台北縣府大樓背拉深開挖工程案例之探討

A Case Study of Tie Back Deep Excavation Work of Taipei County Hall

林泰煌(Tai-Huang Lin)

《地工技術》 97期 (2003/09) Pp. 15-24

https://doi.org/10.30140/SG.200309.0002

摘要

台北縣政府新建大樓之地下室開挖工程在考量工期和施工之條件下，施工單位提出背拉地錨替代方案，以取代原設計之內撐島區開挖工法。本工程之開挖深度20m，採用7階背拉地錨，因受限基地環境之限制，本工程採用長度較短之錐形擴座地錨，共計1920支，其中大部份地錨是鋼腱可回收式地錨。本文將先就本工程之背拉地錨設計和配置作介紹，並探討地下水位變化對地錨預力變化之影響。此外，本文也說明地錨施工過程中所進行之各項地錨試驗，包括適用性試驗、特別驗收試驗和群錨試驗等。由於本工程之背拉地錨施工是在高地下水位下之粉質砂土層中進行，施工中曾有湧水、湧砂的情形發生，經以水玻璃藥液高壓噴射樁處理後，湧砂現象即獲控制。在回收地錨部份，因有些地錨之鋼絞線在施工過程中，絞在一起，致使無法順利回收，但回收率仍高達98.6%。本案之設計與施工在國內為首次嘗試，所以在施工過程中偶有問題發生，但在整體上，背拉地錨系統仍可發揮功能，控制連續壁之側向位移量，使本工程能如期如質地完成結構體興建，並獲頒「89年度公共工程品質金質獎」。

關鍵字

擴座可回收式地錨 ； 群錨試驗 ； 湧水 ； 湧砂

並列摘要

After carefully considering about schedule and working condition of Taipei county hall's basement excavation, the contractor proposed a tie back system alternative to replace the original design of island strutting system. For the limited surrounding area of the building, a tie back system with 7-level shorten length cone shape earth anchors was adopted for this project's 20m deep basement excavation. A total of 1920 anchors was used most of them are extractable earth anchors. This paper introduces the design and arrangement of the tie back system and describes the impact to the pre-stress force of tie back system owing to the variation of ground water level and also introduces suitability test, special acceptance test and group test during earth anchor construction. During construction of tie back system under high water level silty sand condition, water inflow and sand inflow problems have been controlled by using c.c.p. method. There are some problems caused by steel strand installation, a few earth anchors could not be smoothly extracted. However, the extracted rate of anchors still reached 98.6%. This is the unique case of cone shape earth anchors used in deep excavation project being designed and constructed in Taiwan. Although there are some problems during construction, this tie back system basically is effective and side deflection of diaphram wall still under control. As a result, foundation and structure works of Taipei county hall was completed on time with good quality. This project also won the Golden Quality Award of Best Infrastructure sponsored by the Public Construction Commission in 2000.

並列關鍵字

cone shape extractable earth anchor ； group test of anchor ； water inflow ； sand inflow