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Piled Raft Foundation

1.0 Introduction

This tutorial demonstrates some of the support systems in RS3. This tutorial models a piled raft foundation.

All tutorial files installed with RS3 can be accessed by selecting File > Recent > Tutorials folder from the RS3 main menu. The finished product of this tutorial can be found in the Piled Raft Foundation.rs3dmodel file. The starting file can be found in Piled Raft Foundation - starting file.rs3dmodel file.

2.0 Starting the Model

Open the starting file from File > Recent > Tutorials > Piled Raft Foundation - starting file.rs3dmodel

The model should have initial project settings already defined for the user. Please check the following inputs:

Project Settings icon Select: Analysis > Project setting

Stages: Number of Stages = 2, Stage 1 = Initial, Stage 2 = Piled Raft Foundation

Groundwater: Phreatic Surfaces, Unit Weight = 9.81 kN/m3

3.0 Defining the Materials

Geology Workflow tab

Under the same tab (Geology or Excavations) you can assign the materials and properties of the model through materials setting.

The model should have the materials already defined for the user. Please check the following inputs:

Define Materials icon Select: Materials > Define Materials

In the [Strength] tab, check the strength parameters.

Material 1 [Strength]:

Material Properties dialog box

Material Properties dialog box

In the [Stiffness] tab , check the stiffness conditions.

Material Properties dialog box

4.0 Creating Geometry

Geology workflow tab

Ensure the Geology tab is selected from the workflow at the top of the screen.

Select: Geometry > Create External Box.

A Create External dialog will open, enter First Corner (x, y, z) = (0, -160, 0), Second Corner (x, y, z) = (160, 10, -40), then press OK.

Create External dialog box

Select: Geometry > 3D Primitive Geometry > Box, to create a box.

First Corner (x, y, z) = (72, -88, 0), and Second Corner = (88, -72, -3), OK.

Create Box dialog box

Divide All Geometry icon Select: Geometry > 3D Boolean > Divide All Geometry.

With default setting, Select OK.

5.0 Adding Supports

Support workflow tab

5.1 ADDING LINERS

Select Support tab from the workflow at the top of the screen. Before you can add the liner, we must select the faces they will be applied to first. In Selection Modes in the top right of the screen, select Faces Selection Faces Selection icon . Select the top small body’s top face as shown below, then

Image of selecting top small body's top face

Add Lining icon Select: Support > Liners > Add Lining.

Press the pencil icon beside the name to open the Liner Properties dialog, and again, press the pencil (under column Edit) to open the Liner Layer Properties

Line Composition dialog box

Enter the following values for the liner parameters:

Name

Young's Modulus (kPa)

Poisson's ratio

Thickness (m)

Include Weight in Analysis

Unit Weight (kN/m3)

Liner 1

Raft Foundation

35000000

0.2

0.5

Active

25

After entering those values, the dialog should look as the following:

Line Properties dialog box

Select OK to exit the liner properties, then select OK to exit the lining composition.

In Add Lining dialogue, Select install at stage: 'Piled raft foundation'.

Edit Liner dialog box

Select OK.

Adding Piles

Note: In RS3, a pile is simulated as a beam. Therefore, beam properties are used when defining pile properties, such as Young’s Modulus, Poisson’s ratio and the pile dimensions. Material properties distinct for a pile, such as the soil-pile interaction, are found in the Pile Properties dialog.

Select: Support > Beams > Define Beams.

Enter the following values for the beam parameters:

Name

Young's Modulus (kPa)

Poisson's ratio

Area (m2)

I-min (m4)

I-max (m4)

Include Weight in Analysis

Unit Weight (kN/m3)

Beam 1

Beam 1

35000000

0.2

0.076

0.00048

0.00048

Active

25

Beam Properties dialog box

Hide the liner by pressing the eye Eye icon in the visibility pane to make adding the piles easier.

Before the next step, select Faces Selection Face Selectionn icon under “Selection Modes” in the toolbar and select the top face of the smallest box body again as shown in the image below:

Image of selecting top face of the smallest box

Add Piles or Forepoles icon Select: Support > Piles or Forepoles > Add Piles or Forepoles

Press the pencil icon beside the pile name to open the edit Pile Properties dialog.

Enter the following parameter inputs:

Set Connection Type = Rigid,

Shear Stiffness = 5000, Normal Stiffness = 50000, Base Normal Stiffness = 50000,

Base Force Resistance = 100, Skin Resistance = C and phi, Perimeter = 1.1,

Cohesion = 3.2, Residual Cohesion = 3.2,

Friction Angle = 24.79, Residual Friction Angle = 24.79,

Shear Resistance Cutoff = Active, then press OK.

