3D2010 1 Tutorial Plaxis

8/13/2019 3D2010 1 Tutorial Plaxis

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PLAXIS 3D

Tutorial Manual

2010


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Build 4111


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TABLE OF CONTENTS

TABLE OF CONTENTS

1 Introduction 5

2 Lesson 1: Foundation in overconsolidated clay 7

2.1 Geometry 7

2.2 Case A: Rigid foundation 8

2.3 Case B: Raft foundation 20

2.4 Case C: Pile-Raft foundation 26

3 Lesson 2: Excavation in sand 31

3.1 Geometry 32

3.2 Mesh generation 37

3.3 Performing calculations 37

3.4 Viewing the results 40

4 Lesson 3: Load capacity of a suction pile 454.1 Geometry 45

4.2 Mesh generation 48

4.3 Performing calculations 49

4.4 Viewing the results 50

Appendix A - Menu tree

Appendix B - Calculation scheme for initial stresses due to soil weight

PLAXIS 3D 2010 | Tutorial Manual 3


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TUTORIAL MANUAL

4 Tutorial Manual | PLAXIS 3D 2010


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INTRODUCTION

1 INTRODUCTION

PLAXIS is a finite element package that has been developed specifically for the analysis

of deformation and stability in geotechnical engineering projects. The simple graphical

input procedures enable a quick generation of complex finite element models, and the

enhanced output facilities provide a detailed presentation of computational results. Thecalculation itself is fully automated and based on robust numerical procedures. This

concept enables new users to work with the package after only a few hours of training.

Though the various lessons deal with a wide range of interesting practical applications,

this Tutorial Manual is intended to help new users become familiar with PLAXIS 3D. The

lessons should therefore not be used as a basis for practical projects.

Users are expected to have a basic understanding of soil mechanics and should be able

to work in a Windows environment. It is strongly recommended that the lessons are

followed in the order that they appear in the manual. The tutorial lessons are also

available in the examples folder of the PLAXIS program directory and can be used tocheck your results.

The Tutorial Manual does not provide theoretical background information on the finite

element method, nor does it explain the details of the various soil models available in the

program. The latter can be found in the Material Models Manual, as included in the full

manual, and theoretical background is given in the Scientific Manual. For detailed

information on the available program features, the user is referred to the Reference

Manual. In addition to the full set of manuals, short courses are organised on a regular

basis at several places in the world to provide hands-on experience and background

information on the use of the program.



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LESSON 1: FOUNDATION IN OVERCONSOLIDATED CLAY

2 LESSON 1: FOUNDATION IN OVERCONSOLIDATED CLAY

In this chapter a first application is considered, namely the settlement of a foundation in

clay. This is the first step in becoming familiar with the practical use of the program.

The general procedures for the creation of a geometry, the generation of a finite elementmesh, the execution of a finite element calculation and the evaluation of the output results

are described here in detail. The information provided in this chapter will be utilised in the

following lessons. Therefore, it is important to complete this first lesson before attempting

any further tutorial examples.

18.0 m

75.0 m

75.0 mBuilding

Clay

x

x

y

z

z = 0z = -2

z = -40

40.0

Figure 2.1 Geometry of a square building on a raft foundation

2.1 GEOMETRY

This exercise deals with the construction and loading of a foundation of a square building

in a lightly overconsolidated lacustrine clay. Below the clay layer there is a stiff rock layer

that forms a natural boundary for the considered geometry. The rock layer is not included

in the geometry; instead an appropriate boundary condition is applied at the bottom of the

clay layer. The purpose of the exercise is to find the settlement of the foundation.

The building consists of a basement level and 5 floors above the ground level (Figure

2.1). To reduce calculation time, only one-quarter of the building is modelled, using

symmetry boundary conditions along the lines of symmetry. To enable any possible

mechanism in the clay and to avoid any influence of the outer boundary, the model is

extended in both horizontal directions to a total width of 75 m.

The model is considered in three different cases:

Case A: The building is considered very stiff and rough. The basement is simulated by

means of non-porous linear elastic volume elements.



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Case B: The structural forces are modelled as loads on a raft foundation.

Case C: Embedded piles are included in the model to reduce settlements.

2.2 CASE A: RIGID FOUNDATION

In this case, the building is considered to be very stiff. The basement is simulated by

terms of non-porous linear elastic volume elements. The total weight of the basement

corresponds to the total permanent and variable load of the building. This approach leads

to a very simple model and is therefore used as a first exercise, but it has some

disadvantages. For example it does not give any information about the structural forces in

the foundation.

Objectives:

Starting a new project.

Creation of soil stratigraphy using a single borehole. Creation of material data sets.

Creation of volumes usingCreate surfaceand Extrudetools.

Assigning material.

Local mesh refinement.

Generation of mesh.

Generating initial stresses using theK0 procedure.

Defining aPlasticcalculation.

2.2.1 GEOMETRY INPUT

Start the PLAXIS 3D program. TheQuick selectdialog box will appear in which you

can select an existing project or create a new one (Figure2.2).

Figure 2.2 Quick selectdialog box

ClickStart a new project. TheProject propertieswindow appears, consisting of

ProjectandModeltabsheets.



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Project properties

The first step in every analysis is to set the basic parameters of the finite element model.

This is done in theProject propertieswindow. These properties include the description of

the problem, the basic units and the size of the draw area.

To enter the appropriate properties for the foundation calculation follow these steps: In theProjecttabsheet, enter "Lesson1" as the Titleof the project and type

"Settlements of a foundation" in theCommentsbox (Figure2.3).

Figure 2.3 Projecttabsheet of theProject propertieswindow

Proceed to theModeltabsheet by clicking either the Nextbutton or the Model tab

(Figure2.4).

Keep the default units in theUnitsbox (Length =m; Force =kN; Time =day). TheGeneralbox indicates a fixed gravity of 1.0 G, in the vertical direction downward

(-z). The value of the acceleration of gravity (1.0G) can be specified in theEarthgravitybox. This should be kept to the default value of 9.810m/s2 for this exercise.In thewaterbox the unit weight of water can be defined. Keep this to the defaultvalue of10 kN/m3.

Define the limits for the soil contour asxmin=0,xmax =75,ymin=0 and ymax =75 intheContourgroup box.

Figure 2.4 Model tabsheet of the Project propertieswindow



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Click theOKbutton to confirm the settings.

Hint: In case of a mistake or for any other reason that the project properties need

to be changed, you can access the Project propertieswindow by selecting

the corresponding option in the Filemenu.

Definition of soil stratigraphy

When you click the OKbutton theProject propertieswindow will close and theSoilmode

view will be shown. Information on the soil layers is entered in boreholes.

Boreholes are locations in the draw area at which the information on the position of soil

layers and the water table is given. If multiple boreholes are defined, PLAXIS 3D will

automatically interpolate between the boreholes, and derive the position of the soil layers

from the borehole information.

Hint: PLAXIS 3D can also deal with layers that are discontinuous, i.e. only locally

present in the model area. See Section4.2.2of the Reference Manual for

more information.

In the current example, only one soil layer is present, and only a single borehole is

needed to define the soil stratigraphy. In order to define the borehole, follow these steps:

Click theCreate boreholebutton in the side toolbar to start defining the soil

stratigraphy. Click on position (0; 0; 0) in the geometry. A borehole will be located at

(x, y)= (0; 0). TheModify soil layerswindow will appear.

Figure 2.5 Modify soil layerswindow

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In theModify soil layerswindow add a soil layer by clicking on the Addbutton. Keep

the top boundary of the soil layer atz= 0and set the bottom boundary to z= 40m.

Set theHeadvalue in the borehole column to 2m (Figure2.5). The creation ofmaterial data sets and their assignment to soil layers is described in the following

section.

2.2.2 MATERIAL DATA SETS

In order to simulate the behaviour of the soil, a suitable material model and appropriate

material parameters must be assigned to the geometry. In PLAXIS soil properties are

collected in material data sets and the various data sets are stored in a material

database. From the database, a data set can be assigned to one or more clusters. For

structures (like beams, plates, etc.) the system is similar, but different types of structures

have different parameters and therefore different types of data sets.

PLAXIS 3D distinguishes between material data sets for Soils & Interfaces,Plates,Geogrids,Beams,Embedded Pilesand Anchors. Before the mesh can be generated

material data sets have to be assigned to all soil volumes and structures.

Open theMaterial setswindow by clicking theMaterialsbutton.

