- Email: [email protected]
Tunnel waterproofing practices in China
TUNNEL WATERPROOFING METHODS
Tunnel Waterproofing Practices in China Y. Yuan, X. Jiang and C. F. Lee A b s t r a c t --Water ingre~s in transportation tunnels not only will shorten the durability of concrete lining and reduce the function of establishments in the tunnel, but also will worsen the tunnel surrounding so much that the traffic will be greatly affected. In this situation, therefore, high maintenance costs are compulsory. In many cases, a perfect appearance is strongly recommended to take measures in order to prevent leakage. However, in China, tunnel waterproof requirements and standards for various special uses are considerably different, such that the basis which engineers apply to design in water-control is insufficient. Especially in montanic region, unpleasant geological condition confines engineers in working out more reasonable methods to stop water seepage, even leakage. In this paper, the current waterproofing requirements and measures in different spec,ial tunnels adopted in China are reviewed. The limitations of the popular methods in several practical cases applied to prevent water leakage, such as watertight lining, drainage system, as well as grouting, are analyzed at length. Then, some available measures, regarding concrete lining, watertight layer, drainage establishments as well as casting watertight concrete, are proposed, which we think indispensable for tunnel engineering to efficiently control water seepage and even completely prevent water leakage. In the end to analyze the seepage field in montanic tunnels, the finite element and boundary element coupling analysis method is presented. As an example, the seepage field in Zhenwushan tunnel of Chongqing is simulated. The calculation results coincide with the in-situ data well, and provide credible evidence for the waterproof measures which will be taken in that tunnel project. The method presented in this paper will save expenditures for surveying measures and will enable more reasonable and reliable waterproofing measures ~.o be taken. © 2000 Published by Elsevier ScienceLtd. All rights reserved.
Introduction ater ingress :in underground works remains quite difficult to assess. In many tunnels built long ago, seepage is unavoidable. Especially for tunnels in frozen zones, the tunnel ground may be icy and the top of the tunnel so covered with hanging icicles that traffic is interrupted. Given this situation, high maintenance costs are compulsory. For watA,~r supply tunnels through sewage layers and those furnished with wiring, a perfect appearance is usually strongly recommended to take measures in order to prevent leakage. However, in China, tunnel waterproofing requirements and standards for various special uses are considerably different, and the basiis on which engineers apply watercontrol design is insvfficient. Especially in mountainous regions, poor geological conditions compel engineers to devise more reasonable methods to step water seepage, and even leakage. As a result, many topics related to waterproofing-including the theoretical basis for water-control design, optimization of waterproof measures, and rationality of tunnel waterproof system--require further investigation.
W
Present addresses: Yuan Y. Ryan, Professor and Deputy Dean of the Department of Buildi:ag Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China; X. Jiang, Ph.D. candidate, Department of Building Engineering, Ton~i University, 1239 Siping Road, Shanghai 200092, China; C. F. Lee, Professor and Dean of the Department of Civil Engineering, The University of Hong Kong, Pokfulam l~bad, Hong Kong, China.
To treat underground water seepage reasonably and comprehensively by means of drainage and prevention, it is crucial for designers to understand the distribution of underground seepage field and the potential permeable volume at places excavated. During construction, the most critical zone is located at the tunnel face, where the decompression owing to excavation and water seepage forces generated by the water flow toward the face can lead to collapse of the face. Up to now, only a few papers have dealt with methods of assessing the supporting pressure and seepage volume at the tunnel face. Several of these methods have been based on the plasticity principle. Davis et al. (1980) established an analytical expression for cohesive and frictional soil in undrained conditions. Leca and Panet (1988) have studied the more complex case of cohesive and frictional soil in drained conditions. Descoeudres and Rybisaial have reviewed tunnel methods adopted in China. In this paper, the limitations of the popular methods in several practical cases applied to prevent water leakage, such as watertight lining, drainage systems, and grouting, are analyzed at length. Then some available measures relating to concrete lining, watertight layer, drainage establishment, and casting watertight concrete, are proposed. The authors consider these measures indispensable for tunnel engineering in order to efficiently control water seepage or even completely prevent water leakage. In addition, based on Darcy's law and the Finite Element Method along with Boundary Element Method, the threedimensional numerical simulation is employed to model the disturbance of the initial hydraulic conditions. That is, the
www, elsevier.comflocate/tust 7hnneUing and Underground Spa~:eTechnology,VoI. 15, No. 2, pp. 227-233, 2000 0886-7798/00/$ - see front matter © 2000 Published by Elsevier Science Ltd. All rights reserved. PII: S0866-7798(00)00048-1
Pergamon
Figure 1. Construction of the Zhenwu Mountain Tunnel. underground water level and hydraulic heads under or above the potential tunnel are adopted to determine boundary conditions; then a three-dimensional finite element analysis model of stratum seepage is established. In the last step of the research, a two-dimensional finite element equilibrium analysis for the Chongqing Zhenwushan Tunnels is performed to find the largest permeable volume and seepage forces around tunnel. Two kinds of cases are simulated: namely, seepage water is (1) drained out or (2) stopped. The results of these analyses results have become the important theoretical basis for waterproofing measures employed in Zhenwushan Tunnel (Fig. 1). The longest portion of this tunnel is 2040 m long, and its elevation in the roadway surface is +352.4 m. The tunnel lies in the hilly region in southeast of Chongqing, which belongs to the subtropical zone and has a moist climate and abundant rainfall. The area is full of underground rivers and pipes with water for the whole year; the highest water level is +457 m high. A section profile is shown in Figure 2.
2. Waterproof Criteria and Their Limitations in Chinese Tunnel Engineering 2.1 Waterproof Criteria in Chinese Tunnel Engineering A general waterproof requirement is stipulated in '%VaterproofCriterions in Underground Engineering" (GBJ10887). This requirement stipulates that prevention, drainage, interception and caulking should be integrated in synthetically controlling of water ingress in underground engineering. For various tunnel engineering works such as railway, highway and metro, a specific waterproof requirement and rank should be constituted according to the requirements on function and construction cost, as well as appearance. The general waterproof requirement is also set forth in "Design Criterions of Railway Tunnel" (TBJ3-85), "Construction Criterions of Railway Tunnel" (TBJ204-86) and "NATM Directory of Railway Tunnels". In addition, a complete preventive and drainage system is required to achieve a reliable and economical waterproof system. On the basis of general waterproofing requirements, surface water and underground water are controlled in the "Technical Standard of Highway Engineering" (JTJ01-88). Reliable prevention and drainage measurements are required for highways and A-class roads, in order to insure
228 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
safe transportation and a practicable drainage fixture in tunnels. "Design Specification for Highway Tunnel" (JTJ026-90) sets forth special requirements for A-road tunnels. This specification stipulates no water drops on the top arch and lateral walls, no accumulation of water on the tunnel ground, and no seepage surrounding the equipment holes. In addition, in frozen zones and during the frozen period, there must be no accumulation water behind the tunnel lining and no freezing water in the drainage ditch. In the "Code for the Design of Metros" (GB50157-92), it is demanded that (1) no seepage occur in the sections that are full of stations and equipment, and (2) no moisture appears on the surface. Further, no line-flow and no slurry-sand leakage should appear in other sections as well as in average tunnel works. Otherwise, if a small quantity seepage appears, its leaking capacity should be not more than 0.5L/m 2per day and night. In addition, some reinforcement should be employed at such special parts as movementjoints, construction joints, and preestablished pipes. If only waterproof concrete is employed in a corrosive medium, its anti-corrosion coefficient should not be less than 0.8; otherwise, other reliable measures should be taken.
