ABSTRACT
In recent years, there has been increased land development and construction in unsaturated soil slopes in Northern Taiwan due to economic growth and urbanization (Lin et al., 2016). Consequently, slope stability problems have received increased attention. Since most soils occur in unsaturated state in nature, it is prudent to incorporate the contribution of apparent cohesion in slope stability analysis which is attributable to the presence of matric suction in the unsaturated layer of the soil. Consequently, a parametric study is conducted on c-Ф’ soils taking into consideration the apparent cohesion in the unsaturated layer by dividing the substrata into different layers and conferring to each layer a particular cohesion value. A parallel set of analyses is carried out by directly inputting unsaturated soil parameters, ψ_aev, Ф^b in the RS2 program. The two approaches use the strength reduction technique. According to the findings of this study, the first approach named ‘apparent cohesion method’ yields consistent, reliable and conservative results in comparison with the second approach, ‘the unsaturated effect method.’ Thus, it is a viable alternative slope stability analysis method.
ABSTRACT
In recent years, there has been increased land development and construction in unsaturated soil slopes in Northern Taiwan due to economic growth and urbanization (Lin et al., 2016). Consequently, slope stability problems have received increased attention. Since most soils occur in unsaturated state in nature, it is prudent to incorporate the contribution of apparent cohesion in slope stability analysis which is attributable to the presence of matric suction in the unsaturated layer of the soil. Consequently, a parametric study is conducted on c-Ф’ soils taking into consideration the apparent cohesion in the unsaturated layer by dividing the substrata into different layers and conferring to each layer a particular cohesion value. A parallel set of analyses is carried out by directly inputting unsaturated soil parameters, ψ_aev, Ф^b in the RS2 program. The two approaches use the strength reduction technique. According to the findings of this study, the first approach named ‘apparent cohesion method’ yields consistent, reliable and conservative results in comparison with the second approach, ‘the unsaturated effect method.’ Thus, it is a viable alternative slope stability analysis method.
TABLE OF CONTENTSACKNOWLEDGEMENTS iABSTRACT iiCHAPTER 1. INTRODUCTION 11.1 Background 11.2 Research Objectives 21.3 Thesis Structure 2CHAPTER 2. LITERATURE REVIEW 32.1 Major Causes of Slope Failure 32.1.1 Infiltration of Precipitation 32.1.2 Presence of Clay Minerals 32.1.3 Cyclic Loading 42.1.4 Weathering 42.1.5 Excavation or Cutting of a Slope 42.2 Types of Slope Movement at Failure 52.3 Role of Soil Suction in Unsaturated Soil 62.3.1 Estimating Matric Suction using SWCC 72.3.2 Suction Profiles in Unsaturated Soil 92.3.3 Capillary Zone in Unsaturated Soil 102.3.4 Ground Surface Flux Boundary Conditions 122.4 Apparent Cohesion in Unsaturated Soils 142.4.1 Shear Strength in Unsaturated Soils 142.4.2 Case study of Hong Kong cut slopes 222.5 c-φ soils 232.5.1 Silts 232.5.2 Clays 242.6 Cohesionless Soils 24CHAPTER 3. METHODOLOGY 273.1 Finite Element Method (FEM) 273.2 Phase2 RocScience Software 283.2.1 Functionality of RS2 283.2.2 Material Model & Input Parameters 353.3 Analysis Methods 443.3.1 Apparent Cohesion Method 443.3.2 Unsaturated Effect Method 463.4 Summary of RS2 Slope Analysis Procedure 47CHAPTER 4. RESULTS & DISCUSSION 484.1 Mesh Size Selection 484.2 Stability charts for c-Ф’ unsaturated soil slopes 504.2.1 Application of Stability Charts for this study 504.2.2 Standard Procedure for use of Stability Charts 504.3 Changes in Slope Height, H & Slope Angle, β 714.4 Changes in Cohesion, c’ & Friction Angle, Ф’ 714.5 Changes in Air-entry values, ψaev 714.6 Changes in Unsaturated Zone Depth 724.7 Comparison between Apparent cohesion & Unsaturated effect methods 734.7.1 Difference in FOS values 734.7.2 Reliability of the apparent cohesion method 744.8 Slope Failure Mechanism 774.8.1 Material Properties 784.8.2 Slope Geometry Properties 814.8.3 Comparison of critical failure surfaces for apparent cohesion and unsaturated effect method 86CHAPTER 5. CONCLUSION & FUTURE STUDIES 895.1 Conclusion 895.2 Future Study 89
REFERENCES
1. Bjerrum, L. (1967). 'Progressive failure in slopes in overconsolidated plastic clays and clay-shale', Terzaghi Lecture, Soil Mech. Found. Eng. ASCE, 93: 3-49.
