Shear Strength and Stability of Highway Embankments in Ohio A thesis presented to the faculty of the Russ College of Engineering and Technology of Ohio University In partial fulfillment of the requirements for the degree Master of Science Xiao Han March 2010 © 2010 Xiao Han. All Rights Reserved. 2 This thesis titled Shear Strength and Stability of Highway Embankments in Ohio by XIAO HAN has been approved for the Department of Civil Engineering and the Russ College of Engineering and Technology by Teruhisa Masada Professor of Civil Engineering Dennis Irwin Dean, Russ College of Engineering and Technology 3 ABSTRACT HAN, XIAO, M.S., March 2010, Civil Engineering Shear Strength and Stability of Highway Embankments in Ohio (182 pp.) Director of Thesis: Teruhisa Masada One of the primary factors that control the stability of earthen embankments is the shear strength of embankment fill soils. Karl von Terzaghi and U.S. Navy found empirical correlations between soil shear strength and lab or in-situ soil test results. Subsequently, the Navy proposed typical effective friction angle values for different soils types. However, it is not certain if these correlations and standard values are reliable for Ohio soils. The main objective of this thesis is to establish reliable correlations between shear strength and index properties/in-situ test measurements for embankment fill soils existing in Ohio. Relatively undisturbed soil samples were gathered from nine highway embankment sites spread throughout Ohio. Tri-axial compression tests were performed to determine the shear strength of these soil samples. During data analysis, statistical methods, such as regression analysis and T-tests, were utilized to assess the correlations. Through the statistical analysis, optimized correlations were identified between shear strength and other characteristics of soil have been found. Once the optimum correlations were established, soil shear strength properties were applied to sophisticated geotechnical software to perform a series of slope stability analysis for highway embankments. Lastly, results from the laboratory testing, field 4 testing, statistical data analysis, and slope stability analysis were all combined to suggest technical guidelines for highway embankment design/constructions in Ohio. Approved: _____________________________________________________________ Teruhisa Masada Professor of Civil Engineering 5 ACKNOWLEDGMENTS I would like to show my appreciation to my advisor, Dr. Teruhisa Masada, for assisting me through out my Master’s Program. I would also like to thank him for encouraging me to be diligence on this thesis and teaching me the skills that will be very helpful in my future career. I would also like to thank Dr. Greg Springer, Dr. Munir Nazzal, and Dr. Omer Tatari for being members of my thesis committee. Finally, I would like express my appreciation to my parents who supported me in many ways through out the years I worked on my Master’s degree. 6 TABLE OF CONTENTS Page Abstract .............................................................................. Error! Bookmark not defined. Acknowledgments.............................................................. Error! Bookmark not defined. List of Tables ..................................................................... Error! Bookmark not defined. List of Figures .................................................................... Error! Bookmark not defined. Chapter 1 : INTRODUCTION......................................................................................... 15 1.1 Background ....................................................................................................... 15 1.2 Objectives ......................................................................................................... 16 1.3 Outline of Thesis ............................................................................................... 16 Chapter 2 : Ohio Geology ................................................................................................ 18 2.1 Geological Conditions ...................................................................................... 18 2.2 Soil Classifications ............................................................................................ 20 Chapter 3 : Research Methodologies ............................................................................... 22 3.1 Site Screening and Sample Collection .............................................................. 22 3.1.1 Site Locations and Distribution ................................................................ 22 3.1.2 Standard Penetration Test ......................................................................... 24 3.1.3 Soil Sampling Method .............................................................................. 26 3.2 Experiment ........................................................................................................ 28 3.2.1 Triaxial Compression Test - Introduction ................................................. 28 3.2.2 C-U Triaxial Test Procedure and Equipment ............................................ 30 Chapter 4 : Results and Data Analysis ............................................................................. 37 4.1 Introduction of Basic Theory ............................................................................ 37 4.2 Methodology to analyze the correlations .......................................................... 40 4.3 Effective Internal Friction Angle vs. Plasticity Index (by Terzaghi) ................ 42 4.4 SPT-N vs. Unconfined Compression Strength (by Department of Navy) ........ 47 4.5 A Values and Level of Consolidation ................................................................ 52 4.6 T-test for Three Major Soils .............................................................................. 56 4.7 Single Variable Regression Analysis ................................................................ 69 4.7.1 Single Variable Regression Analysis for A-4a Soils ..................................... 71 7 4.7.2 Single Variable Regression Analysis for A-6a Soils ..................................... 79 4.7.3 Single Variable Regression Analysis for A-6b Soils ..................................... 89 4.7.4 Single Variable Regression Analysis for A-7-6 Soils ................................. 102 4.8 Multiple Variables Linear Regression Analysis (Part I) ................................. 112 4.9 Multiple Variables Linear Regression Analysis (Part II) ............................... 117 4.10 Closing Remarks ............................................................................................. 124 Chapter 5 : Highway Embankment Slope Stability ....................................................... 127 5.1 Soil Slope Stability Theory ............................................................................. 127 5.2 Embankment Model Assumptions .................................................................. 132 5.3 Results of Highway Embankment Slope Stability Analysis ........................... 138 5.3.1 Homogeneous Embankments...................................................................... 138 5.3.2 Outcomes of Embankments Built on Two Soil Layers .............................. 155 Chapter 6 : Summary and Conclusions .......................................................................... 174 6.1 Summary ......................................................................................................... 174 6.2 Conclusions ..................................................................................................... 175 6.2.1 Conclusions on Empirical Correlations ...................................................... 175 6.2.2 Conclusions from T-Tests Performed ......................................................... 176 6.2.3 Conclusions from Single-Variable Regression Analysis ............................ 177 6.2.4 Conclusions from Multi-Variable Linear Regression Analysis .................. 178 6.2.5 Conclusions from Slope Stability Analysis ................................................ 179 References ....................................................................................................................... 181 8 LIST OF TABLES Page Table 2.1: AASHTO Classifications for Fine-Grained Soils ........................................... 20 Table 4.1: Effective Internal Friction Angle vs. Plasticity Index by Terzaghi ................. 42 Table 4.2: SPT-N vs. Unconfined Compression Strength (psi) by Department of Navy . 47 Table 4.3: The A value for A-4a soil ................................................................................. 53 Table 4.4: The A value for A-6a soil ................................................................................. 54 Table 4.5: The A value for A-6b soil ................................................................................. 54 Table 4.6: The A value for A-7-6 soil ............................................................................... 55 Table 4.7: The Critical Value of T-Distribution ................................................................ 58 Table 4.8: Summary of T Tests Performed on A-4 Soil Subsets ...................................... 59 Table 4.9: Summary of T Tests Performed on A-6 Soil Subsets ...................................... 60 Table 4.10: The Calculation for T Value of A-4a in Various Locations (North and South) ..........................................................................................................................................