影響扶壁及地中壁行為施工特性之研究

Study on Construction Details That Affecting the Behavior of Buttress and Cross Walls

盧怡志(Yi-Chih Lu)

指導教授 ： 陳水龍

國立臺北科技大學/工程學院/土木與防災研究所/碩士(2007年)

https://doi.org/10.6841/NTUT.2007.00224

摘要

扶壁及地中壁於近年已逐漸取代地質改良，廣泛應用於台灣都會區之深開挖工程。扶壁及地中壁之功能與地質改良相同，皆可用於提高軟弱地層之開挖穩定性、減少壁體變位量及降低損鄰之可能性。扶壁及地中壁採用與連續壁相同之方法施作，幾乎沒有壁體強度及完整性不足之現象發生，因此近年來之設計遂逐漸改採扶壁及地中壁為深開挖工程之輔助工法。
扶壁及地中壁之功能有以下四種：一、有效抑制連續壁體側向變位量。二、避免基礎差異沈陷量。三、解決結構體抗浮力不足。四、減少連續壁配筋量。就設計理論而言，扶壁及地中壁之行為類似地質改良，其功效經適當之轉換可考慮為土壤強度及地盤反力係數之提高。另槽溝穩定性為扶壁及地中壁施工成效重要影響因素。因此本文探討連續壁之掘削工法，及掘削機器選擇，說明如何進行單元分割，以使扶壁及地中壁與主體連續壁連結處之混凝土緊密相接。
扶壁及地中壁與主體連續壁之T型界面須緊密相接，但往往因忽略施工特性或不了解設計理念而無法達成，導致扶壁及地中壁之功效大打折扣。扶壁及地中壁之規劃須考慮現場施工之可行性，並不能完全依照設計者之主觀認知進行。本文由施工實務角度切入，討論如何處理扶壁及地中壁與主體連續壁之交界面，並依據施工基本條件與施工作業研究，探討扶壁最佳長度與最佳配置間距。文末並以軟弱黏土之地質深開挖監測案例，說明T型界面處理良窳、及扶壁配置長度、配置間距，對壁體變位之影響。

關鍵字

地中壁 ； 扶壁 ； 連續壁 ； T型界面 ； 扶壁長度 ； 扶壁間距 ； 壁體變位量

並列摘要

In recent years, buttress wall and cross wall have replaced grouting. It’s widely used in deep excavation projects in Taiwan metropolitan areas. Functions of the buttress and cross walls are the same as grouting. Both can be used to increase the stability of excavation in soft ground, to reduce diaphragm wall displacement and to minimize damage to adjacent buildings. Buttress and cross walls are constructed the same way as diaphragm wall, so they rarely encounter integrity and strength problems. Due to the above considerations, deep excavation design has adopted buttress and cross wall instead of grouting in recent years.
There are 4 functions of buttress and cross walls： 1. To effectively limit displacement of diaphragm wall. 2. To prevent foundation settlement. 3. To provide uplift resistance. 4. To reduce the amount of reinforcement required in the diaphragm wall. Theoretically, behavior of buttress and cross wall are similar to grouting. They can be used to increase the subgrade resistance of soil.
Stability of trench is a critical issue in construction of buttress and cross wall. Factors including trenching method, excavation machine selection, panel layout, etc., are also important to make tight contact between main diaphragm wall and buttress / cross walls.
Buttress and cross wall need to be tightly connected to the main diaphragm wall at the interface. However, in many cases tight connection can not be achieved either because designing concept is not fully understood or the construction details are not fully carried out. As a result, the effect of buttress and cross wall has not been fully achieved. Designing of buttress and cross wall needs to consider the site conditions, sometimes the design can not be carried out. This article discuss how to resolve difficulties when constructing the interface between buttress and cross wall from a practical point of view. Cross wall’s optimal length and optimal spacing are also addressed.
Finally, case histories in soft ground are provided to illustrate the importance of tight connection between buttress / cross wall and main diaphragm wall. The effects of buttress / cross wall length and spacing on diaphragm wall displacement are addressed.

並列關鍵字

buttress ； cross wall ； T section interface ； buttress length ； buttress spacing ； diaphragm wall displacement

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