Three-dimensional numerical simulation of a mechanized twin tunnels in soft
ground
朱据
Ngoc-Anh Do a ,d ,Daniel Dias b ,⇑,Pierpaolo Oreste c ,Irini Djeran-Maigre a
a
University of Lyon,INSA of Lyon,Laboratory LGCIE,Villeurbanne,France b
Grenoble Alpes University,Laboratory LTHE,Grenoble,France c
Politecnico of Torino,Department of Environmental,Land and Infrastructural Engineering,Italy d
Hanoi University of Mining and Geology,Department of Underground and Mining Construction,Faculty of Civil Engineering,Hanoi,Viet Nam
a r t i c l e i n f o Article history:
Received 8April 2013
Received in revid form 15January 2014Accepted 2February 2014
Available online 25February 2014Keywords:儿童面条
Numerical modelling Twin tunnel
Segmental lining Lining respon Settlement
a b s t r a c t
The increa in transportation in large cities makes it necessary to construct of twin tunnels at shallow depths.Thus,the prediction of the influence of a new tunnel construction on an already existing one plays a key role in the optimal design and construction of clo parallel shield tunnels in order to avoid any damage to the existing tunnel during and after excavation of the new tunnel.
Most of the reported cas in the literature on parallel mechanized excavation of twin tunnels have focud on the effects of the ground condition,tunnel size,tunnel depth,surface loads,and relative posi-tion between the two tunnels on tunnel behaviour.The numerical investigation performed in this study,using the FLAC 3D finite difference element programme,has made it possible to include the influence of the construction process between the two tunnels.The structural forces induced in both tunnels and the development of the displacement field in the surrounding ground have been highlighted.
The results of the numerical analysis have indicated a great impact of a new tunnel construction on an existing tunnel.The influence of the lagged distance between the two tunnels faces has also been high-lighted.Generally,the simultaneous excavation of twin tunnels caus smaller structural forces and lin-ing displacements than tho induced in the ca of twin tunnels excavated at a large lagged distance.However,the simultaneous excavation of twin tunnels could result in a higher ttlement ab
ove the two tunnels.
Ó2014Elvier Ltd.All rights rerved.
1.Introduction
In recent years,many tunnels have been built in urban environ-ments;this often involves the construction of twin tunnels in clo proximity to each other.In addition,in many cas,the new tunnel is often excavated adjacent to an already existing one.Thus,the prediction of the influence of new shield tunnel construction on the existing tunnel plays a key role in the optimal design and construction of clo parallel shield tunnels in order to avoid any damage to the existing tunnel during and after excavation of the new tunnel.
Interactions between cloly-spaced tunnels were studied in the past using a variety of approaches:physical model testing,field obrvations,empirical/analytical methods and finite element modelling.
Kim et al.(1996,1998)performed physical tests to investigate the respon of the first tunnel lining on the approaching of the cond shield.The results of their model tests showed that the interaction effe
cts are greater in the spring line and crown of the existing tunnel.Chapman et al.(2007)described results from a ries of small-scale (1/50)laboratory model tests carried out in a kaolin clay which focud on studying the short-term ground movements associated with cloly spaced multiple tunnels.The influence of tunnel distance,tunnel depth and tunnel number were highlighted.The results showed asymmetrical ttlement troughs,greater ttlement above the cond of the twin tunnels con-structed.Their study also demonstrated that the commonly ud mi-empirical method to predict the short-term ttlement above twin tunnels,using the summation of Gaussian curves,can give inaccurate results.In the study by Choi and Lee (2010),the influ-ence of the size of an existing tunnel,the distance between tunnel centres and the lateral earth pressure factor on mechanical behav-iour of the existing and new tunnels was investigated by quantify-ing the displacement and crack propagation during the excavation
/10.1016/j.tust.2014.02.001
0886-7798/Ó2014Elvier Ltd.All rights rerved.
⇑Corresponding author.Tel.:+33476635135;fax:+33476825286.
E-mail address:daniel.dias@ujf-grenoble.fr (D.Dias).
of a new tunnel constructed near an existing tunnel.A ries of experimental model tests was performed and analyd.It was found that the displacements decread and stabilized as the dis-tance between the tunnel centres incread,depending on the size of the existing tunnel.
