Concrete slab over buried pipe??? 1

[sali123]

Hi

I should install a repartition concrete slab over pipe along the road. i have 2 problems:
1- how can i calculate trafic load/m² over slab
2- how can i calculate load distrubution generated by slab/m² over pipe.

 

[LittleInch]

Normally you don't.

The slab is there to stop people digging it up, not to act as a load spreader.

Use API RP 1104 to determine the loads and stress on the pipe which varies depending on the type of road surface and traffic.

What sort of pipe and size? Steel? concrete? paper?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[sali123]

@LittleInch (Petroleum)
Thack you for your response
steel gaz pipe with 600 mm of diameter and at depth of 1200 m, the pipe will installed under a hight trafic load .
the client required a construction of reinforced concrete slab for load distrubution above pipe.

Now i am thinkig about de behavior of slab in soil and stress distrubution below slab.

does the slab reduce the load distrubution above the pipe?

 

[robyengIT]

before the slab you should consider to make a very good bedding of the pipe itself so to have a good bedding factor. Have a look at ACPA American Concrete Pipe Association for how to do the calculation of traffic load and determination of bedding load

https://www.concretepipe.org/pipe-box-resources/design/design-manual/

 

[HTURKAK]

Yes ...the slab reduces the load distribution above the pipe. You may use Boussinesq soil distribution or distribute the traffic load stress with trapezoidal approximation having slope 1/1 etc.

The sketch in French , implies EC valid.. If this is the case, you may look EN 13480-32012 Part 6 Additional requirements for buried piping .

 

[Settingsun]

Did the client have any detailed requirements? I've seen slabs that also have a strip footing each side of the pipe and something compressible/ uncompacted above the pipe, which reduces the load on the pipe more than what you've shown. Are they expecting that system?

 

[sali123]

thack you all for your interest
@HTURKAK (Structural)

how does the slab reduces the load distribution above the pipe?
the slab will be installed at middepth of trench.
we have two load dispersion:
1- from the trafic load to slab
2- from the slab to pipe

Boussinesq soil distribution : do you mean, the use of trafic load distrubution above slab + weigth of soil above slab as uniform load? and calcuulate the the stress increases above the pipe?

@steveh49 (Structural)

No detailled requiermentnts

Yes ..Reinforced slab above a strip footing may an intersting solution...
yes they are excepting that system


Thanck you

 

[r13]

Please see the linked article on distribution of traffic load on buried pipe. Link. Slab itself does not generate load, but impose self weight onto soil as surcharge load. The slab shall be checked/reinforced to prevent damaged by wheel load.

 

[r13]

Here is an UK article written by software company. Link

 

[geotechguy1]

I would have thought that at 1.2m depth the additional load on a pipe due to traffic would relatively negligible. If you're using a conservative value for soil unit weight like 20 kN/m^3 it might be a bit of a wash anyway.

 

[robyengIT]

traffic load is negligible after 10 feet (3 meters)

 

[HTURKAK]

sali123 , double posting is against the forum rules .. delete your thread in the other forum.. Your questions implies you are a fresher and i will suggest you to ask the services of an experienced engineer. Your sketch implies , the trench and so the PL will be installed under the road in parallel direction. You did not mention the type of road ( a major high way or a simple village access road ?) is this a crossing or parallel to the road?

The slab will only reduce the traffic load . The surcharge load will be the same..( 1.2 m * ϒ soil) but for traffic loading, take a 1 m strip . and find the effects of design tire loading ( 1 tire will be on the PL ) with using Boussinesq formula and distribute the equivalent uniform loading with using truncated pyramid analogy with side slopes 2V: 1H.

If you provide space under the slab to cover the trench width ( with compressible board or uncompact the above the pipe ) as steveh49 proposed, the slab will also be effective for surcharge soil loading.

I will suggest you to look the following documents to get the concept;

- Buried Pipe Design (by A. P. Moser ,Steven Folkman ),
- ASCE Manual No. 119 Buried Flexible Steel Pipe Design and Structural Analysis ,
- BS EN 1295 Structural design of buried pipelines under various conditions of loading,
- Guidelines for buried buried steel pipelines at the following link;

If you want to get better responds, provide more better information..

 

[STrctPono]

We call them relief slabs in the bridge world. It's basically a concrete slab constructed above a structure (culvert, utility pipe, etc) that needs to bridge over it in order to avoid surcharging it.

As was mentioned by stevh49, place a 1" thick piece of premolded joint filler beneath your relief slab except at the very ends. The ends will act as your footings. Any overburden material or traffic load above will be carried completely by the relief slab and will have zero impact on the buried pipe. Just make sure that the "footings" for your relief slab are far enough away so as not to surcharge and load the pipe below. Also make sure your relief slab is strong enough to handle to loads above.

As far as how to apply traffic loads to the relief slab..... Well, that is not as easily answered. If this is highway loads, then pick up your local bridge design code (AASHTO in the States) and figure out how to run a moving load analysis with and without distribution through soil fill. If this is passenger type vehicles with no chance of a heavy truck then 64 psf uniform load will more than suffice.

You should check out this previous thread concerning a relief slab over a pipe. LittlInch provided some very interesting information on just how little stress is induced on these buried pipes from traffic load above.

https://www.eng-tips.com/viewthread.cfm?qid=475037