以經驗方法評估潛盾隧道施工遭遇卵礫石地盤引致之地表沉陷

Abstract

根據現地監測資料，本研究探討潛盾隧道施工國內外遭遇卵礫石地盤造成之地表沉陷歷時曲線及地表沉陷槽。本研究探討利用雙曲線模式模擬地表沉陷歷時曲線之適用性。本研究探討潛盾隧道於卵礫石地盤施工引致之地表沉陷槽寬度i值及最大地表沉陷量Smax，並獲得以下各項結論。 1.桃園國際機場聯外捷運系統CU02A標；潛盾隧道施工遭遇地層之卵石含量為55%，礫石含量為30%，砂之含量為11%，粉土及黏土含量為4％，此地盤含量最多的是卵石，其餘為礫石土壤，故此土層稱為卵礫石土壤（Cobble and Gravelly Soil）。 2.大部分地表沉陷在潛盾機首通過後10天至30天內完成。潛盾隧道施工引致隧道中心線上方之地表沉陷歷時曲線，可以使用雙曲線關係加以模擬。 3.潛盾隧道施工所產生之沉陷縱剖面可分為六個階段，分別為：(1)先行沉陷、(2)開挖面到達前擠壓隆起、(3)開挖面前地盤損失、(4)盾身通過造成之沉陷、(5)盾隙閉合沉陷、及(6)後續沉陷。 4.地表沉陷槽可使用常態分佈曲線模擬。隧道中心線深度愈深，潛盾隧道造成之地表沉陷槽寬度則愈寬。在地下水位以下之卵礫石土層開挖潛盾隧道引致之沉陷寬度，較於砂土層及黏土層開挖隧道造成之沉陷槽為寬。 5.地表最大沉陷量Smax範圍僅2.8~9.0 mm，明顯小於砂土及黏土層造成之最大沉陷範圍，推測其原因，由於卵礫石地層勁度模數大、剪力強度高，及自立性高，因此潛盾機掘進時造成地表沉陷Smax比於其它土層造成者小。

In this thesis, an empirical method is proposed to estimate the ground settlement due to shield tunneling in gravelly soil. Surfae settlement data monitored in the field are collected during the construction of shield tunnels in gravelly soil. Based on the field data, the hyperbolic model is proposed to simulate the settlement-time relationship due to shield tunneling. Base on the field data, this study analyzes the settlement trough width parameter i and maximum surface settlement Smax as a function of tunnel depth Z and tunnel radius R. Base on this study, the following conclusions can be made for shield tunneling in gravelly soil. 1.For the Taoyuan International Airport Access MRT System Case, the grain size analysis indicates the soils to be excavated contained 55% cobble, 30% gravel, 11% sand, and 4% of silt and clay. So the ground to be driven is called cobble and gravelly soil. 2.The settlement-time relationship induced by shield tunneling in gravelly soils can be described with the hyperbolic model. Field data indicates the maximum surface settlement Smax was reached in 10 days to 30 days after the passage of the tunnel face. 3.Based on the longitudinal settlement profile, the ground settlement due to shield tunneling can be separated into six stage; namely: preceding settlement; face-pushing heaving; face loss settlement; shield passage settlement; tail-void closure settlement and succeeding settlement. 4.The surface settlement trough can be approximated by the normal distribution curve suggested by Peck. Field data indicates the settlement-trough width increases with the increasing tunnel depth. The width of settlement trough in gravelly soil is wider than that in sandy and clayey soils. 5.In gravelly soil, the maximum surface settlement Smax measured above the center of the tunnel was only 2.8 to 9.0 mm. This value was much smaller than the Smax due tunneling in sandy and clayey soils. This is probably because of the stiffness and shear strength of the gravelly soil is much higher than that for sandy and clayey soils.