On September 29th 2008, a landslide happened in Maokong area around pile T16 of Gondola, Taipei. The landslide looks like mudflow on the bottom of the slope. To confirm the landslide type, it is needed a study in rheology, for mud is a viscous liquid that flow under its own mass by gravity force.
The soil starts to behave like a fluid when the water content of the soil passes over liquid limit state. To conduct the liquid limit state there are two classic ways of tests, Atterberg limit test and fall cone test. In this research there is another way to get liquid limit besides the classic tests, by observing shear strength of the soil in the solid phase and in liquid phase. To observe the solid phase of the soil, direct shear test is a way to test the soil at low water content. To define the shear strength of the soil in liquid phase it is needed to conduct a study in rheology in a form of a test called moving ball test. The rheological parameters of the soil will be the best way to get the shear strength at very high water content.
The liquid limit values that resulted from Atterberg limit tests, fall cone test and direct shear and moving ball test are close. The similarity of liquid limit values leads to the similarity of soil classifications. The Atterberg limit and fall cone test point ML or OL, CL-M, CL as the soil types of on the slope, and moving ball test and direct shear test as well conclude that the soil type should be ML or OL and CL-ML.
Analyzing the shear strength of those tests above, Atterberg limit test can not provide any information, while fall cone give a certain value of 1.6 kPa for all cohesive soil types, and moving ball test with direct shear test gives various values of shear strength of the soil. These values are 0.5 to 0.99 kPa at range 25 to 33% of liquid limit. These values are agreeable with Karlsson’s (1977) range of 0.5 – 4.0 kPa for all cohesive soils.
Confirming the factor of safety along the slope by numerical analysis, it is revealed that along the slope of Maokong after 24 hours rain only several places are unsecure. After 48 hours and 72 hours of rain, all places along the slope have factor of safety less than 1. In general meaning, after the rain the landslide that occurs is truly mudflow.

1. A.A Balkema. (1996). Landslide. Proceedings of The 8th International Conference and Field Trip on Landslide, Granada, Spain, A.A. Balkema: Rotterdam, The Netherlands, pp. 47 – 51.
2. Al-Khafaji, A. W. and Andersland, O. B. (1992). Geotechnical Engineering and Soil Testing, Saunders College Pub., Orlando, USA.
3. ASCE (1961). Research Conference on Shear Strength of Cohesive Soils. American Society of Civil Engineers, pp. 113 – 115.
4. ASTM (2000). Standard Test Methods for Liquid Limit, Plastic Limit and Plasticity Index of Soils. Std. ASTM D4318-Engl 2000, ASTM: US.
5. Bowles, J.E. (1979). Physical and Geotechnical Properties of Soils. McGraw-Hill Book Company: USA.
6. Bowles, J.E. (1988). Foundation Analysis and Design, 4th edition, McGraw-Hill: New York.
7. Bowles, J.E. (1992). Engineering Properties of Soils and their Measurement. McGraw-Hill Science: US.
8. Broms, B.B. and Wong, K.S. (1991). Landslides. Foundation Engineering Handbook, 2nd ed. Chapman & Hall: New York, pp. 411 – 446.
9. Brunsden, D. and Prior, D.B. (1984). Slope instability, John Wiley & Sons Ltd., UK.
10. Bruus, H. (2007). Theoritical Microfluidics. Oxford University Press.
11. Casagrande, A. (1958). Notes on The Design of The Liquid Limit Device, Geotechnique Vol. 8 No. 2, pp. 84-91.
12. Cengel, Y.A. and Cimbala, J.M. (2006). Fluid Mechanics. Fundamental and Applications. McGraw-Hill Company, Inc.: New York.
13. Chen, C.L. (1988). Generalized Viscoplastic Modeling of Debris Flow, Journal of Hydraulic Engineering vol. 114, issue 3, pp. 237-258.
14. Das, B.R. (1994). Principle of Geotechnical Engineering, 3rd ed., PWS Publishing Company, Boston, US.
15. Day, R.W. (2005). Foundation Engineering Handbook: Design and Construction with 2006 International Building Code. McGraw-Hill: New York, pp. 10.1 – 10.59.
16. Day, R. W. (1999). Slope Failures in Tertiary Expansive OC Clays, Journal of Geotechnical and Geoenviromental Engineering vol. 125, issue 5, pp. 427-428.
17. Gupta, V. and Gupta, S.K. (1984). Fluid Mechanics and Its Applications. Willey Eastern Limited: New Delhi.
18. HRB (1958). Landslides and Engineering Practice. Highway Research Board, Special Report 29, USA, pp. 48 – 68.
19. Houlsby, G..T. (1982). Theoritical Analysis of The Fall Cone Test. Geotechnique vol. 32, no. 2, pp. 111 – 118.
20. Head, K.H. (1986). Manual of soil laboratory testing, vol. 2. Willey and Sons: New York.
21. IUPAC. (1997). Bingham Flow, International Union of Pure and Applied Chemistry, Compendium of Chemical Terminology 2nd edition.
22. Kolmayer, P., Fernandes, R. and Chavant, C. (2004). Numerical implementation of a new rheological law for argillites, Applied Clay Science Vol. 26, Issue 1-4 SPEC. ISS., pp. 499 – 510.
