土木工程建筑外文翻译外文文献英文文献地铁地表沉降

1、文档来源为 :从网络收集整理 .word 版本可编辑 .欢迎下载支持1文档收集于互联网，如有不妥请联系删除外文原文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

2、 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 (EPB) tunnel boring machines (TBMs) tha

3、t 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 performed with finite element method by using

4、 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. Geology in the study area is composed of f

5、ill, 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 results indicate that the FE model predi

6、cts 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. It is suggested that grouting of the exca

7、vation 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 prediction _ Finite element method _ Ana

8、lytical method _ Semi-theoretical method _ EPB-TBM tunneling _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

9、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 remedial precautions against any damage to existing structure

10、s 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 deformations are ground conditions, technical/environmental parameters

11、and tunneling or construction methods (O Reillyand 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 文档来源为 :从网络收集整理 .word 版本可编辑 .欢迎下载支持2文档收集于互联网，如有不妥请联系删除investigations should b

12、e 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 diameter -line -grade, single or double track lines and ne

13、ighboring 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 acceptablelevel. Excavation method, face support pressure,

14、 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, is conver

15、gence 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 ground (vo

16、lume) loss inside the tunnel (O Reilly 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 generalized

17、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 bentonite -water mixture or foam-processed muck. The ground loss is usually more in granular soils than in cohesive soils for similar constructio

18、n 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-term set

19、tlements (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 the unde

20、rground 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 for mechanized tu

21、nnel 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 experie need field engin

22、 eer in desig ning the stage of an excavati on project.In this study, all three prediction methods are employed for a critical zone to predict the short-term maximum surface settleme nts above the twin tunn els of the cha in age between 0 ? 850 and 0 ? 900 m between Esenler and Kirazl ? stations of

23、Istanbul Metro line, which is 4 km in length. Plaxis finite element modeling program is used fornu merical modeli ng; the method suggested by Loga natha n and Poulos (1998) is used for the an alytical soluti on. A few differe nt semi-theoretical models are also used for predict ions. The results are

24、 compared and validated by field measureme nts.文档来源为：从网络收集整理.word版本可编辑.欢迎下载支持3文档收集于互联网，如有不妥请联系删除Descriptio n of the project, site and con structi on methodThe first con struct ion phase of Ista nbul Metro line was started in 1992 and ope ned to public in 2000. This line is being exte nded gradually,

25、 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 started in May 2006. Currently, around 1,400 m of excavationhas already been completed. The region is hi

26、ghly populated including several story build in gs, in dustrial zones and heavy traffic. Alig nment and stati ons of the metro line betwee nEse nlerand Basaksehir is prese nted in Fig. 1.Totally four earth pressure balance (EPB) tunnel boring machines (TBM) are used for excavation of the tunnels. Th

27、e metro lines in the study area are excavated by a Herrenknecht EPB-TBM in the right tube and a Lovat EPB-TBM in the left tube. Right tube excavatio nfollows around 100 m behind the left tube. Some of the technical features of the mach ines are summarized in Table 1.Excavated material is removed by

28、auger (screw con veyor) through the mach ine to a belt conveyor and than loaded to rail cars for transporting to the portal. Since the excavated ground bears water and includes stability problems, the excavation文档来源为 :从网络收集整理 .word 版本可编辑 .欢迎下载支持4文档收集于互联网，如有不妥请联系删除chamber is pressurized by 300 kPa an

29、d conditioned by applying water, foam, bentonite and polymers through the injection ports. Chamber pressure is continuously monitored by pressure sensors inside the chamber and auger. Installation of a segment ring with 1.4-m length (inner diameter of 5.7 m and outer diameter of 6.3 m) and 30-cm thi

30、ckness is realized by a wing-type vacuum erector. The ring is configured as five segments plus a key segment. After installation of the ring, the excavation restarts and the void between the segment outer perimeter and excavated tunnel perimeter is grouted by300 kPa of pressure through the grout can

31、nels in the trailing shield. This method of construction has been proven to minimize the surface settlements.The study area includes the twin tunnels of the chainage between 0 + 850 and 0 +900 m, between Esenler and Kirazl? stations. Gungoren Formation of the Miosen age is found in the study area. L