Suwansawat and Einstein(2007)introduced interestingfield measurement results on ground movements induced by parallel EPB tunnels excavated in soft ground in Bangkok.They showed that the operational parameters,such as face pressure,penetration rate,grouting pressure andfilling,have significant effects on the maximum ttlement and extent of the ttlement trough.They also showed that the maximum ttlement for twin tunnels is not usually located over the midpoint between the two tunnels and that the ttlement trough is often asymmetric.
Chen et al.(2011)prentedfield measurements conducted on parallel tunnels using EPB shields in silty soil.Their results showed a great dependence of the ground movements on the distance be-tween the cond tunnel face and the monitored ction.They also indicated that the two ttlement troughs caud by the construc-tion of thefirst and the cond tunnel had similar shapes.However, the cond tunnel trough was shallower and wider than that of the first tunnel.Thefirst tunnel made the symmetric axis of thefinal trough of the parallel tunnels incline towards thefirst tunnel.In the study by Ocak(2012),thirty longitudinal monitoring ctions, obtained through EPB tunnelling,were ud to
determine the interactions of the longitudinal surface ttlement profiles in shal-low twin tunnels.He et al.(2012)carried outfield and model tests, bad on Chengdu Metro Line1in China,to study the surface t-tlement caud by twin parallel shield tunnelling in sandy cobble strata.The surface ttlement mechanism and the effect of tunnel distance on the surface ttlement were also studied using the dis-crete element method(DEM).They showed that when the spacing between two tunnels is higher than twice the tunnel diameter,an independent collapd arch can form.However,in any of the above studies,the resulting structural forces induced in the tunnel lining were not mentioned.
我们永远不分开
Field obrvations remain the key to understanding the interac-tion between adjacent tunnels.Unfortunately,however,field data are often incomplete.It is clear that model testing can only be ud to study limited interaction behaviour.Empirical and analytical methods,using the superposition Wang et al., 2003;Hunt,2005;Suwansawat and Einstein,2007;Yang and Wang,2011),have been ud on the basis of the prediction of each individual excavation in order to obtain thefinal accumulated t-tlement trough.Generally,superposition method cannot take into account rigorously the effect of an existing tunnel and the repeated unloading of the ground caud by the previous excavation of the first tunnel and,therefore,the ttlement curves do not reprent thefinal displacement very well(Divall et al.,2012).Furthermore, empirical and analytical methods als
o introduce drawbacks for tho cas in which complex geological ultilayer strata)are expected.The u of afinite element model ems to be a promising way of addressing this issue.
Leca(1989),Addenbrooke and Potts(1996),Yamaguchi et al. (1998),Sagata et al.(1999),Hefny et al.(2004),Ng et al. (2004),Karakus et al.(2007),Hage Chehade and Shahrour(2008), Afifipour et al.(2011),Chakeri et al.(2011),Ercelebi et al.(2011), Mirhabibi and Soroush(2012),Hasanpour et al.(2012)have all car-ried out numerical analysis of this interaction problem.Most of the studies focud on considering the effect of the ground con-dition,tunnel size,tunnel depth,surface loads,and relative posi-tion between two tunnels on the surface ttlement.Their results were similar in that the influence of the cond tunnel on the pre-viously installed lining of thefirst one has been shown to depend on the relative position of the tunnel and on the spacing between the two tunnels.
The literature reviewed above clearly indicates that an exten-sive amount of rearch has been conducted on tunnel interactions between parallel tunnels.Most of this rearch has focud on the influence of twin tunnels on ground deformation.However,less work has been devoted to the influence of the interaction between tunnels on the structural forces induced in a tunnel lining.
Ng et al.(2004)performed a ries of three dimensional(3D) numerical simulations to investigate the interactions between two parallel noncircular tunnels constructed using the new Austrian tunnelling method(NATM).Special attention was paid to the influence of the lagged distance between the excavated faces of the twin tunnels(L F)and the load-transfer mechanism between the two tunnels.It was found that L F has a greater influence on the horizontal movement than on the vertical movement of each tunnel and that the magnitude of the maximum ttlement is inde-pendent of L F.They showed that the distributions of the bending moment induced in the tunnel lining are similar in shape,but different in magnitude in the two tunnels.
In the study by Liu et al.(2008),the effect of tunnelling on the existing support shotcrete lining and rock bolts)of an adjacent tunnel was investigated through full3Dfinite element calculations,coupled with an elasto-plastic material model.It was concluded that the driving of a new tunnel significantly af-fects the existing support system when the advancing tunnel face pass the existing support system and has less effect when the face is far from the system.It was also pointed out that the effects of tunnelling on the existing support system depend to a great extent on the relative position between the existing and new tunnels.