Click theNewbutton on the lower side of the Material setswindow. TheSoilwindow

will appear. It contains five tabsheets: General,Parameters,Flow parameters,

Interfacesand Initial.

In theMaterial setbox of theGeneraltabsheet (Figure2.6), write "Lacustrine Clay"

in theIdentificationbox.

SelectMohr-Coulombas the material model from the Material modeldrop-down

menu andDrained from theDrainage typedrop-down menu.

Figure 2.6 General tabsheet of theSoil & Interfacesdata set window



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Enter the unit weights in theGeneral propertiesbox according to the material data

as listed in Table2.1. Keep the unmentioned Advanced parametersas their default

values.

Click theNextbutton or click the Parameterstab to proceed with the input of model

parameters. The parameters appearing on the Parameterstabsheet depend on the

selected material model (in this case the Mohr-Coulomb model). The Mohr-Coulombmodel involves only five basic parameters (E', ', c',','). See the Material ModelsManual for a detailed description of the different soil models and their corresponding

parameters.

Enter the model parametersE',',c'ref,' and ofLacustrine clayaccording toTable2.1in the corresponding boxes of the Parameterstabsheet (Figure2.7).

Figure 2.7 Parameters tabsheet of theSoil & Interfacesdata set window

No consolidation will be considered in this exercise. As a result, the permeability of

the soil will not influence the results and the Flow parameterswindow can be

skipped.

Table 2.1 Material properties

Parameter Name Lacustrine clay Building Unit

General

Material model Model Mohr-Coulomb Linear elastic

Drainage type Type Drained Non-porous

Unit weight above phreatic level unsat 17.0 50 kN/m3

Unit weight below phreatic level sat 18.0 kN/m3

Parameters

Young's modulus (constant) E' 1 104 3107 kN/m2

Poisson's ratio ' 0.3 0.15

Cohesion (constant) c'ref 10 kN/m2

Friction angle ' 30.0

Dilatancy angle 0.0

Initial

K0 determination Automatic Automatic

Lateral earth pressure coefficient K0 0.5000 1.000



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Since the geometry model does not include interfaces, theInterfacestab can be

skipped.

Click theInitialtab and check that theK0 determinationis set toAutomatic. In thatcaseK0 is determined from Jaky's formula: K0 =1 sin.

Click theOKbutton to confirm the input of the current material data set. The createddata set appears in the tree view of the Material setswindow.

Drag the setLacustrine clay from theMaterial setswindow (select it and hold down

the left mouse button while moving) to the graph of the soil column on the left hand

side of theSoilwindow and drop it there (release the left mouse button). Notice that

the cursor changes shape to indicate whether or not it is possible to drop the data

set. Correct assignment of the data set to the soil layer is indicated by a change in

the colour of the layer.

The building is modelled by a linear elastic non-porous material. To define this data set,

follow these steps:

Click theNewbutton in theMaterial setswindow.

In theMaterial setbox of theGeneraltabsheet, write "Building" in theIdentification

box.

SelectLinear elasticas the material model from the Material modeldrop-down

menu andNon-porousfrom theDrainage typedrop-down menu.

Enter the unit weight in theGeneral propertiesbox according to the material data set

as listed in Table2.1. This unit weight corresponds to the total permanent and

variable load of the building.

Click theNextbutton or click the Parameterstab to proceed with the input of themodel parameters. The linear elastic model involves only two basic parameters (E',

').

Enter the model parameters of Table2.1in the corresponding edit boxes of the

Parameterstabsheet.

Click theOKbutton to confirm the input of the current material data set. The created

data set will appear in the tree view of the Material setswindow, but it is not directly

used.

Click theOKbutton to close the Material setswindow.

Click theOKbutton to close the Modify soil layerswindow.

Hint: PLAXIS 3D distinguishes between a project database and a global database

of material sets. Data sets may be exchanged from one project to another

using the global database. The global database can be shown in the Material

setswindow by clicking theShow globalbutton. The data sets of all lessons

in the Tutorial Manual are stored in the global database during the installation

of the program.



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2.2.3 DEFINITION OF STRUCTURAL ELEMENTS

The structural elements are created in theStructuresmode of the program. Click the

Structuresbutton to proceed with the input of structural elements. To model the building:

Click theCreate surfacebutton. Position the cursor at the coordinate (0; 0; 0).

Check the cursor position displayed in the cursor position indicator. As you click, thefirst surface point of the surface is defined.

Define three other points with coordinates (0; 18; 0), (18; 18; 0), (18; 0; 0)

respectively. Press the right mouse button or to finalize the definition of the

surface. Note that the created surface is still selected and displayed in red.

Click theExtrude objectbutton to create a volume from the surface.

Change thezvalue to 2in theExtrudewindow (Figure2.8). Click theApplybuttonto close the window.

Figure 2.8 Extrudewindow

Click theSelectbutton. Select the created surface using the right mouse button.

SelectDeletefrom the appearing menu. This will delete the surface but the building

volume is retained.

The shape of the building, as well as the corresponding material data sets have now

been created.

2.2.4 MESH GENERATION

The model is complete. In order to proceed to the Meshmode click theMeshbutton.

PLAXIS 3D allows for a fully automatic mesh generation procedure, in which the

geometry is divided into volume elements and compatible structure elements, if

applicable. The mesh generation takes full account of the position of the geometry

entities in the geometry model, so that the exact position of layers, loads and structures is

accounted for in the finite element mesh. A local refinement will be considered in the

building volume. To generate the mesh, follow these steps:

Click theRefine meshbutton in the side toolbar and click the created building

volume to refine the mesh locally. It will colour green.

Click theGenerate meshbutton in the side toolbar or select theGenerate mesh

option in theMeshmenu. Change theElement distributionto Coarsein theMeshoptionswindow (Figure2.9) and clickOK to start the mesh generation.



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Figure 2.9 Mesh optionswindow

Hint: By default, theElement distributionis set to Medium. TheElement

distributionsetting can be changed in the Mesh optionswindow. In addition,

options are available to refine the mesh globally or locally (Section 7.1ofReference Manual).

The finite element mesh has to be regenerated if the geometry is modified. The automatically generated mesh may not be perfectly suitable for the

intended calculation. Therefore it is recommended that the user inspects the

mesh and makes refinements if necessary.

As the mesh is generated, click the View meshbutton. A new window is opened

displaying the generated mesh (Figure2.10).

Figure 2.10 Generated mesh in theOutputwindow

Click theClosebutton to go back to the Meshmode of theInputprogram.

2.2.5 PERFORMING CALCULATIONS

Once the mesh has been generated, the finite element model is complete. Click Staged

constructionto proceed with the definition of calculation phases.



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Initial conditions

The 'Initial phase' always involves the generation of initial conditions. In general, the initial

conditions comprise the initial geometry configuration and the initial stress state, i.e.

effective stresses, pore pressures and state parameters, if applicable. The initial water

level has been entered already in the Modify soil layerswindow. This level is taken into

account to calculate the initial effective stress state. It is therefore not needed to enter theWater levelsmode.

When a new project has been defined, a first calculation phase named "Initial phase", is

automatically created and selected in the Phases explorer (Figure2.11). All structural

elements and loads that are present in the geometry are initially automatically switched

off; only the soil volumes are initially active.

Figure 2.11 Phases explorer

In PLAXIS 3D two methods are available to generate the initial stresses, Gravity loading

or theK0 procedure. TheK0 procedureis the default calculation type for the Initial phase.Note thatK0 procedureis indicated by the 'K' letter in the Phases explorer.

Hint: TheK0 proceduremay only be used for horizontally layered geometries witha horizontal ground surface and, if applicable, a horizontal phreatic level.

See Section7.3of the Reference Manual for more information on the K0

procedure.

ThePhaseswindow (Figure2.12) is displayed by clicking the Edit phasebutton or

by double clicking on the phase in the Phases explorer.

ClickOK to close thePhaseswindow.

Make sure that all the soil volumes in the project are active and the materialassigned to them isLacustrine clay.

Construction stage

After the definition of the initial conditions, the construction of the building can be

modelled. This will be done in a separate calculation phase, which needs to be added as

follows:

Click theAddbutton in the Phases explorer. A new phase, named Phase_1will be

added in thePhases explorer.

Double-click thePhase_1to open thePhaseswindow.



