都會區捷運系統，由於路權取得困難，有許多隧道緊鄰建物基礎或穿越建物基礎而過。位於軟弱土層中的隧道，由於盾尾間隙閉合將引起應力釋放，因而造成隧道周圍地盤變位。此種地盤變位包含垂直方向及水平方向的變位，會造成位於沉陷槽內之鄰近建物基礎的損害。因此，為了使工程師能提出有效且經濟的建物保護施工計畫，必須先行探討此種土壤移動對基礎的影響程度。 本研究利用離心模型試驗，探討於砂土層中進行隧道掘進導致之地盤變位，對鄰近隧道的既存基樁之影響。本研究分別 (1) 探討於自由場狀態下，位於砂質地盤中之單隧道開挖所引致之地盤變位。(2)探討單隧道開挖引致之地盤變位對鄰近基樁的影響程度，主要在釐清位於不同深徑比的隧道開挖案例中，距隧道中心不同距離處，基樁之樁身彎矩分佈型態、軸向力分佈型態及樁頭變位，進而對基樁之荷重傳遞行為能有所了解。 試驗結果顯示，於砂質地盤中進行隧道施工時，土壤漏失量大於3.5%之後，隧道隨即劇烈地產生大量的土壤漏失，亦即砂質地盤中隧道的破壞產生於一瞬間。另必須注意在土壤漏失量約為3.5%之前，鄰近隧道的基樁樁身之彎矩和軸向力隨即快速增加。 Tunnels are driven nearby or underpass buildings as closely as possible due to the difficulty of land use in rapid transit system construction projects in urban areas. The stress relaxation due to the close of tail voids for tunnels in soft soils may cause the ground deformations around the tunnel. The ground deformations (including lateral and vertical soil movements) will damage nearby buildings and building protection measures must be properly taken during constructions. The load transfer mechanisms of the piles embedded in the movable soils are considerably complex and need to study in detail. A series of centrifuge model tests have been performed to assess tunnelling-induced ground deformations in sandy ground and their effects on adjacent pile foundations. Two topics have been investigated in this study. First of all, the free-field ground deformations induced by tunneling in sandy ground have been measured. Secondly, the load transfer mechanism (such as bending moment, axial force and pile head deformation) of the piles has been analyzed in the different conditions, including the cover-to-depth ratios, and the distance of the pile and the tunnel. When the measured ground loss induced by tunneling in sandy ground is greater than 3.5%, a large quantity ground loss will be caused violently. The result displays that the time of collapse in sandy tunnels will arise in the twinkling of an eye. In addition, when the ground loss is less than 3.5%, the bending moment and axial force of the nearby pile foundations have been occurred rapidly.