In order to investigate the influence of new shield tunnel exca-vation on the internal forces and defor
mations in the lining of an existing tunnel,Li et al.(2010)prented a ries of3D numerical simulations of the interaction between two parallel shield tunnels and parametric analys.Unfortunately,the existence of the joints in the gmental lining,the construction loads induced during shield tunnelling,such as face pressure,jacking force, grouting pressure,were not simulated in this numerical model. The impact of the new tunnel excavation on the existing tunnel during the advancement of the new tunnel was not considered either.
The purpo of a numerical mechanized tunnelling(TBM) model is to take into consideration the large number of process that take place during tunnel excavation.In order to conduct a rigorous analysis,a3D numerical model should be ud.Obviously, there is not a full3D numerical simulation for mechanized twin tunnels in soft ground that allows both ground displacement and structural lining forces to be taken into consideration.
The main purpo of this study was to provide a full3D model which would allow the behaviour of the interaction of mechanized twin tunnels to be evaluated,in terms of structural forces induced in the tunnel lining and ground displacement surrounding the two tunnels.Most of the main elements of a mechanized excavation can be simulated in this model:the conical geometry of the shield, the face pressure,the circumferential pressure acting on the cylin-drical surface of the excavated ground in th
e working chamber be-hind the tunnel face,the circumferential pressure caud by the migration of the grout acting on the excavated ground at the shield tail,the grouting pressure acting simultaneously on the excavated ground and on the tunnel structure behind the shield tail,progres-sive hardening of the grout,the jacking force,the weight of the shield machine,the weight of the back-up train behind the shield machine and the lining joint pattern,including the gment joints, the ring joints and their connection condition.The CYsoil model, which is a strain hardening constitutive model,has been adopted. The Bologna–Florence high speed railway line has been adopted in this study as a reference ca.
N.-A.Do et al./Tunnelling and Underground Space Technology42(2014)40–5141
2.Numerical model
2.1.Three-dimensional numerical model
The numerical model,the 3D simulation procedure of a single tunnel and the parameter calibration of the CY soil model were described in Do et al.(2013a).Therefore,only a short overview is given here.However,the numerical model introduced by Do et al.(2013a)has been improved and some other components of the tunnelling process have been simulated in the prent study.It includes the weight of the shield machine and the weight of the back-up train behind the shield machine.
The tunnel construction process is modelled using a step-by-step approach.Each excavation step corresponds to an advance-ment of the tunnel face of 1.5m,which is equal to the width of a lining ring.A schematic view of the prent model is provided in Fig.1.
Face pressure has been estimated depending on the horizontal stress induced in the ground in front of the tunnel face (Mollon et al.,2013).This face pressure has been modelled by applying a pressure distribution to the excavation face using a trapezoidal profile in order to account for the slurry density.Owing a slight overcutting,a possible slurry migration could occur over a short distance behind the cutting wheel.Therefore,in addition to the pressure acting on the tunnel face,a pressure,caud by the slurry solution,has also been applied to the cylindrical surface just be-hind th
e tunnel face.The shield machine has been simulated using ‘‘fictive’’shield introduced by Mollon et al.(2013),Dias et al.(2000)and Jenck and Dias (2004).The geometrical parameters of the shield are prented in Fig.1.
The lf-weight of the shield is simulated through the vertical loads acting on the grid points of the ground mesh at the tunnel bottom region over an assumed range of 90°in the cross-ction and over the whole shield length,as can be en in Figs.1and 2.In this study,a shield weight value of 6000kN,which refers to a tunnel diameter of 9.4m (JSCE,1996),has been adopted.
The distribution of the jacking force has been assumed to be lin-ear over the height of the tunnel.The jacking forces were t on each gment,considering three plates located at 1/6,1/2,and 5/6of the gment length.A total jacking force of about 40MN was adopted in the prent model on the basis of the theoretical method propod by Rijke (2006).