2.2 Limitations of Chinese Tunnel Waterproof Criteria In most tunnel engineering, waterproofing methods should follow relative technical codes. Unfortunately, in China these criteria have limitations. First, waterproofing categories are ambiguous. Compared with those in other countries, waterproofing requirements and ranking methods are unclear. Since there is no specific approach, it is very difficult for engineers to deal with water ingress in design and construction practice based on vague concepts such as 'allowable seepage' or 'seepage prohibited'. Second, the definition of the waterproofing standard is relatively vague for different tunnel criteria. For example, except for a general waterproofing specification, no detailed requirements are established in the regime of railway tunnels. Furthermore, an A-class waterproofing design in a railway tunnel is by far different from that in a highway tunnel.
,F155,'.0cm Figure 2. Section of the Zhengwushan Tunnel.
Volume 15, Number 2, 2000
\ % K\, ,,\+ , \\, \
// /
/ ,.,.q
..,,,°,.
,°.4
/
, /
,,
,/,,/. ;,;4 ///#", '/' \\
X,,.//. f,.//t ,/,
I
I Waterproofing system with~l, second protection layer
Waterproofing system with second protect/on layer
Figure 3. Composite liining waterproofing method.
There are three main construction methods generally used in tunnel engineering in China: • the Deep Buried Method, which is mainly adopted for underwater tunnels; • the New Austrian Tunnel Method (NATM), which is mostly used for tunnels in mountainous geology; and • the Shield Tunnel Method, which is often employed for such metropolitan soft-soft underground engineering as metro. In many tunnel waterproofing technologies, a combination of watertight lining, drainage system, concrete grouting are the most popular methods of waterproofing in tunnel engineering.
With a smooth and glossy surface, the waterproof layer in a composite lining, which is mostly composed of PVC, ECB, EVA, LDPE and HDPE, should be fixed between the timbering and the moulding concrete. To prevent the watertight membrane from damage and assure a reliable waterproof layer, a 4-5-mm-thick foam plastic lining or 2.6~3.2m m waterproofing geo-textiles should be placed behind the watertight membrane, the joints of which should be fixed with plastic pipes, plastic washers, steel washers, wooden screw, etc. Two popular types of waterproof operations with composite lining are shown in Figure 3. The composite lining solution has been applied in many tunnel engineering projects, such as the Tokyo Gulf Underwater Highway Tunnel, Beijing-Xidan subway line, and Beijing-Jiujiang Wuzhishan Railway Tunnel. Because of problems with the previous waterproofing measures in the Fujian Gangtuo Mountain Tunnel work, which was composed of 2-cm sand-plasm smooth face, geotextiles and PE plastic waterproof layer, the waterproofing design was modified to a representative composite lining waterproofing method efficient enough to fulfill the waterproofing requirements. However, there are some inevitable disadvantages in this method. It is relatively difficult to protect timbering forms in the initial stages, and it requires a long construction period and is a rather complex operation to perform. Moreover, the means of its joint connection between waterproof planks cannot be guaranteed, and furthermore requires high-class welding craft. In addition, the waterproof plank is quite difficult to fix on the lateral tunnel, and thus is prone to damage during the operation process of the second lining. To achieve a complete watertight tunnel, as a consequence, a composite lining waterproofing should usually be combined with such other waterproof methods, such as drainage and grouting concrete.
3.1 Composite Lining
3.2 Double Lining
Composite lining is made up of timbering, moulding concrete and waterproof membrane. Because of its rationality and reliability, it is the most popular method of NATM in the world. It is apt to be erected in a dry or wet environment at lower cost, mid its operation process can be easily inspected. In a sufficiently reasonable tunnel operation, a watertight tunnel can be guaranteed. The gasket, if installed between lining layers, should be strong enough to bear hydraulic pressure.
Double lining, where a second lining separates moisture and oxygen in tunnels from the initial lining, is mainly used in shielding tunnelling. Because of the difficulties of ensuring a watertight pipe joint, when a higher waterproof rank is required, waterproof planks must be inserted between pipes and the second lining (see Fig. 4). A double lining can enhance the anti-permeability quality of the lining owing to its substantiality and concrete rigidity; waterproof concrete with high anti-permeability
Third, waterproof operation is unsatisfactory. Neither a general waterproofing provision nor systematic research on waterproof operations with respect to economy and efficiency has been realized in China. The standard on waterproofing operation and measurements is poorly constituted. Because no uniform assessment system is established, various waterproofing operations can be carried mainly on the basis o:Fpractical experience which, to some extent, has been proven unscientific by the water leakage that has occurred on finished tunnels. Practically, data provided to tunnel waterproofing designers is insufficienlL Because of the complex geological conditions and the high costs of engineering investigation, it is difficult to completely master information about underground water around tunnels. Consequently, the authors suggest testing along with reliable estimation as the evidence on which to bm,te waterproofing steps.
3. Current Application Status of Tunnel Waterproof in Chin~a
Volume 15, Number '2, 2000
TUNNELLINGANDUNDERGROUNDSPACE TECHNOLOGY229
1
5
-kl//i,/i/i,/i/I/i tl I I I
•
I I i ~ i I -I e l i
It 4 II
~
II
II
~
il
I I •i I I* I I I I I I I I I t i l ~ 2
'
'
.
1.RC pipes 2.Waterproofplank(t:2mm) 3.Second lining Concrete 4.Transerve section of stopping water construction 5.geotextiles 6.Concrete joints
Figure 4. Double lining waterproofing method. (>$8) therefore, is required. However, the tiny water seepage carries impurities that will leave an unsightly stain. More seriously, concrete cracks in the curing process, and water will find its way through even the finest of cracks resulting from the rigidification of concrete, despite the provision of adequate drainage systems in the invert. It is the capillary effect which draws water into these fine voids. Consequently, extra care must be taken with both the lining junctures and construction joints in deep-buried tunnels. To assure a long service period and reliable waterproofing action on the entire lining, emphasis should be paid to the water-cement ration of the concrete, and construction joints should be decreased to the greatest extent possible in order to control shrinkage cracks in moulding concrete. Furthermore, careful attention should be paid to waterproofing of construction joints when phase casting is done, and to treatment of junctures when precast brickwork lining is used. As a result, to create a watertight shield tunnel it is necessary to decrease cracks in the lining concrete; assure excellent waterproofing design and construction of joints; and insert a high-quality waterproof layer between the linings. For example, with a comprehensive waterproofing design ofjoints, lining and waterproofing coat, the waterproofing requirements for the East Yan'an Road cross-river Tunnel in Shanghai have been completely achieved.
tween the inner and outer layer and should be absorbed by the whole lining system. If concrete grouting is mixed with particle quartz, its density and anti-causticity will be improved and the strength to resist compression will be also enhanced, but its rebound value will be lowered. The spacing ratio in those mixtures with particle quartz are largely reduced due to its high water-absorbing quality, while its ability to resist sulphate and chloride is to some event strengthened. In addition, a single lining has no expansion joints. During the dangerous period of strength rising of the grouting concrete, stress resulting from subsidence should be lower than the tension strength of concrete by way of decreasing hydration heat, slightly grouting, and curing. As a consequence, the longitudinal reinforcement will prevent the tunnel structure from subsiding so that those specific expansion joints are unnecessary. Finally, a single lining does not require joints. Because of its favorable viscidity, concrete grouting can completely eliminate operation joints, which enables the single jet tunnel far from joints. However, drainage waterproofing is usually used in cooperation with other waterproofing methods.
