1、PDF外文：http:/ 5351 字 出处： Environmental Earth Sciences, 2011, 62(2): 357-365 外文原文 Surface settlement predictions for Istanbul Metro tunnels excavated by EPB-TBM S. G. Ercelebi H. Copur I. Ocak Abstract In this study, short-term surface settlements are predicted for twin tunnels, whi
2、ch are to be excavated in the chainage of 0 ? 850 to 0 ? 900 m between the Esenler and Kirazl stations 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
3、 (EPB) tunnel boring machines (TBMs) that have twin tubes of 6.5 m diameter and with 14 m distance 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 perfo
4、rmed with finite element method by using Plaxis finite element program. Excavation, ground support and face support steps in FEM analyses are simulated as applied in the field. Predictions are performed for a typical geological zone, which is considered as critical in terms of surface settlement. Ge
5、ology in the study area is composed of fill, very stiff clay, dense sand, very dense sand and hard 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
6、results indicate that the FE model predicts well the short-term surface settlements for a given volume 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. I
7、t is suggested that grouting of the excavation void should be performed as fast as possible after excavation 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
8、 prediction _ Finite element method _ Analytical method _ Semi-theoretical method _ EPB-TBM tunneling _ Istanbul Metro Introduction Increasing demand on infrastructures increases attention to shallow soft ground tunneling methods in urbanized areas. Many surface and sub-surface structures make
9、 underground construction works very delicate due to the influence of ground deformation, which should be definitely limited/controlled to acceptable levels. Independent of the excavation method, the short- and long-term surface and sub-surface ground deformations should be predicted and reme
10、dial precautions against any damage to existing structures planned prior to construction. Tunneling cost substantially increases due to damages to structures resulting from surface settlements, which are above tolerable limits (Bilgin et al. 2009). Basic parameters affecting the ground deforma
11、tions are ground conditions, technical/environmental parameters and tunneling or construction methods (OReilly and New 1982； 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 investigatio
12、ns should be performed to find out the physical and mechanical properties of the ground and existence of underground water, as well as deformation characteristics, especially the stiffness. Technical parameters include tunnel depth and geometry, tunnel diameterlinegrade, single or double track lines
13、 and neighboring structures. The construction method, which should lead to a safe and economic project, is selected based on site characteristics and technical project constraints and should be planned so that the ground movements are limited to an acceptable level. Excavation method, face support p
14、ressure, advance (excavation) rate, stiffness of support system, excavation sequence and ground treatment/improvement have dramatic effects on the ground deformations occurring due to tunneling operations. The primary reason for ground movements above the tunnel, also known as surface settlements, i
15、s convergence of the ground into the tunnel after excavation, which changes the in situ stress state of the ground and results 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 gr
16、ound (volume) loss inside the tunnel (OReilly and New 1982). Ground loss can be classified as radial loss around the tunnel periphery 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 gene
17、ralized in any study. However, it is possible to diminish or minimize the face loss in full-face mechanized excavations by applying 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 const
18、ruction conditions. The width of the settlement trough on both sides of the tunnel axis is wider in the case of cohesive soils, 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-t
19、erm settlements (Attewell et al. 1986). Short-term settlements occur during or after a few days (mostly a few weeks) of excavation, assuming that undrained soil conditions are dominant. Long-term settlements are mostly due to creep, stress redistribution and consolidation of soil after drainage of t
20、he underground water and elimination of pore water pressure inside the soil, and it may take a few months to a few years to reach a stabilized level. In dry soil conditions, the long-term settlements may be considered as very limited. There are mainly three settlement prediction approaches fo
21、r mechanized tunnel excavations: (1) numerical analysis such as finite element method, (2) analytical method and (3) semi-theoretical (semi-empirical) method. Among them, the numerical approaches are the most reliable ones. However, the results of all methods should be used carefully by an experienc
22、ed field engineer in designing the stage of an excavation project. In this study, all three prediction methods are employed for a critical 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 statio
23、ns of Istanbul Metro line, which is 4 km in length. Plaxis finite element modeling program is used for numerical modeling； the method suggested 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
24、compared and validated by field measurements. Description of the project, site and construction method The first construction phase of Istanbul 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 othe
25、r 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 started in May 2006. Currently, around 1,400 m of excavation has already been completed. The region is highly populated including several story buildings, industrial zones and heavy traffic. Alignment and stations of the metro line between Esenler and Basaksehir is presented in Fig. 1.
