台北捷運土城線延伸頂埔段CD271A標為三環三線中第三環的重要一段，頂埔車 站主體連續壁係於卵礫石層及砂岩層中施作，而台北捷運以往的車站主要位於松山 層，土層多以黏土層及砂土層的互層為主，較少遇到卵礫石層或卵礫石與砂岩層的混 合地盤，因此當連續壁於卵礫石層施工時將遭遇的問題有逸水、坍孔、漏漿及刃齒損 耗等。 廠商為因應上述現象，除於施工前已事先研擬了因應對策，如：針對連續壁單元 的分割型式、單元形狀進行研擬及挑選適當的逸水防止材等措施外，於施工過程中又 陸續對施作完成之連續壁進行檢討並提出許多的精進與求新的方式，如：連續壁單元 寬度、於鋼筋籠的開挖側外層鋼筋與帆布之間加設夾板，連續壁翼尾加設鋼板等來減 少漏漿，另廠商藉由各種抓掘壓力的測試，以挑選對機具抓戽刃齒損耗為最小的最佳 挖掘壓力，而這些問題及因應對策將於本文中一一說明，以作為未來施工廠商的一個參考。

Contract CD271A of the Tucheng extension to Dingpu is an important section of the Taipei MRT “Three Rings & Three Lines.” The geological profi le at the Dingpu Station site, a stratum of gravel underlain by sandstone, is very different from the Songshan Formation composed of alternate layers of clay and sand on which most underground stations of the Taipei MRT were built. Therefore, the problems faced in diaphragm wall construction at Dingpu Station may not be easily solved using experience accumulated in the past. The main issues encountered during diaphragm wall construction on gravel stratum include the drawdown of slurry, trench collapses, concrete leakage, and abrasion of dredge bits. Prior to construction, the above issues were studied and construction details were planned, such as the type of panel, pattern of steel cage, and type of anti-drawdown material. During construction, the work process was reviewed constantly and new remedial measures were proposed, such as revising the width of panels, placing a plywood board between the steel cage and the vinyl sheet, and adding a steel plate to reinforce the end-plate of the steel cage. In addition, the optimum pressure of the hydraulic bucket was obtained by various in-situ trials in order to minimize the abrasion of the dredge bits. These problems and the corresponding measures are described in this paper. The experience learned can be used as a reference for similar work in the future.