Geotechnical Stability Analysis Using Student Versions of FLAC, PLAXIS
Total Page:16
File Type:pdf, Size:1020Kb
University of Southern Queensland Faculty of Health, Engineering & Sciences Geotechnical Stability Analysis Using Student Versions of FLAC, PLAXIS and SLOPE/W A dissertation submitted by Michael Peter Serra in fulfilment of the requirements of Courses ENG 4111/2 Research Project towards the degree of Bachelor of Engineering (Civil) Submitted: October, 2013 Abstract Slope stability analysis is of particular importance to Geotechnical Engineers as slope failures can have devastating social and economic impacts. There are several software packages developed for stability analysis which utilise the Limit Equilibrium (LE) Method, Finite Element (FE) method and Finite Difference (FD) method. The majority of published information is in regards to the slope stability analysis methods of Limit Equilibrium, Finite Element and Finite Difference and not the software packages themselves. Several studies have suggested that the FE and FD methods provide greater benefits than the LE method; however other studies have suggested that the simplicity of the LE method outweighs the complexity of the FE and FD methods. The purpose of this research project is to compare the student versions of FLAC, PLAXIS and SLOPE/W and their use in Geotechnical stability analysis. FLAC is a software package using the FD method; PLAXIS the FE method and SLOPE/W the LE method. From this report it can be concluded that for software packages using the FE or FD method the type of ‘mesh’ generated and utilised in calculating the FOS value has a significant effect on accuracy of the results. Due to the limit in the amount of zones allowed within the FLAC student version and in general only allowing a coarse mesh analysis it can be considered that the FOS values calculated are less accurate compared to the student versions of PLAXIS and SLOPE/W. Each package has its own benefits and limitations and it is recommended that the users choose the package that best suits the models requirements and its complexity. The student versions should be used as an indication only and any detailed analysis requires the use of a full licensed version of the chosen software package. Michael Serra 001025484 Page ii ENG 4111/2 Research Project University of Southern Queensland Faculty of Health, Engineering & Sciences ENG 4111/2 Research Project Limitations of Use The Council of the University of Southern Queensland, its Faculty of Health, Engineering & Sciences, and the staff of the University of Southern Queensland, do not accept any responsibility for the truth, accuracy or completeness of material contained within or associated with this dissertation. Persons using all or any part of this material do so at their own risk, and not at the risk of the Council of the University of Southern Queensland, its Faculty of Health, Engineering & Sciences or the staff of the University of Southern Queensland. This dissertation reports an educational exercise and has no purpose or validity beyond this exercise. The sole purpose of the course pair entitled “Research Project” is to contribute to the overall education within the student’s chosen degree program. This document, the associated hardware, software, drawings, and other material set out in the associated appendices should not be used for any other purpose: if they are so used, it is entirely at the risk of the user. Prof Frank Bullen Dean Faculty of Health, Engineering & Sciences Michael Serra 001025484 Page iii ENG 4111/2 Research Project Certification I certify that the ideas, designs and experimental work, results, analyses and conclusions set out in this dissertation are entirely my own effort, except where otherwise indicated and acknowledged. I further certify that the work is original and has not been previously submitted for assessment in any other course or institution, except where specifically stated. Michael Peter Serra Student Number: 001025484 MICHAEL SERRA Signature 19TH OCTOBER 2013 Date Michael Serra 001025484 Page iv ENG 4111/2 Research Project Acknowledgements Without the help and my supervisor, Dr Jim Shiau this research project would not have been possible. His guidance and support throughout the project enabled me to further enhance my understanding of the topic. Michael Serra 001025484 Page v ENG 4111/2 Research Project Contents ABSTRACT .......................................................................................................... II ACKNOWLEDGEMENTS .................................................................................. V CONTENTS ......................................................................................................... VI LIST OF FIGURES ............................................................................................ XI LIST OF TABLES ........................................................................................... XIV NOMENCLATURE ........................................................................................... XV CHAPTER 1: INTRODUCTION ......................................................................... 1 1.1 INTRODUCTION ................................................................................................. 1 1.2 BACKGROUND ................................................................................................... 2 1.3 METHODOLOGY ................................................................................................ 2 1.4 OBJECTIVES ...................................................................................................... 3 1.5 REPORT STRUCTURE ......................................................................................... 3 CHAPTER 2: LITERATURE REVIEW ............................................................. 5 2.1 INTRODUCTION ................................................................................................. 5 2.2 LIMIT EQUILIBRIUM (LE) METHOD ................................................................... 5 2.2.1 Vertical Slices .......................................................................................... 6 2.2.2 Benefits ..................................................................................................... 8 2.2.3 Limitations ............................................................................................... 8 2.2.4 Factor of Safety (FOS) ............................................................................. 8 2.3 FINITE ELEMENT (FE) METHOD ...................................................................... 10 2.3.1 Finite Difference (FD) Technique ......................................................... 11 2.3.2 Benefits .................................................................................................. 12 2.3.3 Limitations ............................................................................................. 13 2.3.4 Factor of Safety (FOS) .......................................................................... 13 Michael Serra 001025484 Page vi ENG 4111/2 Research Project CHAPTER 3: SOFTWARE PACKAGES ......................................................... 15 3.1 OVERVIEW ...................................................................................................... 15 3.2 SLOPE/W ...................................................................................................... 15 3.2.1 Required Soil Properties ........................................................................ 16 3.2.2 Slip Surface Entry & Exit ....................................................................... 16 3.2.3 SOLVE Process ...................................................................................... 16 3.2.4 Morgenstern-Price Method .................................................................... 17 3.3 FLAC ............................................................................................................. 18 3.3.1 Required Soil Properties ........................................................................ 19 3.3.2 FLAC/Slope ............................................................................................ 20 3.4 PLAXIS .......................................................................................................... 21 3.4.1 Required Soil Properties ........................................................................ 22 3.4.2 Elastic Modulus (E) ............................................................................... 22 3.4.3 Staged Construction ............................................................................... 23 3.4.4 Phi-c Reduction ...................................................................................... 23 CHAPTER 4: SCENARIO 1 – SIMPLE HOMOGENEOUS SOIL SLOPE AT VARYING HEIGHTS ............................................... 24 4.1 GEOTECHNICAL MODEL .................................................................................. 24 4.1.1 Material Properties ................................................................................ 25 4.1.2 Units ....................................................................................................... 25 4.2 FLAC/SLOPE ANALYSIS ................................................................................. 26 4.2.1 Methodology........................................................................................... 26 4.2.2 Results .................................................................................................... 28 4.3 SLOPE/W ANALYSIS ....................................................................................