深開挖基地三維幾何配置於連續壁壁體變位之影響

The Effect of Three Dimensional Configurations on the Diaphragm Wall Displacements Due to Deep Excavation

張智博(Chih-Po Chang)

指導教授 ： 葛宇甯

國立臺灣大學/工學院/土木工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201600809

摘要

連續壁常見於深開挖工程之擋土系統，用以抵抗側向土壓力並防止開挖工址周圍產生過大的地表沉陷量造成損鄰。目前實務中，連續壁設計方法多建立於平面應變條件之上；然而此條件適於較淺且較廣的開挖工程，即開挖長度(L)與開挖深度(He)比值高於6者。因空間有限，臺灣現今於市區及近郊的深開挖工程多呈小且深之設計，已不符平面應變條件之假設；倘若不思三向度效應，將導致擋土系統過度設計，所耗成本甚鉅。
為發展考量三向度效應之連續壁設計方法，此研究採用有限元素分析軟體Plaxis模擬於砂土中開挖引致的連續壁壁體變形行為，分析三向度幾何因子，如壁體厚度、平均垂直與水平支撐間距、開挖基地之長與寬等，以及外力因子，基地內外最大水頭差，對於連續壁壁體最大變形量所造成的影響。
根據上述之模擬結果，歸納出可考量三向度效應的新系統勁度。因本研究著眼於砂土中開挖的連續壁壁體變形行為，故採用地層主要由砂性土壤組成之案例驗證所提出之系統勁度。
本研究提出之系統勁度於高勁度擋土系統之預測較為準確。

關鍵字

砂土 ； 深開挖 ； 三向度效應

並列摘要

Diaphragm walls are often used to resist lateral earth pressure and prevent excess ground settlement and wall movements during excavations. There are several practical methods for diaphragm wall design, based on the assumption of plane strain condition. This assumption is valid for shallow and wide excavations, with L/He value greater than 6 (L: length of diaphragm wall, He: depth of excavation). Due to limited available space in urban area, lots of excavations are small but deep in Taiwan. Without considering the three dimensional effects, it leads to an over conservative design for the diaphragm wall.
To develop an economical method for diaphragm wall design with consideration of three dimensional effect, the finite element software “Plaxis” was used to examine the maximum wall deflection in various combinations of thickness of wall, average vertical and horizontal spacing of struts, length and width of excavation, and maximum ground water head difference.
From the simulation results, the new system stiffness was proposed. As the current study focuses on the excavations in sand, case histories excavated mainly in the sandy layer were selected to verify the applicability of the proposed system stiffness. It was concluded that the proposed system stiffness can quantify the wall stiffness more precisely with consideration of the three dimensional effects, especially in the condition of high system stiffness.

並列關鍵字

sand ； excavation ； three dimensional effect

參考文獻

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