stawal manual

Version 18.2

Stawal

Oasys Ltd

13 Fitzroy StreetLondon

W1T 4BQ

Central SquareForth Street

Newcastle Upon TyneNE1 3PL

Telephone: +44 (0) 191 238 7559Facsimile: +44 (0) 191 238 7555

e-mail: [email protected]: http://www.oasys-software.com/

© Oasys Ltd. 2007

All rights reserved. No parts of this work may be reproduced in any form or by any means - graphic, electronic, ormechanical, including photocopying, recording, taping, or information storage and retrieval systems - without thewritten permission of the publisher.

Products that are referred to in this document may be either trademarks and/or registered trademarks of therespective owners. The publisher and the author make no claim to these trademarks.

While every precaution has been taken in the preparation of this document, the publisher and the author assume noresponsibility for errors or omissions, or for damages resulting from the use of information contained in thisdocument or from the use of programs and source code that may accompany it. In no event shall the publisher andthe author be liable for any loss of profit or any other commercial damage caused or alleged to have been causeddirectly or indirectly by this document.

This document has been created to provide a guide for the use of the software. It does not provide engineeringadvice, nor is it a substitute for the use of standard references. The user is deemed to be conversant with standardengineering terms and codes of practice. It is the users responsibility to validate the program for the proposed designuse and to select suitable input data.

Printed: April 2007

Stawal Oasys Geo Suite for Windows

© Oasys Ltd. 2007

Stawal Oasys Geo Suite for WindowsI

© Oasys Ltd. 2007

Table of Contents

Part I About Stawal 2

................................................................................................................................... 21 General Program Description

................................................................................................................................... 22 Components of the User Interface

................................................................................................................................... 33 Program Features

Part II Methods of Analysis 7

................................................................................................................................... 71 General

......................................................................................................................................................... 7Fixed Earth Mechanisms

......................................................................................................................................................... 8Free Earth Mechanisms

......................................................................................................................................................... 9Active and Passive Limits

.................................................................................................................................................. 10Intermediate levels

.................................................................................................................................................. 11Uniformly distributed loads

.................................................................................................................................................. 12Strip surcharges

Part III Input 15

................................................................................................................................... 151 Assembling Data

................................................................................................................................... 152 Opening the Program

......................................................................................................................................................... 17Titles

.................................................................................................................................................. 18Titles window - Bitmaps

................................................................................................................................... 183 Data Input

......................................................................................................................................................... 19Units and Preferences

......................................................................................................................................................... 20Analysis Options

......................................................................................................................................................... 21Material Properties

......................................................................................................................................................... 22Material Layers

......................................................................................................................................................... 23Groundwater

.................................................................................................................................................. 24Groundwater Flow

......................................................................................................................................................... 25Surcharges

......................................................................................................................................................... 27Struts or anchors

......................................................................................................................................................... 27Graphical Input

.................................................................................................................................................. 28Entering new graphical data

.................................................................................................................................................. 29Graphical Input view operation and commands

.................................................................................................................................................. 29Material Layers - Graphical Input

.................................................................................................................................................. 30Groundwater - Graphical Input

IIContents

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.................................................................................................................................................. 31Surcharges - Graphical Input

.................................................................................................................................................. 32Struts - Graphical Input

Part IV Output 34

................................................................................................................................... 341 Analysis and Data Checking

................................................................................................................................... 352 Tabular Output

......................................................................................................................................................... 36Results

................................................................................................................................... 373 Graphical Output

Part V List of References 40

................................................................................................................................... 401 References

Part VI Manual Example 42

................................................................................................................................... 421 General

Part VII Brief Technical Description 44

................................................................................................................................... 441 Stawal

Index 46

About Stawal

Part

I

2About Stawal

© Oasys Ltd. 2007

1 About Stawal

1.1 General Program Description

Stawal - Stability of retaining Walls.

Stawal can be used for the analysis of cantilever (Fixed earth) or propped (Free earth) retainingwalls, e.g. sheet pile or diaphragm walls.

