本文探討一以低滲透性土壤為回填土，而加勁材則使用加勁格網之多階加勁擋土邊坡，受降雨入滲作用後之破壞案例分析。此邊坡高為26公尺，共4階，而跟一般設計規範所要求的不同，此加勁邊坡之回填土屬於細粒料含量超過60%的砂質粉土質黏土(CL-ML)。此種土壤因滲透性較低，且其坡背之風化岩層為不穩定之狀態，故受降雨影響後孔隙水壓累積，其剪力強度亦會因土壤含水量增加而有明顯降低的現象。此加勁邊坡在2010-2012年間受颱風豪雨的影響產生持續性的變形。在2012年六月到十二月間，此牆的坡頂沉陷累積達到140公分，雖然後續相關單位已採取補強措施，在2013年八月因兩個颱風接踵而至，導致此加勁邊坡發生崩塌破壞。本研究進行一系列的土壤力學試驗，除了求取該回填土之土壤基本物理性質、土壤礦物成分與工程性質外，亦對其不飽和土壤水分特性參數進行求取，並使用有限元素法進行滲流與應力耦合分析加以釐清此加勁擋土牆的破壞機制。透過此案例分析，本文也詳細討論以低滲透性土壤為回填土之加勁擋土邊坡，受颱風降雨作用下，在設計與施工上的相關重要考量。

This paper presents a failure case investigation of a multi-tier geosynthetic-reinforced soil slope with marginal backfill subjects to rainfall infiltration. The considered slope is 26 m high, 4 tier geogrid-reinforced structure constructed for traffic demands in mountain area in Taichung, Taiwan. Contrary to the backfill recommendations in design guidelines, low permeability sandy silt (CL-ML) with over 60% of fines was used as backfill in the reinforced zone. The shear strength of this kind of soil would decrease according to the increasing pore water pressure triggered by the low permeability. This GRS structure first experienced excessive deformation after seasons of typhoon and heavy rainfall from 2010-2012, and the measured settlement at wall crest were 140 cm from June to December 2012. Although an immediate remediation had been conducted for the excessive deformation, the slope finally collapsed caused by two sequential typhoon events in August 2013. A series of soil mechanic laboratory test will be used in this study, including mineral components, physical and engineering properties of the soil. However, not only those properties mentioned above will be done, but also unsaturated one, such like pressure plate test to determine soil-water characteristic curve (SWCC). After soil laboratory tests have been done, a numerical finite element study using hydro-mechanical coupling analysis will be used to investigate the failure mechanisms of this GRS structure. According to the analysis, this study will propose design and construction implication for GRS structures with marginal backfill subject to heavy rainfall.

AASHTO. (2002). Standard specifications for highway bridges. American Association of State Highway and Transportation Officials, Sevententh Edition, Washington, D.C., with interms.
ASTM D421, (2007). “Standard Practice for Dry Preparation of Soil Samples for Particle-Size Analysis and Determination of Soil Constants.”Designation: D421-85
ASTM D4318, “Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils.”Designation: D4318-84
ASTM D4767, “Standard Test Method for Consolidated Undrained Triaxial Compression Test for Cohesive Soils.”Designation: D4767-11
ASTM D5084, “Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter.”Designation: D5084-16
ASTM D6836, “Standard Test Methods for Determination of the Soil Water Chararcteristic Curve for Desorption Using a Hanging Column, Pressure Extractor, Chilled Mirror Hygrometer, and/or Centrifuge.”Designation: D6836-02
ASTM D7928, “Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis.” Designation: D7928-16
ASTM D854, “Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer.” Designation: D854-14
Azam, S., Ito, M., & Khan, F. (2015). “Influence of cracks on soil water characteristic curve.” Bioinspired Photonics: Optical Structures and Systems Inspired by Nature, 217.
Bishop, A.W. (1959). “The principle of effective stress.” Teknisk ukeblad, 39, 859-863.  