32、aboratory and in situ tests are applied to define the geotechnical features of the formations that the tunnels pass through. The name, thickness and some of the geotechnical properties of the layers are summarized in Table 2 (Ayson 2005). Fill layer of 2.5-m thick consists of sand, clay, gravel and

33、some pieces of masonry. The very stiff clay layer of 4 m is grayish green in color, consisting of gravel and sand. The dense sand layer of 5 m is brown at the upper levels and greenish yellow at the lower levels, consisting of clay, silt and mica. Dense sand of 3 m is greenish yellow and consists of

34、 mica. The base layer of the tunnel is hard clay, which is dark green, consisting of shell. The underground water table starts at 4.5 m below the surface. The tunnel axis is 14.5 m below the surface, close to the contact between very dense sand and hard clay. This depth isquite uniform in the chaina

35、ge between 0 + 850 and 0 + 900 m.Surface settlement prediction with finite element modelingPlaxis finite element code for soil and rock analysis is used to predict the surface settlement. First, the right tube is constructed, and then the left tube 100 m behind the right tube is excavated. This is b

36、ased on the assumption that ground deformations caused by the excavation of the right tube are stabilized before the excavation of the left tube. The finite element mesh is shown in Fig. 2 using 15 stress point triangular elements. The FEM model consists of 1,838 elements and 15,121 no des. In FE mo

37、deli ng, the Mohr-Coulomb failure criteri on is applied.Staged construction is used in the FE model. Excavation of the soil and the construction of the tunnel lining are carried out in different phases. In the first phase, the soil in front of TBM is excavated, and a support pressure of 300 kPa is a

38、pplied at the tunnel face to prevent failure at the face. In the first phase, TBM is modeled as shell elements. In the second phase, the tunnel lining is constructed using prefabricated concrete ring segments, which are bolted together within the tunnel boring machine. During the erection of the lin

39、ing, TBM remains stationary. Once a lining ring has been bolted, excavation is resumed until sufficient soil excavation is carried out for the next lining. The tunnel lining is modeled using volume elements. In the second phase, the lining is activated and TBM shell elements are deactivated.文档来源为：从网

40、络收集整理.word版本可编辑.欢迎下载支持5文档收集于互联网，如有不妥请联系删除When applying finite element models, volume loss values are usually assumed prior to excavation. In this study, the FEM model is run with the assumption of 0.5, 0.75, 1 and 1.5% volume loss caused by the conv erge nee of the ground into the tunnel after excav

41、ati on. Figures 3 and 4 show total and vertical deformati ons after both tubes are eon structed. The vertical ground settleme nt profile after theright tube con structi on is give nin Fig. 5, which is in theshape of a Gaussia n curve,and that after con struct ion of both tubes is give n in Fig. 6. F

42、igure 7 shows the total deformati on vectors.The maximum ground deformations under different volume loss assumptions are summarized in Table 3.Surface settleme nt predictio n with semi-theoretical and an alytical methods Semi-theoretical predictions for short-term maximum settlement are performed us

43、ing the Gaussian curve approach, which is a classical and conventional method. The settlement parameters used in semi-theoretical estimations and notations are prese nted in Fig. 8.The theoretical settlement (Gaussian) curv e is presented as in Eq. 1 (O ReillyandNew 1982):(1)where, S is the theoreti

44、cal settlement (Gauss error function, normal probability curve), Smax is the maximum short-term (in itial, undrain ed) settleme nt at the tunnel centerline (m), x is the transverse horizontal distance from the tunnel center line (m), and i is the point of inflexion (m). To determine the shape of a s

45、ettlement curve, it is n ecessary to predict i and Smax values.There are several suggested methods for prediction of the point of inflexion (i).Estimati on of i value in this studyis based on averages of some empirical approachesgiven in Eqs. 2 -6:where, Z0 is the tunnel axis depth (m), 14.5 m in th

46、is study, and R is the radius oftunnel, 3.25 m in this study. Equation 3 was suggested by Glossop (O Reilly and N1982) for mostly cohesive grounds; Eq. 4 was suggested by O Reilly and New (1982)for excavation of cohesive grounds by shielded machines; Eq. 5 was suggested bySchmidt (1969) for excavati

