以經驗方法評估潛盾隧道施工引致之地表沉陷

Abstract

依據國內外151個潛盾隧道施工之監測結果，本研究提出一簡單的經驗方法，評估單一潛盾隧道施工引致之地表沉陷。Peck（1969）建議隧道施工引致之地表沉陷槽可以常態分佈曲線加以模擬，其主要參數為沉陷槽寬度參數i及地表最大沉陷量Smax，其中Smax可由現地測得之地盤漏失量Gl求出。本研究收集自1971年至2005年間台灣、日本、英國及美國等國家之潛盾隧道施工案例，針對寬度參數i與地盤漏失Gl進行案例分析，並獲得以下各項結論。 (1)隧道中心線深度越深，潛盾隧道施工造成之地表沉陷槽寬度則越寬。本研究依潛盾機型式與土壤種類將寬度參數案例分為六類，各類之隧道深度Z0與寬度參數i之關係可以 之經驗公式表示。 (2)相較於早期之開放式潛盾機，土壓平衡式潛盾機採用密閉式開挖面施工，施工人員可控制開挖面上之土壓力，對鄰近地盤之擾動較小，可有效降低因施工造成之地盤漏失。 (3)於非凝聚性土壤中採用土壓平衡式潛盾機施工引致之沉陷槽寬度參數i值，較過去學者建議之i值為大。這可能由於土壓平衡式潛盾機之密閉式開挖面無地下水入侵之問題，故較少於開挖面附近採用輔助工法，因此潛盾機掘進時對鄰近地盤造成之擾動較大。 (4)除選擇性能優良的潛盾機外，設計人員於施工前充份了解開挖土壤性質，及施工人員之技藝水準，為判斷地盤沉陷表現良劣之重要因素。 (5)本經驗方法依據國內外已完成之施工案例評估採用不同機型、隧道深度、及隧道直徑於不同土層條件開挖潛盾隧道造成之地表沉陷槽，故其結果具實用價值。

Based on the field measurement data, this study proposed an empirical procedure to evaluate the surface settlement induced by shield tunneling. Peck (1969) suggested that the surface settlement trough due to tunneling can be approximated by normal distribution curve. The main parameters associated with the function are the trough width parameter (i) and maximum surface settlement (Smax), which can be calculated by the measured ground loss (Gl). This research collected shield tunneling cases in different countries reported from 1971 to 2005. Based on the case studies of width parameter i and ground loss Gl, the following conclusions are drawn. 1.The settlement trough width increases with the increasing tunnel depth. This study classified the tunneling cases into 6 categories according to the soil type encountered and the shield machine used. The relationship between the tunnel depth Z0 and the width parameter i can be approximated by the simple empirical equation . 2.In granular soils, because the compressed-air method and chemical grouting method were commonly adopted at the cutting face of an open shield, the ground disturbance in front of an EPB shield would be greater than that in front of an open shield. As a result, the ground loss Gl and the settlement trough width parameter i due to the EPB shield were larger compared with those due to the open shield. 3.For tunneling with the closed EPB shield, the groundwater intrusion problems are not encountered, and the auxiliary methods were generally not adopted. The absence of additional measurement at the cutting face caused greater ground disturbance during tunneling. 4.The understanding of in-situ ground properties and workmanship of the tunneling crew are important factors to estimate the surface settlement due to tunneling. 5.Based on the 151 tunneling cases, an empirical method was proposed to evaluate the surface settlement trough due to shield tunneling with different shield machines, tunnel depth, tunnel diameter, and soil type.