3.4 Drainage Waterproofing Predicting the likely amount of water seepage into an underground structure is first employedto decideon drainage measures. Drainage waterproof measures can be executed according to the following steps. • S t e p 1. D r a i n i n g prior to lining. To enable the wall rock to drain easily, a large amount of underground water should be gathered into a longitudinal ditch before the lining is carried out. This method can be used as a lasting waterproofing measure to cure ungrouted tunnels. • S t e p 2 . S e t t i n g the w a l l r o c k d r a i n a g e groove. A wall rock drainage groove can be set up prior to or after the lining is installed in order to complement beforehand drainage, especially for seepage through diffusing, or to divert underground seepage water into the soffit of the lining so as to decrease the permeable pressure on the lining. • Step 3. P l a c i n g a l i n i n g d r a i n a g e trench. A trench with varying sections can be set up along or perpendicular to the lining joints. In "Technical Standard of Highway Engineering" (JTJ01-88), the least drainage slope is stipulated for drainage measures in tunnel engineering. To avoid too deep a wall footing or too low an excavation elevation in the bottom of the inverted arch, a central drainpipe should be provided
Inner Waterproofing
rock~?hoicret.
3.3 Single Lining Single lining, which is divided into two types of meas u r e s - n a m e l y , inner lining waterproofing and outer lining waterproofing--is an extension of the NATM, as shown in Figure 5. First of all, this type of lining is permeable. A permeable fast-setting agent must be employed into the outer grouting layer, while the inner grouting layer must be watertight. All hydraulic pressure acted the contact face be-
230 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
Outer Waterproofinz
~"
,hoicrete~rock
I "~
w°.e.p.oo..g \
WALLS
I INvKIrr
Figure 5. Single lining waterproofing method.
Volume 15, Number 2, 2000
forthose tunnels with an inverted arch or deep-buried ditch. In order to ensure the concrete lining without hydraulic pressure, an outer drainpipe should be set up at the base ofeach side ofthe concrete arch, outside concrete lining and waterproof membrane so as to reduce the seepage water out of the tunnels. Usually, drainage waterproofing is used in combination with other waterproof measures (see Fig. 6).
3.5 Concrete Grouting Waterproofing
Concrete grouting waterproofing, joints caulking and leakage jamming are employed for shield tunnels. Concrete grouting can improve the integrity of the wall rock in tunnels and can ameliorate hydraulic pressure on the lining. Chemical grouting and particle cement grouting are two kinds of common grouting measures that can be used to cure the seepage of i~inished tunnels, as well as efficiently prevent gushing during construction period (see Fig. 7). When common soil shielding and earth pressure shielding are dredging up, filling is jet-grouted into the outer space of the tube ~Lng to provide the correct grouting thickness. This procedure not only protects against tube seepage, but also ena~fles the groutinglayer to bring its own waterproof qualities into full play. If watertight materials with lasting stability are used, concrete grouting waterproofing can result in a permanent waterproofing effect. In addition, concrete grouting can be employed to treat movement joints of tunnels. For example, satisfactory waterproofing results were achieved with this method in the Beijing Fucheng Road Underground Heating Power tunnel and the Shanghai Dapujiang Road cross-river tunnel. However, there are some disadvantages to the concrete grouting waterproofing method. First, it is too expensive. Second, this method is far harder to control than other methods; in particular, it is difficult to inspect the installation procedure. Third, it is almost impossible to realize a complete watertight tunnel using only concrete grouting. In addition, the installation process is prone to injure the operators. Finally, it pollutes the environment. As a result, concrete grouting is taken as an accessory measure to tunnel waterproofing in China. For instance, both types of wall rock grouting--r.Lamely, in the entire section prior to lining and circularly after l i n i n g ~ a r e employed in the Ba Pang Lin Tunnel.
l.Wall rocks 2.Grouting 3.Pipes
Figure 7. Grouting in shield tunnels. Obviously, since little tunnel waterproofing research has been carried out in recent years in China, classification of tunnel waterproofing requirements is still unclear in various underground tunnels, and the design basis for waterproofing is far from sufficient. Therefore, it is essential to further investigate the optimization, economics and rationality of tunnel waterproofing measures. In the following sections, the water seepage volume in the mountain tunnel is reasonably estimated by means of a coupling analysis of the finite element method and boundary element method, which presents a reliable theoretical basis for waterproofing m e a s u r e s in the Chongqing Zhengwushan Highway Tunnel.
4. Numerical Modeling of Seepage Field 4.1 Darcy's Law Darcy's law [1] can be expressed as
v,=k~-~--k,,-~-k,z-~--(i
=x,y,z)
where v, is the seepage volume through unit area, and k~, k~y, and k~ are, separately, the seepage vector in the direction ofx, y, andz. Ifx andy are the total plane coordinate and z is the perpendicular coordinate, the hydraulic function is
h =z +P
2
(1)
o
(2)
in which z is THE position head obtained from a certain norm height, and p is the underground water pressure at some research point, and yis the specific weight of water. As for the incompressible fluid, its continuous equation is v~ - Q0 = 0 (3) in which Qo is underground water resource. If we assume that the research region is an ideal homogeneous media, then k . k,. k~ is constant and the partial differential equation o~see~age field can be obtained. k ~ (~---12+k i,
+Qo=O
(4)
On the basis of determinate boundary conditions and deviation theory, the following expression can be obtained through solving extremum:
l.Sprin8 Drainpipe 2.Jet concrete 3.Waterproof layer 4.Mouldin8 Concrete 5.Grainage aperture 6.Central draixtpipe7.roadsm'face
(5) in which Q is the unit seepage volume on the boundary, is the solving region on boundary F. If ~/(h) is equal to zero, then equation (4) can be obtained.
Figure 6. Drainage waterproofing.
Volume 15, Number 2, 2000
TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY231
4.2 Finite Element Method Based on the Finite Element Method, region ~ is discretized into n elements and, in term of element displacement function, certain elements of the hydraulic head function can be obtained. h = [N] {h}e (6) Then, [Kllh ie +{Q}e=O
(7)
n=l
where {Q}e is the seepage volume through the boundary or the seepage volume of equivalent joints from the boundary resource, [K]e is the element transmit matrix, and [K? =~ve[B]t[k][B]dV, in which [k] is the permeability coefficient and [B] is the geometrical matrix. We assume m joints per element; then
]
[~N1
aN=
/~N:
0N~
i (8)
[B =--~-/0Ni W -
Through assembly into a total matrix, the seepage volume governing equation for finite element analysis can be obtained. [K] {h} = {Q} (9)
4.3 Boundary Element Theory On the condition that F is the total boundary( F~ is the boundary of a certain tunnel in region ~ with homogeneous permeability medium_(its permeability coeffÉcient is k), and both hydraulic head h in partial boundary F and hydraulic head h / in partial boundary F, can be determined, then hydraulic head function in region l-I should conform to the following Laplasian expression. ~2h + ~2h ~2h =0 ~x 2 - ~ + ~--~which describes hydraulic head of any point in underground three-dimensional seepage field. Function h(x,y,z) is its solution and can lead to an equivalent hydraulic head figure. In this paper, the boundary region, which conforms to the above equation, is diverted into a specific boundary element. The total matrix is assembled according to the Finite Element Method, and then the underground water seepage volume can be conveniently obtained. The coupling method presented in this paper can be applied to problems regarding non-homogeneous and nonlinear seepage fields. In the following section, the seepage field simulation for the Chongqing Zhenwushan Tunnels is carried out.