The grouting action is modelled in two phas:(1)the liquid state (state 1)reprented by a certain pressure acting on the
ground surface and on the tunnel lining;(2)the solid state (state 2).The distributional radial pressure has been ud to simulate this kind of pressure.The grouting pressure has been estimated dependin
g on the ground overburden pressure at the crown of each tunnel (Mollon et al.,2013).The grout was simulated by adopting a uniform pressure which was applied to both the cylin-drical surface of the excavated ground and the external surface of the tunnel lining.As for the face pressure,the annular void be-tween the outside surface of the shield and the excavated ground made the migration of some grout towards the shield possible.This migration was simulated by means of a triangular pressure over the length of one ring (1.5m).The grout was assumed to harden beyond this length and was simulated by means of volume ele-ments with perfect elastic behaviour,and with the elastic charac-teristics E grout =10MPa and m grout =0.22(Mollon et al.,2013).
In the prent model,the tunnel gments have been modelled using a linear-elastic embedded liner element.The gment joints have been simulated using double node connections.The stiffness characteristics of the joint connection have been reprented by a t compod of a rotational spring (K h ),an axial spring (K A )and a radial spring (K R )(Do et al.,2013a,2013b ).
In the same way as for the gment joint,the ring joint has also been simulated using double connections.In this study,the rigidity characteristics of the ring joint connection have been reprented by a t compod of a rotational spring (K h R ),an axial spring (K AR )and a radial spring (K RR ).The interaction mechanism of each spring is the same as that applied for a gment j
oint.
Once the TBM back-up train enters the excavated tunnels dur-ing the excavation process,it is necessary to take its lf-weight into consideration.In a study performed by Lambrughi et al.
F a c e p r e s s u r e
Shield
Cutting wheel
Segmental lining
Fresh grout
Hardened grout
幸运就是遇到你Grouting pressure Jacking force
1.5m 1.5m
7.5m
1.5m
1.5m
1.5cm
2.5cm 12.5cm农药标签
9.1m
Shield weight
Back-up train weight
Fig.1.Layout of the propod TBM model (not scaled).
42N.-A.Do et al./Tunnelling and Underground Space Technology 42(2014)40–51
(2012),this weight was simulated by artificially increasing the density value of the concrete lining.Kasper and Meschke(2004, 2006)instead modelled the back-up train using an assumed load-ing scheme along the tunnel axis.In the prent study,a total weight of3980kN for the back-up train h
as been simulated through the distribution loads which act on the lining elements at the tunnel bottom region over an assumed angle of90°in the cross-ction and over a tunnel length of72m behind the shield tail(Kasper and Meschke,2004)(e Fig.1).
2.2.Simulation procedure of mechanized twin tunnels
The twin tunnel excavation quence was modelled as follows: (i)excavation of thefirst tunnel(left);(ii)excavation of the cond tunnel(right)with a lagged distance L F behind the face of thefirst tunnel.The plan view and typical cross ction of the twin tunnel excavation procedure is illustrated in Figs.3and4.
In this work,two different lagged ,L F=0D and 10D)that correspond to L F=0and7.875L S,in which L S is the shield length(L S=12m in the prent model),between the tunnel on the left and the one on the right have been adopted and analyd.The ca of L F=0D corresponds to the situation in which two tunnel faces are excavated simultaneously in parallel.The ca of L F=10D means that the cond(new)tunnel is excavated when the lining structure behaviour and ground displacement caud by thefirst(existing)tunnel excavation appear to have reached a steady state.The latter ca usually occurs in reality.The twin tun-nels in the Bologna–Florence railway line 意识形态学习内容
project prented in this paper is a typical example.In fact,the distance between the two tunnels in the Bologna–Florence railway line project is15m (Croce,2011).However,in order to highlight the influence of the excavation process of a new tunnel on an existing tunnel,a dis-tance from centre to centre of11.75m(1.25D)has been adopted in this study.
A full model of the twin tunnels considering a height of60m and a width of131.75m has been adopted.The mesh length of the model is equal to120m.The nodes at all the sides of the model werefixed in the horizontal directions on the x–z and y–z planes (i.e.y=0,y=120,x=À71.75and x=60),while the nodes at the ba of the model(z=À40)werefixed in the vertical(z)direction. The perspective view of the developed numerical model,which is compod of around1,100,000grid points and900,000zones,is prented in Fig.5.
The positions of the gment joints in each ring are prented in Table1.Finally,it should be mentioned that the average time nec-essary for one calculation is approximately340h when a2.67GHz core i7CPU ram24G computer is ud.
3.Numerical results and discussion
In order to understand the behaviour of twin tunnels during the excavation process of the new tunnel
(right),this ction prents variations in the structural lining forces induced in the existing
Measured ring (30) First tunnel (left)
Second tunnel (right)
Tunnel face
Y MS
Tunnelling direction
y
x Shield
Segmental lining B
L F
L S
立秋美图
L S Shield
Fig.3.Plan view of the twin tunnels(not scaled).
