摘 要 國內外的開挖工程，大都採用連續壁作為擋土設施，隨著挖土作業的逐漸進行，圍苓及水平支撐逐層施作，以達到擋土的目的。但是如果進行大面積的開挖，則水平支撐的架設顯得無效率，而且挖土作業及後續的地下結構物的構築也不方便。因此工程界逐漸於較堅硬的土層中發展出雙排樁無支撐開挖工法。 本研究利用離心模型試驗，藉由模擬開挖過程，探討於砂土層中以自承式單排或雙排鋼軌樁擋土系統作為擋土設施時，不同的開挖與貫入深度比對擋土系統及鄰近地盤之影響。 研究結果顯示，砂土層中以自承式單排或雙排鋼軌樁擋土系統作為擋土設施時，開挖所引致之地表沉陷槽皆屬於三角槽型，影響範圍皆為鋼軌樁擋土壁壁後1.1倍樁長之遠，而壁後最大地表沉陷量可利用樁頂水平變位求得。然而在相同的開挖貫入比之下，使用雙排樁擋土系統之樁頂水平變位、壁後最大地表沉陷量與鋼軌樁樁身所產生之彎矩與剪力確實會比單排樁小；因此，使用雙排鋼軌樁將能大幅提升擋土系統之穩定性。研究結果亦指出，當開挖進行時，雙排樁之前後排樁會透過頂繫樑的束制而產生互拉的作用，進而影響彎矩與剪力的分佈；另外，將雙排鋼軌樁擋土系統視為一重力式擋土牆來進行穩定分析為一可行之方法。 ABSTRACT Diaphragm walls are frequently adopted as soil retaining systems for excavation. However, it is inefficient to excavate in a vast area by using horizontal struts and it is not convenient to do the underground construction work afterward. As a consequence, a double-wall retaining system was developed and used for excavation in a good ground condition. In this research, centrifuge modeling tests were adopted to simulate the process of excavation to investigate the effects upon adjacent area in various excavation depths and penetration depths by using a single-rail pile wall or a double-rail pile wall as retaining systems. The results show that the shape of the ground settlement induced by excavation in this study was a triangular one, when a single-rail pile wall or a double-rail pile wall was selected to be the retaining system in sandy layer. The extent of affected area was 1.1 times the pile length behind the wall. Furthermore, the maximum surface settlement can be calculated from the horizontal deformation of the top of pile. Nevertheless, in the same excavation/penetration depth ratio, the horizontal displacement on the top of pile and the maximum surface settlement induced by the single-rail pile wall system were larger than those induced by the double-rail pile wall retaining system. Moreover, the moment and shear force which occurred in the double-rail pile wall system were also less than those in the single-rail pile wall system. Therefore, it would be more stable if the double-rail piles were used as a retaining system. The research also indicated that the front piles and the rear piles would interact with each other during excavation due to the constraint of the cap beam and the distribution of moment and shear force is quite different. According to the research, it may be suitable to assess the stability of the double-rail pile wall system by treating it as a gravity type retaining wall.