(10)
tions, only half the space of the studied domain was discretized. Eight-node isoparametric elements with Gauss points were used. The computational analysis was performed for a steady state. The result gives the hydraulic heads at each node and the flow velocities at each Gauss point. The first step is to analyze the seepage distribution of mountain mass before excavating tunnels. Where the underground water level is the highest, a calculation section containing the tunnel transverse section is extracted. The boundary conditions were fixed after an examination of evolution of the hydraulic heads. That is, because of quasihydrostatic state of the water level above the tunnels before the excavation of tunnel, a constant hydraulic potential was imposed over the entire field. Thus, the boundary hydraulic head h at water level and h under the tunnels are taken as bo'undary elements, of whlch h is zero, and h; can be determined. The permeability coeffici'ent can be determined. Thus, the potential was prescribed around the tunnels. The second case assumes that drainpipes will drain all the seepage water from the mountain mass. In fact, at least prior to lining, the seepage water in tunnels will nearly be drained out. In this case, the hydraulic head h, in inner boundary of tunnel is zero, meaning that no hydraulic pressure was imposed on the lining. The calculated results obtained from the first case can be considered as other boundary conditions in this case. Thus, the contour of equivalent hydraulic heads at this transverse section around the tunnels can be obtained (see Fig. 8). The largest seepage volume at this studied position amounts to 250.8 cndday' m 2. In the final case, the NATM or other waterproof measures are employed so as to guarantee that no seepage water appears in the inner surface of tunnels, or all the drainpipes around tunnels are blocked. In this case, the tunnel face is impermeable, as is the tunnel lining, and all seepage hydraulic pressure from mountain mass will directly act on the lining of tunnels (see Fig. 9). The result indicates that, in the studied section, the greatest hydraulic pressure acting on tunnel surface amounts to a hydraulic head of 81 m.
6. Conclusions and Comments It has been proven that it is nearly impossible to achieve a completely watertight tunnel using one waterproofing
ttii it
b--...,
i,,
,71,
",,i l))l i i l ; t
13 i2 tI
852|. $ 7517.4 7:313.5 6~'ol. T
10 9
~los. o 55ol.
8 4e'se. ! 7 42~4.2 6 se,so. s 5 3086.5
z '
d 3
2482.6 lets. #
2 12T4.,J
I
~ r l . o4
I. sT. i t 6
5. Seepage Field Simulation In Zhenwushan Tunnels The numerical code solves the governing equation of seepage field in porous media. Because of the symmetry of the geometry and the boundary condi-
Figure 8. Seepage equivalent hydraulic heads around tunnels in the case of drainage (cm).
232 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
Volume 15, Number 2, 2000
$01T. e
--
-.,~..--..~.~..~.,-~,)..:"
"
~
"r-
$
"rlS0. 2
"t S3~J. 0
T$O~i. 2
,...-~.................................................................................................................
1,4,,.,
seepage takes place in tunnels, antipermeability ratings in corresponding tunnel parts should be stipulated, and a composite waterproof system should be encouraged. 6. Although there are some limitations in practice, the waterproofing application in the Zhenwushan Tunnel shows that it is indeed possible to achieve a completely watertight tunnel. The future development of tunnel waterproofing should encourage designers to use numerical methods for better prediction of seepage volume, leading to a economical and reasonably watertight tunnel.
7. References
Construction Ministry of China. 1988. t6~,0. I Waterproof Criterion in Underground Engineering (GBJ108-87). Beijing: Construction Press. Figure 9. Seepage equivalent hydraulic heads around tunnels in the case o f Davis, H.E.; Gunn, M.J.; Mair, R.J.; and no drainage (cm) . Seneviratne, H.N. 1980. The stability of shallow tunnels and underground openings in cohesivematerials. C-eotechnique30:397method alone, Consequently, multiple waterproofing mea416. sures must be integrated in underground works. Only Descoeudres, F. and Rybisar, J. 1987. Ecoulement d'une nappe through multiple waterproofing measures and layer upon livre vers un tunnel. Publication de la Socidtd Suisse de Mecaniq ue layer protection can tunnels without seepage be achieved. des Sols et des Roches, 115:3-7. The authors recommend that the following principles should Jaby J.F.; Mahuet J.L.; and Reith J.L. 1998. Improving of French specifications and techniques in waterproofing for underground be adhered to: works. Proceedings of the World Tunnel Congress'98 on Tunnels 1. Reasonable geological investigation should be carried and Metropolises, Sao Paulo, Brazil, 495-500. out as far as possible and as much information as Kondoh, Michio ; Matsuike, Takashi ;Kurano, Akiol and Kisaichi, possible obtained from the results of the investigation. Shin. 1998. Development of the waterproof membrane spraying 2. On the basis of the geological situation obtained, method in NATM tunnels. Proceedings of the World Tunnel prevention, dral~age, caulking and intercepting should Congress' 98 on Tunnels and Metropolises, Sao Paulo, Brazil, 515-521. synthetically be, employed to the tunnel waterproofKriekemans, Bert P. 1998. Polyurethane grouting for sealing leakage ing. Rigid waterproofing should be integrated with in tunnels. Proceedings of the World Tunnel Congress' 98 on flexible waterproofing. In addition, each waterproofTunnels and Metropolises, Sao Paulo, Brazil, 501-504. ing method should be evaluated according to it parLeca, E. and Panet, M. 1998. Application du calcul h la rupture fi la ticular characteristics with regard to underground stabilitd du front de taille d'un tunnel. Revue Francaise de works. Geotechnique 43:5-19. 3. A complex lining or double lining waterproofing sysMinistry of Railway. 1986. Design Criterions of Railway Tunnel (TBJ3-85). Beijing: Railway Press. tem should be a top priority and is highly recomMinistry of Railway of China. 1986. Construction Criterions of mended. Watertight lining should be brought into full Railway Tunnel (TBJ204-86). Beijing: Railway Press. action and both drainpipes and drain ditches should Ministry of Transportation of China. 1995. Technical Standard of be reasonably laid out. Highway Engineering (JTJ01-88), Beijing: Jiao Tong Press. 4. A high-performance waterproof layer and self-waterMinistry ofTransportation of China. 1990. Design Specification for proof lining materials should be used. Waterproofing Highway Tunnel (JTJ026-90). Beijing: JiaoTong Press. treatment of joints and movement should receive Planning Committee of Beijing. 1993. Code for the Design of Metro(GB50157-92). Beijing:Planing Press. special attention. Pellet, Frederic; Desceudres, Francois; and Egger, Peter. 1993. The 5. Three-dimensio~aal finite element analysis model has effect of water seepage on the face stability of an experimental been established in this paper and two-dimensional microtunnel. Canadian Geotechanical Journal 30,363-369. analysis has e~iciently shown the seepage distribuWallis, Shani. 1992. Putting paid to water leakage costs. Tunnels tion around tunnel sections. To guarantee that no & Tunnelling (January 1992),.51-54.
