Protection of HDPE conduits

[killswitchengage]

Hello
I am currently working for the survey of the construction of a container terminal area. We use HDPE conduits between culverts for the storm water drainage system. Problem is some conduits which are under reinforced concrete slabs are not well protected ( if we add only 20 cm of sandy coating material , the slab will be above the conduit literally ) . The subgrade material consists of silty fine sand and the slab is 25 cm thick reinforced with 8 mm bars .
The following picture may help you to get an idea, i also draw two possible solution to the problem. Anyway, we classify HDPE in France according to the nominal pressure it can withstand and in this case its a 6 bars class HDPE. The subgrade soil is in a loose state.

Thanks

 

[SlideRuleEra]

Instead of full encasement in concrete, perhaps you could consider full encasement in flowable fill. Here is general information on flowable fill: Link

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[killswitchengage]

ok that's nice to hear about, but what about my solutions are they correct ? which one should i use ?

 

[cvg]

assuming the pipes are already installed?

the concrete arch is cheaper as you will not have to remove and reinstall the existing HDPE pipe. with full encasement, you will have to completely remove and replace the pipes. if you were to do that, than just use stronger pipes? if you go the full encasement route, than use the flowable fill.

 

[SlideRuleEra]

If you use the reinforced concrete arch, the backfill material to the side of the arch and its proper compaction becomes very important. Any settlement of the backfill that is beside the arch will cause the reinforced concrete arch to compress the pipe.

IMHO, I would not take that risk. Full encasement with flowable fill would be my preference.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[cvg]

I would not use the arch as sketched above. extend the excavation on each side of the pipe down to the bottom of the trench and do not construct the arch on fill at all. nothing should be resting on backfill material.

 

[killswitchengage]

thank you all , and no the pipes are not installed yet. I was thinking that the full encasement in low density reinforced concrete would be best especially knowing that the subgrade soil is pretty weak . Could you guys point me to technical guides or books on this ?

 

[cvg]

http://www.nrmca.org/aboutconcrete/cips/17p.pdf

 

[Ron]

killswitchengage.....your material around the pipe does not have to be reinforced with anything....use flowable fill as SRE noted. Make sure you have an elastic buffer between the slab and the top of the fill. If you don't have that, load on the slab gets transferred directly to the encapsulating block, which would eventually result in issues with the pipe. The elastic buffer can either be a layer of sand, preferably in the 200 to 250mm range or you could just use a lower strength flowable fill material....300 to 400 psi (2 to 3 MPa).

If your HDPE pipe is less than 12 inches in diameter and 500mm or more below the slab, I wouldn't worry about it, just make sure everything is well compacted and the pipe is well bedded.

 

[killswitchengage]

Thanks.
I want to know if i deliver 1.25 mpa to the rc slab , and the slab has a compressive strength of 25 mpa how much pressure gets transfered to the soil?
The client insists on a protective idea so i have no choice

 

[killswitchengage]

Thanks.
I want to know if i deliver 1.25 mpa to the rc slab , and the slab has a compressive strength of 25 mpa how much pressure gets transfered to the soil?
The client insists on a protective idea so i have no choice

 

[Ron]

What is the source of this loading? Is this a contact pressure for tires/wheels? If you have a concentrated load, such as a wheel load, then you have to be more concerned. Most container terminals have high wheel loads and high point loads on the pavement. It also makes a difference whether your loads will primarily be crossing the pipe or running along the pipe.

 

[killswitchengage]

See that's why we are concerned, container lifters but most importantly trucks with containers are the most deadly . Having little time to actually calculate the pressure delivered to the pipe and with no finite element software i am going to build the full encasement solution with reinforcement .

 

[hokie66]

There is another major problem with your proposal, unrelated to the pipes. I assume your slab is jointed. With the subgrade in a "loose state", and sand used directly below the slab, you will have sand pumping out of the joints when it rains. Sand is not the material to use directly under the concrete.

 

[killswitchengage]

No need to worry , we use a crushed stone aggregate 0/40 mm compacted with 95% optimum proctor