本研究為一個關於加勁擋土邊坡其邊緣回填土壤受降雨入滲導致破壞之案例研究。本案之邊坡為4階層，高26公尺之加勁擋土結構，因應台灣台中山區的交通需求而建造。回填土壤則與設計規範中相佐，為超過60％細粒的低塑性粉質黏土（CL）回填於加勁區。這可能是由於試圖減少開挖後原土壤之處理及運輸設計規範所建議之土壤至工地，所需之相關的成本和對環境的影響。回填土是來自風化泥岩和頁岩局部可用之殘餘土壤，當土壤因雨水滲入而變為較濕時，可發現土壤剪力強度明顯降低。在2010 - 2012年GRS邊坡因颱風和降雨季節後，首次出現過度變位。2012年6月至12月，坡頂沉陷量和水平變位，經量測為140 cm和80 cm。儘管對邊坡過度變位立即進行修復，但由於兩次連續的颱風事件，累積總雨量超過600 mm，加勁擋土邊坡終究於2013年8月發生破壞。本研究進行了一系列數值和物理調查，以驗證破壞的機制和導致破壞的原因。藉由歷史雨量資料、量測之剪力強度參數和現況地質及瞬時邊坡穩定性分析，以重建破壞事件。探討從這個案例中獲得之經驗。

The research presents a failure case study on a geosynthetic-reinforced soil wall with marginal backfill subject to rainfall infiltration. The considered wall is a 26 m high, 4 tier geogrid-reinforced structures constructed for traffic demands in mountain area in Taichung, Taiwan. Contrary to the backfill recommendations in design guidelines, low plasticity silty clay (CL) with over 60% of fines was used as backfill in the reinforced zone. This could have been as a result of attempting to reduce cost and environmental impact associated with transportation of recommended backfills to construction site and disposal of excavated in-situ soils. The backfill material is a locally available residual soil from weathered mudstone and shale and the soil shear strength are found can be significantly reduced when soil become wet. The GRS slope first experienced excessive deformation after seasons of typhoon and heavy rainfall from 2010-2012. The measured settlement and horizontal deflection at wall crest were 140 and 80 cm from June to December 2012. Although an immediate remediation had been conducted for the wall excessive deformation, the wall finally collapsed caused by two sequential typhoon events with total accumulated rainfall over 600 mm in August 2013. A series of numerical and physical investigation were performed to examine the failure mechanism and causes contributing to the failure. Using recorded rainfall, measured shear strength parameters and site geology, transient slope stability analyses were conducted to reconstruct the failure event. Lessons learned from this case history are discussed.

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