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Figure 2.12 TheGeneral tabsheet in the Phaseswindow forInitial phase

In theGeneraltabsheet, write (optionally) an appropriate name for the new phase in

theIDbox (for example " Building") and select the phase from which the current

phase should start (in this case the calculation phase can only start from Initial

phase, which contains the initial stress state).

Leave theCalculation typeas Plasticand click theParameterstab to open the

Parameterstabsheet. TheParameterstabsheet (Figure2.13)contains the calculation control parameters.

Keep the default settings in the Iterative procedurebox and keep the number of

Additional stepsto 250.

The calculation parameters for phaseBuildinghave now been set. Click OK to

close thePhaseswindow.

Right-click the building volume. From theSet materialoption in the appearing menu

select theBuildingoption.

Hint: Calculation phases may be added, inserted or deleted using theAdd,Insert

andDeletebuttons in thePhases exploreror in thePhaseswindow.

Execution of calculation

All calculation phases (two phases in this case) are marked for calculation (indicated

by a blue arrow). The execution order is controlled by the Start from phase

parameter.

Click theCalculatebutton to start the calculation process. Ignore the warning that

no nodes and stress points have been selected for curves.



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Figure 2.13 TheParameterstabsheet in the Phaseswindow forBuildingphase

During the execution of a calculation, a window appears which gives information about

the progress of the actual calculation phase (Figure 2.14).

Figure 2.14 Active taskwindow displaying the calculation progress



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The information, which is continuously updated, shows, amongst others, the calculation

progress, the current step number, the global error in the current iteration and the number

of plastic points in the current calculation step.

It will take a few seconds to perform the calculation. When a calculation ends, the

window is closed and focus is returned to the main window.

The phase list in thePhases explorer is updated, showing green tick marks to

indicate that the calculations were finished successfully. An unsuccessful calculation

would be indicated with a red cross.

Before viewing results, save the project.

Viewing calculation results

Once the calculation has been completed, the results can be displayed in the Output

program. In theOutputprogram, the displacement and stresses in the full three

dimensional model as well as in cross sections or structural elements can be viewed.

The computational results are also available in tabular form. To view the current results,follow these steps:

Select the last calculation phase (Building) in the Phases explorertree.

Click theView calculation resultsbutton in the side toolbar to open theOutput

program. TheOutputprogram will, by default, show the three dimensional deformed

mesh at the end of the selected calculation phase. The deformations are scaled to

ensure that they are clearly visible.

SelectTotal Displacements |u| from theDeformationsmenu. The plot showscolour shadings of the total displacements (Figure2.15).

Figure 2.15 Shadings ofTotal displacementsat the end of the last phase



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A legend is presented with the displacement values at the colour boundaries. When

the legend is not present, select the Legendoption from theViewmenu to display it.

In theOutputwindow click theIso surfacesbutton to display the areas having the

same displacement.

Hint: In addition to the Total displacements, theDeformationsmenu allows for the

presentation ofIncremental displacementsand Phase displacements.

The incremental displacements are the displacements that occurred in onecalculation step (in this case the final step). Incremental displacements may

be helpfull in visualising failure mechanisms.

Phase displacements are the displacements that occurred in one calculationphase (in this case the last phase). Phase displacements can be used to

inspect the impact of a single construction phase, without the need to reset

displacements to zero before starting the phase.

2.3 CASE B: RAFT FOUNDATION

In this case, the model is modified so that the basement consists of structural elements.

This allows for the calculation of structural forces in the foundation. The raft foundation

consists of a50 cm thick concrete floor stiffened by concrete beams. The walls of the

basement consist of30 cm thick concrete. The loads of the upper floors are transferred

to the floor slab by a column and by the basement walls. The column bears a load of

11650kN and the walls carry a line load of 385 kN/m, as sketched in Figure2.16.

12.0 m12.0 m

6.0 m6.0 m

385 kN/m385 kN/m

11650 kN

5.3 kN/m2

Figure 2.16 Geometry of the basement

In addition, the floor slab is loaded by a distributed load of 5.3 kN/m2. The properties of

the clay layer will be modified such that stiffness of the clay will increase with depth.

Objectives:

Saving project under a different name.

Modifying existing data sets.

Defining a soil stiffness that increases with depth.

Modelling of floors and defining material data set for floors.

Modelling of beams and defining material data set for beams.



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Modelling of columns and defining material data set for columns.

Assigning point loads.

Assigning line loads.

Assigning distributed loads to surfaces.

Deleting phases.

Activation and deactivation of soil volumes.

Activation and deactivation of structural elements.

Activation of loads.

Zooming inOutput.

Drawing cross sections inOutput.

Viewing structural output.

Geometry input

The geometry used in this exercise is the same as the previous one, except that

additional elements are used to model the foundation. It is not necessary to create a new

model; you can start from the previous model, store it under a different name and modify

it. To perform this, follow these steps:

Start the PLAXIS 3D program. The Quick selectdialog box will appear in which

select the project of case A.

Select theSave project asoption in theFilemenu to save the project under a

different name (e.g. "Lesson 1b").

The material set for the clay layer has already been defined. To modify this material set to

take into account the stiffness of the soil increasing with depth, follow these steps:

Go to theSoilmode.

Open theMaterial setswindow by clicking theShow materialsbutton.

Select theLacustrine claymaterial set and click the Editbutton.

In theParameterstabsheet, change the stiffness of the soil E' to5000kN/m2.

Enter a value of500 in theE'incbox in theAdvancedparameters. Keep the default

value of0.0 m forzref. Now the stiffness of the soil is defined as 5000kN/m2

atz= 0.0m and increases with 500 kN/m2 per meter depth.

ClickOK to close theSoilwindow.

ClickOK to close theMaterial setswindow.

Definition of structural elements

Proceed to theStructuresmode to define the structural elements that compose the

basement.

Click theSelectionbutton.

Right click the volume representing the building. Select theDecompose into

surfacesoption from the appearing menu.



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Delete the top surface by right-clicking on it and selecting theDeleteoption from the

displayed menu.

Select the volume representing the building. Click the visualisation toggle in the

Selection explorerto hide the volume.

Right-click the bottom surface of the building. Select theCreate plateoption fromthe appearing menu.

Assign plates to the two vertical basement surfaces that are inside the model.

Delete the remaining two vertical surfaces at the model boundaries.

Figure 2.17 Location of plates in the project

Hint: Multiple entities can be selected by holding the button pressed while

clicking on the entities.

A feature can be assigned to multiple similar objects the same way as to asingle selection.

Open the material data base and set theSet typeto Plates.

Create data sets for the basement floor and for the basement walls according to

Table2.2.

Drag and drop the data sets to the basement floor and the basement walls

accordingly. It may be needed to move the Material setswindow by clicking at its

header and dragging it.

Click theOKbutton to close the data set.

Right-click the bottom of the surface of the building volume and select theCreate

surface loadoption from the appearing menu. The actual value of the load can be

assigned in the Structuresmode as well in the Phase definitionmode. In this

example, the value will be assigned in the Staged constructionmode.

Table 2.2 Material properties of the basement floor and basement walls

Parameter Name Basement floor Basement wall Unit

Thickness d 0.5 0.3 m

Weight 15 15.5 kN/m3

Type of behaviour Type Linear, isotropic Linear, isotropic

Young's modulus E1 3 107 3107 kN/m2

Poisson's ratio 12 0.15 0.15



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Click theCreate linebutton in the side toolbar.

Select theCreate line loadoption from the additional tools displayed.

Click the command input area, type "0 18 0 18 18 0 18 0 0" and press .

Line loads will now be defined on the basement walls. The defined values are the

coordinates of the three points of the lines. Click the right mouse button to stopdrawing line loads.

Click theCreate linebutton in the side toolbar. Select the Create beamoption from

the additional tools displayed.

Click on (6; 6; 0) to create the first point of a vertical beam. Keep the key

pressed and move the mouse cursor to (6; 6; -2). Note that while the key is

pressed the cursor will move only vertically. As it can be seen in the cursor position

indicator, thezcoordinate changes, whilexandycoordinates will remain the same.

Click on (6; 6; -2) to define the second point of the beam. To stop drawing click the

right mouse button.

Create horizontal beams from (0; 6; -2) to (18; 6; -2) and from (6; 0; -2) to (6; 18; -2).

Hint: By default, the cursor is located at z=0. To move in the vertical direction,

keep the key pressed while moving the mouse.

Open the material data base and set theSet typeto Beams.

Create data sets for the horizontal and for the vertical beams according to Table2.3.

