Final Report SOIL NAILING FOR STABILIZATION OF STEEP SLOPES NEAR RAILWAY TRACKS Submitted to Research Designs and Standards Organization (RDSO), Lucknow Prepared by Dr Amit Prashant Ms Mousumi Mukherjee Department of Civil Engineering Indian Institute of Technology Kanpur August, 2010 ACKNOWLEDGEMENTS At the onset, the authors thank Research Designs and Standards Organization (RDSO), Lucknow for providing necessary financial support The authors also express their gratitude to the Department of C.
Final Report SOIL NAILING FOR STABILIZATION OF STEEP SLOPES NEAR RAILWAY TRACKS Submitted to Research Designs and Standards Organization (RDSO), Lucknow Prepared by Dr Amit Prashant Ms Mousumi Mukherjee Department of Civil Engineering Indian Institute of Technology Kanpur August, 2010 ACKNOWLEDGEMENTS At the onset, the authors thank Research Designs and Standards Organization (RDSO), Lucknow for providing necessary financial support The authors also express their gratitude to the Department of Civil Engineering and the dean of research and development at Indian Institute of Technology, Kanpur for providing constant encouragement and necessary infrastructural support The authors would like to appreciate the contributions made by Mr Akhilesh Rawal, Mr Sudeep Kumar Singh, and Mr Manash Chakraborty in completing this report Dr Amit Prashant Ms Mousumi Mukherjee LIST OF SYMBOLS Symbols Description α Inclination of slice base β Inclination of slice top θ Angle subtended by the slip circle at centre α1 Inclination of the back slope β1 Slope face angle with respect to the vertical θ1 Inclination of failure plane φ Soil effective angle of internal friction c Soil effective cohesion L Length of failure plane W Weight of the sliding mass Q Surcharge load NF Normal force on failure surface SF Shear force on failure surface R Radius of circular slip surface Su Undrained shear strength x Horizontal distance between circle centre and the centre of the sliding mass Rc Perpendicular distance from the circle centre to shear force Larc , Lchord Lengths of the circular arc and chord defining the failure surface δ Angle of line of action of surcharge with vertical b Width of slice h Average height of slice Sa Available strength SF Mobilized strength λ λj Nail inclination of equivalent nail tensile force th Nail inclination of j nail nl Total number of nail used TEQ Equivalent nail tensile force Tj Tensile force in jth nail Tn Nail tensile forces for the reinforcement emerging out from the base of ith slice kv Vertical seismic coefficient kh Horizontal seismic coefficient N c , Nγ Bearing capacity factor γ Unity weight of soil behind wall H Height of the wall (excavation depth) ΔH Equivalent overburden H eq Equivalent wall height Be Width of excavation B' Width of influence Le Length of excavation q Mobilized bond stress p Perimeter of the nail d ψ hj Diameter of the nail Mobilized soil-nail interface friction angle Depth of the midpoint of j th nail from ground surface le Length of the nail behind the failure surface in case of nailed slope FSG Factor of safety against global stability FSSL Factor of safety against sliding stability FSH Factor of safety against bearing capacity FSP Factor of safety against pullout strength FST Factor of safety against nail-tensile strength FSFF Factor of safety against facing failure FSFP Factor of safety against punching failure FSHT Factor of safety against headed-stud tensile failure CF Correction Factor β eq Equivalent back slope angle K Coefficient of lateral active earth pressure CONTENTS CHAPTER INTRODUCTION 1.1 Nails and soil nailing 1.2 Various types of soil nailing 1.3 Elements of nailed structure 1.4 Advantage and disadvantage of soil nailing 1.4.1 Advantage of soil nailing 1.4.2 Disadvantage of soil nailing 1.5 Various issues affecting soil nailed slope 1.6 Construction procedure of nailed structure 1.7 Testing and inspection 11 1.8 Scope of the document 12 CHAPTER GEOTECHNICAL INVESTIGATION AND TESTING 2.1 Introduction 13 