PLAXIS Groundwater flow Tutorial manual
78 Pages
English

PLAXIS Groundwater flow Tutorial manual

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PLAXFLOW
Tutorial Manual
Version 1.4



















































TABLE OF CONTENTS

TABLE OF CONTENTS
1 Introduction..................................................................................................1-1
2 Getting started .............................................................................................2-1
2.1 Installation2-1
2.2 General modelling aspects .....................................................................2-1
2.3 Input procedures ....................................................................................2-3
2.3.1 Input of geometry objects ..........................................................2-3
2.3.2 Input of text and values..............................................................2-3
2.3.3 Input of selections......................................................................2-4
2.3.4 Structured input..........................................................................2-5
2.4 Starting the program ..............................................................................2-6
2.4.1 General settings2-6
2.4.2 Creating a geometry model........................................................2-8
3 Flow through an embankment (Lesson 1) .................................................3-1
3.1 Case A: steady-state flow.......................................................................3-2
3.1.1 Creating input ...

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PL
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Tutorial Manual
Version 1.4
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TABLE OF CONTENTS
TABLE OF CONTENTS 1nctioudortnI..................................................................................................1-12Getting started.............................................................................................2-12.1Installation ............................................................................................. 2-12.2 2-1General modelling aspects .....................................................................2.3 2-3Input procedures ....................................................................................2.3.1Input of geometry objects ..........................................................2-32.3.2Input of text and values ..............................................................2-32.3.3 ......................................................................2-4Input of selections2.3.4Structured input..........................................................................2-52.4Starting the program .............................................................................. 2-62.4.1General settings..........................................................................2-62.4.2 ........................................................2-8Creating a geometry modelFlow through an embankment (Lesson 1).................................................3-13.1 3-2Case A: steady-state flow.......................................................................3.1.1Creating input.............................................................................3-23.1.2Performing calculations ...........................................................3-143.1.3Viewing output results .............................................................3-163.2Case B: transient flow with step-wise conditions ................................ 3-183.2.1Creating input...........................................................................3-183.2.2Performing calculations ...........................................................3-213.2.3Viewing output results .............................................................3-223.3 3-22Case C: transient flow with time-dependent conditions.......................3.3.1Creating input...........................................................................3-233.3.2Performing calculations ...........................................................3-243.3.3Viewing output results .............................................................3-254around a sheet pile wall (lesson 2)Flow .....................................................4-14.1 4-1Creating input .............. .......................................................................... 4.2Performing calculations ....................................................................... 4-104.3 ......................................................................... 4-11Viewing output results5Filling of a cofferdam (lesson 3)..................................................................5-15.1Input ....................................................................................................... 5-15.2 5-7Performing calculations .........................................................................5.3Output .................................................................................................... 5-76Potato field moisture content (lesson 4).....................................................6-1 6.1Input ....................................................................................................... 6-16.2Calculation ............................................................................................. 6-66.3Output .................................................................................................... 6-7Appendix A - Menu structure....................................................................................A-1