Blake, J., Renaud, J.-P., Anderson, M., & Hencher, S. (2003). “Prediction of rainfall-induced transient water pressure head behind a retaining wall using a high-resolution finite element model.” Computers and Geotechnics, 30(6), 431-442.
Bolton, M. (1986). “The strength and dilatancy of sands.” Geotechnique, 36(1), 65-78.
Brand, E.W., Premchitt, J., & Phillipson, H. (1984). Relationship between rainfall and landslides in Hong Kong (Vol. 1): Proceeding of the Forth International Symposium in Landslides, Torontom Canada.
Brooks, R.H., & Corey, A.T. (1964). “Hydraulic properties of porous media and their relation to drainage design.” Trans. ASAE, 7(1), 26-0028.
Croney, D., & Coleman, J. (1948). “Soil thermodynamics applied to the movement of moisture in road foundations.” proc. 7th Int. Cong. Appl.Mech., Vol. 3, 163-177.
Duncan, J.M., & Chang, C.-Y. (1970). “Nonlinear analysis of stress and strain in soils.” Journal of Soil Mechanics & Foundations Div.
Elias, V., Christopher, B.R., and Berg, R., (2001). “Mechanincally stabilized earth walls and reinforced soil slopes design and construction guidelines.”Report No. FHWA-NHI-00-043, National Highway Institute, Federal Highway Administration, Washington, D.C.
Fredlund, D., Morgenstern, N.R., & Widger, R. (1978). “The shear strength of unsaturated soils.” Canadian geotechnical journal, 15(3), 313-321.
Fredlund, D.G. (2006). “Unsaturated soil mechanics in engineering practice.” Journal of Geotechnical and Geoenvironmental Engineering, 132(3), 286-321.
Fredlund, D.G., & Morgenstern, N.R. (1977). “Stress state variables for unsaturated soils.” Journal of Geotechnical and Geoenvironmental Engineering, 103(ASCE 12919).
Fredlund, D.G., & Rahardjo, H. (1993). Soil mechanics for unsaturated soils: John Wiley & Sons.
Fredlund, D.G., & Xing, A. (1994). “Equations for the soil-water characteristic curve.” Canadian geotechnical journal, 31(4), 521-532.
Fredlund, M.D., Fredlund, D.G., Houston, S.L., & Houston, W.B. (2003). Assessment of unsaturated soil properties for seepage modeling through tailings and mine wastes. Paper presented at the Proc., 10th Int. Conf. on Tailings and Mine Wastes.
Goodman, R.E. (1989). Introduction to Rock Mechanics (Second ed.): Wiley.
Ho, D.Y., & Fredlund, D.G. (1982). Increase in strength due to suction for two Hong Kong soils. Paper presented at the Proceedings of the Conference on Engineering and Construction in Tropical and Residual Soils,[Honolulu].
Iryo, T., & Rowe, R.K. (2005). “Infiltration into an embankment reinforced by nonwoven geotextiles.” Canadian geotechnical journal, 42(4), 1145-1159.
Kim, B.-S., Park, S.-W., Takeshita, Y., & Kato, S. (2016). “Effect of Suction Stress on Critical State of Compacted Silty Soils under Low Confining Pressure.” International Journal of Geomechanics, 16(6), D4016010.
Kondner, R.L., & Zelasjo, J.S. (1963). “Hyperbolic Stress-Strain Response: Cohesive Soils.” Journal of the Soil Mechanics and Foundations Division, 89(1), 115-144.
Krahn, J., & Fredlund, D.G. (1972). “On total, matric and osmotic suction.” Soil Science, 114(5), 339-348.
Lamb, T.W., & Whitman, R.V. (1979). Soil Mechanics, SI Version: Wiley, New York.
Lazzarte, C.A., Elias, V., Espinoza, R.D. and Sabatini, P.J. (2003), “Geotechnical Engineering Circle NO.7.”FHWA-IF-03-017, Federal Highway Administration.
