EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL LINING CONSTRUCTED IN LAYERED SOIL

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1 Journal of Engineering Sciences, Assiut University, Vol. 38, No. 5, pp , September EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL LINING CONSTRUCTED IN LAYERED SOIL Mostafa Abdou Abd El-Naiem Associate Prof., Civil Engineering Department, Faculty of Engineering, Assiut University, Assiut, Egypt Mohamed Abdel-Basset Abdo Associate Prof., Civil Engineering Department, Faculty of Engineering, Assiut University, Assiut, Egypt (Received June 24, 2010 Accepted August 12, 2010) The study of the behavior of underground structures, such as transportation tunnels, pipe lines, or etc. to different types of loads is an engineering problem of soil-structure interaction. Numerical models for soil-tunnel have been considered as important design tools for many years. The accuracy of the results obtained depends on the knowledge of the input data for the tunnel and the surrounding soil. Many problems arise when the soil profile consists of layers including soft clay. One of these problems is expected to occur related to tunnel lining stability when soft clay layer lies upper, around or below tunnel lining. Even though in engineering practice tunnels are often designed considering only static or quasi static (creep), loading conditions, a non-negligible research effort has been devoted to investigate their behavior in layer soil including soft clay layer. In the present study, the behavior of tunnels constructed in layered soil including soft clay layer by using Finite Element Method has been studied. The tunnel lining is meshed with two dimensional elements, called BEAM 6 element. The soil is meshed with another two dimensional elements called LST, (Linearly Varying Strain Triangular Element). In this study, the main parameters were taken into consideration are the position and thickness of soft clay layer. It can be concluded that existing of soft clay layer lies near the tunnel lining strongly effects on the behavior of tunnel lining. For application of this study, Cairo Metro Tunnel- Line 2, was chosen. The results obtained from this study were compared with the initial values obtained from case of does not include soft clay layer. KEYWORDS: Tunnel, Soil-structure interaction, Finite Element Method, Stresses, Internal forces, deformation, soil, soft clay, Construction 1. INTRODUCTION The construction of tunnels is a subject of considerable importance to geotechnical and structural engineers. The study of the behavior of these structures, such as transportation tunnels, pipe lines, or etc. in layered soil including soft clay layer is 1101

2 1102 Mostafa Abdou Abd El-Naiem, Mohamed Abdel-Basset Abdo considered one of the most important problem in geotechnical engineering and considered one of the problematic soil, so, due to construction of tunnel lining in layered soil including soft clay layer, many geotechnical challenges are expected to occur related to soft clay layer, especially, if this layer exists upper, around or below tunnel lining. One of these problems arises when the tunnel constructed in layered soil due to compressibility of soft clay layer. To control the potential problem, the national authority for tunnels (NAT) has applied grouting to the soil around the tunnel lining. Consequently, the measured settlement in the field when the tunnel construction advanced was found to be significantly less than the estimated value without grouting and well within the allowable limit of 10 mm, set by the Egyptian standards (Abdel Salam, 1998: Documented file issued by NAT, 1999), [1]. Many problems related to the soil and tunnel stability were expected during the construction of the tunnel. In the present study, the behavior of tunnels constructed in layered soil including soft clay layer is studied. To asses and understand effect of existing soft clay layer in layered soil on the behavior of tunnel lining has been performed. The study is conducted using a 2-D finite element model. This study is carried out to investigate the behavior of tunnel lining constructed in layered soil including soft clay layer. Many level positions and thicknesses of soft clay layer to represent all expected possible cases were studied. The major objectives of this research are: (i) determination the effect of level of soft clay layer on the behavior of tunnel lining, (ii) determination the effect of soft clay layer thickness on the behavior of tunnel lining, (iii) determination the changes in normal force, shearing force and bending moment in tunnel lining due to existing of soft clay layer, and (iv) try to present the critical cases of study to take into consideration for design. 2. FINITE ELEMENT MODEL The finite element computer program FINAL (Swoboda, [2]) has been used in this study. This finite element model takes into account the effects of the vertical overburden pressure and the lateral earth pressure using two methods of solution, Dead Loads or Initial Stresses, in this analysis, Dead Loads method has been used. Also, this program takes into account the nonlinear properties of the soils and the linear properties of tunnel lining. Figure 1 shows the layout of 2-D soil-tunnel model and the used boundary conditions. The model has a length of 54.0 m and a height of 50.0 m including tunnel lining. The finite element model is shown in Figure 2. In addition, the dimensions of the 2-D model have been determined in order to eliminate the size effect in the prediction of the performance of tunnel lining. The soils, tunnel lining and the grouting are simulated using appropriate finite elements. A finite element model for soil, grouting, and tunnel lining for soil-tunnel interaction model was built. The soils and grouting were modeled using the 2-D elements, called LST elements, (Linearly Varying Strain Triangular Element), whereas, a tunnel lining was modeled using another 2-D elements, called BEAM 6 elements. Both BEAM 6 and LST elements have six nodes, each having two translation degrees of freedom as mentioned by Swoboda [3], and as shown in Figure 3. Calculations are carried out on the assumption that the tunnel lining is perfectly bonded to the surrounding grouting,