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TUTORIAL MANUAL
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INTRODUCTION
1IRONTTCUDNOI PLAXFLOW is a finite element program for groundwater flow analysis in geotechnical engineering. PLAXFLOW a simple graphical input procedure which enables a provides quick generation of complex finite element models. It also provides enhanced output facilities with detailed presentation of computational results. The calculation is fully automated and based on robust numerical procedures. This enables users with no or little knowledge of finite element procedures to perform their projects after only a few hours of training. This Tutorial Manual is intended to help new users become familiar with PLAXFLOW. The various lessons deal with a wide range of interesting practical applications and cover most of the program features. Users are expected to have a basic understanding of groundwater flow mechanics and able to work in a Windows environment. It is strongly recommended that the lessons are followed in the order presented in the manual. The tutorial lessons are also available in the examples folder of the PLAXFLOW program directory and can be used to check 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 models available in the program. The latter can be found in the Reference Manual, and theoretical background is presented 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 around the world to provide hands-on experience and background information on the use of the program.
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TUTORIAL MANUAL
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GETTING STARTED
2GETTING STARTED This chapter describes some of the notation and basic input procedures that are used in PLAXFLOWmanuals, buttons, menu items or parameters appearing in the. In the program are printed inItalics. Whenever keys on the keyboard need to be pressed, this is marked with the name of the key in brackets, (for example the <Enter> key).
2.1ONTILAALTSNI For the installation procedure the user is referred to the General Information section, i.e. the first part of this manual.
2.2GENERAL MODELLING ASPECTS For each new project it is important to create a geometry model first. A geometry model is a 2D representation of a real three-dimensional problem and consists of points, lines and clusters. A geometry model may include soil layers, structural objects, construction stages and flow conditions. The three types of components in a geometry model are described below in more detail. Points Points form the start and end of lines. Points can also be used for local refinements of the finite element mesh. Lines Lines are used to define physical boundaries, model boundaries and discontinuities in the geometry such as screens or drains, separations of distinct soil layers or construction stages. Clusters Clusters are areas that are fully enclosed by lines. PLAXFLOW identifies automatically clusters based on the input of geometry lines. Within a cluster the soil properties are homogeneous. Hence, clusters can be regarded as parts of soil layers. Actions related to clusters apply to all elements in the cluster. After the creation of a geometry model, a finite element mesh can automatically be generated, based on the composition of clusters and lines in the geometry model. In a finite element mesh three types of components can be identified, as described below.
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TUTORIAL MANUAL Elements During the generation of the mesh, clusters are divided into triangular elements and a linear 3-node element is taken by default. As an alternative 15-node elements and 6-node elements can be selected to ensure compatibility between the PLAXFLOWprogram and the PLAXISdeformation program. One should be aware, however, that flow calculations are carried out using 3-node elements. Higher-order 15-node elements are simply divided in sixteen 3-node elements and 6-node elements are divided in four 3-node elements as shown in Figure 2.1. Considering the same element distribution (for example a default coarse mesh generation) the user should be aware that meshes composed of 15-node elements are actually much finer than meshes composed of 6-node elements or 3-node elements, and that calculation times are also longer.
(a) 15-node elements
(b) 6-node elements
nodes
nodes
stress points used for flow calculation
stress points used for flow calculation
stress points used for output purposes
stress points used for output purposes
nodes stress points used stress point used for flow calculation for output purposesFigure 2.1 Elements, nodes and stress points
(c) 3-node elementsNodes A 15-node element consists of 15 nodes, a 6-node element is defined by 6 nodes and a 3-node element contains 3 nodes. The distribution of nodes over the elements is shown in Figure 2.1. Adjacent elements are connected through their common nodes. During a finite element calculation, pore pressure heads are calculated at the nodes. Nodes may be selected for the generation of pore pressure head vs. time curves. Stress points Unlike the pore pressure head, the degree-of-saturation and the flow velocity are calculated at Gaussian integration points (stress points). A 15-node triangular element originally contains 12 stress points as indicated in Figure 2.1a and a 6-node triangular element contains 3 stress points as indicated in Figure 2.1b. Figure 2.1c indicates the 2-2
PLAXFLOW
GETTING STARTED
