not to install this casing.... since we have located our line and know it's exact location.

 

[GregLocock]

"Could anyone provide any thoughts on this situation?"

I know nothing about pipes but enough about vibration to be dangerous.

1. Dig a 15' trench around your pipe and secure it with skyhooks while the pile is being driven.
2. Could you fabricate a copy of your pipe setup, and stick it on a shaker at 14.3 ips?
3. I'd have thought the cone of compression below the driven pile would be a very exciting environment. Maybe they could drill for the casing to beyond 14' so that your pipe was never in the compression cone.

 

[LittleInch]

Please don't double post - It's not allowed.

 

[Claudia_C]

Sorry about that. One will be deleted

 

[Claudia_C]

Please don't double post - It's not allowed.

Could you please post your thoughts on this post? The other was deleted. Thank you