3 EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL 1103 which actually bonded to the surrounding soils. BEAM 6 element provides an acceptable solution for the finite element modeling problem, as it considers all possible deformations of tunnel lining. The advantages of this element are that, (i) it can describe the real behavior of the lining as an arched frame, (ii) it can combine with LST finite elements used for grouting and soil, (in this case it combines with LST grouting elements), and (iii) the number of elements required to model the lining with an acceptable accuracy is very small, Moussa [4]. Many studies have been presented to investigate the behavior of different structures in soft soil such as Wheeler et al. [5], Lee et al. [6], and Zhang [7]. Analysis of deformations or displacements in tunnel lining, grouting and soils, also, internal forces in tunnel lining was carried out using a 2-D plane strain finite element taking into consideration the linear elastic behavior of tunnel lining and plastic behavior of the ground materials as mentioned by Hasan, et al. [8]. Tunnel dimensions Figure 1. Layout of the model Figure 2. Finite element model Figure 3: Combined action between BEAM 6 and LST elements (after Swoboda [4])

4 Study Cases Mostafa Abdou Abd El-Naiem, Mohamed Abdel-Basset Abdo A cross section of tunnel opening is a circle has D inner diameter of 8.35 m and 0.40 m concrete lining thickness. A tunnel opining is surrounded with 0.20 m thickness grouting material. In this study, seven cases for different positions and thicknesses (H), of soft clay layer were studied. The details of each study case are presented in Table 1. Study case Table 1. Details of the study cases Soft clay layer Tunnel opening Position C.L. level H (m) C.L. level D (m) Case I (Initial case) No soft clay layer, - - (-17.5 m) 8.35 Case II Layer 2 (-7.5 m) 5.0 (-17.5 m) 8.35 Case III Layer 3 (-12.5 m) 5.0 (-17.5 m) 8.35 Case IV Layer 4 (-17.5 m) 5.0 (-17.5 m) 8.35 Case V Layer 5 (-22.5 m) 5.0 (-17.5 m) 8.35 Case VI Layer 6 (-37.5 m) 25.0 (-17.5 m) 8.35 Case VII Layers (-17.5 m) 15.0 (-17.5 m) 8.35 Where D is the inner diameter of an tunnel opening, H is the soil thickness of soft clay layer, and C.L. is the centre line of soft clay layer or tunnel opening Material Constants The material constants of tunnel line-2 of Cairo Metro, Egypt, at Km 4.234, were chosen for this study to represent the real practical properties of soil profile. These constants such as modulus of elasticity (E), Poisson s ratio (ν), density (γ), angle of internal friction ( ), cohesion (C and compressive strength (F c ) for different elements of the model are tabulated in Table 2, Mansour [9]. For properties and positions of soft clay layer were reasonably assumed to represent a case of study may be occurred in practical field, specially, soft clay soil always spreads in many regions in Egypt, and makes many problems in underground constructions. Material constant Soil Layer 1 Table 2. The Material constants of model Soil Layer 2 Soil Layer 3 Soil Layer 4 Soil Layer 5 Soil Layer 6 Conc. Lining 0.4 m Thick. Grouting 0.2 m Thick. E (KN/m 2 ) 6.0E6 9.0E6 36.0E6 80.0E6 95.0E6 16.0E7 33.5E9 1.1E9 ν γ (KN/m 3 ) C(KN/m 2 ) F c (Mpa)

