The following input lines are repeated NLAYERS times.

The PISA soil layer profile methodology requires that all layers use only PISA* soil methodologies.

Soil layer profile’s mudline

The figure above shows how the soil layer profile’s mudline is defined either relative to the sea floor or fixed with respect to the mean sea level. Also shown is the local z-axis definition for the soil layer profile, which is pointed downwards and zero at the mudline. For a position relative to the seafloor the mudline will be below the seafloor, and UPZVAL is given as a positive value. For a mudline at fixed position, the provided Z-coordinate is in the global coordinate system with zero at the mean sea level, meaning that UPZVAL will be negative. Placing the mudline beneath the sea floor gives some allowance for scour. Fixing the position of the mudline in the global coordinate system allows the soil layer profile to be kept at a constant depth even when the sea floor depth varies.

The figure above shows a pile embedded in the subsurface: layers of soil beneath a mudline. A soil layer profile is defined as a sequence of values for the vertical thickness of each layer, starting from the mudline. Each layer is defined through its thickness, stiffness, strength and other characteristics, together with a reference to a soil type which gives further characteristics.

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).

The following input line is given if PROFMET = PISA and is repeated NLAYERS times. The sequence defines the soil layer profile, listed from top to bottom. Strength and stiffness values are given for both the upper and lower position of each layer. Linear interpolation is applied within each layer. Undrained shear strength Su is used for clay, dummy otherwise. Relative density is used for general Dunkirk sand, dummy otherwise. Only SOIL-ID layers with SOILMET = PISACLAY, PISASAND or PISADUNK are accepted.

The figure above shows a simplification of a monopile modelled as a slender structure embedded in the subsurface. The subsurface consists of multiple soil layers, which influence 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 following input line is repeated NLINES times.

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.