1. Pisa Soil Layer Profile

  • Seafloor offset: Offset between the seafloor and the top of the upper soil layer

    • if Top level position = Relative to sea floor :

      • Offset between Z-coordinate of seafloor and upper soil layer top position (>= 0)

    • if Top level position = Fixed depth :

      • Fixed Z-coordinate of upper soil layer top position ( < 0).

2. Specification of the soil sequence

The sequence defines the soil layer profile, listed from top to bottom, see Figure 1. The strength and stiffness values are given for both the upper and lower position of each layer. Linear interpolation is applied within each layer.

For each soil layer, specify the

  • soil type: name of the soil type. Available soil materials are

  • Delta Z : height of the soil layer

  • G0 upper : Shear modules at the top of the soil layer

  • G0 lower : Shear modules at the top of the soil layer

  • \(\gamma\) upper : effective soil weight at top of the soil layer

  • \(\gamma\) lower : effective soil weight, \(\gamma\), at bottom of the soil layer

  • Su Upper, default 0 : Undrained shear strength at top of the layer. Clay only, otherwise dummy

  • Su lower, default 0 : Undrained shear strength at bottom of the layer. Clay only, otherwise dummy

  • Dr , default 100% : Relative density used for scaling the the soil curve. Dunkirk sand only, otherwise dummy

Su upper and Su lower applies for clay only
Dr applies for Dunkirk sand only
soil layer profile
Figure 1. Soil layer profile

Figure 2 shows a simplification of a monopile modelled as a slender structure embedded in the subsurface. The subsurface consists of multiple soil layers. This influences the pile through reaction forces coupled to lateral deflection and cross-section rotation, leading to lateral force and bending moment respectively. The displacement-reaction force relationship is modelled through springs attached to element nodes.

The vertical pile is modelled as one or more lines connected to the profile. The connection adds stiffness to the pile; this is modelled through attaching soil springs to the nodes of the line elements. Placement and definition of soil reaction curves for the soil springs requires a depth relative to the mudline (z) and a pile diameter (D). This is in addition to soil characteristics and soil layer profile data. The value of z is determined when the soil springs are activated during static analysis. The bottom node of each pile is identified as a base node.

For further information on how lines are connected to a soil layer profile, see Connection of line(s)

pisa soil layer profile
Figure 2. PISA soil layer profile with pile

3. Specification of the embedded lines connection

  • A list of the lines

Each line can only be connected to one soil layer profile. Repeating the same line as input in more than one profile will lead to an error.

If a profile-connected line extends beneath the depth of its soil layer profile an error will result. The line is allowed to extend above the mudline; elements whose mid-point is above the mudline do not feel any soil stiffness (the soil springs are inactive for elements above the mudline).

The bottom element of each line is a candidate for being considered a base element. If some of the lines in the profile are connected to each other, only the bottom element of the bottom line is a base element. The bottom node of the base element is connected to base soil springs (using base soil reaction curves).

The lines attached to a soil layer profile must be reasonably vertical in a stress-free static configuration (when the soil springs are activated during static analysis). The analysis will exit with an error if a criterion for being vertical fails. The criterion is set at a maximum of 10 % inclination.