The program uses methods of limit equilibrium to determine the penetration required to preventrotational instability of the wall. It then calculates the bending moments and shear forcesoccurring in the wall at the limiting condition.

For the Free earth mechanism, the strut force about which the wall is assumed to rotate is alsocalculated.

1.2 Components of the User Interface

The principal components of Stawal's user interface are the Gateway, Table Views, GraphicalInput, Graphical Output, Tabular Output, toolbars, menus and input dialogs. Some of these areillustrated below.

3 Stawal Oasys Geo Suite for Windows

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1.3 Program Features

The main features of Stawal are summarised below.

· The wall can be designated as either "Fixed earth" cantilever or "Free earth" propped wall.

· The pressures behind the wall are deemed to start at the active limit with the pressures in frontstarting at the passive limit.

4About Stawal

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· The wall is tested for rotational failure about the base for a fixed earth wall and about thelocation of the prop for a free earth wall.

Note : Stawal does not calculate the required depth of the wall for failure due to: rotation of thesoil mass, failure of the props or anchors or failure of the wall in bending.

· The top of the wall is assumed to be at the top level of the highest soil stratum on the 'activeside'.

· Soil profiles are represented by a series of horizontal soil strata that may be different eachside of the wall. A soil stratum can be specified with a linear variation of cohesion with level.

· Water pressures can be entered as either hydrostatic or user-specified (i.e. piezometric).


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· Strut forces can be specified at any level on the passive side.

Note: The exception is for the "Free earth" mechanism where the strut level about which therotation of the wall is calculated is specified separately

· Surcharges can be either uniformly distributed or strip loads. These may also be applied atany level.

Note: Only uniformly distributed surcharges are allowed on the 'passive side'.

· Output is given in the form of soil and water pressures and bending moments and shear forcesdown the line of the wall. The results are given at intervals specified as an output increment.

Note: The lowest possible level of the base of the wall is assumed to be at a depth of 50 timesthe 'output increment' below the top of the wall.

Methods ofAnalysis

Part

II


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2 Methods of Analysis

2.1 General

The calculations performed by Stawal assume limit equilibrium, i.e. limiting active and passivestates either side of the wall.

These pressures are used to calculate the required penetration of the wall to achieve rotationalstability.

Note : No factors of safety are applied by the calculations. Factors of safety must therefore beincorporated into the input data by the user.

Stawal can solve two statically determinate mechanisms in the form of "Fixed earth" cantileverand "Free earth" propped retaining walls.

For either problem several struts with specified forces can be applied.

Note : The user should be aware that other mechanisms of collapse may exist for the problemwhich can not be studied with Stawal. These include rotation of the soil mass, failure of theprops/anchors or failure of the wall in bending.

2.1.1 Fixed Earth Mechanisms

This method is used to model cantilever walls.

The mechanism assumes that the wall is fixed by a passive force developing near its base. Thelevel of the base of the wall is calculated to give equilibrium under this assumed pressuredistribution.

8Methods of Analysis

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Pressure diagram for Fixed Earth mechanism

2.1.2 Free Earth Mechanisms

This method is used to model propped walls.

The mechanism assumes rotation about a specified strut and calculates the level of the base ofthe wall and the force in the strut required to give equilibrium.

Pressure diagram for Free Earth mechanism


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2.1.3 Active and Passive Limits

Active and passive pressures are calculated at the top and base level of each stratum and atintermediate levels. These are placed where there is a change in linear profile of pressure withdepth.

The generation of intermediate levels ensures the accuracy of the calculation of bendingmoments and shear forces.

The effective active and passive pressures are denoted by p'a and p'p respectively. These are

calculated from the following equations:-

p'a = ka s'v - kacc'

p'p = kp s'v + kpcc'

wherec' = effective cohesion or undrained

strength as appropriates'v = vertical effective overburden pressure

Note : Modification of the vertical effective stress due to wall friction should be made by takingappropriate values of ka and kp.

ka and kp = horizontal coefficients of active andpassive pressure

kac and kpc = cohesive coefficients of active andpassive pressure

kac and kpc can be evaluated as:

Where cw = wall adhesion


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Note : For conditions of total stress ka = kp = 1.