5 EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL 1105 In the case of any layer which is taken as soft clay one, its constants will be taken as shown in Table 3. Material constant Table 3. The Material constants of soft clay layer E (KN/m 2 ) ν γ (KN/m 3 ) C(KN/m 2 ) Soft clay layer 36.0E ANALYSIS OF RESULTS AND DISCUSSIONS To study the behavior of tunnel lining due to existing of soft clay layer upper, around or below it, the internal forces in the critical points on tunnel lining have been determined. These critical points such as Crown, Shoulder_R and L, spring line_r and L, Knee_R and L, and Invert whose corresponding to position numbers 1, 2, 3, 4, 5, 6, 7, and 8, respectively, were chosen as shown in Figure 4. Figure 4: Layout of tunnel lining and critical points (R means Right, and L means Left) To analyze and illustrate the behavior of tunnel lining, many Figures were plotted such as deformation shapes, displacements, normal force diagrams, shearing force diagrams, and bending moment diagrams Deformation Shapes and Displacements The deformation shapes for tunnel lining and additional vertical displacements for soiltunnel model due to excavation of tunnel in layered soil including soft clay layer at different previous position were studied. a) The Deformation Shapes The deformation shapes of tunnel lining due to excavation of tunnel for all cases of study were illustrated as shown in Figure 5. The shapes are symmetrically about vertical centre line axis of a model, so, we consider only half model of tunnel lining.

6 1106 Mostafa Abdou Abd El-Naiem, Mohamed Abdel-Basset Abdo Case I (Initial case) Case II Case III Case IV Case V Case VI Case VII Figure 5. Deformation shapes of tunnel lining for all cases of study. From the deformation shapes of tunnel lining shown in Figure 5, in the case of soft clay layer level lies upper or at the centre line level of tunnel opening and its bottom level is upper the bottom level of tunnel lining (Invert) such as cases II, III, and IV, it can be found that the deformation shapes are approximately the same as the initial deformation shape obtained from case I (case of initial soil profile). On the other hand, when soft clay layer level lies under the centre line level of tunnel opening and its bottom level is under the bottom level of tunnel lining (Invert) such as cases V, VI, and VII, it can be found that the deformations are more than these obtained from other cases, and this due to compressibility of soft clay layer. Also, in the case of increasing thickness of soft clay layer leads to increase of deformations in tunnel lining as shown in case VII. b) The Displacements The displacements of soil-tunnel model for all cases of study were illustrated as shown in Figure 6. The displacements are symmetrically about vertical centre line axis of a model, so, we consider only half model of tunnel lining.

7 EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL 1107 Case I (Initial case) Case II Case III Case IV Case V Case VI Case VII Figure 6. Vertical displacements of soil-tunnel model for all cases of study. From the vertical displacements of soil tunnel shown in Figure 6, in the case of soft clay layer level lies upper or at the centre line level of tunnel opening and its bottom level is upper the bottom level of tunnel lining (Invert) such as cases II, III, and IV, it can be found that the displacements are approximately the same as the initial displacements obtained from case I (case of initial soil profile). On the other hand, when soft clay layer level lies under the centre line level of tunnel opening and its bottom level is under the bottom level of tunnel lining (Invert) such as cases V, VI, and VII, it can be found that the displacements are more than these obtained from other cases, and this due to compressibility of soft clay layer. Also, it can be noticed that by increasing thickness of soft clay layer leads to increase of displacements in soil layers as shown in case VII. From Figure 6, it can be concluded that existing part or whole of soft clay layer under the bottom level of tunnel lining (Invert point) strongly effect on the vertical

8 1108 Mostafa Abdou Abd El-Naiem, Mohamed Abdel-Basset Abdo displacements of tunnel lining, and also, deformation shapes and vertical displacements of soil layers Internal Forces in Tunnel Lining For all considered study cases, the normal forces, shearing forces and bending moments were plotted in the following Figures. The internal forces in critical nodes at tunnel lining were tabulated as shown in Table 4. Also, the maximum and minimum internal forces and their positions were tabulated in Table 5. Table 4. Internal forces in critical tunnel lining points for different study cases Internal forces Position of soft clay layer (KN) or Case Case Case I Case II Case III Case IV Case VI (KN.m) V VII N N N N N N N N Q Q Q Q Q Q Q Q M M M M M M M M

