不飽和土壤理論是過去幾十年許多研究之焦點。眾多重要不飽和土壤之剪力強度模式也在這時期被提出。根據過去不飽和土壤之研究，許多相關之試驗程序和設備也都相當完備。本研究專注在Fredlund (1978) 提出之延伸莫爾庫倫理論和Lu and William (2006) 提出之吸應力理論。兩者在傳統上皆需施作不飽和三軸試驗以求得不飽和剪力強度參數。但此試驗操作困難、費時且需特殊儀器，因此在工程應用上不易被視為務實之試驗方法。
一套分別採用上述兩種不飽和土壤強度理論的方法因此在本研究中被建立。本研究利用傳統土壤力學試驗以及特定之假設與計算方法，進而求得視凝聚力與吸應力。本研究以砂崙仔崩塌地採集之崩積土壤進行一系列試驗並對此評估不同方法取得之結果的差異。
試驗及評估結果顯示崩積土壤之視凝聚力與吸應力與先前研究的趨勢相當一致且合理。雖然為了進一步驗證結果之準確性與工程上的實用性，此方法與不飽和三軸之結果的比較仍有其必要性，但本研究所提供之方法已展示它未來的利用潛力。

Unsaturated soil theories have been the focus of many studies in the past few decades. Numerous models regarding the shear strength of unsaturated soils have been proposed during the development process. Based on the former studies, the corresponding test approaches and their apparatus have also been well developed. In specific, the extended Mohr-Coulomb model proposed by Fredlund (1978) and the suction stress model proposed by Lu and William (2006) are the focus of this study. Both theories require the unsaturated shear strength parameters obtained by conducting the unsaturated strength test. However, it is often difficult to conduct, time consuming and requires special apparatus. Thus, it may be not considered as the practical experiment in the engineering field.
A new method that adopts two of the unsaturated theories mentioned above is therefore established in this study to estimate the apparent cohesion of unsaturated soils. It mainly utilizes the conventional tests with some assumptions and specified calculation processes. This new method is applied to the colluvial soil collected from Shaluntz to investigate the unsaturated shear strength properties and to evaluate the difference of the results obtained from various methods.
The apparent cohesions and the suction stresses calculated for the studied colluvial soil show reasonable trends and are consistent with the studies of former researches. Although the comparison to the unsaturated triaxial test result is still essential in order to verify the accuracy and the feasibility for the engineering application, the potential of this proposed method is still promising in the future.

Chen, S. Y. (2009). Particle Size Distribution Condition on The Unsaturated Soil Suction of Colluvium Soils. (Master degree), National Taiwan University of Science and Technology, Taipei, Taiwan. (in Chinese)
Fredlund, D. G., & Morgenstern, N. R. (1977). Stress State Variables for Unsaturated Soils. ASCE Journal of the Geotechnical Engineering Division, 103, 447–464.
Fredlund, D. G., Morgenstern, N. R., & Widger, R. A. (1978). The Shear Strength of Unsaturated Soils. Canadian Geotechnical Journal, 15, 313–321.
Fredlund, D. G., & Rahardjo, H. (1993). Soil Mechanics for Unsaturated Soils. New York: Wiley Publications.
Fredlund, D. G., & Xing, A. (1994). Equations for The Soil-Water Characteristic Curve. Canadian Geotechnical Journal, 31.
French, C. A. I. (1992). Alluviated Fen-Edge Prehistoric Landscapes in Cambridgeshire, England. Archeologia del Paesaggio, 709–731.
Gan, J. K.-M. (1986). Direct Shear Strength Testing of Unsaturated Soils. (Master degree), University of Saskatchewan, Saskatoon, SK.
Gan, J. K.-M., & Fredlund, D. G. (1996). Shear Strength Characteristics of Two Saprolitic Soils. Canadian Geotechnical Journal, 33(4), 595–606.
Hillel, D. (1980). Applications to Soil Physics. New York: Academic Press.
Ho, D. Y. F., & Fredlund, D. G. (1982). Increase in Shear Strength due to Soil Suction for Two Hong Kong Soils. Paper presented at the Geotechnical Conference on Engineering and Construction in Tropical and Residual Soils, Honolulu, Hawaii.
Hsiao, S. T. (2011). Influence of Shallow Hydrologic Characteristics on Slope Stability of Unsaturated Colluvium Soil. (Master degree), National Taiwan University of Science and Technology, Taipei, Taiwan. (in Chinese)
Hung, H. M. (2010). Stability Analysis of Unsaturated Colluvium Soil Slope Using Soil-Water Characteristic Curve. (Master degree), National Taiwan University of Science and Technology, Taipei, Taiwan. (in Chinese)
Jeng, C. J., Chu, B. L., & Lin, T. (2007). In-Situ Monitoring and Undisturbed-Sample Laboratory Test for The Unsaturated Colluvium Slope in The Huafan University Paper presented at the The 12th conference on current researches in geotechnical engineering in Taiwan.
Jhang, J. L. (2012). Characteristics of Matric Suction and Shear Strength of Shallow Unsaturated Colluvium Soils. (Master degree), National Taiwan University of Science and Technology, Taipei, Taiwan. (in Chinese)
Krahn, J., & Fredlund, D. G. (1972). On Total, Matric and Osmotic Suction. Soil Science, 114(5), 339–348.
Liu, T. L. (2012). Evaluation of Various Design Methods for Predicting Reinforcement Loads within Two Different Facing Stiffness Geosynthetic-Reinforced Soil Structures. (Master degree), National Taiwan University of Science and Technology, Taipei, Taiwan. (in Chinese)
Lu, N., Godt, J. W., & Wu, D. T. (2010). A closed‐form Equation for Effective Stress in Unsaturated Soil. WATER RESOURCES RESEARCH, 46.
Lu, N., & Griffiths, D. V. (2004). Profiles of Steady-State Suction Stress in Unsaturated Soils. Journal of Geotechnical and Geoenvironmental Engineering, 130(10).
Lu, N., & Likos, W. J. (2006). Suction Stress Characteristic Curve for Unsaturated Soil. Journal of Geotechnical and Geoenvironmental Engineering, 132(2).
Tien, K. C. (2008). Development and Applications of A Triaxial Testing Device for Unsaturated Soils Using Fiber Optic Sensors. (Master degree), National Chiao Tung University, Hsinchu, Taipei. (in Chinese)
Van Genuchten, M. T., Leij, F. J., & Yates, S. R. (1980). A Closed‐Form Equation for Predicting Thehydraulic Conductivity of Unsaturated Soils. Soil Science Society of America Journal, 44, 892–898.
Vanapalli, S. K., Fredlund, D. G., & Pufahl, D. E. (1999). The Influence of Soil Structure and Stress History on The Soil Water Characteristic of A Compacted Fill. Geotechnique, 49(2), 143-159.
Vanapalli, S. K., Fredlund, D. G., Pufahl, D. E., & Clifton, A. W. (1996). Model for The Prediction of Shear Strength with Respect to Soil Suction. Canadian Geotechnical Journal, 33(3), 379-392.
Wulfsohn., D., Adams, B. A., & Fredlund, D. G. (1996). Application of Unsaturated Soil Mechanics for Agricultural Conditions. Canadian Agricultural Engineering, 38(3), 173–181.