Assign the data set to the corresponding beam elements by drag and drop.

Table 2.3 Material properties of the basement column and basement beams

Parameter Name basement column basement beam Unit

Cross section area A 0.49 0.7 m2

Volumetric weight 24.0 6.0 kN/m3

Type of behaviour Type Linear Linear

Young's modulus E 3107 3107 kN/m2

Moment of Inertia I3 0.020 0.058 m4

I2 0.020 0.029 m4

Click theCreate loadbutton in the side toolbar.

Select theCreate point loadoption from the additional tools displayed. Click at (6; 6;

0) to add a point load at the top of the vertical beam.

Proceed to theMeshtabsheet to generate the mesh.

Mesh generation

Click theGenerate mesh. Keep theElement distributionas Coarse.

Inspect the generated mesh.

As the geometry has changed, all calculation phases have to be redefined.



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2.3.1 PERFORMING CALCULATIONS

Proceed to theStaged constructionmode.

Initial conditions

As in the previous example, theK0 Procedure will be used to generate the initialconditions. It is indicated by the K letter in thePhases explorer. In the model:

All the structural elements should be deactivated in the Initial Phase.

No excavation is performed in the Initial Phase. So, the basement volume should be

active and the material assigned to it should beLacustrine clay.

Construction stages

Instead of constructing the building in one calculation stage, separate calculation phases

will be used. In Phase1, the construction of the walls and the excavation is modelled. In

Phase2, the construction of the floor and beams is modelled. The activation of the loadsis modelled in the last phase (Phase 3). To define these construction stages, follow these

steps:

In thePhases explorerselect thePhase_1and rename it to "Excavation".

Deactivate the soil volume located over the foundation by selecting it and by clicking

on the square in front of it in the Selection explorer.

In theModel explorerclick the square in front of the plates corresponding to the

basement walls to activate them.

In thePhases explorerclick theAdd phasebutton. A new phase (Phase_2) is

added. Double-clickPhase_2. ThePhaseswindow pops up.

Rename the phase by defining itsIDas "Construction". Keep the default settings in

theParameterstab. Close thePhaseswindow.

In theModel explorerclick the square in front of the plate corresponding to the

basement floor to activate it.

In theModel explorerclick the square in front of the beams to activate all the beams

in the project.

Add a new phase following theConstructionphase. Rename it to "Loading".

In theModel explorerclick the square in front of the Surface loadsto activate thesurface load on the basement floor. Set the value of thezcomponent of the load to5.3. This indicates a load of 5.3 kN/m2, acting in the negative zdirection.

In theModel explorer, click the square in front of theLine loadsto activate the line

loads on the basement walls. Set the value of the zcomponent of each load to385. This indicates a load of 385 kN/m, acting in the negative zdirection.

In theModel explorerclick the square in front of the Point loadsto activate the point

load on the basement column. Set the value of the zcomponent of the load to11650. This indicates a load of 11650kN, acting in the negativezdirection.

Click thePreviewphase button to check the settings for each phase.

As the calculation phases are completely defined, calculate the project. Ignore the



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warning that no nodes and stress points have been selected for curves.

Save the project after the calculation.

Viewing calculation results

SelectConstructionin thePhases explorer. Click theView calculation resultsbutton to open the Output program. The deformed

mesh at the end of this phase is shown.

Select the last phase in the drop-down menu to switch to the results at the end of

the last phase.

In order to evaluate stresses and deformations inside the geometry, select the

Vertical cross sectiontool. A top view of the geometry is presented and the Cross

section pointswindow appears. As the largest displacements appear under the

column, a cross section through this column is most interesting. Enter (0.0; 6.0) and

(75.0; 6.0) as the coordinates of the first point (A) and the second point (A')respectively in theCross section pointswindow. Click OK. A vertical cross section is

presented. The cross section can be rotated in the same way as a regular 3Dviewof the geometry.

SelectTotal displacements uzfrom theDeformationsmenu Figure2.18). Themaximum and minimum values of the vertical displacements are shown in the

caption. If the title is not visible, select this option from theViewmenu.

Figure 2.18 Cross section showing the total vertical displacement

Press and to move the cross section.

Return to the three dimensional view of the geometry by selecting this window from

the list in theWindowmenu.

Double-click the floor. A separate window will appear showing the displacements of

the floor. To look at the bending moments in the floor, select M11 from theForces

menu.

Click theShadingsbutton. The plot in Figure2.19will be displayed.



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Figure 2.19 Bending moments in the basement floor

To view the bending moments in tabulated form, click the Tableoption in the Tools

menu. A new window is opened in which a table is presented, showing the values of

bending moments in each node of the floor.

2.4 CASE C: PILE-RAFT FOUNDATION

As the displacements of the raft foundation are rather high, embedded piles will be used

to decrease these displacements. These embedded piles represent bored piles with a

length of20 m and a diameter of1.5 m.

Objectives:

Using embedded piles.

Defining material data set for embedded piles.

Creating multiple copies of entities.

Geometry input

The geometry used in this exercise is the same as the previous one, except for the pile

foundation. It is not necessary to create a new model; you can start from the previous

model, store it under a different name and modify it. To perform this, follow these steps:

Start the PLAXIS 3D program. The Quick selectdialog box will appear in which

select the project of Case B.

Select theSave project asoption in theFilemenu to save the project under a

different name (e.g. "Lesson 1c").



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Definition of embedded pile

Proceed to theStructuresmode.

Click theCreate linebutton at the side tool bar and select the Create embedded pile

from the additional tools that appear.

Define a pile from (6; 6; -2) to (6; 6; -22).

Open the material data base and set theSet typeto Embedded piles.

Create data sets for the embedded file according to Table2.4.The value for the

cross section areaA and the moments of inertiaI2,I3 andI23 are automaticallycalculated from the diameter of the massive circular pile. Confirm the input by

clickingOK.

Hint: Multiple entities can be selected by holding the button pressed while

clicking on the entities.

A feature can be assigned to multiple selection by right-clicking the drawarea and selecting the corresponding option in the appearing menu.

Table 2.4 Material properties of pile foundation

Parameter Name Pile foundation Unit

Young's modulus E 3107 kN/m2

Unit weight 6.0 kN/m3

Pile type - Predefined

Predefined pile type - Massive circular

pile

Diameter Diameter 1.5 mSkin resistance Type Linear

Maximum traction allowed at the top of the

embedded pile

Ttop,max 200 kN/m

Maximum traction allowed at the bottom of

the embedded pile

Tbot,max 500 kN/m

Base resistance Fmax 1104 kN

Drag and drop thePiledata to the embedded pile in the draw area. The embedded

pile will change colour to indicate that the material set has been assigned

successfully.

Click theOKbutton to close the Material setswindow.

Hint: A material set can also be assigned to an embedded pile by right-clicking it

either in the draw area or in the Selection explorer andModel explorerand

selecting the material from theSet materialoption in the displayed menu.

Click theSelectbutton and select the embedded pile.

Click theCreate arraybutton.

In theCreate arraywindow, select the 2D, in xy planeoption for shape.



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Keep the number of columns as2. Set the distance between the columns to x= 12

andy= 0.

Keep the number of rows as2. Set the distance between the rows to x= 0andy = 12(Figure2.20).

PressOKto create the array. A total of 2x2 = 4piles will be created.

Figure 2.20 Create arraywindow

Mesh generation

As the geometry model is complete now, the mesh can be generated.

Create the mesh. Keep the Element distributionas optionCoarse.

View the mesh.

Click theHide soilbutton. Press the key and click on the soil volume to hide

it. The embedded piles can be seen. The key selects all elements in a

cluster simultaneously.

Close the mesh preview.

Performing calculations

After generation of the mesh, all construction stages must be redefined. Even though in

practice the piles will be constructed in another construction stage than construction of

the walls, for simplicity both actions will be done in the same construction stage in thislesson. To redefine all construction stages, follow these steps:



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Switch to theStaged constructionmode.

Check if theK0 procedureis selected as Calculation typefor the initial phase. Make

sure that all the structural elements are inactive and all the soil is active. The

material assigned to it is Lacustrine clay.

Select theExcavationphase in the Phases explorer. Make sure that the basement soil is excavated and the basement walls are active.

Activate all the embedded piles.

In thePhases explorerselect theConstructionphase. Make sure that all the

structural elements are active.

In thePhasestree select the Loadingphase. Make sure that all the structural

elements and loads are active.

Calculate the project.

