蘆洲地區深開挖施工中壁體變形行為之案例分析

Deformation Behavior of Diaphragm Wall of a Deep Excavation Case in Luzhou Area

溫廷睿(Ting-Rui Wen)

指導教授 ： 陳正興

國立臺灣大學/工學院/土木工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.01894

摘要

近年來都會區深開挖工程的規模與深度均與日俱增，而在施工過程中，因開挖所引致的損鄰事件也時有所聞。有鑑於此，本研究以蘆洲地區一深開挖工程為案例，收集施工期間的監測資料，探討擋土壁體的變形行為。研究中探討三個階段的擋土壁體變形行為，分別為地盤改良時期、開挖期間與回水灌漿階段，分析壁內傾度管與支撐應變計的量測數據，討論在不同時期下壁體變形與支撐軸力的反應，並試著將歸納結果以量化的方式表現。
首先於地盤改良階段，壁體受灌漿影響而產生向外的擠壓變形，其最大變位量約發生於改良樁的頂部位置；並且在灌漿完成後的靜置時期內，變位具有回復的現象。
本研究案例於開挖期間採取順打工法進行（10撐11挖），並將每一階施工過程再細分為4個階段：開挖前的靜置時期(P1)、開挖期間(P2)、支撐架設期間(P3)與施加支撐預力階段(P4)，探討在不同階段壁體變形與支撐的反應行為。分析結果顯示，於P1期間壁體變形均有增加的趨勢但軸力無明顯變化；P2期間的變位則有顯著的增加，其最大變形量約在開挖面附近左右，且軸力有顯著增加的現象；而P3期間的壁體變形則隨靜置時間而變大；至於P4期間受施加預力影響，造成壁體局部向內變形，而上層支撐軸力均普遍減小。同時經由監測軸力反算牆後土壓的分佈顯示，反推結果均大於理論主動土壓力。
　　開挖時的壁面漏水事件導致壁體變形與軸力瞬間增大；隨後的搶救過程中，於開挖區內灌水可有效減緩持續的變形且能分擔支撐的受力，但擋土壁面外側的止水灌漿卻增加額外的擠壓變形，並使得支撐軸力急遽上升。由簡化分析結果得知，灌漿所傳遞至壁體的壓力，從開挖底面逐漸向上遞減，約為灌漿壓力的1/3~1/6。

關鍵字

開挖工程 ； 壁體變形 ； 支撐軸力 ； 土壓力

並列摘要

This study selected a deep excavation case in Luzhou area to investigate the deformation behavior of diaphragm wall during the whole process of construction. By using the data measured from inclinometers buried in the wall and strain gages installed on the strut, the history of load~deformation of diaphragm during various stages of construction can be thoroughly investigated.
During the period of ground improvement before the excavation, the wall experienced significant outward displacement by jet grouting. The maximum deformation occurred at the depth near the top of grouting area. After the grouting, the wall deformation would rebound gradually with time.
During the process of braced excavation, the total deformations of wall at each stage of excavation can be separated into four parts, resulted from the periods of standing-by(P1), excavating soils(P2), installing struts(P3) and preloading of struts(P4), respectively. At P1 stage, there is likely an increasing trend of wall movements and the strut loads remain unchanged. At P2 stage, the maximum displacement usually occurs below the excavation surface and the strut load is increased accordingly. At P3 stage, the wall deflection will increase continuously with time. Due to the effect of preload in P4 stage, the wall will move inwardly and the loads at upper struts will decrease simultaneously. The results of back analysis demonstrate that the estimated earth pressures deduced from the strut loads are larger than the theoretically predicted values.
The leakage of water from wall surface caused the wall deformation and strut load increased immediately. Then the action of water refilling slows down the wall deformation and provides lateral support simultaneously. However the actions of seal-off grouting will result the increase of wall deformation and strut load. By simplification analysis, the pressure on the wall due to grouting is estimated to be around 1/6 of the grouting pressure.

並列關鍵字

deep excavation ； wall deformation ； strut load ； earth pressure

參考文獻

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