9 EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL 1109 Table 5. Maximum and minimum internal forces for different study cases Study case Case I (Initial) Case II Case III Case IV Case V Case VI Case VII N (KN) Q (KN) M (KN.m) Value Position Value Position Value Position -854 Between 2,3 ±94 5 (Invert) 82 1 (Crown) -232 Between 4,5 ±3 1 (Crown) 2 Many points -872 Between 2,3 ±94 5 (Invert) 87 1 (Crown) -229 Between 4,5 ±2 1 (Crown) 1 Between 1, Between 2,3-157 Between 1, (Crown) -167 Between 4,5-5 Between 5,6 2 Many points 3 (Spring 3 (Spring Between 3,4-178 line) line) (Crown) 9 Between 4,5 Between 4, ± Between 3,4 1 (Crown) 3 (Spring line) 5 (Invert) 3 (Spring line) Between 4,5-155 ±1-82 ± Between 5,6 1 (Crown) Between 1,2 1 (Crown) 4(Knee_R) Between 4, Between 3,4 Between 4,5 1 (Crown) Between 3,4 3 (Spring line) Between 5,6 From Tables 5 and 6, it can be noticed that, for the same point, compared with initial study case (Case I), value of internal normal force increases or decreases according to location of point at tunnel lining and position of soft clay layer relative to tunnel opening. Also, it can be found that, in some study cases, at the same point, the normal forces changed from compression to tension and vice versa, Also, values of shear forces and bending moments changed from positive to negative and vice versa. a) Normal Forces Figure 7 shows a comparison between the normal forces in tunnel lining obtained from initial study case (Case I) and these obtained from other study cases. (a) Initial N.F.D. (Case I) (b) N.F.D. (Case II)

10 1110 Mostafa Abdou Abd El-Naiem, Mohamed Abdel-Basset Abdo (c) N.F.D. (Case III) (d) N.F.D. (Case IV) (e) N.F.D. (Case V) (f) N.F.D. (Case VI) (g) N.F.D. (Case VII) Figure 7. N.F.D in tunnel lining for different study cases. Figure 7 shows the effect of soft clay layer in the values of internal normal forces in tunnel lining due to construction of tunnel opening in layered soil. From initial case I (which it does not include soft clay layer) and other six study cases with including of soft clay layer at different levels, it can be noticed that, for case II, the values of normal forces are approximately the same as these obtained from initial case (case I), as shown in Figure 7 (b), and this is because the centre line level of soft clay layer lies upper and far from the centre line level of tunnel opening. Whereas, for case

11 EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL 1111 III, because the centre line level of soft clay layer lies upper and near the centre line level of tunnel opening, the effect of soft clay layer began to appear and the maximum value of normal force in tunnel lining is more than 1.4 times that for initial case I as shown in Figure 7 (c). On the other hand, for case IV, because the centre line level of soft clay layer lies at the centre line level of tunnel opening, the effect of soft clay layer strongly appeared, and in spite of decreasing in the maximum value of normal force in tunnel lining compared with initial case, but there is another dangerous problem appeared where at some points the values of normal forces changed from compression to tension such as points around Crown, Knee_R and Knee_L as shown in Figure 7 (d). For case V, because the centre line level of soft clay layer lies below the centre line level of tunnel opening, the effect of soft clay layer strongly appeared, and in spite of decreasing in the maximum value of normal force in tunnel lining to half time compared with initial case, but there are some points have the values of normal forces changed from compression to tension such as points around Invert as shown in Figure 7 (e). For case VI, because the centre line level of soft clay layer lies deeply below the centre line level of tunnel opening, a little effect for soft clay layer appeared, and the values of normal forces in tunnel lining are approximately back to these obtained from initial case, as shown in Figure 7 (f). To show the effect of soft clay thickness, case VII were studied. The centre line level of soft clay layer lies at the centre line level of tunnel opening, and has 15.0 m thickness and a tunnel opening has 8.35 m internal diameter, and 0.4 m thickness of tunnel lining. This means that whole tunnel lining lies inside soft clay layer. From this study case, it can be found that in spite of decreasing in the maximum value of normal force in tunnel lining to become 0.9 time compared with initial case, but there are some points have values of normal forces changed from compression to tension such as points around Crown and Invert as shown in Figure 7 (g). Also, maximum value of tension normal force in tunnel lining is approximately two third time the maximum compression normal force obtained from initial case I. This means that this value of tension normal force should be taken into consideration in design of tunnel lining. So, it can be mentioned that, study case VII represents a critical case for design of tunnel lining. b) Shearing Forces Figure 8 shows a comparison between the shear forces in tunnel lining obtained from initial study case (Case I) and these obtained from other study cases. (a) Initial N.F.D. (Case I) (b) N.F.D. (Case II)

