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HDPE pipe Under Railway Loading 1
- Thread starter SJcivil
- Start date
civilperson
Structural
Use a casing, then slide the HDPE through the casing. Check with the owner of the railroad for limitations on cover and start/end points.
the railroad owner should have criteria for the live-load influence envelope..this will determine your length of culvert. also, the owner should be able to provide depth, size and material of the sleeve---if you chose to use a sleeve---some owners give you the choice, conditionally. moreover, some owners require that any new ditches or culverts in their ROW pass the 100-yr.. you may want to contact them for guidance.
h.
h.
Most of the railroads have specific engineering standards for crossings and require casings. Check with the railroad. It would be best if you contacted the RR before starting your design work so you do not end up having to rework a non compliant design.
- Thread starter
- #5
Thanks, we have gotten permission to not have to use a casing pipe from the owner, and they have used HDPE DR11 in previous cases, I am doing my due diligence to confirm the design, I just am looking for guidance on evaluating the HDPE design requirements.
Thanks
Thanks
What is the topside reference elevation for your five "feet of bury" associated with this railroad crossing (e.g. is the upper reference plane to be the flow line of the ditch or ground surface, or the base of the rail or what?) I would be careful in general with the use of the terminology “bury” particularly if it is not accompanied by further explanation or illustrative drawings, as I have seen at least per many references/in some areas and in the contexts of buried piping that the word "bury" does not mean the same as arguably harder to confuse cover or pipe invert/~depth trench conventions (“bury” means e.g. the depth of the trench or to the bottom of the connecting pipe as per AWWA Manual M17 for the installation of fire hydrants, and major manufacturers in accordance with same e.g. page 2 at ).
In any case (while what would happen may in part be a function of the soils etc. and the skill of the driller etc.) five feet just sounds awful shallow and I do believe some "due diligence" is in order, particularly for a HDD application that normally involves some degree of over-cut and then injecting pressurized fluid into whatever the foundation soils are slightly below the ballast (and of course below something as heavily traveled as a railroad). If this is large pipe and you really do mean five feet depth to invert (was this how prior crossings were done?), it sounds like it could be REAL shallow (and you might wish pipe had a casing if plastic pipe were to somehow cut or pull loose under track supporting ballast!)
In any case (while what would happen may in part be a function of the soils etc. and the skill of the driller etc.) five feet just sounds awful shallow and I do believe some "due diligence" is in order, particularly for a HDD application that normally involves some degree of over-cut and then injecting pressurized fluid into whatever the foundation soils are slightly below the ballast (and of course below something as heavily traveled as a railroad). If this is large pipe and you really do mean five feet depth to invert (was this how prior crossings were done?), it sounds like it could be REAL shallow (and you might wish pipe had a casing if plastic pipe were to somehow cut or pull loose under track supporting ballast!)
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1
- #7
The dynamic loading should be provided by the railroad unless defined in national standards.
Then you can determine the stress, strain, deflecction, combined loading and buckling criteria in accordance with an appropriate reference.
A key issue is whether it is intended to pressure grout following the direction drilling? If not the deflectin may be uncontrolled and you will not be able to determine the criteria.
References include:-
Structural Mechanics of Buried Pipelines-Watkins
Buried Pipeline Design-Moser
Australian Standard AS 2566.1 Buried Flexible Pipelines- Design
These available from virtual libraries for IMechE or IEAust members.
Then you can determine the stress, strain, deflecction, combined loading and buckling criteria in accordance with an appropriate reference.
A key issue is whether it is intended to pressure grout following the direction drilling? If not the deflectin may be uncontrolled and you will not be able to determine the criteria.
References include:-
Structural Mechanics of Buried Pipelines-Watkins
Buried Pipeline Design-Moser
Australian Standard AS 2566.1 Buried Flexible Pipelines- Design
These available from virtual libraries for IMechE or IEAust members.
Contact ISCO, they should be able to assist you:
If you design the DPE pipe with the same strength as the steel pipe that is normally used, you should have no problem. See the link to the RR drawing:
Hi bimr,
I took at the Union Pacific RR pipeline crossing detail from the link you provided. It appears to me...
1. that this is a detail that requires a steel casing and whatever carrier pipe (unlike the present inquiry, that I understood to be uncased pe pipe).
2. that this is a conventional, basically horizontal crossing detail, I suspect likely intended for normal bored or open-cut installation (again different than much HDD that ends up with a belly of sorts). [You may however be interested in the document at it appears from the same railroad that however appears to be specific to HDD method and with far different depth requirements.]
In any case, I believe there could well be concerns in some areas involved with HDD of some shallow uncased pipelines that are not necessarily anticipated by the specific detail you provided. Where HDD is however allowed, I guess I was trying to say that I would suspect some authorities (maybe like Union Pacific?) might well require such construction operations to be deeper, and/or maybe even also for various reasons also require metal.
In any case I guess in a sense what you said might be pretty safe, as no pe pipe has all the strengths of steel pipe! ;>) Everyone have a good weekend.
I took at the Union Pacific RR pipeline crossing detail from the link you provided. It appears to me...
1. that this is a detail that requires a steel casing and whatever carrier pipe (unlike the present inquiry, that I understood to be uncased pe pipe).
