現今都市發展快速，為了因應各種需求，建築物之結構規模逐漸增大，且期望可支撐較大的載重，則經常採用深基礎作為設計。由於樁基礎於軟弱黏土層中，近於地表處之土壤無法提供較大的水平支撐力，因此限制了樁基礎側向抵抗之能力。克服此項限制，以提升基礎之側向承載力之改善方式有兩種方式，第一種方式為提升基樁本身強度，第二種為增加樁周土壤支承力。 本研究嘗試以ABAQUS有限元素軟體進行一系列之數值模擬，並且使用水泥對樁周土壤進行地盤改良，增加土壤強度減少樁基礎之側向變形，加以探討此改良方式對於基樁之側向阻抗效果，期望可歸納出最佳的改良範圍，以供日後有關基樁側向阻抗改良設計之參考。 由分析結果得知，對於群樁樁周土壤進行地盤改良，改良深度大於四倍樁徑時，則地表處樁身位移減少量開始有趨緩現象，且改良效果亦有趨緩現象產生，因此可以得知改良深度為四倍樁徑時為較佳之改良深度。 The cities in the world developed very fast recently, the building scales were increased in order to satisfy various demands. The deep foundation is often used to support the heavy loading of the building. As the pile foundation was set in the soft clay layer, the soil beneath the ground surface cannot provide enough horizontal support and lateral resistance of the pile foundation will be restricted. Therefore, two kinds of methods can be used to improve the horizontal support of the foundation by increasing the strength of pile foundation or raising the soil resistance. The soil which was improved by mixing with cement around the pile foundation can increase the strength and reduce the lateral displacement of pile shaft. The treated soil can also provide lateral resistance for the pile group which bears lateral load. The lateral bearing behaviors of pile group in soft clay layer were analyzed by the finite element method. To perform the numerical analysis, FEM based software named ABAQUS was used in this research. The numerical results displayed that by using soil improvement with 4D of the treated depth (where D is the diameter of pile), the reduction of the lateral displacement of pile shaft at ground surface became gently. The treated effect was also presented slowly. Therefore, 4D of the treated depth was the better treated depth.