Calculations of Downward vertical soil stiffness
The soil range of importance for the Downward vertical soil stiffness is from the pipeline axis to 1.5 diameter under the pipeline axis.
NEN36501992
For the NEN36501992 calculation methodology two formula's are used to calculate the Downward vertical soil stiffness, one for sandy soil types and one for clayey/peaty soil types.
Sandy:
Clayey/peaty:
kv 
Downward vertical soil stiffness 
Pwe 

D 
Outer diameter of pipeline 
cuo 
Undrained cohesion (averaged over range from pipeline axis to 1.5 diameter below pipeline axis) 
H 
Height of soil coverage on top of pipeline 
NEN36501:2017
The NEN36501:2017 calculation methodology uses the following formula's. There are two formula's for trench installation: one for sandy soil types and one for clayey/peaty soil types and there is one formula for nontrench installation. A trench installation is either 1)Trench uncompressed fill or 2)Trench compressed fill and a nontrench installation is either 3)Boring or 4)HDD.
Trench, Sandy:
Trench, Clayey/peaty:
Nontrench:
kv 
Downward vertical soil stiffness 
Pwe 

D 
Outer diameter of pipeline 
Eo 
Effective Young's modulus calculated for range from pipeline axis to 1.5 diameter below pipeline axis, using depth at bottom of pipe (for Trench given in N/mm2, factor 0.5 is not dimensionless) 
cuo 
Undrained cohesion (averaged over range from pipeline axis to 1.5 diameter below pipeline axis) (given in N/mm2, factor 250 is not dimensionless) 
m 

l 

λ 

ν 

φo 
Angle of internal friction (averaged over range from pipeline axis to 1.5 diameter below pipeline axis) 
Epipe 
Young's modulus of pipe material 
Ib 

Di

Inner diameter of pipeline 
Last changed: 10/30/2019