潛盾隧道施工造成之意外事及故復舊工程

Abstract

本研究收集國內潛盾隧道施工造成之意外事故及復舊工程案例，進行探討及分析。本研究共分為兩部份，第一部份為板橋線CD266標隧道接頭漏水意外事故案例，本研究收集意外事故發生之經過、相關應變措施，及其復舊工程。本研究對復舊工程中所採用之地盤冷凍工法之凍土測溫結果，及國內首次採用之SJM工法之力學性質進行探討。獲得以下各項結論。 1.復舊工程之SJM地盤改良結果顯示，因SJM工法造成之改良體樁徑大，對於改良範圍較大之施工區域，可減少改良樁施作數量和縮短工期。配合改良樁徑之測音作業，能確保改良體之樁徑，有效增加施工品質。但採用SJM工法時也需注意因土壤之高置換率可能造成之地盤沈陷。 2.SJM改良土取樣率介於90%至99%之間，改良土之取樣率明顯高於施工單位設定之檢驗標準80%。SJM改良土之岩心品質指標RQD介於79%至97%間，其平均值達88%，顯示改良土品質良好。 3.砂質土SJM改良土的單軸抗壓強度介於3.65至22.6 MPa之間，黏性土改良土之qu介於1.88至10.0 MPa之間，試驗結果皆符合設計之要求。 4.SJM改良土的彈性模數介於350至1,990 MN/m2之間，皆符合日本Superjet研究會要求的砂質土改良土E50≧300 MN/m2，黏性土改良土E50≧100 MN/m2。 5.SJM改良土之滲透係數介於3.2至6.6 × 10-7 cm/sec之間，明顯低於設計值10-5 cm/sec，可知改良土止水效果良好。

第二部份探討內湖線CB420標潛盾隧道施工造成之跑道隆起事故，本研究收集潛盾施工之相關參數及各項壓力管理值，進行地表沉陷槽之分析，並探討實際施工造成之地表沉陷量，及跑道隆起之可能原因。依據盾首加泥灌漿、背填灌漿、二次灌漿施工壓力數據可發現，上述灌漿壓力大部分皆已超過規定之管理值，甚至大於覆土壓力（5.1 kgf/cm2）。在一般情況下，當潛盾機通過時，會因盾尾間閉合隙產生地盤沉陷情況，但本標工程環片脫離盾尾位置反而在跑道造成隆起，顯然表土層內部有漿液壓力之蓄積。由施工單位在機場草坪取出冒漿材為盾首加泥材，可初步推測機場跑道隆起之可能原因，為施工時灌漿壓力過大且注入量過多，受壓灌漿無處宣洩，在地層中四處流竄，進而產生冒漿及跑道隆起之情形。

In this paper, two accidents due to shield tunneling and its restoration are reported. In the first part of this thesis, the case history associated with the geological conditions, causes of failure, and restoration related to the shield tunneling of Taipei Rapid Transit Systems（TRTS） Panchiao Line lot CD266 is investigated. Based on the field data, mechanical properties of Superjet-Midi（SJM）soilcrete are found. 1.SJM method can cause larger soilcrete column in the ground, and reduce the time for grouting. 2.Core recovery of samples varies from 90% to 99%, which is higher than the design requirement of 80%. Rock Quality Designation（RQD）of the specimen varies from 79% to 97%. 3.The uniaxial compressive strength qu of the sandy soilcrete varies from 3.65 to 22.6 MPa, which is greater than the design requirement of 3.0 MPa. The qu for clayey soilcrete varies from 1.88 to 10.0 MPa, which is higher than the design requirement of 1.0 MPa. 4.The modulus of elasticity of soilcrete varied from 350 to 1990 MN/m2. 5.The permeability of soilcrete changes from 3.2 to 6.6 × 10-7 cm/sec, which is significantly lower than the design requirement of 10-5 cm/sec. In the second part of this thesis, the heaving of runway of Song-Shan Airport due to tunneling with a shield machine for TRTS lot CB420 is investigated. It is found that, the mud injection pressure at the face, backfill pressure, and secondary grouting pressure are significantly greater than the limiting values assured for construction. The mud injection pressure at the face was even higher than the vertical overburden pressure（5.1 kgf/cm2）. The fluid ejected to the ground surface was found to be the same as the mud injected at the face. It is reasonable to expect that, the amount and injection pressure applied to the mud at the face was too much high. The excess pressure in the ground causes an upward flow of fluid. The flow produces upward acting forces on soil layers and runway. The escaping grout tends to flow through localized cracks, and lift up the runway of the airport.