Fig.5.Perspective view of the developed numerical model introduced into FLAC3D.
N.-A.Do et al./Tunnelling and Underground Space Technology42(2014)40–5143
the ground displacement during
structural forces in the new
been extracted at the ction
which hereafter is called the measured negligible at this ction.In Figs.7–9,11and13,and Table2,the Y MS value prents the distance from the new tunnel face(right) to the measured ction.In Figs.10,12and14,and Table3,the Y FT value prents the distance from the faces of the two tunnels, which are excavated simultaneously,to the measured ction.In Tables2–4,the R values prent the ratios between the results ob-tained in the ca of twin tunnels with L F=0D or10D and the cor-responding one obtained in the ca of a single tunnel.
The influence of the tunnel length advancement on the mea-sured lining ring(ring30)has been evaluated for a single tunnel, which corresponds to the tunnel construction on the left before interacting with the tunnel on the right,considering the instanta-neous variation in structural forces between two successive steps (Do et al.,2013a).The numerical results show that the instanta-neous variation in the structural force induced in the measured lin-ing ring between two excavation steps,which correspond to the installation of rings54and55,is approximately zero.This means that the structural forces determined at this excavation step can
Ring 1
Ring 2
Fig.6.Considered lining models.
Table1
Location of the gment joints in a ring h(degree)(measured counter clockwi from
the right spring line)(e Fig.6).
Joint location
0;60;120;
30;90;
Fig.7.Surface ttlements above the twin tunnels.
44N.-A.Do et al./Tunnelling and Underground Space Technology42(2014)40–51
Fig.7a shows the development of the surface ttlement trough in the transver ction during the face advancement of the new tunnel on the right in the ca of L F =10D.This figure shows that the twin tunnels cau an increa in the surface ttlement.This could be explained by the accumulate
d loss of the ground in both two tunnels.In the considered ca,the maximum ttlement
measured above the twin tunnels is 47.4%higher than that devel-oped above a single tunnel.In addition,the ttlement profile is asymmetric.This means that the maximum ttlement is not located over the mid-point between the two tunnels.During the new tunnel advancement (right),the ttlement trough shifts gradually from the left to the right.An asymmetric profile of the ttlement trough has also been obrved through field measure-ments obtained at shield tunnelling sites (Suwansawat and Einstein,2007;Chen et al.,2011),analytical results using the superposition technique (Suwansawat and Einstein,2007)and laboratory model tests (Chapman et al.,2006;2007).
Fig.7b shows that the two ttlement troughs caud by the construction of the tunnels on the left and right have a similar shape.The ttlement trough above the new tunnel (right)is deter-mined on the basic of the final ttlement trough of the twin tun-nels minus the one developed above the existing tunnel (left)before it interacts with the new tunnel.However,the ttlement trough caud by the excavation of the new tunnel is shallower and wider than the one caud by the existing tunnel.The con-clusions are in good agreement with field obrvations made by Chen et al.(2011),and He et al.(2012)during the excavation of twin tunnels through respectively silty and sandy soil.The volume loss ratios,determined at the final state as the ratio of ttlement trough area develo
ped on the ground surface to the cross-ction area of the tunnel,of the existing tunnel and new tunnel are sim-ilar and equal to about 0.92%and 0.79%,respectively,and the total volume loss above the twin tunnels is equal to 1.71%.Above result are however different from the laboratory results obtained from the work of Chapman et al.(2007)conducted in clay.Their work showed a greater ttlement above the cond tunnel.This differ-ence could be attributed to the influence of the soil type or due to the undrained behaviour of soils.
Fig.7b also prents a comparison of the final ttlement troughs for the different construction procedures (L F =0D and 10D).The maximum ttlement above the twin tunnels of about 43.8mm (0.47%D)(Table 4)and the volume loss ratio of 1.81%are obrved in the L F =0D ca.The results are 109%and 106%higher than the corresponding ones for the L F =10D ca.However,the widths of the ttlement troughs are similar in both cas.
In立冬南方吃什么
Fig.8.Horizontal displacements between the twin tunnels,for the L F =10D ca.
Fig.9.Normal displacement in measured lining ring 30of the existing (left)tunnel,for the L F =10D ca.
displacement in measured lining ring 30of the tunnel ca.
Space Technology 42(2014)40–5145