2. Blyth, F.G.R, and de Freitas. (1974). 'A Geology for Engineers' (London).
3. BoR. 1998. "Earth Manual." In, edited by U.S Department of Interior, 348. Denver, Colorado: U.S Government Printing Office.
4. Bowles, J.E. (1997). 'Foundation Analysis & Design' (McGraw-Hill Book Co: Singapore).
5. Buzzi, O, S Fityus, and D Sheng. (2009). 'Unsaturated Soils, Two Volume Set: Experimental Studies in Unsaturated Soils and Expansive Soils (Vol.1) & Theoretical and Numerical Advances in Unsaturated Soil Mechanics' (CRC Press: London).
6. Cheng, Y. M., T. Lansivaara, and W. B. Wei. (2007). 'Two-dimensional slope stability analysis by limit equilibrium and strength reduction methods', Computers and Geotechnics, 34: 137-50.
7. Ching, R. K. H, J. Sweeney, and D.G. Fredlund. 1984. "Increase in factor of safety due to soil suction for two Hong Kong slopes." In International Symposium on Landslides, 617-23. Toronto, ON.
8. Chowdhury, R, P Flentje, and G Bhattacharya. (2010). 'Geotechnical Slope Analysis' (Taylor & Francis Group: Great Britain).
9. Duncan, J. Michael, G. Stephen Wright, and Brandon. L. Thomas. (2014). 'Soil Strength and Slope Stability' (John Wiley & Sons, Inc.: Canada).
10. Eid, T. Hisham. (2014). 'Stability charts for uniform slopes in soils with nonlinear failure envelopes', Engineering Geology, 168: 38-45.
11. Fredlund, D.G. (2000). 'The 1999 R.M. Hardy Lecture: The implementation of unsaturated soil mechaics into geotechnical engneering', Can. Geotech. J., 37: 963-86.
12. Fredlund, D.G. , and Anqing Xing. (1994). 'Equations for the soil-water characteristic curve', Can. Geotech. J., 31: 521 - 32.
13. Fredlund, D.G., N.R. Morgensten, and R.A. Widger. (1978). 'The shear strength of unsaturated soils', Can. Geotech. J., 15: 313-21.
14. Fredlund, D.G., H Rahardjo, and M.D. Fredlund. (2012). 'Unsaturated Soil Mechanics in Engineering Practice' (John Wley & Sons, Inc.: Canada).
15. Fredlund, D.G., H Rahardjo, and J.K.M Gan. 1987. "Non-Linrearity of Strength Envelope for Unsaturated Soils." In Proceedings of the 6th International Conference on Expansive Soils, 49-54. New Delhi, India.
16. Gan, J.K.M. (1986). 'Direct shear strength testing of unsaturated soils', University of Saskatchewan, Saskatoon, Sask.
17. Gan, Julian, D.G. Fredlund, and H. Rahardjo. (1988). 'Determination of the shear strength parameters of an unsaturated soil using the direct shear test', Can. Geotech. J., 25: 500-10.
18. Gao, Y. F., Fei Zhang, G. Lei, and D. Y. Li. (2013). 'An extended limit analysis of three-dimensional slope stability'.
19. Griffiths, D. V., and P. A. Lane. (1999). 'Slope stability analysis by finite elements', Geotechnique, 49: 387-403.
20. Krahn, J. 2007. "Limit equilibrium, strength summation and strength reduction methods for assessing slope stability." In Canada-U.S. Rock Mechanics Symposium. Vancouver, BC, Canada.
