Dear Mr./Mrs.

I am now calculating the maximum settlement value for specific pipes. The assumption is simple, a straight pipe with infinite open model boundary, in the middle of the pipe, there is a double shape settlement loading. The aim is to find the maximum tolerant value.

Background
According to paragraph 4.5 in the “theoretical manual” published in 1989 march, version 3.02, the resulting soil reaction will be where

- K represents the soil stiffness

- ∆S is the movement of the soil, input SUBZMAX in function 4.2

- ∆P is the distance with which the pipeline move together with the soil movement, output U-Z in function 5

And there will be two cases,

- the pipe follows the soil settlement completely, ∆P=∆S, then U-Z=SUBZMAX

- the pipe is rigid, ∆P<∆S, then U-Z<SUBZMAX

Example
Pipe: DN800 water pipe with a wall thickness 9.52mm

Loading: pressure 5 bar and the settlement (-44mm, uncertainty factor 2)

From the calculation results, the input subsidence length has a large influence to the stress, see pictures below, the blue colour is SUBZMAX and the pink colour is U-Z.

//pictures resized by moderator//

Questions
- In the third case with a 24 m length, why the U-Z could be larger than the SUBZMAX? The pipe could either completely follow the soil or rigid enough move less than de soil. What is the physical meaning if ∆P>∆S?

- If the input length follows NEN-3650, in this case, would be 20 m. Then the maximum settlement is larger than case 1 and case 2, which will show the similar shape as the length is 24 m. How could you determine an optimum length for specific pipe?