潛盾隧道施工遭遇卵礫石地盤引致之地盤沉陷案例研究

Abstract

摘要 本研究蒐集國內外遭遇卵礫石地盤之潛盾隧道施工案例，探討潛盾機於高透水及高強度卵礫石地盤施工之特殊考量。依據現地監測資料評估潛盾隧道於卵礫石地盤施工引致之最大地表沉陷量Smax。本研究並探討以雙曲線模式於卵礫石層潛盾施工造成地表沉陷歷時曲線之適用性，獲得以下各項結論與建議。 （1）新竹新工高壓電纜線洞道工程與桃園國際機場捷運工程施工案例皆發現，潛盾機切刃轉盤嚴重磨損位置皆發生於面盤中心向外約2/3R處，研判其原因，卵礫石受切刃盤旋轉切削掘進之影響，導致開挖面上部周圍卵礫石向下崩落，由於螺運機取土口位於切刃盤中心線之後方，崩落之卵礫石逐漸向切刃盤中心線集中，並造成切削切刃嚴重磨損。建議在日後設計切刃旋轉盤時可加入考量此特殊之切刃盤磨耗行為。 （2）於所蒐集之17個案例中，潛盾隧道施工遭遇卵礫石地盤造成之最大地表沉陷範圍僅為11~28 mm，明顯小於Fujita提出潛盾機在砂土層與黏土層開挖造成之最大地表沉陷範圍。 （3）採用密閉式潛盾機（泥水式與土壓平衡式潛盾機）施工，本研究所蒐集15個案例之深徑比（Z/D）介於1.17至3.44間，隨著潛盾隧道深徑比Z/D之逐漸增加，正規化最大地表沉陷量Smax/D有逐漸減小之趨勢。這是由於當潛盾隧道位置愈深，隧道上方覆土層之拱效應愈強烈，因此開挖對隧道周圍土體所造成的擾動，傳遞至地表面者明顯減少，因此施工導致地表沉陷量越小。此外，本研究發現開挖地盤之含卵礫石量越高，隧道直徑D越小，潛盾施工所導致之地表沉陷量越小。 （4）依據密閉式潛盾機於卵礫石地盤之施工案例，本研究提出下列經驗式評估施工造成之最大地表沉陷Smax：( Smax/D ) × 100 = 0.62 - 0.12（Z/D）。當設計者得知潛盾隧道深度Z與隧道直徑D時，可依此經驗公式初步預估在卵礫石地盤潛盾施工造成之最大地表沉陷量Smax。沉陷量可作為評估隧道沿線建物保護設計之參考。 （5）由國內案例之監測地表沉陷對時間資料得知，潛盾機在卵礫石地盤施工引致隧道中心線上方之地表沉陷歷時曲線，可以下列雙曲線關係 加以模擬，其中a及b為雙曲線參數。 （6）潛盾隧道案例之國內現地監測資料顯示，土壓平衡式潛盾機在卵礫石地盤施工造成之地表沉陷，大部分在潛盾機盾首通過後10天至30天內完成。

ABSTRACT This paper investigated the difficulties encountered during the construction of shield tunnels through gravelly soils. Case histories reported in the literature were studied. Recommendations were made regarding how to solve difficulties associated with tunneling though gravelly soils with high permeability, high stiffness and high shear strength in gravelly soils. Based on the field monitored data, this study analyzed the maximum surface settlement Smax above the centerline of the tunnel. The hyperbolic model was used to simulate the surface settlement-time relationship due to shield tunneling constructed. Base on this study, the following conclusions were made. （1）The contraction of the high-voltage cable tunneling Hsinchu industrial Park , and the mass Rapid Transit tunnel of Taoyuan international Air port were investigated for both cases tunnel was drives with a shield machines through gravelly soils, It was found that the cutter disc was seriously worn at a location 2R/3 (R=radius) from the center of the cutter disc. It was speculated that during the rotation and pushing of the disc, the gravelly soil at the upper part of the face was cut and disturbed and dropped. The soil intake of the screw conveyor was located right behind the centerline of the disc. The have gravel and cobble particles gradually moved toward the centerline of the disc at 2R/3 from the center of the disc, causing the major worn away of the disc at this special position. （2）The maximum surface settlement measured was between 11 to 28 mm, which was much the smaller than Smax due tunneling in sand and clay suggested by Fujita（1982）. （3）It was found that the maximum surface settlement Smax increased with increasing tunnel diameter D. It is also found that Smax decreased with increasing depth Z of the tunnel centerline. （4）Base on the field data, an empirical relationship between the maximum surface settlement trough parameter Z/D and Smax/D,. It was established as follows: ( Smax/D ) × 100 = 0.62 - 0.12（Z/D）. （5）Field monitored data indicated that the surface settlement-time relationship induced by shield tunneling in gravelly soils can be properly described with the hyperbolic model. （6）Field monitored data indicated that maximum surface settlement Smax was reached in about 10 days to 30 days after the passage of the tunnel face.