Maximum Soil Spacing

Good day to you Mahmoud, 

Please see the following AutoPIPE help section:
Help > Contents> Search Tab> enter "Defining Soil Points in AutoPIPE" (include the quotes), press List Topics button, double click on the selected topic from the list provided to see more information.

This will explain how maximum spacing values are calculated and used by the program. 

Try to understand what is happening here. In real life, buried piping is encased in a continuous support along its length. Most stress analysis software application approximate this continuous support by adding supports at some distance. The question becomes how close should these supports be placed to approximate actual soil: 5m, 10ft, 1 inch, 1mm, etc.. 

Note as the number of soil points increases due to short spacing values, so does the accuracy of the approximating actual soil conditions. However this comes at a steep cost of potentially managing 1000's of soil supports and waiting longer time for the software to analyze, longer time to produce results, etc... Experience has shown that modeling a few soil points provides reasonable accuracy where adding additional soil points may only minimally increase accuracy. 

Suggest an iterative solution, start by using the aforementioned AutoPIPE help to calculate a Maximum spacing  for the different zones and use as it as a starting point to run analysis and generate results. Then consider reducing the soil spacing by some percent (ex. 20%) to see how this affects both the analysis time and results. Repeat previous steps until satisfied with the results. 

To answer your question,

Question: Is it possible to have a certain spacing for all the pipes in the network

Answer:

Absolutely.

Question. What value should be used. 

Answer:

You may consider using the smallest suggested Max spacing mentioned in AutoPIPE Help. Again, this may make your input easier, but the down sides could be  1. Exceeding the maximum number of node points allowed in a model and 2. Extensive time required to Analysis and produce results.

Question. Is there a certain criteria to go with for spacing instead of go through the equations?

Answer:

Again the equations are to be used as a suggestion and are not the only answer. With experience analyzing many buried piping systems, your company may standardize on max spacing based on pipe size and soil conditions. Other criteria would be as mentioned before, iterative solution, try a value. run aanlyiss, review results, reduce value, and repeat until satisfied with results. 

In conclusion, even with the best geotechnical data, soil properties are one of the most elusive values to represent correctly in any model. 

- How far apart are the bore holes, knowing that in a short distance soil conditions could be significantly different 

- Open trench and back file, 100% guarantee that trench bottom, backfill, and compaction are identical along length of pipeline

Therefore, suggest to follow the iterative approach mentioned above.

Regards,

Mike Dattilio
Bentley Systems Design Analyst
Design Engineering Analysis group
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