Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: Modeling Subarea: Original Author: Bentley Technical Support Group Attention: Please see the following AutoPIPE help sections: Help Contents Contents Tab 1. Reference Information Pipe Soil This section will provide information on a. Model Discretization b. Defining Soil Points in AutoPIPE c. Soil Restraint Properties in AutoPIPE d. Calculation of Soil Restraint Properties - AutoPIPE Method e. Calculation of Soil Restraint Properties - ASCE Method f. Comparison of Soil Restraint Properties g. Soil overburden stresses application on AutoPIPE points 2. Modeling Approaches Example systems PIPE-SOIL Interaction: Transition Example. The purpose of the following example system is to demonstrate the procedure required to a. Calculate soil properties using AutoPIPE and ASCE method b. Verification of values with hand calculations c. Determine the location of critical piping points to be defined for the above to below ground (transition) piping system shown in the Figure below. In this example, the piping system is subjected to a temperature rise of 230°F, and an internal pressure of 100 psi. For simplicity, a single soil will be assumed to interface with the pipe over the entire length of the buried portion of the system. This online help section will provide step by step procedure of modeling soil properties in AutoPIPE. Comments, Questions, and Answers about Soil Properties, Soil Calculator, and Underground Piping: Item #1, Question: What will be the yield displacement value for following - yield displacement to calculate longitudinal loose clay soil spring stiffness; - yield displacement to calculate longitudinal loose sandy soil spring stiffness; Answer: Per the online help for this parameter, Longitudinal Yield Displacement, y1L [inch] Enter the longitudinal yield displacement. The value is used when calculating the soil resistance, p1, in the longitudinal direction. Defaults: Low = D/60, High = D/25. Also, per the AutoPIPE soil example (mentioned above): For medium sand, assume the value of yield displacement to be d/45. Bentley is not able to provide a specific values for modeling, must use engineering judgement or consult a soil engineer when determine values such as this. In addition, AutoPIPE's Soil calculator can consider high, low, and avg values when generating soil spring stiffness values based on soil parameters. Item #2, Question: Would it be appropriate to design fault line crossings by applying an offset to the pipeline? Are there any other way to model this? Answer: AutoPIPE provides the ability to the user to be able to generate soil stiffness properties using the method provided in ALA guideline (ASCE 2001: Guidelines for the Design of Buried Steel Pipe). Using the imposed support displacement with a buried pipe model, it may be possible to model a fault line crossing. There is no specific workflow currently in AutoPIPE to model a fault line crossing. You can model a buried pipeline by provide the soil stiffness values in four directions, and then apply imposed support displacement values (e.g. If your total fault line displacement is say 10", you may start by providing 1" imposed support displacement from one piping node, increment that until you reach 10" total displacement). You may continue the imposed displacement after the fault line crossing keeping it at 10" until a virtual anchor is reached. The displaced model would look something like the one shown below: Item #3, Question: I have been doing a hand calc verification of the American lifeline s alliance (ALA) soil calculator, and cannot validate AutoPIPEs results, specifically for the Qu term (vertical up) for sand. The equations should be Qu = Nqv * Density * H * D, where Nqv = (phi * H) / (44 * D) I ran a coarse parameter study with many cases, and got proportionality for phi and density (which is good) and weirdly proportional to H/D. With my second parameter study, just looking at H/D, it looks like there is an additive term that I can't identify. what is causing the difference? Answer: There are 2 calculation differences identified from your had calculation and that in AutoPIPE. 1. Value of Nqv should be taken as less than Nq value: 2. Please note that gamma*H*D is meant to calculate the weight of soil on top of pipe. AutoPIPE calculates the weight of soil on top of pipe + considering the weight effects on sides of pipe as well. Thereby calculating weight of soil more accurately than found in the code: AutoPIPE calculates Qu as Note: cohesion of soil c = 0. Item #4, Question : Can you help with modeling a 420 km long buried pipe, including traffic loads and large radius bends in order for the pipe to travel under a river. I do not have much personal experience with buried piping and these details. Any recommendations? Answer: Bentley Technical support does not have any example models of a pipeline as described above. However the online help and example documents cover all these topics in detail. It would be just a matter of applying typical AutoPIPE commands and information from various documents, online help or WIKIs to the situation. For the pipeline example above: Route the pipe as needed using typical AutoPIPE commands Model a large radius bend with the Ring Command or as 1 large bend The soil tutorial PDF's (available in AutoPIPE V8i 09.06.xx.xx and higher, folder location = C:\ Bentley\ AutoPIPE V8i SELECTseries\ Documents) installed with program are a good starting point to understanding soil in AutoPIPE. Apply soil properties as needed along the pipe Apply traffic loads as needed with the Edit Soil properties Soil Overburden Loads command (refer to the "Tutorial - Soil Overburden and Seismic Wave Propagation in AutoPIPE.pdf" in the folder location mentioned above for an example.) Item #5, Question : In the Virtual Anchor Length equation (La = Co * Lm), how can the value for Co be adjusted? Answer: From the online help: Co = Dimensionless constant which lies in the range from 1.0 ("stiff" soils) to about 2 (soft soils). The magnitude of "Co" can be greater than 2.0 if the longitudinal yield strength (P1 ) is not achieved by the soil.Comparison of analysis results for similar system models with various virtual anchor lengths indicate that estimated values of "Co" should be limited to the following range (unless a larger value can be justified): 1.5 /= Co /= 2.0 The system model can be terminated and anchored at a distance away from a bend (or tee) equal to the virtual anchor length (La) without any loss of accuracy to the analyzed results. Depending on the overall configuration of the piping system and the type of analysis to be performed, the inclusion of Zone 3 in the system model may or may not be necessary or desirable. This decision is left to the judgement of the Engineer/modeler. In conclusion, AutoPIPE does not currently (v.09.06.xx.xx and lower) allow the value of "Co" to be adjusted by the user. It is set at a constant value of Co = 2.0. With regards to modeling, having an adjustable value of "Co", the virtual anchor length "La" value will only be shorten by a small order of magnitude. Item #6, Question: How to model horizontal buried piping going under roadways / railways? Answer: 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. Item #7, Question How to model vertical Air Shafts - large diameter vertical underground piping up to a half mile long, going straight down with external ring braces every 10 to 15 feet. Answer: Consider the following modeling approach: 1. Model vertical piping with the correct pipe properties as needed.. Confirm code requirements for D/t are not exceeded (typically D/t = 100). 2. Apply soil properties as needed to the vertical piping (may needed more than 1 soil property). 3. Account for the ring braces: "Waiting for CAE development team comment before finishing this response " Item #8, Question: Why does adding a node point on s segment with soil settlement (impose displacement) already defined make a big difference in the results. See following image and results At node A03 & B02. See Also Bentley AutoPIPE External Links Bentley Technical Support KnowledgeBase Bentley LEARN Server Comments or Corrections? 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