Lu, N., Godt, J.W., & Wu, D.T. (2010). “A closed‐form equation for effective stress in unsaturated soil.” Water resources research, 46(5).
Lu, N., & Likos, W.J. (2004). Unsaturated soil mechanics.
Lu, N., & Likos, W.J. (2006). “Suction stress characteristic curve for unsaturated soil.” Journal of Geotechnical and Geoenvironmental Engineering, 132(2), 131-142.
Mein, R.G., & Larson, C.L. (1973). “Modeling infiltration during a steady rain.” Water resources research, 9(2), 384-394.
Mitchell, J.K., & Soga, K. (2005). Fundamentals of soil behavior.
Morse, M.S., Lu, N., Wayllace, A., Godt, J.W., & Take, W. (2014). “Experimental test of theory for the stability of partially saturated vertical cut slopes.” Journal of Geotechnical and Geoenvironmental Engineering, 140(9), 04014050.
NCMA. (2010). “Design manual for segmental retaining walls.” Herndon, Virginia, USA.
Oh, S., & Lu, N. (2015). “Slope stability analysis under unsaturated conditions: Case studies of rainfall-induced failure of cut slopes.” Engineering Geology, 184, 96-103.
Raisinghani, D., & Viswanadham, B. (2011). “Centrifuge model study on low permeable slope reinforced by hybrid geosynthetics.” Geotextiles and Geomembranes, 29(6), 567-580.
Schanz, T., Vermeer, P., & Bonnier, P. (1999). “The hardening soil model: formulation and verification.” Beyond 2000 in computational geotechnics, 281-296.
Terzaghi, K.V. (1936). The shearing resistance of saturated soils and the angle between the planes of shear. Paper presented at the Proceedings of the 1st international conference on soil mechanics and foundation engineering.
van Genuchten, M.T. (1980). “A closed-form equation for predicting the hydraulic conductivity of unsaturated soils.” Soil science society of America journal, 44(5), 892-898.
Vanapalli, S., Fredlund, D., Pufahl, D., & Clifton, A. (1996). “Model for the prediction of shear strength with respect to soil suction.” Canadian geotechnical journal, 33(3), 379-392.
Vanapalli, S.K., Fredlund, D.G., & Pufahl, D.E. (1999). “The influence of soil structure and stress history on the soil-water characteristics of a compacted till.” Geotechnique, 49(2), 143-159.
Yang, K.-H., Uzuoka, R., Lin, G.-L., & Nakai, Y. (2017). “Coupled hydro-mechanical analysis of two unstable unsaturated slopes subject to rainfall infiltration.” Engineering Geology, 216, 13-30.
Yoo, C., & Jung, H.-Y. (2006). “Case history of geosynthetic reinforced segmental retaining wall failure.” Journal of Geotechnical and Geoenvironmental Engineering, 132(12), 1538-1548.
中華民國大地工程技師公會. (2014). 103年度大里區掩埋場邊坡加勁擋土牆崩坍原因鑑定報告書.
李豪智. (2016). 「乾溼化路徑下基質吸力對不飽和夯實紅土應變相依土壤模數之影響.」, 國立台灣科技大學營建工程系碩士論文, 台北.
林俐玲及黃國鋒. (2011). “台灣中部崩塌地土壤水份滲透特性之研究.” 坡地防災學報, 10(1), 27-41.
拱祥生. (1999). 「降雨對不飽和土壤邊坡穩定性之影響研究.」, 國立臺灣科技大學碩士論文, 台北.
拱祥生. (2011). 「不飽和紅土基質吸力行為及其在工程上之應用.」, 國立臺灣科技大學博士論文, 台北.
范嘉程及馮道偉. (2003). “以有限元素法探討暴雨時邊坡之穩定分析.” 地工技術(95), 61-74.
陳宗顯. (2007). 「降雨引致地下水位變化之研究-以那菝, 六甲與東和地下水位站為例.」 成功大學水利及海洋工程學系學位論文, 台南.