12 1112 Mostafa Abdou Abd El-Naiem, Mohamed Abdel-Basset Abdo (c) N.F.D. (Case III) (d) N.F.D. (Case IV) (e) N.F.D. (Case V) (f) N.F.D. (Case VI) (g) N.F.D. (Case VII) Figure 8. S.F.D in tunnel lining for different study cases. Figure 8 shows the effect of soft clay layer in the values of internal shearing forces in tunnel lining due to construction of tunnel opening in layered soil. From initial case I (which it does not include soft clay layer) and other six study cases with including of soft clay layer at different levels, it can be noticed that, for case II, the values of shearing forces are approximately the same as these obtained from initial case (case I), as shown in Figure 8 (b), and this is because the centre line level of soft clay layer lies upper and far from the centre line level of tunnel opening. Whereas, for case III, because the centre line level of soft clay layer lies upper and near the centre line level of tunnel opening, the effect of soft clay layer began to appear and the maximum value of shearing force in tunnel lining (at Shoulders) is more than and approximately 1.55 times that for initial case at invert point as shown in Figure 8 (c). On the other hand, for case IV, because the centre line level of soft clay layer lies at the

13 EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL 1113 centre line level of tunnel opening, the effect of soft clay layer strongly appeared, and the maximum value of shearing force in tunnel lining (points between Spring line and Knee) is more than and approximately 2.5 times that for initial case at invert point, but there is another dangerous problem appeared where at some points the values of shearing forces changed from positive to negative such as some points between Knee_R and Invert, as shown in Figure 8 (d). For case V, because the centre line level of soft clay layer lies below the centre line level of tunnel opening, the effect of soft clay layer appeared, and the maximum value of shearing force in tunnel lining is approximately the same as that in case III but the position of this value is opposite to that in case III, also, there are some points have the values of shearing forces changed from positive to negative and vice versa such as points around Invert as shown in Figure 8 (e). For case VI, because the centre line level of soft clay layer lies deeply below the centre line level of tunnel opening, a little effect for soft clay layer appeared, and the values of shearing forces in tunnel lining are approximately back to these obtained from initial case, as shown in Figure 8 (f). To show the effect of soft clay thickness, case VII were studied. The centre line level of soft clay layer lies at the centre line level of tunnel opening, and has 15.0 m thickness. The whole tunnel lining lies inside soft clay layer. From this study case, it can be found that in spite of decreasing in the maximum value of shearing force in tunnel lining to become 0.9 time compared with initial case, but in the case of shearing forces, at the same points, the values of maximum shearing forces are increasing to approximately 4.0 times these obtained from initial case I and there are some points have values of shearing forces changed from positive to negative and vice versa such as points around Crown and Invert, as shown in Figure 8(g). From Figure 8,(case of shearing forces), it can be found that the critical points whose more affected by soft clay layer are Shoulders and Knee. On the other hand, the Crown and Invert point are less affected by soft clay layer than others. This means that the values of shearing forces should be taken into consideration in design of tunnel lining. So, it can be mentioned that, study case VII represent a critical case for design of tunnel lining. c) Bending Moments Figure 9 shows the relationships between bending moment for the different studied cases. The estimated results were compared with the initial values obtained from initial case I of no existing soft clay layer in layered soil. (a) Initial N.F.D. (Case I) (b) N.F.D. (Case II)

14 1114 Mostafa Abdou Abd El-Naiem, Mohamed Abdel-Basset Abdo (c) N.F.D. (Case III) (d) N.F.D. (Case IV) (e) N.F.D. (Case V) (f) N.F.D. (Case VI) (g) N.F.D. (Case VII) Figure 9. B.F.D in tunnel lining for different study cases. Figure 9 shows the effect of soft clay layer in the values of bending moment in tunnel lining due to construction of tunnel opening in layered soil. From initial case I (which it does not include soft clay layer) and other six study cases with including of soft clay layer at different levels, it can be noticed that, for cases II and III, the values of bending moment are approximately the same as these obtained from initial case (case I), as shown in Figure 7 (b and c), and this is because the centre line level of soft clay layer lies upper and far from the centre line level of tunnel opening. For case IV, because the centre line level of soft clay layer lies at the centre line level of tunnel opening, the effect of soft clay layer strongly appeared, and the maximum value of shearing force in tunnel lining (Spring line) is more than and approximately three times that for initial case I, as shown in Figure 9 (d). Whereas, for case V, because the centre line level of soft clay layer lies below and near the centre line level of tunnel opening, the effect of soft clay layer appeared and there are increasing at some points and decreasing at others in the values of bending moment in tunnel lining compared with initial case I, but there is another dangerous problem appeared, where at some points the values of bending moment changed from negative to positive and vice versa such as points around Invert, Knee_R and Knee_L as shown in Figure 9 (e). For case VI, because the centre line level of soft clay layer lies deeply below the centre line level of tunnel opening, a little effect for soft clay layer appeared, and the values of bending moments in tunnel lining are approximately back to these obtained from initial case I, as shown in Figure 9 (f).