47、o n of clays by shielded machi nes; Eq. 6 was suggested by Arioglu (1992) for excavation of all types of soils by shielded machines. As a result, the average i value is estimated to be 6.6 m in this study.There are several suggested empirical methods for the prediction of the maximum surface settlem

48、ent (Smax).Schmidt suggested a model for the estimation of Smax value for a sin gle tunnel in 1969 as give n in Eq. 7 (through Arioglu 1992):where, K is the volume loss (%). Arioglu (1992), based on field data, found a good relati on ship betwee n K and N (stability ratio) for face-pressurized TBM c

49、ases as in Eq.8:where cn is the natural unit weight of the soil (kN/m3), the weighted averages for all the layers, which is 19 kN/m3 in this study; rS is the total surcharge pressure (kPa), assumed to be 20 kPa in this study; rT is TBM face pressure (kPa), which is 300 kPa in this study; and CU is t

50、he undrained cohesion of the soil (kPa), the weighted averages for all the layers, which is 50 kPa in this study assuming that CU is equal to SU (undrained shear stre ngth of the soil). Allaverages are estimated up to very dense sand, excludi ng hard clay, since the tunnel axis passes around the con

51、 tact betwee n very dense sand and hard clay. The model yields 17.1 mm of in itial maximum surface settleme nt.S文档来源为：从网络收集整理.word版本可编辑.欢迎下载支持6文档收集于互联网，如有不妥请联系删除Herzog suggested a model for the estimation of Smax value in 1985 as given in Eq. 9 for a sin gle tunnel and Eq. 10 for twin tunn els (thro

52、ugh Arioglu 1992):where, E is the elasticity modulus of formation (kPa), the weighted averages for all the layers, which is 30,000 kPa in this study, and a is the dista nee betwee n the tunnel axes, which is 14 m in this study. The model yields 49.9 and 58.7 mm of initial maximum surface settlements

53、 for the right and the left tube tunnel, which is 100 mm beh ind the right tube, respectively.There are several an alytical models for the predictio n of short-term maximum surface settlements for shielded tunneling operations (Lee et al. 1992; Loganathan and Poulos 1998; Chi et al. 2001; Chou and B

54、obet 2002; Park 2004). The method suggested by Loga natha n and Poulos (1998) is used in this study .In this method, a theoretical gap parameter (g) is defined based on physical gap in the void, face losses and workmanship value, and then the gap parameter is incorporated to a closed form soluti on

55、to predict elastoplastic ground deformati ons. The undrained gap parameter(g) is estimated by Eq. 12:where Gp is the physical gap 1 5 ； +representing the geometric clearaneebetween the outer skin of the shield and the liner, is the thickness of the tail shield, d is the cleara nce required for erect

56、 ion of the liner, U*3D is the equivale nt 3D elastoplastic deformation at the tunnel face, and w is a value that takes into account the quality of workma nship.Maximum short-term surface settlementis predicted by theoretical Eq. 13(Loga nathan and Poulos 1998):where, t is undrained Poisson ratio, a

57、ssumed to be of maximum 0.5; g is the gap parameter (m), which is estimated to be 0.0128 m in this study; and x is transverse distance from the tunnel centerline (m) and it is assumed to be 0 m for the maximum surface settlement. The model yields 23.0 mm of undrained maximum surface settleme nt.Othe

58、r parameters of settleme nt such as maximum slope, maximum curvature and so on are not men ti oned in this study.Verificati on of predict ions by field measureme nts and discussi on The results of measurements performed on the surface monitoringpoints, byIstanbul Metropolitan Municipality, are prese

59、nted in Table 4 for the left and right tubes. As see n, the average maximum surface settleme nts are around 9.6 mm for the right tube and 14.4 mm for the left tube, which excavates 100 m beh ind the right tube.Themaximum surface settlements measured around 15.2 mm for the right tube and 26.3 mm for

60、the left tube. Higher settlements are expected in the left tube since the文档来源为：从网络收集整理.word版本可编辑.欢迎下载支持7文档收集于互联网，如有不妥请联系删除previous TBM excavation activities on the right tube overlaps the previous deformati on. The effect of the left tube excavati on on deformati ons of the right tube is prese nted