Volume 15, Number 2:, 2000
TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY233
Tunnel Waterproofing Practices in China Y. Yuan, X. Jiang and C. F. Lee A b s t r a c t --Water ingre~s in transportation tunnels not only will shorten the durability of concrete lining and reduce the function of establishments in the tunnel, but also will worsen the tunnel surrounding so much that the traffic will be greatly affected. In this situation, therefore, high maintenance costs are compulsory. In many cases, a perfect appearance is strongly recommended to take measures in order to prevent leakage. However, in China, tunnel waterproof requirements and standards for various special uses are considerably different, such that the basis which engineers apply to design in water-control is insufficient. Especially in montanic region, unpleasant geological condition confines engineers in working out more reasonable methods to stop water seepage, even leakage. In this paper, the current waterproofing requirements and measures in different spec,ial tunnels adopted in China are reviewed. The limitations of the popular methods in several practical cases applied to prevent water leakage, such as watertight lining, drainage system, as well as grouting, are analyzed at length. Then, some available measures, regarding concrete lining, watertight layer, drainage establishments as well as casting watertight concrete, are proposed, which we think indispensable for tunnel engineering to efficiently control water seepage and even completely prevent water leakage. In the end to analyze the seepage field in montanic tunnels, the finite element and boundary element coupling analysis method is presented. As an example, the seepage field in Zhenwushan tunnel of Chongqing is simulated. The calculation results coincide with the in-situ data well, and provide credible evidence for the waterproof measures which will be taken in that tunnel project. The method presented in this paper will save expenditures for surveying measures and will enable more reasonable and reliable waterproofing measures ~.o be taken. © 2000 Published by Elsevier ScienceLtd. All rights reserved.
Introduction ater ingress :in underground works remains quite difficult to assess. In many tunnels built long ago, seepage is unavoidable. Especially for tunnels in frozen zones, the tunnel ground may be icy and the top of the tunnel so covered with hanging icicles that traffic is interrupted. Given this situation, high maintenance costs are compulsory. For watA,~r supply tunnels through sewage layers and those furnished with wiring, a perfect appearance is usually strongly recommended to take measures in order to prevent leakage. However, in China, tunnel waterproofing requirements and standards for various special uses are considerably different, and the basiis on which engineers apply watercontrol design is insvfficient. Especially in mountainous regions, poor geological conditions compel engineers to devise more reasonable methods to step water seepage, and even leakage. As a result, many topics related to waterproofing-including the theoretical basis for water-control design, optimization of waterproof measures, and rationality of tunnel waterproof system--require further investigation.
W
Present addresses: Yuan Y. Ryan, Professor and Deputy Dean of the Department of Buildi:ag Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China; X. Jiang, Ph.D. candidate, Department of Building Engineering, Ton~i University, 1239 Siping Road, Shanghai 200092, China; C. F. Lee, Professor and Dean of the Department of Civil Engineering, The University of Hong Kong, Pokfulam l~bad, Hong Kong, China.
To treat underground water seepage reasonably and comprehensively by means of drainage and prevention, it is crucial for designers to understand the distribution of underground seepage field and the potential permeable volume at places excavated. During construction, the most critical zone is located at the tunnel face, where the decompression owing to excavation and water seepage forces generated by the water flow toward the face can lead to collapse of the face. Up to now, only a few papers have dealt with methods of assessing the supporting pressure and seepage volume at the tunnel face. Several of these methods have been based on the plasticity principle. Davis et al. (1980) established an analytical expression for cohesive and frictional soil in undrained conditions. Leca and Panet (1988) have studied the more complex case of cohesive and frictional soil in drained conditions. Descoeudres and Rybisaial have reviewed tunnel methods adopted in China. In this paper, the limitations of the popular methods in several practical cases applied to prevent water leakage, such as watertight lining, drainage systems, and grouting, are analyzed at length. Then some available measures relating to concrete lining, watertight layer, drainage establishment, and casting watertight concrete, are proposed. The authors consider these measures indispensable for tunnel engineering in order to efficiently control water seepage or even completely prevent water leakage. In addition, based on Darcy's law and the Finite Element Method along with Boundary Element Method, the threedimensional numerical simulation is employed to model the disturbance of the initial hydraulic conditions. That is, the
www, elsevier.comflocate/tust 7hnneUing and Underground Spa~:eTechnology,VoI. 15, No. 2, pp. 227-233, 2000 0886-7798/00/$ - see front matter © 2000 Published by Elsevier Science Ltd. All rights reserved. PII: S0866-7798(00)00048-1
Pergamon
Figure 1. Construction of the Zhenwu Mountain Tunnel. underground water level and hydraulic heads under or above the potential tunnel are adopted to determine boundary conditions; then a three-dimensional finite element analysis model of stratum seepage is established. In the last step of the research, a two-dimensional finite element equilibrium analysis for the Chongqing Zhenwushan Tunnels is performed to find the largest permeable volume and seepage forces around tunnel. Two kinds of cases are simulated: namely, seepage water is (1) drained out or (2) stopped. The results of these analyses results have become the important theoretical basis for waterproofing measures employed in Zhenwushan Tunnel (Fig. 1). The longest portion of this tunnel is 2040 m long, and its elevation in the roadway surface is +352.4 m. The tunnel lies in the hilly region in southeast of Chongqing, which belongs to the subtropical zone and has a moist climate and abundant rainfall. The area is full of underground rivers and pipes with water for the whole year; the highest water level is +457 m high. A section profile is shown in Figure 2.
2. Waterproof Criteria and Their Limitations in Chinese Tunnel Engineering 2.1 Waterproof Criteria in Chinese Tunnel Engineering A general waterproof requirement is stipulated in '%VaterproofCriterions in Underground Engineering" (GBJ10887). This requirement stipulates that prevention, drainage, interception and caulking should be integrated in synthetically controlling of water ingress in underground engineering. For various tunnel engineering works such as railway, highway and metro, a specific waterproof requirement and rank should be constituted according to the requirements on function and construction cost, as well as appearance. The general waterproof requirement is also set forth in "Design Criterions of Railway Tunnel" (TBJ3-85), "Construction Criterions of Railway Tunnel" (TBJ204-86) and "NATM Directory of Railway Tunnels". In addition, a complete preventive and drainage system is required to achieve a reliable and economical waterproof system. On the basis of general waterproofing requirements, surface water and underground water are controlled in the "Technical Standard of Highway Engineering" (JTJ01-88). Reliable prevention and drainage measurements are required for highways and A-class roads, in order to insure
228 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
safe transportation and a practicable drainage fixture in tunnels. "Design Specification for Highway Tunnel" (JTJ026-90) sets forth special requirements for A-road tunnels. This specification stipulates no water drops on the top arch and lateral walls, no accumulation of water on the tunnel ground, and no seepage surrounding the equipment holes. In addition, in frozen zones and during the frozen period, there must be no accumulation water behind the tunnel lining and no freezing water in the drainage ditch. In the "Code for the Design of Metros" (GB50157-92), it is demanded that (1) no seepage occur in the sections that are full of stations and equipment, and (2) no moisture appears on the surface. Further, no line-flow and no slurry-sand leakage should appear in other sections as well as in average tunnel works. Otherwise, if a small quantity seepage appears, its leaking capacity should be not more than 0.5L/m 2per day and night. In addition, some reinforcement should be employed at such special parts as movementjoints, construction joints, and preestablished pipes. If only waterproof concrete is employed in a corrosive medium, its anti-corrosion coefficient should not be less than 0.8; otherwise, other reliable measures should be taken.