Save the project after the calculation is finished. Select theLoadingphase and view the calculation results.

Double-click the basement floor. Select theM11 option from theForcesmenu. Theresults are shown in Figure2.21.

Figure 2.21 Bending moments in the basement floor

Select the view corresponding to the deformed mesh in theWindowmenu.

Click theHide soilbutton in the side toolbar.

To view the embedded piles press and keep it pressed while clicking on the

soil volume in order to hide it.

Click theSelect structuresbutton. To view all the embedded piles, press

+ keys and double click on one of the piles.



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TUTORIAL MANUAL

Select theNin theForcesmenu to view the axial loads in the embedded piles. The

plot is shown in Figure2.22.

Figure 2.22 Resulting axial forces (N) in the embedded piles



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LESSON 2: EXCAVATION IN SAND

3 LESSON 2: EXCAVATION IN SAND

This lesson describes the construction of an excavation pit in soft clay and sand layers.

The pit is a relatively small excavation of12 by 20 m, excavated to a depth of6.5 m below

the surface. Struts, walings and ground anchors are used to prevent the pit to collapse.

After the full excavation, an additional surface load is added on one side of the pit.

50.0 m

80.0 m

(30; 20) (50; 20)

(30; 32)(50; 32)

Strut

Ground anchors

(34; 19) (41; 19)

(34; 12) (41; 12)

4.0 m

4.0 m

4.0 m

5.0 m5.0 m5.0 m5.0 m

Figure 3.1 Top view of the excavation pit

The proposed geometry for this exercise is 80 m wide and 50 m long, as shown in Figure

3.1. The excavation pit is placed in the center of the geometry. Figure 3.2shows a crosssection of the excavation pit with the soil layers. The clay layer is considered to be

impermeable.

Objectives:

Using the Hardening Soil model

Modelling of ground anchors

Using interface features

Defining over-consolidation ratio (OCR)

Prestressing a ground anchor

Changing water conditions

Selection of stress points to generate stress/strain curves

Viewing plastic points



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z = 0z = -1

z = -4

z = -9.5z = -11

z = -20

Fill

Sand

Sand

Soft clay

Sheet pile walls

(62; 24; -9)(18; 24; -9)

Figure 3.2 Cross section of the excavation pit with the soil layers

3.1 GEOMETRY

To create the geometry model, follow these steps:

Project properties

Start a new project.

Enter an appropriate title for the project.

Define the limits for the soil contour asxmin=0,xmax =80,ymin=0 and ymax =50.

3.1.1 DEFINITION OF SOIL STRATIGRAPHY

In order to define the soil layers, a borehole needs to be added and material propertiesmust be assigned. As all soil layers are horizontal, only a single borehole is needed.

Create a borehole at (0.0; 0.0). The Modify soil layerswindow pops up.

Add4 layers with bottom levels at 1, 9.5, 11, 20. Set theHeadin theborehole column to 4m.

Open theMaterial setswindow.

Create a new data set underSoil and interfacesset type.

Identify the new data set as "Fill".

From theMaterial modeldrop-down menu, selectHardening Soilmodel. In contrastwith the Mohr-Coulomb model, the Hardening Soil model takes into account the

difference in stiffness between virgin-loading and unloading-reloading. For a

detailed description of the Hardening Soil model, see the Chapter 5 in the Material

Models Manual.

Define the saturated and unsaturated unit weights according to Table3.1.

In theParameterstabsheet, enter values forEref50, Erefoed,E

refur , m,c'ref,'ref, and

'uraccording to Table3.1. Note that Poisson's ratio is an advanced parameter.

As no consolidation will be considered in this exercise, the permeability of the soil

will not influence the results. Therefore, the default values can be kept in the Flowparameterstabsheet.

http://3d2010-3-material-models.pdf/http://3d2010-3-material-models.pdf/


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Table 3.1 Material properties for the soil layers

Parameter Name Fill Sand Soft Clay Unit

General

Material model Model Hardening Soil

model

Hardening Soil

model

Hardening Soil

model

Drainage type Type Drained Drained Undrained A

Unit weight above phreatic level unsat 16.0 17.0 16.0 kN/m3

Unit weight below phreatic level sat 20.0 20.0 17.0 kN/m3

Parameters

Secant stiffness for CD triaxial

test

Eref50 2.2104 4.3104 2.0103 kN/m2

Tangent oedometer stiffness Erefoed 2.2104 2.2104 2.0103 kN/m2

Unloading/reloading stiffness Erefur 6.6104 1.29105 2.0104 kN/m2

Power for stress level

dependency of stiffness

m 0.5 0.5 1.0

Cohesion c'ref 1 1 5 kN/m2

Friction angle ' 30.0 34 25

Dilatancy angle 0 4 0

Poisson's ratio 'ur 0.2 0.2 0.2

Interfaces

Interface strength Manual Manual Manual

Interface reduction factor Rinter 0.65 0.7 0.5

Initial

K0 determination Automatic Automatic Automatic

Lateral earth pressure coefficient K0 0.5000 0.4408 0.7411

Over-consolidation ratio OCR 1.0 1.0 1.5

Pre-overburden pressure POP 0.0 0.0 0.0

In theInterfacestabsheet, selectManualin theStrengthbox and enter a value of

0.65for the parameterRinter. This parameter relates the strength of the soil to thestrength of the interfaces, according to the equations:

ci =Rinter csoil andtani =Rinter tani tansoil

Hence, using the enteredRinter-value gives a reduced interface friction and interfacecohesion (adhesion) compared to the friction angle and the cohesion in the adjacent

soil. The default valueRinter =1.0 (rigid) will give:

ci =csoil andi =soil

A more detailed description is given in the Reference Manual.

ClickOKto close the window.

In the same way, define the material properties of the "Sand" and "Soft Clay"

material as given by Table3.1.

Click theOKbutton to close the Modify soil layerswindow.

In theSoilmode right click on the upper soil layer. Select the Filloption from the

menu appearing as the cursor points Set material.

In the same way assignSoft Claymaterial to the soil layer between y= 9.5m andy = 11.0m.

Assign theSandmaterial to the remaining two soil layers.

Proceed to theStructuresmode to define the structural elements.



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TUTORIAL MANUAL

Hint: TheTension cut-offoption is activated by default at a value of 0 kN/m2. Thisoption is found in theAdvancedoptions on theParameterstabsheet of the

Soilwindow. Here theTension cut-offvalue can be changed or the option

can be deactivated entirely.

Table 3.2 Material properties for the beams

Parameter Name Strut Waling Unit

Cross section area A 0.007367 0.008682 m2

Unit weight 78.5 78.5 kN/m3

Material behaviour Type Linear Linear

Young's modulus E 2.1108 2.1108 kN/m2

Moment of Inertia I3 5.073105 1.045104 m4

I2 5.073105 3.66104 m4

3.1.2 DEFINITION OF STRUCTURAL ELEMENTSThe creation of sheet pile walls, surface loads and ground anchors is described as

follows.

Create a surface between (30; 20; 0), (30; 32; 0), (50; 32; 0) and (50; 20; 0).

Extrude the surface to z= 1,z= 6.5and z= 11.

Right-click on the deepest created volume (betweenz=0 and z= 11) and selecttheDecompose into surfacesoption from the appearing menu.

Delete the top surfaces (2 surfaces). An extra surface is created as the volume is

decomposed.

Hide the excavation volumes (do not delete). The eye button in theModel explorer

andSelection explorertrees can be used to hide parts of the model and simplify the

view. A hidden project entity is indicated by a closed eye.

Click theCreate structuresbutton.

Create beams (walings) around the excavation circumference at levelz= 1m.Press the key and keep it pressed while moving the mouse cursor in the zdirection. Stop moving the mouse as the z coordinate of the mouse cursor is 1in the cursor position indicator. Note that as you release the key, the zcoordinate of the cursor location does not change. This is an indication that you can

draw only on thexy-plane located atz= 1.

Click on (30; 20; -1), (30; 32; -1), (50; 32; -1), (50; 20; -1), (30; 20; -1) to draw the

walings. Click on the right mouse button to stop drawing walings.

Create a beam (strut) between (35; 20; -1) and (35; 32; -1). Press to end

defining the strut.

Create data sets for the walings and strut according to Table3.2and assign the

materials accordingly.

Copy the strut into a total of three struts atx =35 (existing),x =40, andx=45.