position of the single stress point in a 3-node element. During a groundwater flow calculation, only stress points of 3-node elements are used, but when higher-order elements have been selected, results are back calculated to the original stress points indicated in Figure 2.1 for the purpose of compatibility with the PLAXISdeforamitnocalculations. Stress points may be selected for the generation of history curves for the degree of saturation or the flow velocity (Darcy flux).
2.3INPUT PROCEDURES In PLAXFLOW, input is specified by a combination of mouse clicking and moving, and by keyboard input. In general, distinction can be made between four types of input:  Input of geometry objects (e.g. drawing a soil layer) Input of text (e.g. entering a project name) Input of values (e.g. entering the unit weight of water) Input of selections (e.g. choosing an unsaturated soil model) The mouse is generally used for drawing and selection purposes, whereas the keyboard is used to enter text and values.
2.3.1INPUT OF GEOMETRY OBJECTS The creation of a geometry model is based on the input of points and lines. This is done by means of a mouse pointer in the draw area. Several geometry objects are available from the menu or on the tool bar. Lines are drawn by clicking the left mouse button at the required position in the draw area. As a result, a first point is created. Moving the mouse to the next position and clicking the left mouse button again, will create a new point, together with a line between the two points. Line drawing can be terminated by clicking the right mouse button or by pressing the <Esc> key on the keyboard.
2.3.2INPUT OF TEXT AND VALUES In PLAXFLOWand values is specified in edit boxes. Multiple edit boxesthe input of text for a specific subject are grouped in windows. The desired text or value can be typed using the keyboard, followed by pressing the <Enter> key or the <Tab> key or by clicking the mouse on another edit box. As a result, the value is accepted and the next input field is highlighted. Many parameters have default values. These default values may be used by just pressing the <Enter> key without other keyboard input. When all input values in a window have been entered, click theOKall values and closes the window. button. This confirms Pressing the <Esc> key or clicking theCancel button will cancel the input and restore the previous or default values before closing the window.
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TUTORIAL MANUAL In some countries, like The Netherlands, the decimal dot in floating point values is represented by a comma. The type of representation that occurs in edit boxes and tables depends on the country setting of the operating system. Values must be entered in accordance with this setting. Thespin boxfeature is shown in Figure 2.2. Just like a normal input field a value can be entered using the keyboard, but it is also possible to left-click theorarrows at the right side of each spin boxto increase or decrease its value by a predefined amount.
Figure 2.2 Spin boxes
2.3.3INPUT OF SELECTIONS Selections are made by means of radio buttons, check boxes or combo boxes as described below. Radio buttons In a window with radio buttons only one item may be active. The active selection is marked with a black dot in the white circle in front of the item. Selection is made by clicking the left mouse button in the white circle or by using the up and down arrow keys on the keyboard. When changing the existing selection to another option, the previous selection will be deselected. An example of a window with radio buttons is shown in Figure 2.3. According to Figure 2.3All stepshas been selected.
Figure 2.3 Radio buttons
Check boxes A check box is used to activate or de-activate an individual item. In a window with several check boxes, more than one item may be activated at the same time. The active selection is marked with a black tick mark in a white square. Activation is done by clicking the left mouse button in the white square or by pressing the space bar on the keyboard. Click again on an activated item to de-activate it. An example of a check box is shown in Figure 2.4.
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PLAXFLOW
Figure 2.4 Check box
GETTING STARTED
Combo boxes A combo box is used to choose one item from a predefined list of possible choices. An example of a window with combo boxes is shown in Figure 2.5. Clicking thearrow at the right hand side of the combo box displays a pull down list that shows the available options. A combo box has the same functionality as a group of radio buttons but is more compact. In Figure 2.5dayis selected as unit of time.
Figure 2.5 Combo box 2.3.4STRUCTURED INPUT The required input is organised as logically as possible. The Windows environment provides several ways of visually organising and presenting information on the screen. To make the reference to typical Windows elements in the next chapters easier, some types of structured input are described below. Page control and tab sheets An example of a page control with two tab sheets is shown in Figure 2.6. In this figure the firstGeneraltab sheet for the input of the model parameters is active. Tab sheets are used to handle large amounts of different types of data that do not all fit in one window. Tab sheets can be activated by left-clicking the corresponding tab or using <Ctrl><Tab> on the keyboard. Group boxes Group boxes are rectangular boxes with a title. They are used to cluster input items that have common features. In Figure 2.6, the active tab sheet contains three group boxes namedMaterial set,ParametersetsandComments.
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