Road for truck across the underground pipeline

Hi all,
Has anyone had the experience about the design road for the container 40ft. truck across the 2 underground water pipelines which spacing between pipeline is 2.20 m. The pipeline is a steel pipe dia. 1.35m and fy = 36 ksi and buried under ground level 1.50 and 3.00 m repectively? The soil in this area is sandy clay. In my opinion I want to use the structure such as U frame or box culvert without bottom slab to carry truck load and transfer the load to footing of the structure at the level 3.00 m below ground but this method will make the contractor to excavate lots of soil and will delay their program. But if I use a normal road (0.3 m of crushed rock with 0.25 m. of concrete slab above )across the pipeline. I' worried the load from truck will make the problem with the pipeline and I'm not sure how to calculate the pressure over the pipline from the truck load and how to check that pipe can resist this load.
Thank you in advance
Cu73

 

[JAE]

In some cases like this, we actually use the pavement as a sort of bridge. We create pad footings on either side of the pipe, large enough to support the weight of the anticipated truck loads as well as the dead weight of the paving which spans across the pipes. We lay a layer of foam or other compressible material over the pipes and then place the concrete "bridge" over that.

The bridge is designed just like a one-way slab bridge. Probably want to provide some kind of joint at either end to separate grade-supported pavement from bridge-pavement.

This method, however, is probably more expensive than your idea of placing a half-pipe over the pipes to protect them from compressive wheel loads.

 

[Ron]

With the amount of cover you indicate over the pipes, the type of soil (provides good lateral resistance to "flattening" the pipe under load), and the type of pavement section you have indicated, you need only to make sure that everything is laterally confined. This can be done by constructing a "headwall" at each side of the roadway to encompass the pipes if open, or if covered (no visible outfall), this can be done by providing select, compacted high modulus material to a thickness of twice the subbase depth for a 1 m wide strip on each side of the pavement.

For the conditions you have outlined, the stresses on the top of the pipe are very small for typical heavy truck wheel loading.

 

Thank you all
And I have more question to both of you as following because your suggestion be helpful and I need some information to decide which method I will use for this situation.
Jae,
How do you think if I use the upside down U shape concrete frame to place over the pipe to protect them and make the road over the pipe?

Ron,
During the construction as your suggestion the compacting force for the crushed rock will make the problem with the pipe or not ? and Do I need to excavate the soft spot and compacted the existing soil in the area I will construct the headwall or not? For the material used for the headwall, do you think the laterite is suitable ? I think to use the 2 layers of compacted laterite which each layer is 300 mm thk. Can you suggest the reference for calculation the pressure over the pipe and to check the pipe?

Thanks again
cu73

 

[JAE]

IF you have an issue/problem (and Ron's post implies you do not) the upside down pipe-halves you are suggesting may work. The thing I would be concerned with is that pressure from the traffic above would be directed down the arched pipes and bear on soil at the edge of the pipe. Your pipe thickness is probably too thin to adequately bear on the soil.

If, however, your pipes are spread apart, then the soil itself could arch along with the pipes and would probably be OK.

 

[Rentapen]

Drill and fill 4 to 6 to concrete pillingsnext to and extend below existing pipes or to hard pack and put a slab on it.
rentapen

 

[dlew]

Generally pipes are placed under roads with no protective structure. There are formulas to calculate the stresses in the pipe based on the vehicle wheel loads, the trenching condition of the pipe (is the pipe in an embankment or in a trench), the depth to the top of the pipe, and the diameter and mechanical properties of the pipe.
You could find those formulas in Civil Engineering Handbooks or in pipe manufacturers' design handbooks.

 

[Ron]

cu73...the compaction will not affect the pipes (assuming you use reasonable, not excessive compactive effort).

I did a quick analysis using an elastic layer approach with assumed soil, rock, and concrete modulus values. There are numerous elastic layer programs out there to do this or you can do it "by hand" (see "Principles of Pavement Design", 2nd Edition, Yoder and Witczak).

Check the US Army Corps of Engineers websites...you can download their pavement analysis programs. Check for vertical stress just above the pipe elevation, then extend that to get the unit load on the pipe. Check that against some of the tabular values given by CMP manufacturers (check ARMCO). I think you'll find it to be insignificant.

 

Thank you everyone again,
RON,
I just got the new condition for my road. The owner of the pipeline don't allow to do the concrete pavement over their pipeline because I will be the problem with their pipeline maintenance so they ask me to use the flexible pavement which I think it will have the effect on the pipe more than the concrete pavement. So I decide to use more thickness for the crushed rock from 0.25 m to be 0.70 m (3 layer of 0.225m, 0.225,0.25 m). and put the 0.10 m of asphalt concrete over it to be the pavement. I found that the existing ground has CBR = 18 % at 90% modified AASHTO and I think it is alright for the flexible pavement, right? by the way If you have any suggestion, please let me know
Thanks
Cu73

 

[Hookem]

Consider Spangler Iowa Formula (API 1102 5th Edition) or less conservative GRI/Cornell (API 1102 6th Edition) for calculation of total effective circumferential stress in pipelines with repetitious traffic wheel or rail loads over them. If the stresses are lower than the allowables, no structure is required (except if you have money to spend or want to sleep at night).