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Modelling ground anchors

In PLAXIS 3D ground anchors can be modelled using theNode-to-node anchorand the

Embedded pileoptions as described in the following:

First the ungrouted part of the anchor is created using the Node-to-node anchor

feature. Start creating a node-to-node anchor by selecting the corresponding buttonin the options displayed as you click on the Create structurebutton.

Click on the command line and type "30 24 1 21 24 7" . Press and to create the ungrouted part of the first ground anchor.

Create a node-to-node anchor between the points (50; 24; -1) and (59; 24; -7).

The grouted part of the anchor is created using the Embedded pileoption. Create

embedded piles between (21; 24; -7) and (18; 24; -9) and between (59; 24; -7) and

(62; 24; -9).

Create a data set for the embedded pile and a data set for the node-to-node anchor

according to Table3.3and Table3.4respectively. Assign the data sets to thenode-to-node anchors and to the embedded piles.

Table 3.3 Material properties for the node-to-node anchors

Parameter Name Node-to-node anchor Unit

Material type Type Elastic

Axial stiffness EA 6.5105 kN

Table 3.4 Material properties for the embedded piles (grout body)

Parameter Name Grout Unit

Young's modulus E 3107 kN/m2

Unit weight 24 kN/m3

Pile type

Predefined

Predefined pile type Massive circular pile

Diameter Diameter 0.14 m

Skin friction distribution Type Linear

Skin resistance at the top of the

embedded pile

Ttop,max 200 kN/m

Skin resistance at the bottom of the

embedded pile

Tbot,max 0.0 kN/m

Base resistance Fmax 0.0 kN

Hint: The colour indicating the material set assigned to the entities in project can

be changed by clicking on theColourbox of the selected material set andselecting a colour from the Colourpart of the window.

The remaining grouted anchors will be created by copying the defined grouted anchor.

Click on theSelectbutton and click on all the elements composing both of the

ground anchors keeping the key pressed.

Use theCreate arrayfunction to copy both ground anchors (2embedded piles +2

node-to-node anchors) into a total of 4 complete ground anchors located at y=24andy=28 by selection the 1D, in y directionoption in theShapedrop-down menuand define the Distance between columnsas 4 m.



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TUTORIAL MANUAL

Multiselect all parts of the ground anchors (8entities in total). While all parts are

selected and the key is pressed, click the right mouse button and select the

Groupfrom the appearing menu.

In theModel explorertree, expand the Groupsby clicking on the (+) in front of the

groups.

Click theGroup_1and rename it to "GroundAnchors".

Hint: The name of the entities in the project should not contain any space or

special character except "_" .

Select all four vertical surfaces created as the volume was decomposed. Keeping

the key pressed, click the right mouse button and select theCreate plate

option from the appearing menu.

Create a data set for the sheet pile walls (plates) according to Table3.5. Assign the

data sets to the four walls.

As all the surfaces are selected, assign both positive and negative interfaces to

them using the options in the right mouse button menu.

Hint: The term 'positive' or 'negative' for interfaces has no physical meaning. It

only enables distinguishing between interfaces at each side of a surface.

Table 3.5 Material properties of the sheet pile walls

Parameter Name Sheet pile wall Unit

Thickness d 0.379 m

Weight 2.55 kN/m3

Type of behaviour Type Linear, non-isotropic

Young's modulus E1 1.46107 kN/m2

E2 7.3105 kN/m2

Poisson's ratio 0.0

Shear modulus G12 7.3105 kN/m2

G13 1.27106 kN/m2

G23 3.82105 kN/m2

Non-isotropic (different stiffnesses in two directions) sheet pile walls are defined.The local axis should point in the correct direction (which defines which is the 'stiff'

or the 'soft' direction). As the vertical direction is generally the stiffest direction in

sheet pile walls, local axis1 shall point in thezdirection. In the Model explorertree expand theSurfacessubtree, set the AxisFunctionto Manualand set the

Axis1z to 1. Do this for all the pile wall surfaces.

Create a surface load defined by the points: (34; 19; 0), (41; 19; 0), (41; 12; 0), (34;

12; 0). The geometry is now completely defined.



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Hint: The first local axis is indicated by a red arrow, the second local axis is

indicated by a green arrow and the third axis is indicated by a blue arrow.

More information related to the local axes of plates is given in Section 5.2.3

of the Reference Manual.

3.2 MESH GENERATION

Proceed to theMeshmode.

Click theGenerate meshbutton. Set the element distribution to Coarse.

View the generated mesh. Use theHide soiloption to view the embedded piles.

3.3 PERFORMING CALCULATIONS

The calculation consists of 6 phases. The initial phase consists of the generation of the

initial stresses using the K0 procedure. The next phase consists of the installation of the

sheet piles and a first excavation. Then the walings and struts will be installed. In phase

3, the ground anchors will be activated and prestressed. Further excavation will be

performed in the phase after that. The last phase will be the application of the additional

load next to the pit.

Click on theStaged constructiontab to proceed with definition of the calculation

phases.

The initial phase has already been introduced. keep its calculation type asK0

procedure. Make sure all the soil volumes are active and that all the structuralelements are inactive.

Add a new phase (Phase_1). Deactivate the first excavation volume (from z= 0toz= 1).

In theModel explorer, activate all plates and interfaces by clicking on the square in

front of them. The active elements in the project are indicated by a green check

mark in theModel explorer.

Add another phase (Phase_2). In theModel exploreractivate all the beams.

Add another phase (Phase_3). In theModel exploreractivate theGroundAnchors

group.

Select one of the node-to-node anchors. In theSelection explorerexpand the

node-to node anchor features. Click the Adjust prestressand change this intoTrue.

Enter a prestress force of 200 kN (Figure3.3).

Do the same for all the other node-to-node anchors.

Add another phase (Phase_4). Proceed to theWater levelsmode. Select the soil

volume to be excavated in this phase (between z 1and z= 6.5).

In theSelection explorerexpand the soil entity and subsequently expand the

WaterConditions feature. Click on theConditionsand selectDry from the

drop-down menu.



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TUTORIAL MANUAL

Figure 3.3 Node-to-node anchor inSelection explorer

Figure 3.4 Water conditionsin Selection explorer

Hide the soil around the excavation.

Select the soil volume below the excavation (betweenz= 6.5and z= 9.5). IntheSelection explorerexpand the soil entity and subsequently expand the

WaterConditions feature. ClickConditionsand selectHeadfrom the drop-down

menu. Enterzref = 6.5m.

Select the soft clay volume below the excavation. Set the water conditions to

Interpolate.

Proceed toStaged constructionmode. Deactivate the volume to be excavated(between z= 1and z= 6.5).

Preview this calculation phase.

Click theVertical cross sectionbutton in thePreviewwindow and define the cross

section by drawing a line across the excavation.

Select thepsteadywith suctionoption from the Stressesmenu.

Display the contour lines for steady pore pressure distribution. Make sure that the

Legendoption is checked in Viewmenu. The steady state pore pressure distribution

is displayed in Figure3.5.Scroll the wheel button of the mouse to zoom in or out to

get a better view.

Return to the Input program.

Add another phase (Phase_5). Activate the surface load and setz = 20kN/m2.

Defining points for curves

Before starting the calculation process, some stress points next to the excavation pit and

loading are selected to plot a stress strain curve later on.

Click theSelect points for curvesbutton. The model andSelect pointswindow will

be displayed in the Output program. (Figure3.6). Define (37.5; 19; -1.5) as

Point-of-interest coordinates.



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Figure 3.5 Preview of the steady state pore pressures inPhase_4in a cross section

Figure 3.6 TheSelect pointswindow

Click theSearch closest. The number of the closest node and stress point will be

displayed.

Click the check box in front of stress point to be selected. The selected stress point

will be shown in the list.

Select also stress points near the coordinates (37.5; 19; -5), (37.5; 19; -6) and (37.5;

19; -7) and close the Select pointswindow.

Close the Output program.

Start the calculation process.

Save the project when the calculation is finished.



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Hint: Instead of selecting nodes or stress points for curves before starting the

calculation, points can also be selected after the calculation when viewing

the output results. However, the curves will be less accurate since only the

results of the saved calculation steps will be considered.

To plot curves of structural forces, nodes can only be selected after the

calculation.

Nodes or stress points can be selected by just clicking them. When movingthe mouse, the exact coordinates of the position are given in the cursor

location indicator bar at the bottom of the window.

