quesiton about hold down during pipe installation

[kfeng]

During installation, if HDPE or PVC pipe is below ground water, what type of hold down device should be used to anchor the pipe? Is there any specification available online? Thank you!

btw, thanks for those who answered my previous two questions.

 

[Ron]

I'm not sure why the pipe would be installed below the water table without backfill. If backfilled, no need for hold-down. If you want temp. hold-down as you are backfilling, use gravel.

 

[stanier]

Fill the pipe with water and you reduce the need for hold down. You really should be dewatering yoiur trench otherwise you wont get the correct bedding or compaction. Have you thought of direction drilling instead.

Submarine lines are floated with concrete weights thereon. Water is introduced slowly into the pipe sothat it sinks.

see the driscopipe site.

 

[mikolay]

Yes, you need to be careful of the uplifting buoyant force during construction, but especially after backfilling and construction, when the groundwater comes back in to its "natural" elevation. You need to calculate the buoyancy force (per lineal foot of pipe) assuming maximum groundwater head over the pipe. Then compare this force to the weight of the pipe (per lineal foot). If the bouyancy force is greater, do not assume the backfill will hold the pipe down,some pipes tend to work themselves up to the surface in these conditions. You can anchor the pipe down by pouring concrete collars over the pipe, located at least at every pipe joint, or use steel cables with attached concrete blocks hanging over the pipes. Steel cables can corrode. Also note that if you have concrete manholes or inlets, these need wide footings over peaty soils, or they can sink out of sight. You have some interesting challenges.
Mikolay

 

[stanier]

One also needs to check for local buckling at any restraints provided for uplift due to groundwater. The sheel of PE or uPVC may deform if the restraints are too widely spaced.