Soil Nailing and Slope Stability in Residual Soil
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SOIL NAILING AND SLOPE STABILITY IN RESIDUAL SOIL BY : NIRAKU ROSMAWATI AHMAD MSC. SOIL MECHANICS 2004 Soil Nailing and Slope Stability in Residual Soil TABLE OF CONTENTS 1.0 INTRODUCTION 1.1 Objectives 1 1.2 Methodology 2 1.3 Topography and Climate ofMalaysia 3 1.4 Residual Distribution in Malaysia 5 2.0 RESIDUAL SOILS 2.1 Definition and formation ofresidual soils 11 2.2 Origin and distribution ofresidual soils 12 2.3 Weathering processes 14 2.3.1 Mechanical weathering 15 2.3.2 Chemical weathering 15 2.3.3 Biological weathering 16 2.4 Tropical Weathering 16 2.4.1 Duricrusts 17 2.4.2 Laterites 17 2.4.3 Saprolites 19 2.4.4 Colluvium 20 2.5 Residual Soil in Partly Saturated Condition 21 2.5.1 Expansive Clays 24 2.5.2 Collapsing Soils 25 2.5.3 Pore Water and Suction 25 3.0 METHODOLOGY (HA 68/94) 3.1 Design Principles 28 3.2 Highway Slope Design with Horizontal Reinforcement 32 3.3 Highway Slope Design with Inclined Reinforcement 38 4.0 A CASE STUDY - THE NORTH-SOUTH EXPRESSWAY 4.1 General Geological aspect ofNorth-South Expressway 47 Soil Nailing and Slope Stability in Residual Soil 4.2 Slope stability analysis 49 4.2.1 Design parameters 51 4.2.2 Slope geometry 52 4.2.3 Design assumptions 54 5.0 RESULTS AND DISCUSSION 5.1 Tmax effect by varying a 55 5.2 Tmax for ru = 0 56 5.3 Design suitability ofthe nailed structure 57 5.4 Surcharge effect 65 5.5 Effect offlooding and suction on the critical Tmax value 66 6.0 RECOMMENDATIONS AND CONCLUSIONS 68 APPENDICES 71 REFERENCES 78 List of Tables Table 1.1 Proposed classification ofresidual rock mass weathering profile in Peninsular Malaysia 10 Table 3.1 Algebraic definitions 37 Table 3.2 Optimum vertical layer depths 43 Table 4.1 Packaging ofthe North-south Expressway and New Klang Valley Expressway 46 Table 5.1 Result (1) 55 Table 5.2a Result (2) Analysis 1 56 Table 5.2b Result (2) Analysis 2 56 Table 5.3.1a Result (3i) Analysis A 57 Table 5.3.1b Result (3i) Analysis B 58 Table 5.3.2a Result (3ii) Analysis A 58 Table 5.3.3a Result (3ii) Analysis A 59 Table 5.3:4a Result (3ii) Analysis A 59 Table 5.3.5a Result (3ii) Analysis A 60 Table 5.3.2b Result (3ii) Analysis B 60 Soil Nailing and Slope Stability in Residual Soil Table5.3.3b Result(3ii) Analysis B 61 Table 5.3.4b Result(3ii) Analysis B 61 Table5.3.5b Result(3ii) Analysis B 62 Table 5.3.6b Result(3ii) Analysis B 62 Table 5.3.7b Result (3ii) Analysis B 63 List of Figures Figure 1.1 Physiography of Peninsular Malaysia 4 Figure 1.2 The geology ofMalaysia 6 Figure 1.3 Typical weathering profile of aresidual soil 8 Figure 2.1 World distribution of theprincipal types ofresidual soil 13 Figure 2.2 Present distribution of weathering types 14 Figure 2.3 Typical saprolite weathering profiles 18 Figure 2.4 Schematic form of theprogression from residual soil through saprolite to laterite 20 Figure 2.5 The four phases of soil 21 Figure 2.6 The global distribution of the arid areas 22 Figure 2.7 Porous saprolite soil from basalt near Londrina, Brazil 23 Figure 2.8 Typical soil profile of expansive clay 24 Figure 2.9 Profile showing pore water pressure above andbelow Phreatic surface 26 Figure 2.10 Shear strength ofMadrid Gray clay at various suction levels 27 Figure 2.11 Shear strength versus matrix suction for Madrid Gray Clay 27. Figure 3.1 Geometry of two-part wedge mechanism 29 Figure 3.2 Forces acting onwedge 31 Figure 3.3 General concepts ofdesign method forhorizontal reinforcement 33 Figure 3.4 Definition oftwo-part wedge geometry 36 Figure 3.5 Types of cutting 40 Figure 3.6 General concepts ofdesign method for inclined reinforcement 41 Figure 4.1 Route and location of theNorth-South and New Klang Valley Expressways 45 Figure 4.2 The variation ofgeology along the North-South Expressway 48 Figure 4.3 Soil profile at Package 10A and 10B 50 Figure 4.4 The existing design layout 51 Soil Nailing and Slope Stability in Residual Soil Figure 4.5 Slope geometry for design purpose 52 Notation c' Effective stress cohesion dhoie Hole diameter h Depth of overburden directly above pointin question H Height of slope Ki Cohesion force acting on base ofwedge 1 K2 Cohesion force acting on base ofwedge 2 Lb Width ofreinforcement zone at base Le Pull out strength Lei Pull out strength for i,h layer ofreinforcement Lt Width ofreinforcement zone at top mechanism (kN/m) N Total number oflayers of reinforcement, not including basal layer N'i Normal effective force on base ofwedge 1 N' 12 Normal effective force on inter-wedge boundary N'2 Normal effective force on base ofwedge 2 Pdes The design value for the reinforcement strength permetre width of slope q Surcharge (kN/m2) Qi Total surcharge force on wedge 1 Q2 Total surcharge forceon wedge2 R' 1 Tangential effectiveforce on base of wedge 1 R'12 Tangential effective force on inter-wedge boundary R'2 Tangential effective force on baseof wedge 2 ru Pore pressure parameter (=u/yh) Sh Horizontal spacing Sv Vertical spacing Ti Sum ofreinforcement forces acting on wedge 1 T12 Inter-wedge reinforcement force T2 Sum ofreinforcement forces acting on wedge 2 Tmax Total reinforcement force for most critical two-part wedge mechanism (kN/m) Tmaxe Total reinforcement force inclined at angle 8 for most critical two-part wedge Soil Nailing and Slope Stability in Residual Soil T0 Refersto any two-part wedge mechanism requiring exactlyzero total restraining force T0s T0 mechanism with 92=-8 T0b T0 mechanism with 92=0 Ui Porewater force acting on base ofwedge 1 U12 Porewater force acting on inter-wedge boundary U2 Porewater force acting on base ofwedge 2 Wi Weight ofwedge 1 W2 Weight ofwedge 2 X x coordinate oftwo-part wedge node Y y coordinate oftwo-part wedge node Zj Depth tolayer ith layer ofreinforcement below crest ofslope 0i Base angle ofwedge 1 02 Base angle ofwedge 2 (=tan"' Y/X) 012 Angle ofinter-wedge boundary y Unit weight ofsoil (kN/m3) yw Unite weight ofwater (kN/ni3) Xs Base sliding factor Xp Pull-out factor 8 Angle ofinclined reinforcement t, Inclined reinforcement factor a Interface sliding factor a'n Average radial effective stress acting on bar o\ Horizontal effective stress cr'v Vertical effective stress o\ Lateral effective stress parallel to slope <£' Effective angle offriction </>' 1 0'desacting on base ofwedge 1 </>'2 </>'des acting on base ofwedge 2 0'12 </>' des acting on inter-wedgeboundary deS subscript denoting value for design purposes Soil Nailing and Slope Stability in ResidualSoil ACKNOWLEDGEMENTS Every beginning has its ending. At last, this project has been completed successfully. I feel happy and grateful to my Lord for He has given me the chance ofa lifetime tofurther my study in Imperial College, London. Without His blessing, everything seems impossible. In the making of this MSc Dissertation, I am indebted to many individuals for the contributions; be it directly or in directly. My very special thanks go to my supervisor, Dr. Standing for his guidance, commentary and patience throughout the making of this dissertation. To all my lecturers and colleagues in Imperial College, thank you isjust not enough. To my sponsor, University Teknologi Petronas, Malaysia - without your sponsorship, I will not be here. To my close friends - 'buddyship forever'. To my housemates; Nadiah, Hareyani and Hazrin - we have finally made it! My sincerity and love also go to my beloved mom and sisters for the unconditional love and undivided support to me throughout my life. To my late father and grandmother, I have always felt your presence and spirit in me. Soil Nailinv ami ,S/ntv Stability in Residual Soil CHAPTER 1 INTRODUCTION As a developing third world country, Malaysia is now going towards a rapid growth of cities, industries and commerce which required innumerable building systems. Thus, a lot of Mega projects to improve the living standard such as highways, high rise structures, embankments, dams and others have been in demand for the past 20 years. These building systems required a better understanding of the soil behaviour and the problems in construction because the soil has a very complexengineeringmaterial. This knowledge has led to the importance of knowing the soil distributions and their general engineering properties. In this chapter, the residual soil distribution of Malaysia particularly of West Malaysia is outlined andthe general engineering properties arebriefly described. 1.1 OBJECTIVES (i) Thisresearch is carried outto study and investigate the engineering behaviour and characteristics oftropical residual soils from Malaysia, (ii) To understand and outline the residual soil distribution and their general engineering properties, (iii) To analysethe internal stability of a soil nailing designby defining the critical Tmax mechanism from a spread sheet based on HA 68/94. Soil Nailine nwi S/olv Stability in Rtsirlunl Snil (iv) To check and compare the design ofthe reinforcement from the existing design layout, (v) To make a parametric and comparison study ofthe influence of suction inslope stability analysis. 1.2 METHODOLOGY The slope stability analysis is carried out by using the method given in advice note HA 68/94; the design manual for the reinforcement of highway slopes by reinforced soil and soil nailing techniques. Residual soil parameters for the study are mainly based on the data collected from the North-South Interurban Expressway and New Klang Valley Expressway located from Rawang - Tanjung Malim.