2. that this is a conventional, basically horizontal crossing detail, I suspect likely intended for normal bored or open-cut installation (again different than much HDD that ends up with a belly of sorts). [You may however be interested in the document at it appears from the same railroad that however appears to be specific to HDD method and with far different depth requirements.]
In any case, I believe there could well be concerns in some areas involved with HDD of some shallow uncased pipelines that are not necessarily anticipated by the specific detail you provided. Where HDD is however allowed, I guess I was trying to say that I would suspect some authorities (maybe like Union Pacific?) might well require such construction operations to be deeper, and/or maybe even also for various reasons also require metal.
In any case I guess in a sense what you said might be pretty safe, as no pe pipe has all the strengths of steel pipe! ;>) Everyone have a good weekend.
rconner,
SJcivil says "we have gotten permission to not have to use a casing pipe from the owner, and they have used HDPE DR11 in previous cases, I am doing my due diligence to confirm the design, I just am looking for guidance on evaluating the HDPE design requirements."
I am not recommending HDPSE, I was just saying that if his proposed HDPE is as strong as the steel pipe that is normally used, he should have no problem.
I would agree with you that in light of all the issues, delays, and aggravations that occur when one is trying to get an approval from a RR, it may be more practical to use the more conservative design than the cheapest design.
SJcivil says "we have gotten permission to not have to use a casing pipe from the owner, and they have used HDPE DR11 in previous cases, I am doing my due diligence to confirm the design, I just am looking for guidance on evaluating the HDPE design requirements."
I am not recommending HDPSE, I was just saying that if his proposed HDPE is as strong as the steel pipe that is normally used, he should have no problem.
I would agree with you that in light of all the issues, delays, and aggravations that occur when one is trying to get an approval from a RR, it may be more practical to use the more conservative design than the cheapest design.
The load will be taken by a combined pipe/soil structure. The design parameters are completely different to designing a rigid pipe as in steel. The concept is that any loading will deflect the pipe and be carried by the soil.
This is why the use of a pressure grout is recommended. ie the soil cannot deflect.
The concept involves the vertical load being translated to a horizontal load into the native soil.
PE having a low modulus will deflect within the bounds of the design standard. This allows the load to be transferred to the native soil without being injurious to the pipe.
AS 2566.1 provides the design criteria for PE, other thermoplastics, ductile iron and steel pipe materials. ou will find others design standards such as AWWA cover this topic as well.
So, no, the PE does not have to be as strong as steel.
This is why the use of a pressure grout is recommended. ie the soil cannot deflect.
The concept involves the vertical load being translated to a horizontal load into the native soil.
PE having a low modulus will deflect within the bounds of the design standard. This allows the load to be transferred to the native soil without being injurious to the pipe.
AS 2566.1 provides the design criteria for PE, other thermoplastics, ductile iron and steel pipe materials. ou will find others design standards such as AWWA cover this topic as well.
So, no, the PE does not have to be as strong as steel.
Stanier - I wasn't aware that steel pipe was considered to be rigid...
quote from American Spiralweld steel pipe design manual
"Predicted Deflection – Because steel pipe is designed as a flexible conduit, significant deflection can occur without damaging the product. Common practice has limited the calculated deflection to 5%, although larger deflections may not affect pipe performance. Deflection limitations are a function of the rigidity of the specific lining and coating being used."
quote from American Spiralweld steel pipe design manual
"Predicted Deflection – Because steel pipe is designed as a flexible conduit, significant deflection can occur without damaging the product. Common practice has limited the calculated deflection to 5%, although larger deflections may not affect pipe performance. Deflection limitations are a function of the rigidity of the specific lining and coating being used."
Hi CVG,
Indeed steel can be rigid or flexible depending of the diameter to wall thickness ratio. Because of the potential for corrosion of steel casings they are sometimes installed with a built in substantial corrosion allowance. In the casse of a railway crossing cathodic protection would need to be used. If the line were electrified this adds complexity of stray induced currents.
AS 2566.1 does consider the design of steel pipe as flexible however in practical terms thick wall pipe does behave like a rigid material.
Stray current induced corrosion is why thermoplastics are enjoying more applications across railways.
Suggested further reading is Technical Summary and Database for Guidelines for Pipeline Crossings Railroads and Highways available from the Gas Research Institute Library Services. It was prepared by Cornell University School of Civil and Environmental Engineering December 1991. # GRI 91/0285 Contrct # 5091-271-2273
Indeed steel can be rigid or flexible depending of the diameter to wall thickness ratio. Because of the potential for corrosion of steel casings they are sometimes installed with a built in substantial corrosion allowance. In the casse of a railway crossing cathodic protection would need to be used. If the line were electrified this adds complexity of stray induced currents.
AS 2566.1 does consider the design of steel pipe as flexible however in practical terms thick wall pipe does behave like a rigid material.
Stray current induced corrosion is why thermoplastics are enjoying more applications across railways.
Suggested further reading is Technical Summary and Database for Guidelines for Pipeline Crossings Railroads and Highways available from the Gas Research Institute Library Services. It was prepared by Cornell University School of Civil and Environmental Engineering December 1991. # GRI 91/0285 Contrct # 5091-271-2273
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