目前工程界於較堅硬的土層中發展出以無支撐雙排鋼軌樁擋土系統做為擋土設施之開挖工法，但對於影響其穩定性之因素、及開挖後對周遭地盤之影響卻未有深入之研究。 本研究利用離心模型試驗，分別探討單排樁樁間距、雙排樁前後排樁間距、雙排樁排間距以及砂土相對密度對自承式鋼軌樁擋土系統穩定性的影響，以及對鄰近地盤和對建物的衝擊。 研究結果顯示，以自承式鋼軌樁擋土系統做為擋土設施時，頂繫梁之施作有一定的必要性，而土壤相對密度之增加及樁間距縮短有助於減少擋土系統之水平變位及整體沉陷量。於雙排鋼軌樁擋土系統中，加大前排樁間距對擋土系統之穩定性有較大的不良影響，而增大排間距會減少擋土系統之變位，有助於擋土系統之穩定。開挖工程進行時，原地表面處樁身軸力會隨著已開挖深度增加而增加。另外，研究中發現僅有擋土系統之鋼軌樁排數會影響最大壁體水平位移與牆後最大地表沉陷量的關係。 Recently the unbraced double-row rail pile retaining system has been developed and used in the good field ground condition. However, there are only a few follow-up researches which study the factors that affect the stability of retaining system, deformation of adjacent ground buildings. In this research, by using the unbraced rail piles retaining system, two series of centrifuge modeling tests are used to study how these five factors, including the piles spacing in the single-row system, the spacing of the front and rear row piles in the double-row system, the distance between the rows in the double-row system, and the relative density of the sand affect the adjacent areas and buildings. The results show the necessity of constructing a tie beam on top of the pile head. Increasing the density of the sand and smaller spacing between the piles in the same row reduce the horizontal deformation and the settlement of the whole retaining system. In the double-row rail piles system, the spacing between the piles in the front row influences the stability of the retaining system more obviously than that in the rear row. Also, increasing distance between the front and rear row in the double-row system reduce the deformation and improve the stability of the retaining system. In the process of the excavation, with the increasing of excavation depth, the axial force of the piles near ground surface also increases. Moreover, the research demonstrates that only the numbers of the row in the retaining system affect the relation between the maximum horizontal displacement of the wall and the maximum surface settlement behind the wall.