Pile/Forepole Properties dialog box

Now we’ve returned to the Add Piles/Forepoles dialog, enter the following:

Flip Orientation = Active, Length = 20, Install at stage = Piled raft foundation, Application = Pile Pattern,

Primary Spacing = 4, Secondary Spacing = 4, Primary Offset = 2, Secondary Offset = 2, and then set the paths.

To set the Primary path, make sure the window below is still on and Primary path (required) and Secondary Path (optional) is enabled.

Add Piles/Forepoles dialog box

1. Select vertices selection Vertices Selection icon

2. Then in the model, select one of the top vertex (1), followed by the right top vertex of the face selected (2). Similarly, set the Secondary Path by selecting the top left vertex (1), then bottom left vertex (3).

Note: the order of vertices on where primary path is selected does not matter in this tutorial as the foundation is square. You can choose any vertices to start, but the following sequence should be the same.

3. Right click on the model, under Pile Pattern > End Point of Secondary Path

Image

You will see the coordinates are automatically entered in Primary path and Secondary Path.

Add Piles/Forepoles dialog box

Select [Preview Pattern] to ensure everything was entered correctly, it should look like below.

Note: Make sure to press Add, otherwise the piles will not be added in the model.

If so, press [Add], then [Done].

Image of Preview Pattern

6.0 Groundwater Conditions

Groundwater workflow tab

Select the Groundwater tab from the workflow at the top of the screen.

Add Water by Location icon Select: Groundwater > Add Water by Location

In the Water by Location dialog, enter the four points

(X, Y, Elevation) = (-10, -170, -3), (170, -170, -3), (170, 20, -3), (-10, 20, -3), OK.

Water by Location dialog box

Note: The just-added water surface has a “X” symbol in the visibility pane because the water condition in the material is undefined, the next steps will address this, and you’ll notice the symbol will update, as well as the viewport

Select: Materials > Define Materials.

Navigate to the Clay’s [Hydraulics] tab. Change the Default Water Condition = Water Surface 1, Press OK. The water surface should now be visible in the viewport in both stages.

7.0 Adding Stress Loading

Loads workflow tab

7.1 ADDING FIELD STRESS

Next we go to the Loads tab. This tab allows you to edit the loading conditions,

Select: Loading > Field Stress

Leave Settings as default. Field Stress Type is set to gravity. Select OK.

Field Stress dialog box

Loading the Raft Foundation

Add Loads Selected icon Select the top face of the foundation, then select Loading > Add Loads to Selected.

Loading the Raft Foundation dialog box

Enter Magnitude = 30, and Install at Stage = Piled raft foundation, [Apply].

8.0 Setting Boundary Conditions

Restraints workflow tab

8.1 ADDING MODEL RESTRAINTS

Move to the Restraints tab to assign restraints to the external boundary of the model. RS3 has a built in “Auto Restrain” tool for use on underground models.

Select: Restraints > Auto Restrain (Surface).

Image of completed constuction of the model ( in terms of geometry)

This completes the construction of the model (in terms of geometry).

9.0 Meshing

Mesh workflow tab

9.1 CONFIGURING AND CALCULATING MESH

10.0 Computing Results

Compute workflow tab

Next we move to Compute tab. From this tab we can compute the results of our model. First, save your model: File > Save As.

Use the Save As dialog to save the file, and next you need to save the compute file: File > Save Compute File. You are now ready to compute the results.

Compute icon Select: Compute > Compute

RS3. 3.0 dialog box

10.0 Interpreting Results

Results workflow tab

10.1 DISPLAYING THE RESULTS

Next we move to Results tab. From this From this tab we can analyze the results of our model. First, refresh the results:

Refresh All Results icon Select: Interpret > Refresh All Results.

On the top right corner of the Results tab, you should see two drop down menus:

Results drop down menu

Ensure [Solids] is selected from the Element drop down menu

We will analyze a number of different “Data Type” results. Let’s turn on the exterior contours so we can see results:

Show Exterior Contour icon Select: Interpret > Show Exterior Contour.

Also select: Interpret > Show data on plane > XZ Plane XZ Plane icon , in the center of the model (X = 80, Y = -80, Z = -20), then hit OK..

Displacement

In the top right corner of the Results tab, ensure Element = Solids, and change data type = Total Displacement:

To see the contour on the XZ Plane, click the Eye icon icon next to Exterior Contour in the Visibility pane to turn off the 3D Contour.

Exterior Contour Plane (Stage 2)

Exterior Contour Plane (Stage 2)

Legend

Contour Plane (Stage 2)

Contour Plane (Stage 2)

The highest displacement, as expected, is in the center of the loaded foundation.

In the top right corner of the Results tab, ensure Element = Beams & Piles, and change the data type = Axial Force:

The Axial Force in the piles at Stage 2 is shown below:

Image of Axial Force in the Piles at Stage 2

The axial force, as expected, decreases with depth into the pile.

Other results are available to view as well. This concludes the tutorial.

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