3.4 VIEWING THE RESULTS

After the calculations, the results of the excavation can be viewed by selecting a

calculation phase from the Phasestree and pressing the View calculation resultsbutton.

Select the final calculation phase (Phase_5) and click the View calculation resultsbutton. The Output program will open and will show the deformed mesh at the end

of the last phase.

The stresses, deformations and three dimensional geometry can be viewed by

selecting the desired output from the corresponding menus. For example, choose

Plastic pointsfrom theStressesmenu to investigate the plastic points in the model.

In thePlastic pointswindow, Figure3.7, select all options except theStress points

option.

Figure 3.7 Plastic pointswindow

Start selecting structures. Click at a part of the wall to select it. Press

simultaneously on the keyboard to select all wall elements. The selected wall

elements will colour red.

While holding the key or key on the keyboard, double click at one of

the wall elements to see the deformations plane of the total displacements |u| in all

wall elements.

To generate a curve, select the Curves manageroption from the Toolsmenu or clickthe corresponding button in the toolbar.



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Figure 3.8 Plastic points at the end of the final phase

All pre-selected stress points are shown in theCurve pointstabsheet of theCurves

managerwindow.

Create a new chart.

Select pointKfrom the drop-down menu for xaxis of the graph. Select 1 underTotal strains.

Select pointKfrom the drop-down menu for yaxis of the graph. Select '1 underPrincipal effective stresses(Figure3.9).

Invert the sign of both axis by checking the corresponding boxes.

ClickOK to confirm the input.

Figure 3.9 Curve generationwindow

The graph will now show the major principal strain against the major principal stress.

Both values are zero at the beginning of the initial conditions. After generation of the

initial conditions, the principal strain is still zero whereas the principal stress is not zero



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TUTORIAL MANUAL

anymore. To plot the curves of all selected stress points in one graph, follow these steps:

SelectAdd curve From current projectfrom right mouse button menu.

Generate curves for point L, M and N in the same way.

The graph will now show the stress-strain curves of all four stress points (Figure 3.10). To

see information about the markers, make sure the Value indicationoption is selectedfrom theViewmenu and hold the mouse on a marker for a while. Information about the

coordinates in the graph, the number of the point in the graph, the number of the phase

and the number of the step is given. Especially the lower stress points show a

considerable increase in the stress when the load is applied in the last phase.

Figure 3.10 Stress - Strain curve

Hint: To re-enter the Curve generationwindow (in the case of a mistake, a desired

regeneration or a modification), the Curve settingsoption from the Format

menu can be selected. As a result theCurves settingswindow appears, on

which theRegeneratebutton should be clicked.

TheChart settingsoption in theFormatmenu may be used to modify thesettings of the chart.

To create a stress path plot for stress pointKfollow these steps:

Create a new chart.

In theCurves generationwindow, select point Kfrom the drop-down menu of thexaxis of the graph. 'yyunderCartesian effective stresses.

Select pointKfrom the drop-down menu of the yaxis of the graph. Select the 'zzunderCartesian effective stresses.

ClickOK to confirm the input (Figure3.11).



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Figure 3.11 Vertical effective stress ('zz) versus horizontal effective stress ('yy)



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TUTORIAL MANUAL



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LESSON 3: LOAD CAPACITY OF A SUCTION PILE

4 LESSON 3: LOAD CAPACITY OF A SUCTION PILE

In this lesson a suction pile in an off-shore foundation will be considered. A suction pile is

a hollow steel pile with a large diameter and a closed top, which is installed in the seabed

by pumping water from the inside. The resulting pressure difference between the outside

and the inside is the driving force behind this installation.

In this exercise, the length of the suction pile is 10 m and the diameter is 4.5 m. An

anchor line is attached on the side of the pile, 7 m from the top. To avoid local failure of

the pile, the thickness of the tube where the anchor line acts on the pile is increased. The

soil consists of silty sand. To model undrained behaviour, an undrained stress analysis

with undrained strength parameters will be performed (Section6.2of the Reference

Manual). This exercise will investigate the displacement of the suction pile under working

load. Four different angles of the working load will be considered. The installation

process itself will not be modelled. The geometry for the problem is sketched in Figure

4.1.

Objectives:

Importing volumes

Undrained effective stress analysis with undrained strength parameters

Soil cohesion increases with depth

Copying material data sets

Changing settings in Output

Selecting a nodeaftercalculation to generate a curve with structural forces

z = -6.5 mz = -7.0 m

z = -7.5 m

z = -10 m

z

x

4.5 m

Figure 4.1 Geometry of the suction pile

4.1 GEOMETRY

An area of60 m wide and 60 m long surrounding the suction pile will be modelled. With

these dimensions the model is sufficiently large to avoid any influence from the model

boundaries.



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TUTORIAL MANUAL

Project properties

To define the geometry for this exercise, follow these steps:

Start theInputprogram and select New project from theCreate/Open projectdialog

box.

Enter an appropriate title for the exercise.

Keep the standard units and set the model dimensions toxmin= 30m, xmax = 30m,ymin= 30m, ymax = 30m.

ClickOK.

4.1.1 DEFINITION OF SOIL STRATIGRAPHY

In the current example only one horizontal soil layer is present. A single borehole is

sufficient to define it.

Add a borehole to the geometry. In theModify soil layerswindow add a soil layer with top boundary at z= 0m and

bottom boundary atz= 30m.

TheHeadvalue is50.0m, which means 50 m depth above the soil.

Open theMaterial setswindow and create the data sets given in the Table 4.1. In

theParameterstabsheet deselect theTension cut-offoption in the advanced

parameters for strength.In this exercise, the permeability of the soil will not influence

the results. Instead of using effective strength properties, the cohesion parameter

will be used in this example to model undrained shear strength. Advanced

parameters can be entered after expanding theAdvanceddata tree in the

Parameterstabsheet.

Hint: TheInterfacedata set can be quickly created by copying the 'Sand' data set

and changing theRinter value.

Assign the 'Sand' material data set to the soil layer and close theMaterial sets

window.

4.1.2 DEFINITION OF STRUCTURAL ELEMENTS

The suction pile is modelled in the Structuresmode using predefined volumes. To model

a suction pile:

Import the standard cylinder. The standard cylinder is saved in the

file in theImportablesfolder of the

installation directory of PLAXIS 3D. The imported volume is edited in the Import

structure volumeswindow. Import solidis a PLAXIS VIP feature.

Modify the scale such that the diameter is4.5 m and the height is 10 m.

Define the coordinates of the insertion point such that the top of the anchor is at the

sea bottom level (z= 0) and the bottom of the anchor is atz= 10(Figure4.2).



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Table 4.1 Material properties of the sand layer and its interface

Parameter Name Sand Interface Unit

General

Material model Model Mohr-Coulomb Mohr-Coulomb

Type of mater ial behaviour Type Undrained B Undrained B

Soil weight unsat, sat 20 20 kN/m3

Parameters

Young's modulus E' 1000 1000 kN/m2

Poisson's ratio ' 0.35 0.35

Shear strength su,ref 0.1 0.1 kN/m2

Friction angle u 0.0 0.0

Dilatancy angle 0.0 0.0

Increase in stiffness E'inc 1000 1000 kN/m2/m

Reference level zref 0.0 0.0 m

Increase in cohesion su,inc 4.0 4.0 kN/m2/m

Reference level zref 0.0 0.0 m

Interfaces

Interface strength

Manual Rigid

Interface strength reduction Rinter 0.7 1.0

Initial

K0 determination Manual Manual

Lateral earth pressure coeff. K0,x,K0,y 0.5 0.5

Figure 4.2 Import structure volumeswindow

Hint: As an alternative for the import of a cylinder, the correspondingcylinder

command can be used to create the suction pile. Information about the

commands available in the program is displayed when the Command

referenceoption is selected in the Helpmenu.



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TUTORIAL MANUAL

Decompose the imported volume into surfaces by right-clicking it and selecting the

Decompose into surfacesoption from the appearing menu.

Make the cylinder mantle into a plate, positive interface and negative interface by

right clicking on it and selecting the corresponding options from the appearing menu.

Open the material data base. SelectPlatesas set type. Create three data setsaccording to the information in the Table 4.2.

Table 4.2 Material properties for the suction pile

Parameter Name Thin wall Thick wall Top Unit

Thickness d 0.05 0.15 0.05 m

Weight 58.5 58.5 68.5 kN/m3

Type of

behaviour

Type Linear, isotropic Linear, isotropic Linear, isotropic

Young's

modulus

E 2.1108 2.1 108 2.1108 kN/m2

Poisson's

ratio

0.1 0.1 0.1

Shearmodulus

G 9.545

107 9.545

107 9.545

107 kN/m2

AssignThin wallto the anchor tube and close the Material data setwindow.

