邊坡穩定是地工重要的課題之一，而使用鑽掘樁穩定邊坡是可行之穩定工法之一。根據前人研究，將單排鑽掘樁安置於邊坡，兩相鄰之鑽掘樁中間會產生土壤拱效應，使得上邊坡土壤之下滑力傳遞至下邊坡時產生折減，進而降低趨動力。此折減效應可應用荷重傳遞因子來評估，因此邊坡之土拱效應以及荷重傳遞因子是值得深入研究的課題。本研究參考前人研究結果，使用PLAXIS 3D進一步分析地下水對以鑽掘樁穩定邊坡穩定性之影響。分析探討的項目包括水平應力分佈、水平位移、安全係數以及荷重傳遞因子。
綜觀本研究之水平應力分佈、水平位移分佈、安全係數以及荷重傳遞因子，PLAXIS 3D可以得到合理的分析結果。地下水上升對邊坡穩定性及荷重傳遞行為有影響。沒有地下水與地下水位較低(10m)尚未達到滑動面深度時之安全係數皆為1.44，而地下水位較高(21m)接近坡頂達到滑動面深度之安全係為1.16，有明顯下降的趨勢。在地下水上升的情形下，不論安全係數是否有明顯下降的趨勢，分析結果所得之位移量皆會較大。而有地下水情況下，荷重傳遞因子也是隨著安全係數上升而下降，其行為類似於前人之分析結果。有無地下水之鋸齒狀鑽掘樁排列分析結果皆顯示，中間鑽掘樁往上邊坡偏移在某個範圍之內(2D)安全係數會增加，但增量不大。但中間鑽掘樁往下邊坡偏移安全係數會有明顯下降趨勢。

Slope stability is an important topic of geotechnical engineering and using drilled shafts is one of the feasible methods to stabilize the slope. According to previous studies, when a row of drilled shafts are installed in the slope, soil arching will be developed between the drilled shafts, resulting in the reduction of the sliding force. This effect can be evaluated by the load transfer factor; therefore, soil arching and load transfer factor warrant further research. Based on previous results, this study use PLAXIS 3D to investigate the groundwater effect of the slope stabilized using drilled shafts. Analysis and discussion items include horizontal stress, horizontal displacements, safety factor and load transfer factor.
Overall examination of horizontal stress, horizontal displacement, factor of safety and load transfer factor of this study show that PLAXIS 3D can give reasonable analytical results. Rising groundwater will affect both the slope stability and the load transfer behavior. When there is no groundwater and the water table is low (10m) such that it does not reach the sliding surface, the factor of safety is the same as 1.44. When the water table is high (21m) and near the top of the slope safety factor significantly reduces to 1.16. When the groundwater is raised larger displacements are observed no matter whether there is significant change in safety factor or not. For cases with groundwater, the load transfer factors also decrease with increasing safety factor. Study of the zig-zag pile arrangement with and without groundwater show that safety factor may increase slightly if the middle pile is moved upslope of a limited distance (2D). However, if the middle pile is moved downward safety factor may decrease significantly.

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