21. Krahn, J., and D.G. Fredlund. (1972). 'On Total, Matric and Osomtic Suction', Soil Science, 114: 339-48.
22. Leong, Eng-Choon, and Hossam Abuel-Naga. (2018). 'Contribution of osmotic suction to shear strength of unsaturated high plasticity silty soil', Geomechanics for Energy and the Environment, 15: 65-73.
23. Lin, H.D., Y-S Jiang, C-C Wang, and H-Y Chen. (2016). "Assessment of Apparent Cohesion of Unsaturated Lateritic Soil Using an Unconfined Compression Test." In Advances in Civil, Environmental and Materials Research (ACEM16). Jeju Island, Korea.
24. Liu, Qiang, Noriyuki Yasuf*cku, Jiali Miao, and Jiaguo Ren. (2014). 'An approach for quick estimation of maximum height of capillary rise', Soils and Foundations, 54: 1241-45.
25. Liu, Yucheng. (2013). 'Effects of Mesh Density on Finite Element Analysis'.
26. Logan, L. Daryl. (2011). 'A First Course in Finite Element Method' (CL Engineering: USA).
27. Look, G. Burt. (2014). 'Handbook of Geotechnical Investigation and Design Tables' (CRC Press: U.K).
28. Lopez-Acosta, N.M., and J.A Mendoza-Promotor. (2016). 'Study of Unsaturated Soils by Coupled Numerical Analyses of Water Flow-Slope Stability', Groundwater - Contaminant and Resource Management.
29. Lu, Ning , and William. J. Likos. (2004). 'Unsaturated Soil Mechanics' (John Wiley & Sons, Inc.: New Jersey).
30. Miller, J. Deborah, and D. John Nelson. (2006). 'Osmotic Suction in Unsaturated Soil Mechanics', ASCE Unsaturated Soils.
31. Oloo, Y. Simon, D.G. Fredlund, and J.K.M Gan. (1997). 'Bearing Capacity of Unpaved Roads', Can. Geotech. J., 34: 398-407.
32. Phillips, F. M., and M. C. Castro.(2003). '5.15 - Groundwater Dating and Residence-time Measurements.' in Heinrich D. Holland and Karl K. Turekian (eds.), Treatise on Geochemistry (Pergamon: Oxford).
33. Potts, M. David, and L. Zdravkovic. (1999). 'Finite element anaysis in geotechnical engineering' (Thomas Telford: London).
34. Rao, Sudhakar M. (1996). 'Role of apparent cohesion in the stability of Dominician allophane soil slopes', Engineering Geology, 43: 265-79.
35. Suriya, P, R Jayalakshmi, and C EswarSudharsan. (2015). 'Factors Influencing the Soil Water Characteristic Curve and its Parameters ', International Journal of Engineering Research and General Science, 3: 741-48.
36. Sweeney, D.J. (1982). 'Some in situ soil suction measurements in Hong Kong's residual soil slopes', Proceedings of the 7th Southeast Asian Geotechnical Conference, 1: 91-106.
37. Taylor, D. W. (1937). 'Stability of earth slopes', J. Boston Soc. Civ. Eng, 24: 197-246.
38. Taylor, D.W. (1948). 'Fundamentals of Soil Mechanics' (Wiley: New York).
39. Tschuchnigg, F., H. F. Schweiger, and S. W. Sloan. (2015). 'Slope stability analysis by means of finite element limit analysis and finite element strength reduction techniques. Part I: Numerical studies considering non-associated plasticity', Computers and Geotechnics, 70: 169-77.
40. Zhang, Lulu, Delwyn G. Fredlund, Murray Fredlund, and G. Ward Wilson. (2014). 'Modeling the unsaturated soil zone in slope stability analysis'.
41. Zhang, Lulu., Jinhui Li, Xu Li, and Zhu Hong. (2016). 'Rainfall - Induced Soil Slope Failure' (CRC Press, Taylor & Francis Group: Shanghai).
全文公開日期 2024/08/22 (校內網路)全文公開日期 2029/08/22 (校外網路)
全文公開日期 2034/08/22 (國家圖書館：臺灣博碩士論文系統)
