FLAC Basics

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this book described the modeling with the software Flac.

Text of FLAC Basics

  • FLACBasics

    COETZEEHARTVARONACUNDALL

    An introduction toand a guide to its

    practical application ingeotechnical engineering

    Foreword byProfessor Charles Fairhurst

    FLAC

    2nd R

    evise

    d Edit

    ion

    1

  • First Edition 1993

    First Revision 1995

    Second Revision 1998

    Authors:

    Coetzee, Matthys J.

    Hart, Dr Roger D.

    Varona, Pedro M.

    Cundall, Dr Peter A.

    Published by:

    Itasca Consulting Group, Inc.

    708 South Third Street

    Minneapolis, Minnesota 55415

    United States of America

    Copyright 1993, 1995, 1998 Itasca Consulting Group:

    All rights reserved. The examples shown in this book may be used for tutorial purposes only. No other

    part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical,

    including photocopying, recording, or by any information storage and retrieval system, without prior

    permission from the publisher.

    Limitation of Liability:

    Itasca assumes no liability whatsoever with respect to any use of FLAC, the tutorial materials in this book,

    or any portion thereof. In no event shall Itasca be responsible for any indirect, special, incidental, or

    consequential damages arising from the use of this material.

    Tradenames and Trademarks:

    In this book, tradenames and trademarks of some companies have been mentioned, and no such uses are

    intended to convey endorsements of or other affiliations with the book. Wherever such tradenames and

    trademarks have been used, they are deemed to be the registered tradenames or trademarks of the relevant

    companies.

    Printed and bound by:

    Advanced Duplicating and Printing, Inc.

    Minneapolis, Minnesota

    United States of America

    Production:

    This book was produced using FLAC 3.4, CorelVentura 8.0 for Windows, PS (a PostScript graphic editor)

    and CorelDraw 8.0, using Times New Roman, Arial and Courier New typefaces.

    Camera ready copy was made on a Hewlett Packard LaserJet 4M PLUS. Layout and cover design by Thys

    Coetzee, Itasca Consulting Group Inc. The cover design reflects the Itasca logo, which shows a

    2-dimensional mesh of a tunnel, with planes of symmetry on the bottom and right faces.

    2

  • FOREWORD

    The five years since publication of the first edition of FLAC Basics have confirmed the expectations

    expressed in the Foreword of the first edition. FLAC, a very robust code that has been in use for 12

    years, is now a standard numerical tool in widespread use internationally by geoscientists and

    geotechnical engineers. Many new code developments are the result of suggestions from users around

    the world. We thank these colleagues for their contributions and hope that the additions to FLAC in

    the past five years and revisions described in the FLAC Manual will make the code a still more

    valuable practical tool. The tug-of-war between experienced users eager to have more specialized

    capabilities added and others seeking more user-friendly features continues. We will continue to

    strive to accommodate both. Your comments on where FLAC can be improved are always welcome.

    The prevailing conditions that initially suggested development of an explicit finite difference approach

    to numerical modeling are still very much predominant in the fields of rock mechanics, soil

    mechanics, and geomechanics. Enhancement of our existing modeling tools and development of new

    ones are still our primary objectives. Dr. Peter Cundall pioneered the creation of such tools in the late

    1960s, starting with the novel departure to a Distinct Element Method, an initial introduction of

    explicit finite difference methods in numerical modeling for geomechanics. Allowing discontinuous

    deformation of assemblages of blocky or particulate rock masses to be modeled over unlimited

    deformationsto equilibrium or collapseled to the development of the two- and three-dimensional

    distinct element codes UDEC and 3DEC. Both codes are, today, valuable analytical and design tools

    in use throughout the world. Application of the same finite difference procedure to continua became

    the basis of the development of FLAC and its three-dimensional counterpart, FLAC3D.