23. Lambe, T.W. and Whitman, R.V. (1969). Soil Mechanics, 1st edition, Wiley: New York, US.
24. Lee, I.K., White, W., Ingles, O.G.. (1983). Geotechnical Engineering. Pitman Publishing Inc.: Massachusetts, US.
25. Lee, S.H.H., Du, Y., Chen, C.C. (2009). Effect of Feldspar Content on the Rheological Parameters of Mud Flow. The 13th Conference on Current Researches in Geotechnical Engineering in Taiwan.
26. Lee, S.H.H, Widjaja, B., Yao, J.H., Du, Y. (2008). A Proposed Method Determining Liquid Limit Based on Shear Strength. PIT XII HATTI: Bandung, Indonesia, pp. III-1 – III-5.
27. Lim, B.H. (2009). The Study of Relation Between Two Feldspar Kaolin of Rheological Parameters for Mudflow, Master Thesis, National Taiwan University of Science and Technology, Taiwan.
28. Liu, Cheng and Evett, Jack B. (2003). Soil Properties Testing, Measurement, and Evaluation, 5th edition, Pearson Education, Inc., New Jersey, USA.
29. Maidment, D.R. (1993). Handbook of Hydrology. McGraw-Hill, Inc.: US, pp. 5.32 – 5.35.
30. McBride, R.A. (1993). Soil Consistency Limits. Soil Sampling and Methods of Analysis, M.R. Carter, ed., Canadian Society of Soil Science Chapter 49, Lewis Publisher.
31. Mitchell, J.K. (1976). Fundamentals of Soil Behavior. John Wiley & Sons, Inc.: Canada.
32. Murray, H.H. (1991). Overview – Clay Mineral Applications. Applied Clay Science vol. 5, Elsevier Science Publishers B. V.: Amsterdam, pp. 379 – 395.
33. Norman, L.E.J. (1959). The One-Point Method of Determining The Value of The Liquid Limit of a Soil. Geotechnique vol. IX, pp. 1 – 8.
34. O’Brien, J.S. and Julien, P.Y. (2000). The Importance of mudflow routing, Proceeding of the 2nd International Conference on Debris Flow Hazard Mitigation, Taipei, Taiwan, pp. 677 – 686.
35. Schlichting, H. (1979). Very Slow Motion. Boundary-layer Theory. 7th ed. Chapter VI. McGraw-Hill Book Company: New York.
36. Sharma, B. and Bora, P. K. (2003). Plastic Limit, Liquid Limit and Undrained Shear Strength of Soil-reappraisal, Journal of Geotechnical and Geoenvironmental Engineering vol. 129 no. 8, pp. 774-777.
37. Taipei Investigation Team. (2008). Taipei City Wan Xan Area, Cheng Ci University Neighborhood after Typhoon Jangmi Impact and Soil-Rock Failure Report, Taipei Professional Civil Engineers Association, Taipei Professional Geotechnical Engineers Association, Taipei Professional Conservation of Water and Soil Engineers Association, and Taipei Professional Structure Engineers Association, Taipei, Taiwan.
38. USDA-NRCS. (2004). Correlations between Soil Plasticity and Strength Parameters, Advanced Engineering Geology & Geotechnics, GE441, USDA-NRCS, US.
39. Whitlow, R. (1995). Basic Soil Mechanics. 3rd ed. Addison Wesley Longman Ltd.: England.
40. Whyte, I.L. (1982). Soil Plasticity and Strength-a New Approach Using Extrusion. Ground Engineering vol. 15, no. 1, pp. 1-2.
41. Worth, C.P. and Wood, D.M. (1978). The Correlation of Index Properties with Some Basic Engineering Properties of Soils. Canadian Geotechnical Journal vol. 15, no. 2, pp. 137 – 145.
42. Vyalov, S. S. (1986). Rheological Fundamentals of Soil Mechanics, Elsevier Science Publisher B.V., the Netherlands.
43. Yang, T. (2008). Pile T16 Maokong Repairing after Slope Failure Project, Chang Shuo Engineering Consultants Ltd., The New Technical Adviser Yang Co., Ltd. and Technical Advisor亚柏Co., Ltd.
44. Yao, C.H. (2007). The Study of Basic Rheological Parameters for the Mudflow, Master Thesis, National Taiwan University of Science and Technology, Taiwan.
45. Rock Destruction. (2005). Anomalous fluids. Notion of rheology (website: http://antirock.ru/?Physical%0D%0Aproperties_of_dispersed_systems:Anomalous%0D%0Afluids.%A0_Notion_of_rheology, accessed on June 11th 2009).
46. Hubber Company. Rheology Technical Buletin. Kelco Oil Field Group (website:http://www.kofg.com/Technical%20Bulletins/E.%20Rheology/5.%20KOFG RheologyEnglish.pdf, accessed on Jan 2nd 2009).
47. X-Ray Diffraction Analysis (website: http://www.plasma-biotal.com/xraydif1.html, accessed on Jan 12th 2009).
48. Wikimedia Foundation (2009). Bingham Plastic. Wikimedia Foundation, Inc (website: http://en.wikipedia.org/wiki/Bingham_plastic, accessed on June 1st 2009).
49. Wikimedia Foundation (2009). Reynolds Number. Wikimedia Foundation, Inc (website: http://en.wikipedia.org/wiki/Reynolds_number, accessed on June 11th 2009).