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*P-Y

Purpose

To define P-y curves for modelling soil structure interaction.

Theory

Refer to Soil Modelling for further information on this feature.

Soil structure interaction can be modelled explicitly by manually specifying P-y curves at different depths, or by utilising one of the three built-in soil models which can generate P-y curves automatically. The three pre-programmed soil models are:

•Sand                (O’Neill & Murchinson, 1983)

•Soft Clay        (Matlock, 1970)

•Stiff Clay        (Reese et al., 1975)

Keyword Overview

The keyword format is a block of lines defining the interaction between a particular structure and the soil. The first line is an optional one which specifies the format in which the properties are input. This is followed by a number of lines defining the actual data. As many blocks as required can be used to specify the soil structure interaction over the complete depth required.

User Format

Data may defined explicitly within the keyword file itself, or defined separately in an external file which is simply referenced using a FILE= entry. The latter approach is highly recommended as it reduces unnecessary clutter in the keyword file, and also helps to improve user interface performance and enhanced user experience.

The format of the block when using directly entered P-y curve data:

[TYPE=USER]

SET=Set Name

DEPTH=Depth

Soil Resistance (P), Deflection (y)

The first line is optional. The second line indicates the element set for which the subsequent P-y curves apply. The next line defines the depth to which the curve relates and marks the start of a block containing the P-y curve data at that depth. This block can be repeated at as many depths as required. The final line is a pair of P, y values. This line will be repeated several times for describe a P-y curve.

The format of the block when using P-y curve data from an external file:

[TYPE=USER]

SET=Set Name

FILE=File Name

The first line is optional. The second line indicates the element set for which the P-y curves apply. The third line specifies an external file containing P-y curve data.

Sand Model

The format of the block when using the built-in soil model for sand:

TYPE=SAND

SET=Set Name

DEPTH=Start Depth, End Depth [, Depth Increment]

Diameter [, Water Table Depth]

[SCOUR=Scour Depth]

Depth, Submerged Unit Weight, Angle of Internal Friction, [C1], [C2], [C3], [K]

The first line is required and indicates that this block describes the properties of for generating P-y curves based on the standard sand model. P-y curves apply. The second line indicates the element set for which the generated P-y curves apply.  The third line indicates the depths at which P-y curves will be generated. The next line defines the nominal element diameter to use when generating the P-y curves and the water table depth, if appropriate. The next line allows the scour depth to be specified, when desired. The final line, which can be repeated as many times as required, allows parameters for the sand to be specified at specific depths.

Soft Clay

The format of the block when using the built-in soil model for soft clay:

TYPE=SOFT CLAY

SET=Set Name

DEPTH=Start Depth, End Depth [, Depth Increment]

[LOADING=STATIC/CYCLIC]

Diameter, J

[SCOUR=Scour Depth]

Depth, Undrained Shear Strength, Submerged Unit Weight [, Strain at Half Max Stress]

The first line is required and indicates that this block describes the properties of for generating P-y curves based on the standard soft clay model. P-y curves apply. The second line indicates the element set for which the generated P-y curves apply.  The third line indicates the depths at which P-y curves will be generated. The next line indicates whether or not P-y curves for a static or cyclical loading should be generated; the default is static. The next line defines the nominal element diameter to use when generating the P-y curves and the empirical constant J for soft clays. The next line allows the scour depth to be specified, when desired. The final line, which can be repeated as many times as required, allows parameters for the soft clay to be specified at specific depths.

Stiff Clay Model

The format of the block when using the built-in soil model for stiff clay:

TYPE=STIFF CLAY

SET=Set Name

DEPTH=Start Depth, End Depth [, Depth Increment]

[LOADING=STATIC/CYCLIC]

Diameter [, Ks]

[SCOUR=Scour Depth]

Depth, Undrained Shear Strength, Submerged Unit Weight, [A], [Strain at Half Max Stress]

The first line is required and indicates that this block describes the properties of for generating P-y curves based on the standard stiff clay model. P-y curves apply. The second line indicates the element set for which the generated P-y curves apply.  The third line indicates the depths at which P-y curves will be generated. The next line indicates whether or not P-y curves for a static or cyclical loading should be generated; the default is static. The next line defines the nominal element diameter to use when generating the P-y curves and the optional empirical constant Ks for stiff clays. The next line allows the scour depth to be specified, when desired. The final line, which can be repeated as many times as required, allows parameters for the soft clay to be specified at specific depths.

Table inputs

P-y Curves - Explicit

P-y Curves - File

Notes

(a)Use as many lines as you need to completely define a particular P-y curve, for a particular combination of element set and depth. Simply leave the Set Name and Depth columns blank for second and subsequent lines of the curve data. For subsequent P-y curves, specify a new Set Name and/or Depth, and specify the P-y data in the same way.

(b)The points defining the P-y curve may be specified in any order. Flexcom subsequently sorts the data pairs into ascending order of deflection.

Sand Model

P-y Curves – Sand – General

P-y Curves – Sand – By Depth

Soft Clay Model

P-y Curves – Soft Clay – General

P-y Curves – Soft Clay – By Depth

Stiff Clay Model

P-y Curves – Stiff Clay – General

P-y Curves – Stiff Clay – By Depth

Notes

(a)Flexcom automatically interpolates the P-y data for nodes located between any two specified depths.

(b)If the deflection at a particular node lies between two P-y data points, Flexcom uses linear interpolation to determine the relevant soil resistance.

(c)If the deflection at the node lies outside the specified range of the P-y curve, then Flexcom simply extrapolates from the first or last section of the curve as appropriate.