Hide the anchor tube and the original volume object using theHideoption in the

right mouse button menu. Note that the top and the bottom surfaces are visible.

Select the top surface and click on the Create arraybutton in the side tool bar.

Select the1D, in z directionoption forShape. Keep the number of columns as 2 and

definezas 6.5for theDistance between columns.

Repeat the previous step to create surfaces atz= 7.0and z= 7.5.

Make the top surface into a plate. AssignTopmaterial data set to it.

Make the bottom surface (z= -10 m) into a negative interface. Assign the 'Interface'

data set to the bottom interface.

Right click on the surface located atz= 7.0m and select the Decompose intooutlinesoption from the appearing menu.

Right click on the point near (2.25; 0.0; -7.0) and select theCreate point loadoption

from the appearing menu. The actual load values will be assigned when the

calculation phases are defined.

The geometry of the project is defined.

4.2 MESH GENERATION

In order to generate the mesh:

The mesh is automatically refined near the plates and load. Select the point load. In

theSelection explorernote that the FinenessFactorvalue is0.5 and it is displayed

in a lighter shade of green in the model.

Generate the mesh. Set the element distribution to Coarse.

Proceed to theStaged constructionmode.



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4.3 PERFORMING CALCULATIONS

The calculation for this exercise will consist of 6 phases. These are the determination of

initial conditions, the installation of the suction pile and four different load conditions. The

effect of the change of the load direction while keeping the magnitude unchanged will be

analysed. Click on theStaged constructiontab to proceed with the definition of the calculation

phases. Keep the calculation type of the Initial phase to K0 procedure. Ensure that

all the structures and interfaces are switched off.

Add a new calculation phase (Phase_1).

Activate all the plates and interfaces in the project. Assign theThick wallmaterial to

the plate sections just above and just below the point load. It may be necessary to

hide (NOT deactivate) the negative interface around the anchor. Load is not active.

Add a new phase (Phase_2). Open thePhaseswindow. Select the Reset

displacements to zerooption in theParameterstabsheet. Set the Max steps savedparameter to 6.

Activate the point load and setFx =3897kN, Fz =2250kN.

Define the remaining phases according to the information in Table4.3. For each

phase check whether the Reset displacements to zerooption in theParameters

tabsheet is selected. Set the Max steps savedparameter to 6.

Calculate the project. The points for curves will be selected after the calculation

process is completed.

Save the project.

Table 4.3 Load information

Phase Reference phase Fx Fz

Phase_2 Phase_1 3897kN 2250kN




Hint: The maximum number of saved steps should be increased for the calculation

phases when the curves are to be generated for structural loads. A more

detailed description is given in Section10.1.3or Reference Manual.

The order of the phases is indicated in the Phases explorer (Figure4.3). Calculation of

Phase_1 starts after the calculation of Initial phase is completed. The calculation of the

remaining phases starts after calculation of Initial phase is completed. In multiple core

processors more than one of these phases (Phases 2, 3, 4 and 5) can be calculated

simultaneously.



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TUTORIAL MANUAL

Figure 4.3 Phases explorer

4.4 VIEWING THE RESULTS

To view the results:

View the results of the last calculation phase. The deformed mesh of the whole

geometry will be shown. In particular, the displacements of the suction pile itself areof interest.

Click on theHide soilbutton. Keep the key pressed and click on the soil to

make the suction pile visible.

Deselect theInterfacesusing thePartial geometryoption in theGeometrymenu.

Click on theSelect structuresbutton and select the pile wall. This will select only a

part of the wall. Press to select all the wall elements of the suction pile.

Keeping the key pressed, double click the pile walls. The results for the wall

of the suction pile are displayed in a new window.

Select the shadings representation and rotate the model such that the xaxis isperpendicular to the screen.

If the axes are not visible, select this option from theViewmenu. It is quite clear that

the point force acting on the pile does not disturb the displacement field locally

indicating that the pile is sufficiently thick here.

In the same manner, the total displacements of the suction pile under a different

direction of the load can be inspected by selecting the appropriate phase from

combo box. In particular, is of interest, as in this phase the horizontal

part of the load will have the largest value (Figure 4.4).



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Figure 4.4 Total displacement of the suction pile at the end ofPhase_2



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APPENDIX A - MENU TREE


A.1 INPUT MENU

INPU

TMENU1

File

Edit

View

Soil

Structures

Mesh

Phases

New

project

Undo

Pancamera

Modifysoillayers

Importsolid

Generatemesh

Editphases

Open

project

Redo

Rotatecamera

Importsoil

Importsurface

Rece

ntprojects

Copyscreenimage

Zoomin

Showmaterial

Showmaterial

Save

project

Delete

Zoomout

Save

projectas

Selectall

Resetzoom

Closeproject

Defaultviews

Proje

ctproperties

Explode

Print

Implode

Exit



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TUTORIAL MANUAL

INPUTMENU

2

Options

Expert

He

lp

Snaptogrid

Examinecommands

Ma

nuals

Showgridandruler

Runcommands

Co

mmandreference

Showcursorlocation

Viewfiles

Ins

tructionmovies

Showlocalax

is

Up

datelicense

Visualisatons

ettings

http://www.p

laxis.n

l

Dis

claimer

About



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A.2 OUTPUT MENU

OUTPUTMENU(1)

File

View

Project

Geometry

Mesh

Openproject

Zo

omout

Nodefixities

Disabledst

ructures

Quality

Closeactiveproject

Resetview

Loadinformation

Phreaticlevel

Qualitytable

Closeallprojects

Viewpoint

Waterloadinform

ation

Loads

Volume

Workdirectory

Sa

veview

Prescribeddisplacementinformation

Fixities

Volumetable

Exporttofile

Sh

owsavedviews

Virtualinterfaceth

ickness

Prescribed

displacements

Connectivityplot

Reportgeneration

Sc

ale

Volumeinformatio

n

Partialgeometry

Elementcontours

Createanimation

Le

gendsettings

Materialinformation(allloadcases)

Filter

Elementdeformatio

ncontours

Print

Sc

anline

Materialinformation(currentloadcases)

Materials

(Listofrecentprojects)

Title

Generalprojectin

formation

Elementnumbers

Exit

Le

gend

Calculationinform

ation

Materialsetnumbers

Ax

es

Calculationinfoperstep

Clusternumbers

Sh

rink

Stepinfo

Nodes

Ex

pand

Structuresperphase

Stresspoints

Ex

plode

Nodenumbers

Im

plode

Stresspointnumbe

rs

Se

ttings



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TUTORIAL MANUAL

OUTPUTMENU(2)

Deformations

Stresses

Forces

Tools

Window

Help

Height

Crosssection

Axia

lforces

Copy

Projectmanager

Manuals

Deformedmesh|

u|

Cartesianeffectivestresses

Shearforces

Selectpointsfor

curves

Duplicatemodelview

http://www.p

laxis.n

l/

Totaldisplacements

Cartesiantotalstresses

Bendingmoments

Curvesmanager

Closewindow

Disclaimer

Phasedisplacements

Principaleffectivestresses

Table

Table

Cascade

Ab

out

Incrementaldisplacements

Principaltotalstresses

Tableofstresspoints

Verticalcrosssection

Tilevertically

Totalcartesianstrain

Stateparameters

Horizontalcross

section

Tilehorizontally

Phasecartesianstrain

Totalincrements

Totalincrements

(Listofactiveviews)

Incrementalcartesianstrain

Porepressures

Freecrosssectio

n

Totalstrain

Plasticpoints

Hintbox

Phasestrain

Incrementalstrains



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APPENDIX B - CALCULATION SCHEME FOR INITIAL STRESSES DUE TO SOIL WEIGHT

APPENDIX B - CALCULATION SCHEME FOR INITIAL STRESSES DUE TO SOIL

WEIGHT

Start

Yes NoHorizontalsurface

Initial stresses

Gravity loading

Gravity loading

Ready

K0-Procedure

-Mweight= 1

-Mweight= 1

Loading input:Total multipliers

Examples of non-horizontal surfaces, and non-horizontal weight stratifications are:



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TUTORIAL MANUAL

3D2010 1 Tutorial Plaxis

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