    Recently the ongoing pursuit of solutions to problems using a continuum formulation has been

    supplemented by a new innovation: the Particle Flow Code (PFC2D and PFC3D). These codes

    simulate the micro-mechanics of deformation, damage, and disintegration of particulate materials,

    including but not limited to rock, soils, cements, concretes, and bitumens, that is, geomaterials.

    Using the same time-stepping, explicit finite difference method used in FLAC and the other Itasca

    codes, the PFC codes present the opportunity to understand and predict the response of rock to more

    complex loading situationsespecially where these may involve irreversible damage or

    collapsedirectly from elemental, particle-to-particle mechanical properties.

    PFCs simpler and potentially more reliable approach to study of damage and disintegration of

    cohesive, particulate materials does not supercede the analytical functions of FLAC. Rather, it is a

    parallel line of approach to the continuum formulation that we believe will yield an ever greater

    analytical capability to the code user. We look forward to a new phase of code development in which

    the power of time-tested tools such as FLAC will not only increase but achieve a new level of utility

    through combined analysis techniques available with the addition of PFC. In this area most

    particularly we recognize the growth and potential for FLAC and Itasca's other modeling codes.

    Charles Fairhurst

    Minneapolis, September 1998.

    Contents iii

    3

  • PREFACE TO SECOND REVISION

    With the release of Version 3.4, Itasca offers a Windows-console version of FLAC. This version

    provides all the powerful capabilities of FLAC plus access to Windows graphics and high resolution

    screen plots. This guide is intended to be a gateway for new users to explore these and all the features

    and capabilities of Version 3.4

    We have also expanded the FLAC documentation, adding many new example applications and

    providing the entire manual in electronic form on CD-ROM. The new manuals and the current

    revision reaffirm Itascas commitment to providing good code and the documentation and support

    needed by users.

    Roger Hart

    Director, Software Services

    Minneapolis, September 1998.

    ACKNOWLEDGEMENTS

    The authors are indebted to the following people, who contributed significantly to the making of this

    book with their reviews, contributions, and overall assistance:

    Dr Margaret Asgian, Itasca England; Dr. Daniel Billaux, Itasca France; Joanne Brosseau, Itasca USA;

    G.W. Byun, Dong Myeong Engineering Consultants, Korea; Jackie Coetzee, Consultant, Minneapolis,

    Minnesota, USA; Dr Michael Coulthard, M.A. Coulthard & Associates, Australia; Alison Cundall,

    Itasca USA; Dr Christine Detournay, Itasca USA; Eileen Goren, Independence Press, Inc., Lakeville,

    Minnesota, USA; Valerie Gustafson, Itasca USA; Trisha Hendren, Itasca, USA; Erik Johansson,

    Saanio & Riekkola, Finland; Prof. Moon Kim, Yonsei University, South Korea; Prof. R.J. Pine &

    Graduate Students, Camborne School of Mines, England; Kathleen Sikora, Itasca USA; Chad Sylvain,

    Itasca USA; David Young, Mott MacDonald, North-East Division, England.

    iv Contents

    4

  • CONTENTS

    Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

    Preface to First Revision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

    Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

    CHAPTER 1

    Welcome to FLAC

    1.1 What is FLAC ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

    1.2 About this Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

    1.3 Range of Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

    1.4 Background and Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

    1.5 User Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

    CHAPTER 2

    Modeling Methodology

    2.1 Modeling Geo-Engineering Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

    2.2 Explicit vs Implicit Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

    CHAPTER 3

    Basic Operation Procedures

    3.1 FLAC Is Command Driven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

    3.2 Installation Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

    3.3 Before You Begin Modeling with FLAC . . . . . . . . . . . . . . . . . . . . . . . . . . 17

    3.3.1 FLAC Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

    3.3.2 Command Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

    3.3.3 Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

    3.4 The Finite Difference Grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

    3.4.1 Zones and Gridpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

    3.4.2 (i, j) vs (x, y) . . . . . . . . . . . . . . . . . . . . . . . . .