槽溝挖掘過程中穩定性之數值分析

Numerical analyses of stability during panel excavation

陳啟煜(Chi-Yu Chen)

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.2007.00214

摘要

根據國內外不同案例的現地監測結果顯示，連續壁施工引致之地盤變位量，最大可達主體開挖所引起的總變位量30%~50%，可知連續壁構築過程對鄰房建物有一定的影響。然而影響連續壁構築過程造成土體位移量的因素甚多，這些影響的變數甚難控制，本研究使用有限元素法軟體PLAXIS 3D，針對連續壁施作過程進行土體解壓狀態與槽溝穩定性分析。首先藉由網格密度、實際施工步驟進行分析，確定最佳模擬方式後，再與相關監測結果進行驗證，以瞭解本方法的適用性與準確性。經由本研究可以發現，在槽溝施築階段的土體側向應力呈現接近或小於靜止土壓力狀況下的側向應力，是為主動狀態趨勢。而在混凝土澆置階段的側向應力則呈現大於或接近靜止土壓力狀況下的側向應力，稱此為土體的「恢復現象」。本研究再針對台北松山層淡二區土層及中和舊沖積層新二區進行連續壁施作過程影響因素分析，模擬成果與現地監測值有一致性的趨勢。連續壁槽溝開挖影響的參數包括：單元長度、單元寬度、單元深度、單元尺寸、穩定液與地下水位液壓差等。連續壁槽溝開挖最後過程是整體壁面最敏感的時刻，在本研究中依據土體主動破壞理論，配合槽溝壁面解壓之應力狀態，作為穩定分析之基礎，由土體解壓過程是否接近於主動破壞，定義其穩定指數；以穩定指數評估連續壁槽溝壁面穩定狀態可有效地觀測出連續壁槽溝開挖完成後，壁面穩定性隨深度變化之情形。

關鍵字

連續壁槽溝 ； 土體解壓 ； 穩定性 ； 數值分析

並列摘要

The job site monitoring results from various international and domestic cases have shown that the ground displacement due to diaphragm wall construction can be as much as 30-50% of the total displacement from excavation, indicating that the construction of diaphragm wall has certain degree of impact to neighboring buildings. However, there are so many variables in diaphragm wall construction that may have influence on the soil displacement, that it is tedious to control all these factors. In this study, an analysis was carried out on the decompression of soil and the stability of trench wall during the construction of diaphragm wall by introducing the finite element analysis software PLAXIS 3D. First, the best simulation method was determined by studying the grid density and actual construction procedures, and then the preliminary results were compared with related monitoring results for verification in order to determine the suitability and accuracy of the method. It was found in this study that the lateral stress of soil body during the excavation of diaphragm wall is close or less than that in static soil pressure, displaying an active tendency, while the lateral stress during concrete pouring is greater than or close to that in static soil pressure, and this is so-called “restoration” of soil body. Further in this study, an analysis was carried out on the influence factors during the diaphragm wall construction for the soils in Light 2 zone of Sung-Shan Layer in Taipei City and New 2 zone of old alluvial deposits in Chung-Ho. The simulation result showed consistency with job site monitoring records. The parameters that may influence the excavation of diaphragm wall trench include length, width and depth of a unit, slurry and pressure difference in groundwater. The final procedure of diaphragm wall excavation is when the overall surface of side wall is most sensitive. The active failure trends were found in this study based on the theory of active failure of soil body and the depth of excavation, and used as the basis of stability analysis in conjunction with the stress states from the decompression of trench walls. The stability index was then defined based on whether the decompression of soil body was close to active failure at any point. The use of stability index in the evaluation of stability of diaphragm wall trench surfaces in this study demonstrated a considerable achievement.

並列關鍵字

Stress path ； stability ； diaphragm wall trench ； numerical analysis

參考文獻

[5] 胡逸舟、秦中天與劉泉枝，「臺北盆地大地工程相關特性之探討」，地工技術，第54期，P5~14，1995。

[6] 陳厚銘與謝百鐘，「以現地試驗調查基隆河新生地黏土之工程性質」，地工技術，第54期，P55~66，1995。

[10] 黃立煌、張政展與林照順，「臺北盆地松山層黏性土側壓計試驗」，地工技術，第54期，P45~54，1995。

[16] 鄧子榆，「以有限元素法進行邊坡穩定分析之研究」， 碩士論文，中原大學土木工程研究所，2001。

[19] 廖庭蔚，「數值分析在連續壁施作過程上的研究」， 碩士論文，國立臺北科技大學土木與防災研究所，2006。