The external loads in the buried pipe stress analysis that must be considered in calculation are live load and dead load. Live load will always changes according to position or distance, while dead load is not depend on these factors but it is determined by design value of dead load itself. The examples of design live loads in buried pipe are truck load, car load, train load and the others.
As for example: truck is located above buried pipe or truck across ground area where pipe is buried in it. Truck is modeled as live load so it will add external load to buried pipe. This truck load is vertical load for buried pipe. It is assumed that the truck load is single load (W) above ground as shown in Figure 1 below.
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| Figure 1: Truck as Live Load on Buried Pipe (source: book-Structural Mechanics of Buried Pipes by Reynold KW, Loren RA) |
The amount of truck load that is received by buried pipes at point A (right above pipe) is:
P1 = N W / H2
Where:
Pl = truck load (N/m2),
W = single truck load (N)
H = height of soil above pipe (m)
R = horizontal distance from the center of pipe to single load (m)
N = coefficient Boussinesq = (3 (H/R)5) / (2π)
Coefficient value of N can be seen from Figure 2. To know the value of N can use the relationship of R (distance W of center pipe) with H (depth pipe in soil). Then the relationship between R / H with N can be obtained as shown in the chart below.
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| Figure 2: Relationship of R/H vs N (source: book-Structural Mechanics of Buried Pipes by Reynold KW, Loren RA) |