2.2 Limitations of Chinese Tunnel Waterproof Criteria In most tunnel engineering, waterproofing methods should follow relative technical codes. Unfortunately, in China these criteria have limitations. First, waterproofing categories are ambiguous. Compared with those in other countries, waterproofing requirements and ranking methods are unclear. Since there is no specific approach, it is very difficult for engineers to deal with water ingress in design and construction practice based on vague concepts such as 'allowable seepage' or 'seepage prohibited'. Second, the definition of the waterproofing standard is relatively vague for different tunnel criteria. For example, except for a general waterproofing specification, no detailed requirements are established in the regime of railway tunnels. Furthermore, an A-class waterproofing design in a railway tunnel is by far different from that in a highway tunnel.
,F155,'.0cm Figure 2. Section of the Zhengwushan Tunnel.
Volume 15, Number 2, 2000
\ % K\, ,,\+ , \\, \
// /
/ ,.,.q
..,,,°,.
,°.4
/
, /
,,
,/,,/. ;,;4 ///#", '/' \\
X,,.//. f,.//t ,/,
I
I Waterproofing system with~l, second protection layer
Waterproofing system with second protect/on layer
Figure 3. Composite liining waterproofing method.
There are three main construction methods generally used in tunnel engineering in China: • the Deep Buried Method, which is mainly adopted for underwater tunnels; • the New Austrian Tunnel Method (NATM), which is mostly used for tunnels in mountainous geology; and • the Shield Tunnel Method, which is often employed for such metropolitan soft-soft underground engineering as metro. In many tunnel waterproofing technologies, a combination of watertight lining, drainage system, concrete grouting are the most popular methods of waterproofing in tunnel engineering.
With a smooth and glossy surface, the waterproof layer in a composite lining, which is mostly composed of PVC, ECB, EVA, LDPE and HDPE, should be fixed between the timbering and the moulding concrete. To prevent the watertight membrane from damage and assure a reliable waterproof layer, a 4-5-mm-thick foam plastic lining or 2.6~3.2m m waterproofing geo-textiles should be placed behind the watertight membrane, the joints of which should be fixed with plastic pipes, plastic washers, steel washers, wooden screw, etc. Two popular types of waterproof operations with composite lining are shown in Figure 3. The composite lining solution has been applied in many tunnel engineering projects, such as the Tokyo Gulf Underwater Highway Tunnel, Beijing-Xidan subway line, and Beijing-Jiujiang Wuzhishan Railway Tunnel. Because of problems with the previous waterproofing measures in the Fujian Gangtuo Mountain Tunnel work, which was composed of 2-cm sand-plasm smooth face, geotextiles and PE plastic waterproof layer, the waterproofing design was modified to a representative composite lining waterproofing method efficient enough to fulfill the waterproofing requirements. However, there are some inevitable disadvantages in this method. It is relatively difficult to protect timbering forms in the initial stages, and it requires a long construction period and is a rather complex operation to perform. Moreover, the means of its joint connection between waterproof planks cannot be guaranteed, and furthermore requires high-class welding craft. In addition, the waterproof plank is quite difficult to fix on the lateral tunnel, and thus is prone to damage during the operation process of the second lining. To achieve a complete watertight tunnel, as a consequence, a composite lining waterproofing should usually be combined with such other waterproof methods, such as drainage and grouting concrete.
3.1 Composite Lining
3.2 Double Lining
Composite lining is made up of timbering, moulding concrete and waterproof membrane. Because of its rationality and reliability, it is the most popular method of NATM in the world. It is apt to be erected in a dry or wet environment at lower cost, mid its operation process can be easily inspected. In a sufficiently reasonable tunnel operation, a watertight tunnel can be guaranteed. The gasket, if installed between lining layers, should be strong enough to bear hydraulic pressure.
Double lining, where a second lining separates moisture and oxygen in tunnels from the initial lining, is mainly used in shielding tunnelling. Because of the difficulties of ensuring a watertight pipe joint, when a higher waterproof rank is required, waterproof planks must be inserted between pipes and the second lining (see Fig. 4). A double lining can enhance the anti-permeability quality of the lining owing to its substantiality and concrete rigidity; waterproof concrete with high anti-permeability
Third, waterproof operation is unsatisfactory. Neither a general waterproofing provision nor systematic research on waterproof operations with respect to economy and efficiency has been realized in China. The standard on waterproofing operation and measurements is poorly constituted. Because no uniform assessment system is established, various waterproofing operations can be carried mainly on the basis o:Fpractical experience which, to some extent, has been proven unscientific by the water leakage that has occurred on finished tunnels. Practically, data provided to tunnel waterproofing designers is insufficienlL Because of the complex geological conditions and the high costs of engineering investigation, it is difficult to completely master information about underground water around tunnels. Consequently, the authors suggest testing along with reliable estimation as the evidence on which to bm,te waterproofing steps.
3. Current Application Status of Tunnel Waterproof in Chin~a
Volume 15, Number '2, 2000
TUNNELLINGANDUNDERGROUNDSPACE TECHNOLOGY229
1
5
-kl//i,/i/i,/i/I/i tl I I I
•
I I i ~ i I -I e l i
It 4 II
~
II
II
~
il
I I •i I I* I I I I I I I I I t i l ~ 2
'
'
.
1.RC pipes 2.Waterproofplank(t:2mm) 3.Second lining Concrete 4.Transerve section of stopping water construction 5.geotextiles 6.Concrete joints
Figure 4. Double lining waterproofing method. (>$8) therefore, is required. However, the tiny water seepage carries impurities that will leave an unsightly stain. More seriously, concrete cracks in the curing process, and water will find its way through even the finest of cracks resulting from the rigidification of concrete, despite the provision of adequate drainage systems in the invert. It is the capillary effect which draws water into these fine voids. Consequently, extra care must be taken with both the lining junctures and construction joints in deep-buried tunnels. To assure a long service period and reliable waterproofing action on the entire lining, emphasis should be paid to the water-cement ration of the concrete, and construction joints should be decreased to the greatest extent possible in order to control shrinkage cracks in moulding concrete. Furthermore, careful attention should be paid to waterproofing of construction joints when phase casting is done, and to treatment of junctures when precast brickwork lining is used. As a result, to create a watertight shield tunnel it is necessary to decrease cracks in the lining concrete; assure excellent waterproofing design and construction of joints; and insert a high-quality waterproof layer between the linings. For example, with a comprehensive waterproofing design ofjoints, lining and waterproofing coat, the waterproofing requirements for the East Yan'an Road cross-river Tunnel in Shanghai have been completely achieved.
tween the inner and outer layer and should be absorbed by the whole lining system. If concrete grouting is mixed with particle quartz, its density and anti-causticity will be improved and the strength to resist compression will be also enhanced, but its rebound value will be lowered. The spacing ratio in those mixtures with particle quartz are largely reduced due to its high water-absorbing quality, while its ability to resist sulphate and chloride is to some event strengthened. In addition, a single lining has no expansion joints. During the dangerous period of strength rising of the grouting concrete, stress resulting from subsidence should be lower than the tension strength of concrete by way of decreasing hydration heat, slightly grouting, and curing. As a consequence, the longitudinal reinforcement will prevent the tunnel structure from subsiding so that those specific expansion joints are unnecessary. Finally, a single lining does not require joints. Because of its favorable viscidity, concrete grouting can completely eliminate operation joints, which enables the single jet tunnel far from joints. However, drainage waterproofing is usually used in cooperation with other waterproofing methods.
