trench or not?
trench or not?
(OP)
An 18" SDR11 HDPE waterline (pumped water, ambient temperature, up to about 100 psi) is installed laying on the ground at approximately 20 - 30 percent slope. Thermal expansion and contraction causes it to move around, shortening the design lifetime. Installation in a trench would be expensive and would require blasting or rock trenching. Cover with available waste rock could be done. Approximately how thick of a cover would be required over the pipe to protect it?





RE: trench or not?
RE: trench or not?
RE: trench or not?
RE: trench or not?
RE: trench or not?
RE: trench or not?
both soil (silty sand) and rock of all sizes are available but I would prefer to use more erosion resistant material. 3 feet is about what I was thinking
RE: trench or not?
http://www.pipesak.com/
RE: trench or not?
I'm thinking about the convection heat transfer that could be calculated by q1=k.delta(T) You can guess the delta(T) between the pipe surface and the ground surface. this should be damped by the pipe cover, so should be equal to the latent heat of the cover which is q2=m.L (m being mass and L the specific latent heat value). assuming q1=q2, inserting your desired delta(T) (considering the expansion factor and your pipeline length, you could have a guess of the max tolerable deltaT before getting to a trouble) and k & L values for rock or soil, then it should give you the required mass of the cover per unit length. Having the pipe diameter, you can get the minimum height of the cover.
As I said, I'm just thinking and not saying this is the solution. But perhaps just an approach.
RE: trench or not?
RE: trench or not?
If you think trenching it will be costly, how much will replacing the line cost.
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: trench or not?
the lines are being replaced after about 10 years in service sitting on top of the ground with no anchors at all. proposed design life is about 5 years and then will only be used sparingly after that. cost to replace is much less than trenching. I hope to increase the life by adding both thermal insulation as well as restraint. My assumption is that trenching will at least double if not triple the installed cost. I'm not even convinced I can (safely) get a rock trencher onto this steep slope.
RE: trench or not?
Trenching or covering it will also protect it - like from animals or possibly flying debris in a storm. I have had squirrels eat just about anything plastic on my house. They even ate the sewer lead pipe vents and an aluminum floodlight!!
RE: trench or not?
good luck to any squirrels who think they can get out here and eat this pipe...
RE: trench or not?
RE: trench or not?
Periodic transverse anchorage e.g. with concrete pier supports built step-wise or pegged down into the slope probably minimize movement of pipeline, help to stabilize the pipeline (and to some extent also backfill/slope?), and also maybe even beneficially interrupt erosive drainage down same.
I believe ductile iron and steel water pipeline installations, often constructed with such features and on slopes, have typical useful lifetimes far greater than 10 years. While I have not yet seen a "squirrel" that could chew through a 30" plastic pipe wall (as I believe rodents, marine borers, and termites etc. indeed have smaller plastic lines), perhaps stronger ductile iron and steel materials do provide perhaps a little extra security from miscellaneous surface/traffic impacts (and errant bullets from even otherwise well-meaning good ol' boy hunters and celebrators?)
RE: trench or not?
maximum particle size for bedding material to 1.25 in. (32 mm)."
RE: trench or not?
RE: trench or not?
RE: trench or not?