2.2 Site reconnaissance 13 2.3 Subsurface investigation 14 2.3.1 Boring 16 2.3.2 Field testing 18 2.3.3 Sampling 20 2.3.4 Stratification 21 2.3.5 Ground water table position 21 Laboratory testing of soil sample 22 2.4 2.4 Field test for pull-out capacity 22 2.5 Summary 25 CHAPTER BACKGROUND THEORY 3.1 Introduction 26 3.2 Slope stability without nails 26 3.2.1 Single-wedge with planar surface 26 3.2.2 Circular arc method 28 3.2.3 Friction circle method 29 3.2.4 Simplified Bishop Method 31 3.2.5 Simplified Janbu Method 34 Slope stability with nails 36 3.3.1 Single-wedge with planar surface 36 3.3.2 Circular arc method 38 3.3.3 Friction circle method 39 3.3.4 Simplified Bishop Method 40 3.3.5 Simplified Janbu Method 42 3.4 Slope stability under dynamic condition 43 3.5 Bearing capacity of nailed wall 45 3.6 Bond strength 49 3.8 Mobilized nail tension 52 3.8 Example problems on stability analysis of unreinforced slope 54 3.8.1 Problem-1 54 3.3 (a) Planar failure surface 55 (b) Circular arc method 57 (c) Simplified Bishop method 59 3.8.2 Problem-2 3.9 (a) Planar failure surface 62 (b) Simplified Bishop method 65 Example problems on stability analysis of nailed slope 67 3.9.1 Problem-1 67 (a) Planar failure surface 68 (b) Circular arc method 70 (c) Simplified Bishop method 72 3.9.2 Problem-2 3.10 61 74 (a) Planar failure surface 75 (b) Simplified Bishop method 78 80 Summary CHAPTER DESIGN OF NAILED SOIL SLOPE 4.1 Introduction 81 4.2 Design requirements 81 4.2.1 Geometry of nailed slope 82 4.2.2 Soil characteristics 83 4.3 Specifications for nailing components 84 4.4 Failure modes of soil nail wall 91 4.4.1 External stability of nailed slope 92 4.4.2 4.4.1.1 Slope stability 92 4.4.1.2 Sliding stability 92 4.4.1.3 Bearing capacity failure 94 Internal stability of nailed slope 95 4.4.2.1 Nail pull-out failure 96 4.4.3 4.5 4.8 4.4.2.2 Nail tensile failure 98 Facing design 100 4.4.3.1 Tensile forces at slope facing 100 4.4.3.2 Facing failure modes 101 4.4.3.3 Facing design procedure 105 Seismic consideration for stability analysis of nailed slope 110 4.5.1 Selection of seismic coefficients 110 4.5.2 Seismic effects on sliding stability 111 4.5.3 Seismic effects on global stability 115 Summary 116 CHAPTER EXAMPLE PROBLEMS ON NAILED SLOPE DESIGN 5.1 Introduction 5.2 Problem-1 5.3 5.4 117 5.2.1 Slope stability without nail 117 5.2.2 Stability of nailed slope 120 5.2.2.1 Internal stability 120 5.2.2.2 External stability 127 Problem-2 5.3.1 Slope stability without nail 136 5.3.2 Stability of nailed slope 139 5.3.2.1 Internal stability 139 5.3.2.2 External stability 140 Problem-3 5.4.1 Slope stability without nail 149 5.5 5.4.2 Stability of nailed slope 151 5.4.2.1 Internal stability 151 5.4.2.2 External stability 152 Problem-4 5.5.1 Slope stability without nail 161 5.5.2 Stability of nailed slope 163 5.5.2.1 Internal stability 164 5.5.2.2 External stability 165 CHAPTER CONSTRUCTION PROCEDURE OF NAILED SLOPE AND CONSTRUCTION EQUIPMENTS 6.1 6.2 Construction procedure of nailed structure 177 6.1.1 Excavation 177 6.1.2 Drilling Nail Holes 179 6.1.3 Nail Installation and Grouting 181 6.1.4 Construction of Temporary Shotcrete Facing 183 6.1.5 Construction of Subsequent Levels 185 6.1.6 Construction of Permanent Facing 186 Construction Materials 187 6.2.1 Steel Reinforcements 187 6.2.2 Grout Mix 187 6.2.3 Shotcrete 188 ... (www.williamsform.com/Ground_Anchors /Soil_ Nails _Soil_ Nailing /soil_ nail _soil_ nailing. html) 1 Fig 1.2 Cross-section of a grouted soil nailed wall (www.williamsform.com/Ground_Anchors /Soil_ Nails _Soil_ Nailing /soil_ nail _soil_ nailing. html) Fig... and disadvantage of soil nailing 1.4.1 Advantage of soil nailing 1.4.2 Disadvantage of soil nailing 1.5 Various issues affecting soil nailed slope 1.6 Construction procedure of nailed structure... nailing Some of the potential disadvantages of soil nail walls are listed below: • In case of soil nailing, the system requires some soil deformation to mobilize resistance Hence soil nailing is