3.4 Drainage Waterproofing Predicting the likely amount of water seepage into an underground structure is first employedto decideon drainage measures. Drainage waterproof measures can be executed according to the following steps. • S t e p 1. D r a i n i n g prior to lining. To enable the wall rock to drain easily, a large amount of underground water should be gathered into a longitudinal ditch before the lining is carried out. This method can be used as a lasting waterproofing measure to cure ungrouted tunnels. • S t e p 2 . S e t t i n g the w a l l r o c k d r a i n a g e groove. A wall rock drainage groove can be set up prior to or after the lining is installed in order to complement beforehand drainage, especially for seepage through diffusing, or to divert underground seepage water into the soffit of the lining so as to decrease the permeable pressure on the lining. • Step 3. P l a c i n g a l i n i n g d r a i n a g e trench. A trench with varying sections can be set up along or perpendicular to the lining joints. In "Technical Standard of Highway Engineering" (JTJ01-88), the least drainage slope is stipulated for drainage measures in tunnel engineering. To avoid too deep a wall footing or too low an excavation elevation in the bottom of the inverted arch, a central drainpipe should be provided
Inner Waterproofing
rock~?hoicret.
3.3 Single Lining Single lining, which is divided into two types of meas u r e s - n a m e l y , inner lining waterproofing and outer lining waterproofing--is an extension of the NATM, as shown in Figure 5. First of all, this type of lining is permeable. A permeable fast-setting agent must be employed into the outer grouting layer, while the inner grouting layer must be watertight. All hydraulic pressure acted the contact face be-
230 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
Outer Waterproofinz
~"
,hoicrete~rock
I "~
w°.e.p.oo..g \
WALLS
I INvKIrr
Figure 5. Single lining waterproofing method.
Volume 15, Number 2, 2000
forthose tunnels with an inverted arch or deep-buried ditch. In order to ensure the concrete lining without hydraulic pressure, an outer drainpipe should be set up at the base ofeach side ofthe concrete arch, outside concrete lining and waterproof membrane so as to reduce the seepage water out of the tunnels. Usually, drainage waterproofing is used in combination with other waterproof measures (see Fig. 6).
3.5 Concrete Grouting Waterproofing
Concrete grouting waterproofing, joints caulking and leakage jamming are employed for shield tunnels. Concrete grouting can improve the integrity of the wall rock in tunnels and can ameliorate hydraulic pressure on the lining. Chemical grouting and particle cement grouting are two kinds of common grouting measures that can be used to cure the seepage of i~inished tunnels, as well as efficiently prevent gushing during construction period (see Fig. 7). When common soil shielding and earth pressure shielding are dredging up, filling is jet-grouted into the outer space of the tube ~Lng to provide the correct grouting thickness. This procedure not only protects against tube seepage, but also ena~fles the groutinglayer to bring its own waterproof qualities into full play. If watertight materials with lasting stability are used, concrete grouting waterproofing can result in a permanent waterproofing effect. In addition, concrete grouting can be employed to treat movement joints of tunnels. For example, satisfactory waterproofing results were achieved with this method in the Beijing Fucheng Road Underground Heating Power tunnel and the Shanghai Dapujiang Road cross-river tunnel. However, there are some disadvantages to the concrete grouting waterproofing method. First, it is too expensive. Second, this method is far harder to control than other methods; in particular, it is difficult to inspect the installation procedure. Third, it is almost impossible to realize a complete watertight tunnel using only concrete grouting. In addition, the installation process is prone to injure the operators. Finally, it pollutes the environment. As a result, concrete grouting is taken as an accessory measure to tunnel waterproofing in China. For instance, both types of wall rock grouting--r.Lamely, in the entire section prior to lining and circularly after l i n i n g ~ a r e employed in the Ba Pang Lin Tunnel.
l.Wall rocks 2.Grouting 3.Pipes
Figure 7. Grouting in shield tunnels. Obviously, since little tunnel waterproofing research has been carried out in recent years in China, classification of tunnel waterproofing requirements is still unclear in various underground tunnels, and the design basis for waterproofing is far from sufficient. Therefore, it is essential to further investigate the optimization, economics and rationality of tunnel waterproofing measures. In the following sections, the water seepage volume in the mountain tunnel is reasonably estimated by means of a coupling analysis of the finite element method and boundary element method, which presents a reliable theoretical basis for waterproofing m e a s u r e s in the Chongqing Zhengwushan Highway Tunnel.
4. Numerical Modeling of Seepage Field 4.1 Darcy's Law Darcy's law [1] can be expressed as
v,=k~-~--k,,-~-k,z-~--(i
=x,y,z)
where v, is the seepage volume through unit area, and k~, k~y, and k~ are, separately, the seepage vector in the direction ofx, y, andz. Ifx andy are the total plane coordinate and z is the perpendicular coordinate, the hydraulic function is
h =z +P
2
(1)
o
(2)
in which z is THE position head obtained from a certain norm height, and p is the underground water pressure at some research point, and yis the specific weight of water. As for the incompressible fluid, its continuous equation is v~ - Q0 = 0 (3) in which Qo is underground water resource. If we assume that the research region is an ideal homogeneous media, then k . k,. k~ is constant and the partial differential equation o~see~age field can be obtained. k ~ (~---12+k i,
+Qo=O
(4)
On the basis of determinate boundary conditions and deviation theory, the following expression can be obtained through solving extremum:
l.Sprin8 Drainpipe 2.Jet concrete 3.Waterproof layer 4.Mouldin8 Concrete 5.Grainage aperture 6.Central draixtpipe7.roadsm'face
(5) in which Q is the unit seepage volume on the boundary, is the solving region on boundary F. If ~/(h) is equal to zero, then equation (4) can be obtained.
Figure 6. Drainage waterproofing.
Volume 15, Number 2, 2000
TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY231
4.2 Finite Element Method Based on the Finite Element Method, region ~ is discretized into n elements and, in term of element displacement function, certain elements of the hydraulic head function can be obtained. h = [N] {h}e (6) Then, [Kllh ie +{Q}e=O
(7)
n=l
where {Q}e is the seepage volume through the boundary or the seepage volume of equivalent joints from the boundary resource, [K]e is the element transmit matrix, and [K? =~ve[B]t[k][B]dV, in which [k] is the permeability coefficient and [B] is the geometrical matrix. We assume m joints per element; then
]
[~N1
aN=
/~N:
0N~
i (8)
[B =--~-/0Ni W -
Through assembly into a total matrix, the seepage volume governing equation for finite element analysis can be obtained. [K] {h} = {Q} (9)
4.3 Boundary Element Theory On the condition that F is the total boundary( F~ is the boundary of a certain tunnel in region ~ with homogeneous permeability medium_(its permeability coeffÉcient is k), and both hydraulic head h in partial boundary F and hydraulic head h / in partial boundary F, can be determined, then hydraulic head function in region l-I should conform to the following Laplasian expression. ~2h + ~2h ~2h =0 ~x 2 - ~ + ~--~which describes hydraulic head of any point in underground three-dimensional seepage field. Function h(x,y,z) is its solution and can lead to an equivalent hydraulic head figure. In this paper, the boundary region, which conforms to the above equation, is diverted into a specific boundary element. The total matrix is assembled according to the Finite Element Method, and then the underground water seepage volume can be conveniently obtained. The coupling method presented in this paper can be applied to problems regarding non-homogeneous and nonlinear seepage fields. In the following section, the seepage field simulation for the Chongqing Zhenwushan Tunnels is carried out.
