C.03. How to model horizontal buried piping going under roadways / railways?

	Applies To
	Product(s):	AutoPIPE,
	Version(s):	2004, XM, & V8i
	Area:	Modeling
	Original Author:	Bentley Technical Support Group

Dec 2014, AutoPIPE V8i 09.06.01.10

Problem:

How to model horizontal buried piping going under roadways / railways?

Solution:

Any piping under a Roadway or Railroad are highly regulated by the respective municipalities (i.e. DOT, CSX Railroad, etc..). These companies will have clear guidelines about any pipeline crossing depending on the depth of cover. Recommend that you refer to these type of design specifications as needed for your design.

Pipeline buried with no casing -

Simply model the pipe routing and apply soil properties as needed. Refer to the "PIPE-SOIL Interaction: Transition Example" in the AutoPIPE's online help for techniques of apply vertical soil and horizontal soil properties.

Pipeline buried with casing -

Typically a carrier pipe will be properly encased within a steel casing of length as determined by the design documentation. See the following procedure:

1. Model the carrier pipe routing as needed. Be sure to add node points on the carrier pipe where spider supports (supports that centers the carrier pipe inside of the casing) are placed inside of the casing over the length of the casing.

2. Insert the casing pipe by selecting the same section of the carrier pipe that matches the casing length, copy, and pasting this section in the exact same location with a slight offset (ex. Dy = 0.1") as a new segment. Finally apply the correct PipeID with casing pipe properties to the new segment.

3. Select the node point on the carrier pipe where the spider supports are to be placed, insert a support (V-stop, Guide, incline), specify the corresponding casing pipe node point for the support's "Connected To:" field. Thus supporting the carrier pipe from the casing pipe.

4. Model the end connections of the casing to the carrier pipe

Rubber boot / Seal-Wrap - not really considered a support, nor does it provide any form of resistance to pipe movement. AutoPIPE modeling approach would be no component at this location.

Casing welded to Carrier pipe - select the casing end point insert a rigid beam to the corresponding carrier pipe node point. Length of rigid beam will be the same as the offset from Step #2 above (ex dy = 0.1").

Pipe Seal / Link Seal - rigid rubber links that are tighten to provide a leak proof seal. AutoPIPE modeling approach, insert another support (i.e. Guide) similar to a spider support with 0.00" gaps in all directions and a higher friction force.

Traffic Load:

AutoPIPE V8i 09.06.xx.xx and higher has the ability to calculate soil overburden stresses for a horizontal buried pipe line crossing a roadway / railway track taking in to account the live load from the traffic.