樁基礎對結構物安全有其重要性且台灣地區多地震及颱風，因此設計基樁時，側向承載能力之評估為不可忽略之重要項目。在地震或其他作用力影響之下，樁體可能產生側向的位移及因彎曲力矩和剪力引起樁體的內應力。因此側向荷重之分析方式應包含側向位移及樁身彎矩。
本研究為探討地中橫樑對基樁側向阻抗之改良成效，利用模型樁承受側向荷重之試驗，觀察比較置放地中橫樑前後，疏鬆砂土中長樁承受側向荷載時樁體之側向位移與樁身彎矩行為。並進一步改變地中橫樑之長度及置放深度等相關參數，探討其樁頭位移量與樁身彎矩。
由實驗結果得知，當模型樁承受之荷重為73.6N，地中橫樑長度為9倍模型樁樁徑，置放深度為1倍樁徑時，其樁頭側向位移之改良成效為48%；而地中橫樑長度為15倍模型樁樁徑時，置放深度為1倍樁徑時，彎矩減少約32%。因此，在接近地表的土層中置放地中橫樑，可提供相當之水平阻抗，有效減少樁身之側向位移。

Pile foundation is important for safety of structures. These structures may support the lateral load of earthquake, typhoon and some other natural disasters. The pile may induce lateral displacement and generate internal stresses due to bending moment and shear stresses. Therefore, the analysis of pile behaviors should include lateral displacement and bending moment.
This study investigated the treated effect of underground crossbeam set in the vicinity of pile head. Using model pile bearing lateral load to observe and compare the both reactions of before and after installing underground crossbeam. Those reactions, pile lateral displacement and bending moment are caused by the lateral load on long model pile in loose sand. Then this study changes the length and setting depth of the underground crossbeam to investigate the best design of improving effect.
The experiential result shows that the improving effects of pile-head lateral displacement is obvious. Applying a load of 73.6N, the length of underground crossbeam is 9 times of model pile diameter, and the underground depth is 1 model pile diameter. The maximum bending moment decreases 32% while the length of underground crossbeam is 15 times of model pile diameter. In sum, installing underground crossbeam in the surface of the sand can provide suitable horizontal resistance, and then decrease the lateral displacement of the pile, and to show apparent improving effects.

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