(10)
tions, only half the space of the studied domain was discretized. Eight-node isoparametric elements with Gauss points were used. The computational analysis was performed for a steady state. The result gives the hydraulic heads at each node and the flow velocities at each Gauss point. The first step is to analyze the seepage distribution of mountain mass before excavating tunnels. Where the underground water level is the highest, a calculation section containing the tunnel transverse section is extracted. The boundary conditions were fixed after an examination of evolution of the hydraulic heads. That is, because of quasihydrostatic state of the water level above the tunnels before the excavation of tunnel, a constant hydraulic potential was imposed over the entire field. Thus, the boundary hydraulic head h at water level and h under the tunnels are taken as bo'undary elements, of whlch h is zero, and h; can be determined. The permeability coeffici'ent can be determined. Thus, the potential was prescribed around the tunnels. The second case assumes that drainpipes will drain all the seepage water from the mountain mass. In fact, at least prior to lining, the seepage water in tunnels will nearly be drained out. In this case, the hydraulic head h, in inner boundary of tunnel is zero, meaning that no hydraulic pressure was imposed on the lining. The calculated results obtained from the first case can be considered as other boundary conditions in this case. Thus, the contour of equivalent hydraulic heads at this transverse section around the tunnels can be obtained (see Fig. 8). The largest seepage volume at this studied position amounts to 250.8 cndday' m 2. In the final case, the NATM or other waterproof measures are employed so as to guarantee that no seepage water appears in the inner surface of tunnels, or all the drainpipes around tunnels are blocked. In this case, the tunnel face is impermeable, as is the tunnel lining, and all seepage hydraulic pressure from mountain mass will directly act on the lining of tunnels (see Fig. 9). The result indicates that, in the studied section, the greatest hydraulic pressure acting on tunnel surface amounts to a hydraulic head of 81 m.
6. Conclusions and Comments It has been proven that it is nearly impossible to achieve a completely watertight tunnel using one waterproofing
ttii it
b--...,
i,,
,71,
",,i l))l i i l ; t
13 i2 tI
852|. $ 7517.4 7:313.5 6~'ol. T
10 9
~los. o 55ol.
8 4e'se. ! 7 42~4.2 6 se,so. s 5 3086.5
z '
d 3
2482.6 lets. #
2 12T4.,J
I
~ r l . o4
I. sT. i t 6
5. Seepage Field Simulation In Zhenwushan Tunnels The numerical code solves the governing equation of seepage field in porous media. Because of the symmetry of the geometry and the boundary condi-
Figure 8. Seepage equivalent hydraulic heads around tunnels in the case of drainage (cm).
232 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
Volume 15, Number 2, 2000
$01T. e
--
-.,~..--..~.~..~.,-~,)..:"
"
~
"r-
$
"rlS0. 2
"t S3~J. 0
T$O~i. 2
,...-~.................................................................................................................
1,4,,.,
seepage takes place in tunnels, antipermeability ratings in corresponding tunnel parts should be stipulated, and a composite waterproof system should be encouraged. 6. Although there are some limitations in practice, the waterproofing application in the Zhenwushan Tunnel shows that it is indeed possible to achieve a completely watertight tunnel. The future development of tunnel waterproofing should encourage designers to use numerical methods for better prediction of seepage volume, leading to a economical and reasonably watertight tunnel.
7. References
Construction Ministry of China. 1988. t6~,0. I Waterproof Criterion in Underground Engineering (GBJ108-87). Beijing: Construction Press. Figure 9. Seepage equivalent hydraulic heads around tunnels in the case o f Davis, H.E.; Gunn, M.J.; Mair, R.J.; and no drainage (cm) . Seneviratne, H.N. 1980. The stability of shallow tunnels and underground openings in cohesivematerials. C-eotechnique30:397method alone, Consequently, multiple waterproofing mea416. sures must be integrated in underground works. Only Descoeudres, F. and Rybisar, J. 1987. Ecoulement d'une nappe through multiple waterproofing measures and layer upon livre vers un tunnel. Publication de la Socidtd Suisse de Mecaniq ue layer protection can tunnels without seepage be achieved. des Sols et des Roches, 115:3-7. The authors recommend that the following principles should Jaby J.F.; Mahuet J.L.; and Reith J.L. 1998. Improving of French specifications and techniques in waterproofing for underground be adhered to: works. Proceedings of the World Tunnel Congress'98 on Tunnels 1. Reasonable geological investigation should be carried and Metropolises, Sao Paulo, Brazil, 495-500. out as far as possible and as much information as Kondoh, Michio ; Matsuike, Takashi ;Kurano, Akiol and Kisaichi, possible obtained from the results of the investigation. Shin. 1998. Development of the waterproof membrane spraying 2. On the basis of the geological situation obtained, method in NATM tunnels. Proceedings of the World Tunnel prevention, dral~age, caulking and intercepting should Congress' 98 on Tunnels and Metropolises, Sao Paulo, Brazil, 515-521. synthetically be, employed to the tunnel waterproofKriekemans, Bert P. 1998. Polyurethane grouting for sealing leakage ing. Rigid waterproofing should be integrated with in tunnels. Proceedings of the World Tunnel Congress' 98 on flexible waterproofing. In addition, each waterproofTunnels and Metropolises, Sao Paulo, Brazil, 501-504. ing method should be evaluated according to it parLeca, E. and Panet, M. 1998. Application du calcul h la rupture fi la ticular characteristics with regard to underground stabilitd du front de taille d'un tunnel. Revue Francaise de works. Geotechnique 43:5-19. 3. A complex lining or double lining waterproofing sysMinistry of Railway. 1986. Design Criterions of Railway Tunnel (TBJ3-85). Beijing: Railway Press. tem should be a top priority and is highly recomMinistry of Railway of China. 1986. Construction Criterions of mended. Watertight lining should be brought into full Railway Tunnel (TBJ204-86). Beijing: Railway Press. action and both drainpipes and drain ditches should Ministry of Transportation of China. 1995. Technical Standard of be reasonably laid out. Highway Engineering (JTJ01-88), Beijing: Jiao Tong Press. 4. A high-performance waterproof layer and self-waterMinistry ofTransportation of China. 1990. Design Specification for proof lining materials should be used. Waterproofing Highway Tunnel (JTJ026-90). Beijing: JiaoTong Press. treatment of joints and movement should receive Planning Committee of Beijing. 1993. Code for the Design of Metro(GB50157-92). Beijing:Planing Press. special attention. Pellet, Frederic; Desceudres, Francois; and Egger, Peter. 1993. The 5. Three-dimensio~aal finite element analysis model has effect of water seepage on the face stability of an experimental been established in this paper and two-dimensional microtunnel. Canadian Geotechanical Journal 30,363-369. analysis has e~iciently shown the seepage distribuWallis, Shani. 1992. Putting paid to water leakage costs. Tunnels tion around tunnel sections. To guarantee that no & Tunnelling (January 1992),.51-54.
Volume 15, Number 2:, 2000
TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY233