STABILITY ANALYSIS OF FILL SLOPE AT SMK SONG NO. 2 S PROJECT USING SLOPE/W NORASMAN BIN KADIR

Transcription

1 54 STABILITY ANALYSIS OF FILL SLOPE AT SMK SONG NO. 2 S PROJECT USING SLOPE/W NORASMAN BIN KADIR A report submitted in partial fulfillment of the requirements for the award of the degree of Master of Engineering (Civil Engineering) Faculty of Civil Engineering Universiti Teknologi Malaysia January 2015

2 iv To Allah S.W.T. who allow me. My dearest wife, children and all my family members; you are my love and inspiration.

3 v ACKNOWLEDGEMENT I wish to express my high appreciation to UTM and the lecturers, especially my supervisor, Associate Professor Dr Nazri Bin Ali for his guidance and motivation during the development of this masters project. My sincere thankful extends to my fellow postgraduate course mates for your cooperation. Lastly but not least, thanks to all who are not listed here for helping me in this masters project; I appreciate it.

4 vi ABSTRAK Kerja pemotongan dan penambakan tanah adalah scenario yang biasa. Oleh itu, analysis kestabilan cerun mesti dilakukan untuk memastikan cerun adalah selamat dan mengelak kejadian kegagalan cerun. Dalam kajian ini, aplikasi perisian daripada GEOSTUDIO 2007 (SLOPE/W) digunakan ke atas satu kes kegagalan cerun yang berlaku di kawasan pembinaan sekolah menengah di Song, Sarawak. Sebahagian kawasan cerun yang dibina dari kerja pemotongan dan penambakan telah gagal. Kegagalan cerun ini dimodelkan terlebih dahulu menggunakan applikasi SEEP/W dan kemudianya dengan SLOPE/W untuk menjana Faktor Keselamatan (FOS), didapati adalah Seterusnya, kerja pembaikan dicadangkan menggunakan sheet piles dan soil nails. Hasilnya, FOS didapati adalah dan masing-masing, Ini bermakna, cadangan menggunakan sheet piles adalah lebih baik.

5 vii ABSTRACT Cut and fill works around the slopes are common scenes. Hence, slope stability analysis must be carried out in order to assure the slope is safe and prevent the slope failure. In this study, software application approach by GEOSTUDIO 2007 (SLOPE/W) is used for the case study, an under-going secondary school project which is located at Song, Sarawak. A portion of the slope where is being constructed on a cut and fill area has failed. The failed slope is modelled first by using SEEP/W (as parent file) and then, by SLOPE/W, to generate the Factor of Safety (FOS), which is obtained at The proposed remedial works are subsequently determined by using sheet piles and soil nails. The obtained FOS is at and respectively. Therefore, the proposal using sheet piles is more acceptable.

6 viii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION ii DEDICATION iv ACKNOWLEDGEMENTS v ABSTRACT vi ABSTRAK vii TABLE OF CONTENTS viii LIST OF TABLES xi LIST OF FIGURES xii LIST OF ABBREVIATIONS xv LIST OF SYMBOLS xvi LIST OF APPENDICES xvii 1 INTRODUCTION Background of the Problem Statement of the Problem Objectives of the Study Scope of the Study Significance of the Study 3 2 LITERATURE REVIEW Introduction Types of Slope Natural Slope 4

7 ix Cut Slope Fill Slope Basic of Slope Failure Sliding Rock Fall and Toppling Spreading Fast Debris Flows Slope Failure Driving Force Factors of Slope Failure The Speed of Slope Failure Slope Stability Analysis Limit Equilibrium Method Introduction Method basic Slip Surface Shapes Limitations General Limit Equilibrium Method Ordinary or Fellenius Method Bishop s Simplified Method Janbu s Simplified Method Spencer Method Morgenstern-Price Method Janbu s Generalized Method Corps of Engineers Method Lowe-Karafiath Method Sarma Method SLOPE/W 40 3 RESEARCH METHODOLOGY Data Collection Material Propeties Numerical Modelling Geometry 44

8 x Region Rainfal Data Surcharge Load Tension Crack Analysis Slope s Model in SEEP/W Slope s Model in SLOPE/W Proposed Remedial Works 51 4 RESULTS AND DISCUSSION Analysis Results 45 5 CONCLUSION Conclusion Recommendation 59 REFERENCES 61 Appendices A J 63-77

9 xi LIST OF TABLES TABLE NO. TITLE PAGE 1 Equations of Statics Satisfied 15 2 Interslice Force Characteristics and Relationships 16 3 Material Properties for Soil 1 42 Material Properties for Soil 2 42

10 xii LIST OF FIGURES FIGURE NO. TITLE PAGE 1 a) Sliding Failure with Multiple Planes. b) 7 Translational Failure 2 Typical Rock Fall 7 3 Rock Toppling 8 4 Spreading 8 5 Debris flows 9 6 Effect of Gravitational Forces on a Mass 10 7 Increasing Slope Will Cause the Sliding of the 10 Material On It 8 Relative Failure Speed for Different Types of Slope 12 Failure 9 Slice Discretization and Slice Forces in a Sliding 14 Mass 10 Condition for a Simple Circular Slip Surface Situation for a Planar Slip Surface Situation for a Typical Composite Slip Surface Typical Situation for a Block Slip Surface A Deep Stability Analysis of a Shoring Wall Half-Sine Interslice Force Function A Factor of Safety versus Lambda (λ) Plot 24

11 xiii FIGURE NO. TITLE PAGE 17 Ordinary FOS computed by SLOPE/W Bishop s Simplified FOS Janbu s Simplified FOS Spencer Typical Slope Stability Situation Interslice Functions for the Spencer Method Results of M-P Analysis M-P FOS with Half-Sine Function Corps of Enginneers Assumption # Corps of Engineer #1 Interslice Function Corps of Enginneers Assumption # Corps of Engineer #2 Interslice Function L-K FOS L-K Interslice Function Data Collection Analysis Type in SEEP/W Analysis Type in SLOPE/W Geometry of Slope s Model Region for Slope s Model Material Properties in SEEP/W Material Properties in SEEP/W Material Properties in SLOPE/W Input of Unit Flux Input for Building s Load Tension Crack Line Slope Model in SEEP/W Slope Model in SLOPE/W Proposed of Sheet Piles and Location Proposed Sheet Piles and Properties Proposed of Soil Nails and Location Proposed Soil Nails and Properties 53

12 xiv FIGURE NO. TITLE PAGE 47 Model of Failed Slope (Pore Water Pressure Profile) Model of Failed Slope (FOS = 0.854) Proposal of using Sheet Piles (Optimum FOS = ) 50 Sheet Piles - Free Body Diagram and Force Polygon 57 (Slice 1) 51 Proposal of using Soil Nails (Optimum FOS = 1.040) : Soil Nails - Free Body Diagram and Force Polygon (Slice 1) 58

13 xv LIST OF ABBREVIATIONS LEM - Limit Equilibrium Method FOS - Factor of Safety M-P - Morgenstern- Price L-K - Lowe-Karafiath

14 xvi LIST OF SYMBOLS τf - resisting force or moment τm - driving force or moment X - interslice shear force, E - interslice normal force, λ - the percentage (in decimal form) of the function used c - effective cohesion Ø - effective angle of friction U - pore-water pressure N - slice base normal force W - slice weight D - line load β, R, x, - geometric parameters f, d, ω - geometric parameters α - inclination of slice base

15 xvii LIST OF APPENDICES APPENDIX TITLE PAGE A Site Plan 63 B Earthwork (Slope s Geometry) 64 C Site Photos 65 D Site Photos 66 E SI Position 67 F Borelog (BH1) 68 G Borelog (BH1) 69 H Borelog (BH1) 70 I Borelog (BH1) 71 J Borelog (BH1) 72 K Summary of Lab Test 73 L Material Properties: BS M Material Properties: PLAXIS Manual 75 N DID Manual 76 O Rainfall Data 77

16 1 CHAPTER 1 INTRODUCTION 1.1 Background of the Study Construction activities on hillside slopes have increased significantly in recent years due to the rapid development of buildings and infrastructure project. Cut and fill works around the slopes are common scenes. These constructed slopes are actually exposed to slope failures if they are not being proper designed and constructed or not well protected enough by weather event, such as heavy raining. As the result, these slope failures can cause losses of life and economic losses. Slope failure can occur due to many factors, but it is more likely to occur in certain season if they are triggered by weather event, that is raining. A heavy intensity of raining can trigger a process that lead to the slope failure by infiltration, seepage and an increase of pore water pressure. It is normally observed that for a soil, there will be an increase of moisture content and reduction of shear strength. As the result, it affects the stability of a soil mass and thus the factor of safety (FOS) for the slope. 1.2 Statement of the Problem

17 2 The case study of the slope failure is located at Song, Sarawak, the undergoing construction project of Cadangan Membina dan Menyiapkan Sekolah Menengah Kebangsaan Song No. 2, Di Atas Lot 1615, Blok 17, Katibas Land District, Song, Sarawak Untuk Kementerian Pelajaran Malaysia (18 BD). This school complex is being constructed on a cut and fill area, where is actually located at the centre of a valley area, flanked by hills on surroundings. A portion of slope at the project area has failed. It was observed that for a few days before the occurrence of the slope failure, Song area has been experiencing an intense rainfall. Therefore, it is important to study and doing the analysis of the case problem in order to determine the suitable action for the proposed remedial works. 1.3 Objectives of the Study Followings are the objectives proposed for this study: 1) To generate the slope model by using SLOPE/W. 2) To simulate the failure mechanism of the failed slope. 3) To propose the remedial works for the failed slope. 1.4 Scope of the Study This study covers the analysis of cut and fill slope failure at under-going construction project of Cadangan Membina dan Menyiapkan Sekolah Menengah Kebangsaan Song No. 2, Di Atas Lot 1615, Blok 17, Katibas Land District, Song, Sarawak Untuk Kementerian Pelajaran Malaysia (18 BD). The analysis is carried by a software application, GEOSTUDIO 2007 (SLOPE/W). The input data, such as soil properties are based on Soil Investigation (SI) s Report, sourced from the consultant of the project and rainfall data, collected from Drainage and Irrigation Department (DID), Sarawak.

18 3 1.5 Significance of the Study This study provides the understanding of the mechanism of the slope failure, specifically through the case study. Therefore, the subsequent remedial works can be proposed to resolve the slope problem by assuring the FOS and hence to build up the confidence level of the public.

19 61 REFERENCES 1. Fredlund, D.G. and Rahardjo, H. (1994). Hillside Slope Stability Assessment In Unsaturated Residual Soils. Proceedings of Seminar On Geotechnical Aspects of Hillside Developments, Kajang, Malaysia. 2. D.G. Fredlund.(2001). The relationship between Limit Equilibrium Slope Stability Methods, Department of Civil Engineering, University of Saskatchewan, Saskatoon, Saskatchewan, Canada pp Rahardjo, H., Lee, T. T., Leong, E. C. and Rezaur, R. B. (2003). Response of a Residual Soil Slope to Rainfall. Canadian Geotechnical Journal. 42: Krahn, John (2003). The Limits of Limit Equilibrium Analyses. NRC Research Press Website. 5. Krahn, John. Stability Modelling with SLOPE/W (GEOSTUDIO 2007). GEO- SLOPE/W International, Ltd., Calgary, Alberta, Canada. 6. Gue, S.S. & Cheah, S.W. (2008). Geotechnical Challenges in Slope Engineering of Infrastructures. International Conference on Infrastructure Development, Putrajaya Mariott Hotel, 7-9 May Gue, S.S.; Wong, S.Y. & Cheah, S.W. (2010). Geotechnical Engineering for Hillsite Development. National Geoscience Conference 2010, Grand Bluewave Hotel, Shah Alam, Selangor, June Slide (2010). 2D Limit Equilibrium Slope Stability for Soil and Rock Slopes. Slope Stability Verification Manual Part 2. Rocscience Inc. 9. Baba, K., Bahi, L., Ouadif, L. and Akhssas, A. (2012). Slope Stability Evaluations by Limit Equilibrium and Finite Element Methods Applied to a Railway in the Moroccan Rif. Open Journal of Civil Engineering, February 2012, Rickard, O.C. and Sitar, N. (2013). bslope: A Limit Equilibrium Slope Stability Analysis Code for ios. Geotechnical Engineering Report No. UCB/GT/ Krisna Prasad Aryal (2006). Slope Stability Evaluation by Limit Equilibrium and Finite Element Methods. Doctor Philosophy, Norwegian University of Science & Technology. 12. Jahidin, M.R. (2010). Slopes Stability Analysis of Critical Slope along North South Highway (Southern Region) Using Limit Equilibrium Method. Master Degree, University Technology Malaysia.

20 Shen, N.K. (2005). Reliability Analysis on the Stability of Slope. Master Degree, University Technology Malaysia. 14. Whitlow, Roy. Basic Soil Mechanics (Fourth Edition 2004). Pearson Education South Asia Pte. Ltd. 15. British Standards Institution (1981). BS 5930: Code of Practice for Site Investigations. London: British Standards Institution. 16. British Standards Institution (1881). BS 6031: Code of Practice for Earthworks. London: British Standards Institution. 17. British Standards Institution (1994). BS 8002: Code of Practice for Earth Retaining Structures. London: British Standards Institution. 18. Department of Irrigation and Drainage. DID Manual: Volume 6 Geotechnical Manual, Site Investigation and Engineering Survey. Kuala Lumpur, Malaysia. 19. Hydrological Year Book Volume 40. Department of Irrigation and Drainage (DID), Sarawak. 20. Construction Drawing. Civil and Structural Cadangan Membina dan Menyiapkan Sekolah Menengah Kebangsaan Song No. 2, Song, Sarawak. Perunding TRA.