For a given depth z

where

gs= unit weight of soil

u = pore water pressureszudl

= vertical sum of pressures of alluniformly distributed loads (udl's) above depth z.

A minimum value of zero is assumed for the value of (kas'v - kacc').

2.1.3.1 Intermediate levels

Stawal inserts intermediate levels where there is a change in the linear profile of pressure withdepth e.g.

· at water table levels/piezometric points

· at surcharge levels

· at intervals of 0.5 units within a stratum with a cohesion strength component

The sub-layering of each side of the wall due to insertion of intermediate levels is shown below. The interval between intermediate levels in cohesive strata is increased above 0.5 units ifnecessary to reduce the number of sub-layers to the program limit of 50.


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2.1.3.2 Uniformly distributed loads

Uniformly distributed loads (udl) may be applied at any level and at either side of the wall.

Below the level of the surcharge, the effective overburden pressure (s'v) is assumed to increase

by the value of the specified surcharge pressure. Active and passive pressures are thusincreased in accordance with the equations given in the section on Active and Passive Limits.


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2.1.3.3 Strip surcharges

Strip surcharges may only be placed to the rear of the wall.

The effect on the active pressure of strip surcharges is calculated by the method of Pappin et al(1986), also reported in Institution of Structural Engineers (1986).

The approximation which has been derived is shown below :

Note : If the width of the load (B) is small, the diagram will become triangular.

Stawal replaces the additional active pressure due to the surcharge by a series of equivalentforces. These act at the same spacing of the output increment down the wall. Thus a smaller


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output increment will increase the accuracy of the calculation.

Varying values of ka

If the active pressure coefficient ka varies with depth, the program chooses a mean value of ka

between any depth z and the level of the surcharge. Stawal then imposes the criterion that theactive force due to the surcharge down to depth z be equal to the force derived from the diagramin above.

This is then subjected to the further limitation that the pressure does not exceed qkaz.

where

q = surcharge pressure.

kaz = active pressure coefficient to depth z.

Input

Part

III


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3 Input

3.1 Assembling Data

It is best to make a sketch of the problem before the computer is approached. This shouldcomprise a cross section of the proposed wall with the:

· ground surface

· location of each soil strata

· parameters of each material

· phreatic surface

· location of any piezometers

· location and magnitude of any loads

· location of any struts

3.2 Opening the Program

The following provides details of all the data required to run the Stawal program.

On selection of the Stawal program the main screen will open. All data, graphics and results areentered and viewed in a series of smaller or "child" windows which are placed inside the mainscreen.

To start a new project file select:

· The "Create a new data file" option on the opening screen,

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· File | New or

· the icon .

This will open a new Titles window and allow you to proceed.

It is possible to open more than one data file at any one time. The file name is thereforedisplayed in the title bar at the top of each child window.


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3.2.1 Titles

The first window to appear for entry of data into Stawal is the Titles window.

This window allows entry of identification data for each program file. The following fields areavailable:

Job Number allows entry of an identifying job number.Initials for entry of the users initials.Date this field is set by the program at the date the file is saved.Job Title allows a single line for entry of the job title.Subtitle allows a single line of additional job or calculation information.CalculationHeading

allows a single line for the main calculation heading.

The titles are reproduced in the title block at the head of all printed information for thecalculations. The fields should therefore be used to provide as many details as possible toidentify the individual calculation runs.

An additional field for Notes has also been included to allow the entry of a detailed description ofthe calculation. This can be reproduced at the start of the data output by selection of Notes using

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File | Print Selection.

3.2.1.1 Titles window - Bitmaps

The box to the left of the Titles window can be used to display a picture beside the file titles.To add a picture place an image on to the clipboard. This must be in a RGB (Red / Green / Blue)

Bitmap format. Select the button to place the image in the box.

The image is purely for use as a prompt on the screen and can not be copied into the output data.

Note : Care should be taken not to copy large bitmaps, which can dramatically increase the sizeof the file.

To remove a bitmap select the button.

3.3 Data Input

Data is input via the Data menu or the Gateway.

The information can be entered in any order but MaterialProperties should be entered before specifying Material Layers.

Once the data has been entered the program places a tick againstthat item in the menu list.

Graphical Input allows the material layers, groundwater,surcharges and struts to be drawn rather than entered as tabularinput.

The following describes each of the menu items in detail.


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3.3.1 Units and Preferences

This option allows the user to specify the units for entering the data and reporting the results ofthe calculations.

Automatic file backup

This option allows a time interval to be set for automatically saving the data file. Automaticsaving can be disabled if required by clearing the "Save file.." check box.

Note! It is good practice to save your file after every new entry of data in each dialog box ortable is completed. The Save icon on the Standard Toolbar or Ctrl + S quick keys can be used tosave the file.

Units

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Default options are the Système Internationale (SI) units - kN and m. The drop down menusprovide alternative units with their respective conversion factors to metric.

Standard sets of units may be set by selecting any of the buttons: SI, kN-m, kip-ft kip-in.

Once the correct units have been selected then click 'OK' to continue.

SI units have been used as the default standard throughout this document.

Company info.

The company information button allows the user to change the company name andlogo on the top of each page of print out. To add a bitmap enter the full path of the file. Thebitmap will appear fitted into a space approximately 4cm by 1cm. The aspect ratio will bemaintained. Note! For internal Arup versions of the program the bitmap option is not available.

3.3.2 Analysis Options

The following general data is entered to define the solution methods.

Collapse mechanism:

Fixed Earth Mechanisms for cantilever walls

Free Earth Mechanisms for propped walls

Strut restraint level

Requires the level of the strut for the "Free earth" mechanism about which the wall rotates.


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Calculation interval

This gives the spacing for reporting of the tabulated results; i.e. soil pressures, bending momentsand shear forces down the wall.

Note: The lowest possible level of the base of the wall is assumed to be at a depth of 50 timesthe calculation interval below the top of the wall. e.g. If the interval is set at 0.2m then the wallcan only be a maximum of 10m long.

The stability is also checked at all levels to this lowest possible level to take into account thepresence of potential soft layers of material at depth.

Iteration limit

This provides a maximum limit to the number of iterations the program will carry out beforereporting the solution.

Note: Convergence is often reached before this limit.

Balance water pressures

If checked, this switches on the option to automatically balance water pressures at the base of thewall. See Groundwater Flow.

3.3.3 Material Properties

The properties for the different materials on either side of the wall are entered in tabular form. Forthe data input select 'Material Properties' from the Data menu or the Gateway.

Brief descriptions for each of the material types can be entered here. The material number

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given to each of the material types. This is located as a default value in the left hand column.This number is used when assigning material types to either side of the wall thereby creating the Material Layers – Graphical Input.

Note: Material type 0 represents air or water.

Material Property Description

g Unit weight defined as the bulk unit weight g.ka Active earth pressure : This can be used to include for the

effect of soil/wall friction.kac Active earth pressure due to cohesion.

kp Passive earth pressure : This can also be used to includesoil/wall friction.

kpc Passive earth pressure due to cohesion.

c (ct, cb) Cohesion Values should be entered for the top and base of the materiallayer. This can be drained (c') or undrained (cu).

Note : If the lowest layer of material has a profile of cohesion then c(bottom) must refer to thevalue at the base of the problem. This is located at 50* the output interval given in AnalysisOptions.

3.3.4 Material Layers

Material layers can be entered in tabular form as described below or graphically. For tabular inputselect 'Material Layers' from the Data menu or the Gateway. For information on Graphical Inputfollow the link.


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In tabular input separate pages are given for the back and front of the wall. The level of the top ofthe layer and the material type must be entered for a valid material layer record. The materialtype is selected from a drop-down list of all the descriptions entered in the Material Propertiesmodule.

Note : The lowest layer on each side of the wall is assumed to extend to the base of the problem,i.e. 50 x the output interval given in the Analysis Options.

3.3.5 Groundwater

Groundwater can be entered in tabular form as described below or graphically. For tabular inputselect 'Groundwater' from the Data menu or the Gateway. For information on Graphical Inputfollow the link.

In tabular input separate pages are given for the back and front of the wall.

If only one data point is entered for either side of the wall, the program will assume a hydrostaticgroundwater distribution on that side of the wall. The pressure specified at the point need notnecessarily be zero. The unit weight of water must be entered for the first point on each side ofthe wall.

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For hydrostatic distributions the water pressure (u) is calculated from

u = zwgw

wherezw = depth below water table level

gw = specified unit weight of water

Thus a partial hydrostatic condition can be modelled by specifying a value of gw less than

10kN/m³.

For piezometric profiles the level and pressure at each known point must be entered. If morethan one data point is entered, the program will assume that the points represent piezometersand the groundwater pressure will be interpolated vertically between the specified points. Belowthe lowest point groundwater pressure will be assumed to extend hydrostatically.

Note : All defined water pressures are assumed to extend infinitely laterally on either side of thewall.

3.3.5.1 Groundwater Flow

Water flow beneath the base of the wall can be modelled by setting the "Balance waterpressures" switch in the Analysis Options dialog box. The program uses the following iterativeprocess.


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1. Carry out initial calculation using input water data to obtain the first estimate of embedmentof the wall (d1).

2. Calculate Uf for embedment d1.

Alter the ground water gradient either side of the wall by specifying a piezometric pressureequivalent to Uf at the base of the wall.

where gw =10.

3. Re-run the Stawal calculation.

4. Check calculated value of d.

5. Repeat steps 2 to 4 until d is consistent with the groundwater profile and Uf is balanced at the

base.

3.3.6 Surcharges

Surcharges can be entered in tabular form as described below or graphically. For tabular inputselect 'Surcharges' from the Data menu or from the Gateway. For information on Graphical Inputfollow the link.

Uniformly distributed surcharges (udl's) can be applied at or below ground level on either sideof the wall.

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Note : Strip loads can only be applied behind the wall.

The input data required for each surcharge is as follows

· The back (or front) of the wall where the surcharge is to be located (click on the down arrowand select the required option from the dropdown list)

· The level

· The pressure

· Offset: Distance of the line of the wall to the nearest edge of the strip.

· Width of load

Note : Tab across both the offset and width columns if the surcharge is a uniformly distributedload (udl). These options are not available for surcharges in front of the wall.

Application of strip loads

Strip loads can only be entered behind the wall.

For details on the method used by Stawal to transfer the applied load to the wall see Stripsurcharges.


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3.3.7 Struts or anchors

Struts or anchors can be entered in tabular form as described below or graphically. For tabularinput select 'Struts' from the Data menu or from the Gateway. For information on Graphical Input.

Struts may be applied at any level down the wall.

All strut forces must be specified apart from the initial strut used by the "Free earth" method,about which the wall is assumed to rotate. The location of this strut is given in Analysis Options.

Note : A positive strut force is deemed to act in the opposite direction to the active pressures nearthe top of the wall.

3.3.8 Graphical Input

Material layers, surcharges and struts can be entered in both tabular and graphical form. Themethods are fully interchangeable.

Select Graphical Input from the Data menu, the Gateway or the Stawal toolbar.

The Graphics menu will beavailable when Graphical Inputview is activated.

28Input

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3.3.8.1 Entering new graphical data

If no data has been entered, the program defaults to show a blank grid extending from –5m to+5m in the x direction and from 0m to –10m in the y direction.

This range can be edited by selecting Set displaylimits from the program's menu.

The snap interval can also be edited if required. This defines the smallest interval onto which thecursor will lock to mark a point.

Note : The minimum level provides the base of the Graphical Input view. It is not the base of theproblem which is defined as 50 x the output interval as specified in Analysis Options.

If data already exists, the limits are set to the current extent of the problem, but this can be editedat any time in the same way.


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3.3.8.2 Graphical Input view operation and commands

Use the mouse to move the cursor around the graphical display. The left and right mouse buttonsallow data to be entered and edited.

Information on entering each type of data is given separately. As graphical data is added, thetabular data screens are automatically updated. Similarly, if the Graphical Input screen is openwhen a data table is edited, the graphical display will be updated.

To change the current problem's minimum and maximum levels and the snap interval, select Setdisplay limits from the program's menu.

The following buttons are available on the Graphics toolbar or via their corresponding commandsfrom the Graphics menu:

Axis : Provides a reference grid behind the drawing.

Set Scale : This allows the user to toggle between the default 'best fit' scale and theclosest available engineering scale. e.g. 1:200, 1:250, 1:500, 1:1000, 1:1250, 1:2500.Alternatively to set any required scale, select "Set exact scale" from the View menu.Save Metafile : This save icon allows the file to be saved in the format of a WindowsMetafile. This retains the viewed scale. The metafile can be imported into otherprograms such as a word processor, spreadsheets and drawing packages.Copy : This icon allows the view to be copied to the clipboard in the form of aWindows Metafile.Zoom Facility : The user can select an area to 'zoom in' to by using the mouse toclick on a point on the drawing and then dragging the box outwards to select the areato be viewed. The program will automatically scale the new view. The original areacan be restored by clicking on the 'restore zoom' icon as shown here.Individual data buttons are described in the relevant section below.

3.3.8.3 Material Layers - Graphical Input

Material layers can be added graphically by selecting the material layers button on theGraphics toolbar or via the corresponding command from the Graphics menu.

1. Highlight the required section of wall by clicking the left mouse button at the top of thesection. Hold down the shift key and then move the cursor to the bottom of the requiredsection (still holding down the SHIFT key). Click the left mouse button again. The selectedsection will be shown highlighted and the top and bottom levels output at the top of thescreen.

2. Move the cursor to either the left or right hand side of the wall.3. Right click on the mouse to activate the material layers dialog box.

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Enter the number of the required soil material in the box and select OK.

Note : If this is the first material layer, it will be assumed to extend to the base of the problem, nomatter what the current selected levels are.

Note: The number of the soil comes from the list of material types created in the MaterialProperties properties table. Air or water are designated as material type 0.

Editing material layers

· The type of material layer can be changed by repeating the procedure above to overwrite theentered data.

· Material layers can be deleted by clicking on the upper boundary line and selecting the deletekey.

· The upper level of a material layer can be moved by highlighting the line and then using theleft mouse button to drag the level up or down.

Note : This will also update the tabular input. If the material layers require additional editing thenthis should be carried out using the tables.

3.3.8.4 Groundwater - Graphical Input

Groundwater data can be entered graphically by selecting the piezometer button on theGraphics toolbar or via the corresponding command from the Graphics menu.

A piezometric groundwater profile can be entered by placing the cursor at the appropriate levelon the Graphical Input view and clicking the left mouse button. This adds a piezometer symbol atthe current level and opens the piezometer data box.


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This allows the level of the piezometer to be confirmed or edited and the corresponding pressureto be entered. The pressure (P) is given as:

P = (hp – hw) gw

where:

hp = The level of the piezometer

hw = The level of groundwater in the piezometer

gw= Unit weight of water – Entered via tabular input see

Groundwater. (Only required if this is the first data pointon either side of the wall)

The data points can be deleted by placing the cursor over the location and clicking the left buttonwhilst holding down the Shift key.

For hydrostatic profiles place a single piezometer at the phreatic surface. Hydrostaticconditions are calculated beneath this point.

Note : This will also update the tabular input. If the piezometers require additional editing thenthis should be carried out using the tables.

3.3.8.5 Surcharges - Graphical Input

Surcharges can be added graphically by selecting the Surcharges button on the Graphicstoolbar or via the corresponding command from the Graphics menu.

To enter a surcharge, click the left mouse button at the left end of the surcharge and drag thecursor to the right end of the surcharge before releasing the mouse button. If the surcharge is onthe passive side of the wall it will be assumed to extend indefinitely, no matter what the selected

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length is.

The surcharge will be shown in pink and the surcharge dialog box will appear.

Enter the required vertical load intensity and press "Add to data" if OK (or "Cancel" to delete theoperation).

Note : This will also update the tabular input. If the surcharge requires additional editing then thisshould be carried out using the tables.

3.3.8.6 Struts - Graphical Input

Struts can be added graphically by selecting the Struts button on the Graphics toolbar or viathe corresponding command from the Graphics menu.

To enter a strut, click the left mouse button at the required strut level. A strut symbol will bedrawn in green and the strut dialog box will appear.

Enter the required strut force and press "Add to data" if OK (or "Cancel" to delete the operation).

Note : This will also update the tabular input. If the struts require additional editing, then thisshould be carried out using the tables.

Output

Part

IV

34Output

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4 Output

4.1 Analysis and Data Checking

Results can be obtained by selection of the Analysis menu:

Prior to analysis the program carries out a data check.

The data checks carried out are as follows:

1. For any voids in the material layers2. That struts and surcharges are all placed at or below ground level and above the base of the

problem.

If the "Balance water pressures" feature is enabled (see Analysis Options on page 14), a warningwill be shown in the Data check dialog.

If no errors are found then the calculation can proceed. Select OK.

Note : The option to Delete Results becomes available once the calculations have beencompleted.


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4.2 Tabular Output

Tabular Output is available from the View menu, the Gateway or the Stawal toolbar. This outputmay include input data and if analysis has been performed, results. The lists of tabulated outputcan be highlighted and then copied to the clipboard and pasted into most Windows typeapplications e.g. Word or Excel. The output can also be directly exported to various text or HTMLformats by selecting Export from the File menu.

Results of AnalysisThe required toe level of the wall [m] = -6.974Ground level active side [m] = 0.0Ground level passive side [m] = -5.000Level Back Front Bending Shear Moment Force Pe u Soil Soil Pe u [m] [kPa] [kPa] [kPa] [kPa] [kNm/m] [kN/m] .00 .00 .00 1 0 .00 .00 0.0 0.0-1.00 .00 .00 1 0 .00 .00 0.0 0.0-1.00 -10.00-2.00 4.13 .00 1 0 .00 .00 9.483 -7.933-3.00 19.25 5.00 2 0 .00 .00 12.77 5.821-4.00 22.75 10.00 2 0 .00 .00 -6.590 34.32-5.00 26.25 15.00 2 2 45.00 .00 -58.70 71.32-6.00 .00 20.00 3 3 452.63 .00 -114.4 25.32-6.62 688.92 26.22 3 3 .00 6.22 -44.63 -252.5-6.74 694.23 27.39 3 3 .00 7.39 -19.88 -169.0-6.86 699.53 28.57 3 3 .00 8.57 -4.983 -84.78-6.97 704.84 29.74 3 3 .00 9.74 -64.85E-6 0.01027

The results can also be exported to csv, txt, rtf or html files by selecting File | Export.

36Output

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4.2.1 Results

The following results are available in the Tabular Output:

· The level of each calculation point. The separation of these points is specified in the AnalysisOptions.

For the Front and Back of the wall:


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· Active and passive pressures (Pe),

· Pore water pressure (u) and material layer number.

· The Bending moment and shear force profiles down the wall.

If the "Balance water pressures" feature is switched on (see Analysis Options on page 14), twosets of results will be shown - the original results with the water data input by the user, and thefinal results obtained by the program after balancing the water pressure at the base of the wall.

4.3 Graphical Output

To obtain a plot of data and results, select Graphical Output from the View menu, the Gateway orthe Stawal toolbar.

Input data is always shown and individual result elements can be switched on or off as requiredusing the buttons on the graphics toolbar.

The following buttons are available on the Graphics toolbar:

Axis : Provides a reference grid behind the drawing.

Set Scale : This allows the user to toggle between the default 'best fit' scaleand the closest available engineering scale. e.g. 1:200, 1:250, 1:500,1:1000, 1:1250, 1:2500, or a user-defined scale.Save Metafile : This save icon allows the file to be saved in the format of aWindows Metafile. This retains the viewed scale. The Metafile can beimported into other programs such as a word processor, spreadsheets anddrawing packages.

38Output

© Oasys Ltd. 2007

Copy : This icon allows the view to be copied to the clipboard in the form ofa Windows Metafile.Zoom Facility : The user can select an area to 'zoom in' to by using themouse to click on a point on the drawing and then dragging the boxoutwards to select the area to be viewed. The program will automaticallyscale the new view. The original area can be restored by clicking on the'restore zoom' icon as shown here.Active and Passive pressures down either side of the wall.

Bending Moments within the wall.

Shear Forces within the wall.

List ofReferences

Part

V

40List of References

© Oasys Ltd. 2007

5 List of References

5.1 References

Institution of Structural Engineers (1989). Soil-structure interaction: the real behaviour ofstructures.

Padfield C J and Mair R J (1984). Design of retaining walls embedded in stiff clay. CIRIAReport No. 104

Pappin JW, Simpson B, Felton PJ and Raison C (1986). Numerical analysis of flexibleretaining walls. Proc. Symp. Computer Applications in Geo.Eng. Midland Geo. Soc, UK.

Manual Example

Part

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42Manual Example

© Oasys Ltd. 2007

6 Manual Example

6.1 General

The data input and results for the Stawal manual example are available in the 'Samples'sub-folder of the program installation folder. The example has been created to show the datainput for all aspects of the program and does not seek to provide any indication of engineeringadvice.

Screen captures from this example have also been used throughout this document.

This example can be used by new users to practice data entry and get used to the details of theprogram.

Brief TechnicalDescription

Part

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44Brief Technical Description

© Oasys Ltd. 2007

7 Brief Technical Description

7.1 Stawal

Stawal - Stability of retaining Walls.

Stawal can be used for the analysis of cantilever (Fixed earth) or propped (Free earth) retainingwalls, e.g. sheet pile or diaphragm walls.

The program uses methods of limit equilibrium to determine the penetration required to preventrotational instability of the wall. It then calculates the bending moments and shear forcesoccurring in the wall at the limiting condition.

The wall can be designated as either "Fixed earth" cantilever or "Free earth" propped wall.

The pressures behind the wall are deemed to start at the active limit, with the pressures in frontstarting at the passive limit.

The wall is tested for rotational failure about the base for a fixed earth wall and about thelocation of the prop for a free earth wall.

Soil profiles are represented by a series of horizontal soil strata that may be different each sideof the wall. Soil stratum can be specified with a linear variation of cohesion with level.

Water pressures can be entered as either hydrostatic or user-specified (i.e. piezometric).

Strut or anchor forces can be specified at any level on the passive side.

Surcharges can be either uniformly distributed, or strip loads. These may also be applied at anylevel.

Output is given in the form of soil and water pressures and bending moments and shear forcesdown the line of the wall. The results are given at the specified output interval.

Index 46

© Oasys Ltd. 2007

IndexA

Active and Passive Limits 9

Analysis and Data Checking 34

Analysis Options 20

Assembling Data 15

C

Components of the User Interface 2

D

Data Input 18

E

Entering new graphical data 28

F

Fixed Earth Mechanisms 7

Free Earth Mechanisms 8

G

Gateway 2

General 7, 42

General Program Description 2

Graphical Input 27

Graphical Input view operation and commands 29

Graphical Output 2, 37

Graphics Toolbar 2

Groundwater 23

Groundwater - Graphical input 30

Groundwater Flow 24

I

Intermediate levels 10

M

Material Layers 22

Material Layers - Graphical input 29

Material Properties 21

O

Opening the Program 15

P

Program Features 3

R

References 40

Results Output 35

S

Standard Toolbar 2

Stawal 44

Stawal Toolbar 2

Strip surcharges 12

Struts - Graphical input 32

Struts or anchors 27

Surcharges 25

Stawal Oasys Geo Suite for Windows47

© Oasys Ltd. 2007

Surcharges - Graphical input 31

T

Table View 2

Tabular Output 2

Tabular Results 36

Titles 17

Titles window - Bitmaps 18

Toolbar 2

U

Uniformly distributed loads 11

Units 19

User Interface 2

stawal manual

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