以Peck-Fujita經驗方法估算潛盾隧道施工所引致之地表沉陷

Abstract

本研究之第一部分提出一個結合Peck與Fujita二者研究之經驗方法，以評估單隧道潛盾施工時所引致之地表沉陷槽。並引用30個國外單隧道施工案例之觀測結果，驗證所建議方法之可行性。實測地表沉陷槽與估計之地表沉陷曲線之比較結果，證明此經驗方法可對不同潛盾機型、土層種類、隧道直徑與隧道深度，適切地估計出地表沉陷槽。並依據實際觀測結果探討各型潛盾機在不同土層內施工所引致地表沉陷與時間之關係。分析結果顯示，於非凝聚性土壤中之潛盾施工，由於砂土之排水迅速，約在潛盾通過一週後，地盤即可恢復穩定；而對於凝聚性土壤中之潛盾施工，開挖方式為密閉型之土壓平衡式潛盾機對開挖面土壤擾動較小，約在潛盾通過40天後，地盤可趨於穩定。而開放型潛盾機則由於經常採用壓氣工法維持開挖面穩定，地盤達到穩定的時間，必須視壓氣釋放之時機而定。 第二部分建議以疊加方法估算平行雙隧道道施工所引致之地表沉陷槽。並以27個國外之平行雙隧道案例之監測結果，驗證經驗方法之可行性。其結果顯示，若雙隧道之間隔夠遠，兩個隧道周圍土壤之塑性區域不到重疊，則所建議之疊加方法，可成功地評估雙隧道施工引致之總地表沉陷槽。並由監測與估計結果皆顯示，當兩隧道間隔較近時，雙隧道總地表沉陷槽呈現單一尖峰特性，若間隔較遠時，便可能出現雙尖峰沉陷槽。 第三部分介紹國立交通大學土木工程研究所計畫於臺北市捷運系統南港線254標潛盾施工段所佈置之蜱測陣列。除了對監測地盤反應之各項儀器加以說明外，並介紹監測陣列佈軒及資料收集計畫。

The first part of ths research proposes an empirical method with informations reported by Peck and Fujita, to estimate the surface settlement trough causd by shield tunnelling. Tunnelling observation data from 30 different cases have been used to justify the feasibility of the suggested method. The comparison between the measured ground settlement trough and the estiamted ground settlement curve proves that Peck-Fujita method can properly estimate the surface settlement troughs for various shield machine types, soil types, tunnel diameters, and tunnel depths. This research also reports the variation of surface settlement as a function of time, for tunnelling in different ground conditions with different shield machines. Field data indicaes that for shield tunnelling in cohesionless soil, ground surface becomes stable one week after the shield machine's passage. This is because the excess pore water pressure dissipates rapidly in cohesionless soils. For excavation with an EPB shield in cohesive soil, the ground stabilizes 40 days after the shield machine's passage. This is because the EPB shield does not disturb the ground too much. When using an open type shield machine, the compressed air method is generally adopted to keep the ground excavated stable. The time required to stabilize the ground is significantly influenced by the time when the compressed air is released. The second part of this study suggests a superposition method to estimate the ground settlement troughs due to parallel twin tunnel constructions. Field data from 27 cases of parallel twin tunnels are used to justify the feasibility of the proposed method. It has been found that if the distance between the two tunnels is far enough so that the plastic zones near the two tunnels are not overlapped, the suggested method could successfully estimate the surface sttlement caused by the two tunnels. Results from both methods indicate that if the distance between the tunnels is small, the total settlement trough reveals a single peak characteristic. However, if the clearance is large , a double peak settlement trough would appear. The third part of this paper introduces the instrumentation array deisgned by National Chial Tung University to Monitor the ground response of Nankang line 254 lot of Taipei MRT sytem. Not only instruments to monitor the ground response is introduced. but the data-collection plan is also discussed.