土木工程 建筑 外文翻译 外文文献 英文文献 地铁地表沉降.doc
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1、外文原文Surface settlement predictions for Istanbul Metro tunnelsexcavated by EPB-TBMS. G. Ercelebi H. Copur I. OcakAbstract In this study, short-term surface settlements are predicted for twin tunnels, which are to be excavated in the chainage of 0 ? 850 to 0 ? 900 m between the Esenler and Kirazl stat
2、ions of the Istanbul Metro line, which is 4 km in length. The total length of the excavation line is 21.2 km between Esenler and Basaksehir. Tunnels are excavated by employing two earth pressure balance (EPB) tunnel boring machines (TBMs) that have twin tubes of 6.5 m diameter and with 14 m distance
3、 from center to center. The TBM in the right tube follows about 100 m behind the other tube. Segmental lining of 1.4 m length is currently employed as the final support. Settlement predictions are performed with finite element method by using Plaxis finite element program. Excavation, ground support
4、 and face support steps in FEM analyses are simulated as applied in the field. Predictions are performed for a typicalgeological zone, which is considered as critical in terms of surface settlement. Geology in the study area is composed of fill, very stiff clay, dense sand, very dense sand and hard
5、clay, respectively, starting from the surface. In addition to finite element modeling, the surface settlements are also predicted by using semi-theoretical (semi-empirical) and analytical methods. The results indicate that the FE model predicts well the short-term surface settlements for a given vol
6、ume loss value. The results of semi-theoretical and analytical methods are found to be in good agreement with the FE model. The results of predictions are compared and verified by field measurements. It is suggested that grouting of the excavation void should be performed as fast as possible after e
7、xcavation of a section as a precaution against surface settlements during excavation. Face pressure of the TBMs should be closely monitored and adjusted for different zones.Keywords Surface settlement prediction _ Finite element method _ Analytical method _ Semi-theoretical method _ EPB-TBM tunnelin
8、g _Istanbul MetroIntroductionIncreasing demand on infrastructures increases attention to shallow soft ground tunneling methods in urbanized areas. Many surface and sub-surface structures make underground construction works very delicate due to the influence of ground deformation, which should be def
9、initely limited/controlled to acceptable levels. Independent of theexcavation method, the short- and long-term surface and sub-surface ground deformations should be predicted and remedial precautions against any damage to existing structures planned prior to construction. Tunneling cost substantiall
10、y increases due to damages to structures resulting from surface settlements, which are above tolerable limits (Bilgin et al. 2009). Basic parameters affecting the ground deformations are ground conditions, technical/environmental parameters and tunneling or construction methods (OReilly and New 1982
11、; Arioglu 1992; Karakus and Fowell 2003; Tan and Ranjit 2003; Minguez et al. 2005; Ellis 2005; Suwansawat and Einstein 2006). A thorough study of the ground by site investigations should be performed to find out the physical and mechanical properties of the ground and existence ofunderground water,
12、as well as deformation characteristics, especially the stiffness. Technical parameters include tunnel depth and geometry, tunnel diameterlinegrade, single or double track lines and neighboring structures. The construction method, which should lead to a safe and economic project, is selected based on
13、 site characteristics and technical project constraints and should be planned so that the ground movements are limited to an acceptablelevel. Excavation method, face support pressure, advance (excavation) rate, stiffness of support system, excavation sequence and ground treatment/improvement have dr
14、amatic effects on the ground deformations occurring due to tunneling operations.The primary reason for ground movements above the tunnel, also known as surface settlements, is convergence of the ground into the tunnel after excavation, which changes the in situ stress state of the ground and results
15、 in stress relief. Convergence of the ground is also known as ground loss or volume loss. The volume of the settlement on the surface is usually assumed to be equal to the ground (volume) loss inside the tunnel (OReilly and New 1982).Ground loss can be classified as radial loss around the tunnel per
16、iphery and axial (face) loss at the excavation face (Attewell et al. 1986; Schmidt 1974). The exact ratio of radial and axial volume losses is not fully demonstrated or generalized in any study. However, it is possible to diminish or minimize the face loss in full-face mechanized excavations by appl
17、ying a face pressure as a slurry of bentonitewater mixture or foam-processed muck. The ground loss is usually more in granular soils than in cohesive soils for similar construction conditions. The width of the settlement trough on both sides of the tunnel axis is wider in the case of cohesive soils,
18、 which means lower maximum settlement for the same amount of ground loss.Time dependency of ground behavior and existence of underground water distinguish short- and long-term settlements (Attewell et al. 1986). Short-term settlements occur during or after a few days (mostly a few weeks) of excavati
19、on, assuming that undrained soil conditions are dominant. Long-term settlements are mostly due to creep, stress redistribution and consolidation of soil after drainageof the underground water and elimination of pore water pressure inside the soil, and it may take a few months to a few years to reach
20、 a stabilized level. In dry soil conditions, the long-term settlements may be considered as very limited.There are mainly three settlement prediction approaches for mechanized tunnel excavations: (1) numerical analysis such as finite element method, (2) analytical method and (3) semi-theoretical (se
21、mi-empirical) method. Among them, the numerical approaches are the most reliable ones. However, the results of all methods should be used carefully by an experienced field engineer in designing the stage of an excavation project.In this study, all three prediction methods are employed for a critical
22、 zone to predict the short-term maximum surface settlements above the twin tunnels of the chainage between 0 ? 850 and 0 ? 900 m between Esenler and Kirazl stations of Istanbul Metro line, which is 4 km in length. Plaxis finite element modeling program is used fornumerical modeling; the method sugge
23、sted by Loganathan and Poulos (1998) is used for the analytical solution. A few different semi-theoretical models are also used for predictions. The results are compared and validated by field measurements.Description of the project, site and construction methodThe first construction phase of Istanb
24、ul Metro line was started in 1992 and opened to public in 2000. This line is being extended gradually, as well as new lines are being constructed in other locations. One of these metro lines is the twin line between Esenler and Basaksehir, which is 21.2 km. The excavation of this section has been st
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