15 EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL 1115 To study the effect of soft clay thickness, case VII were studied. The centre line level of soft clay layer lies at the centre line level of tunnel opening, and has 15.0 m thickness and a tunnel opening has 8.35 m internal diameter. This means that whole tunnel lining lies inside soft clay layer. From this study case, it can be found that the maximum value of bending moment in tunnel lining increased to become 4.4 times these obtained from initial case I and at some points twice times these obtained from case study IV as shown in Figure 9 (d and g), also, there are some points have the values of bending moment changed from negative to positive and vice versa such as points around Invert. This means that both values of positive and negative bending moment should be taken into consideration in design of tunnel lining. From Figure 9, (case of bending moments), it can be found that the critical points whose more affected by soft clay layer are Crown, Invert and Spring lines. On the other hand, the shoulders and Knees are less affected by soft clay layer than others. This means that the changes in the values of bending moments should be taken into consideration in design of tunnel lining. So, it can be mentioned that, study case VII represents a critical case for design of tunnel lining. 4. CONCLUSIONS The present study concerned with the behavior of tunnel lining constructed in layered soil including soft clay layer at different levels. In this study, the main parameters were taken into consideration are position of soft clay layer corresponding to tunnel opening level, thickness of soft clay layer. The results obtained from this study were compared with the initial values obtained from case of no existing soft clay layer. Based on the presented discussion and analysis of obtained results, the following main conclusions are noted: (1) When the whole soft clay layer lies upper or below the whole tunnel opening, the effect is small and can be neglected, such as cases II and VI. (2) In the case of soft clay layer lies upper the centre line level of tunnel opening and its bottom level below top level of tunnel lining (Crown), and its thickness is less than internal diameter of tunnel opening (i.e. part of soft clay layer at zone of tunnel opening, case III), the effect considerably appears and should be taken into consideration in design of tunnel lining. (3) In the case of soft clay layer lies below the centre line level of tunnel opening and its top level upper bottom level of tunnel lining (Invert), and its thickness is less than internal diameter of tunnel opening (i.e. part of soft clay layer at zone of tunnel opening, case V), the effect considerably appears and should be taken into consideration in design of tunnel lining. (4) When centre line of soft clay layer lies at the centre line level of tunnel opening, the behavior of tunnel lining, case IV and VII, (deformations and internal forces), is strongly affect by soft clay layer. Also, this effect increased by increasing the thickness of soft clay layer. So, these previous two cases (IV & VII) represent critical cases for design of tunnel lining. (5) In the case of normal forces or bending moments in tunnel lining, the Crown (node 1) Spring line (nodes 3 & 7), and Invert (node 5) are more affected by soft clay layer than other nodes.

16 1116 Mostafa Abdou Abd El-Naiem, Mohamed Abdel-Basset Abdo (6) In the case of shearing forces in tunnel lining, the Shoulders (nodes 2 & 8) and Knee (nodes 4 & 6), are more affected by soft clay layer than other nodes. (7) The danger of existing soft clay layer in layered soil is that some of internal forces in tunnel lining have been changed in sign from compression to tension or from positive to negative and vice versa. (8) The behavior of tunnel lining is strongly affected by existing of soft clay layer if it exists near the tunnel opening. 5. REFERENCES 1. Abdel Salam, M.E. Urban Constraints on Underground Works the Cairo Metro- Case Histories, Egyptian Society Presentation, Cairo, (1998). 2. Swoboda, G. Program System FINAL- Finite Element Analysis Program for Linear and Nonlinear Analysis, Version 7.1, University of Innsbruck, Austria, Swoboda, G. "Finite Element Analysis of the New Austrian Tunnelling Method" 3 rd International Conference on Numerical Methods in Geomechanics, Aachen, pp , (1979). 4. Moussa, A., Finite Element Modelling of shotcrete in tunnelling, Ph.D. Dissertation, University of Innsbruck, Austria, Wheeler S. J., Naatanaen V. R., Karstunen M., and Lojander M., "An Anisotropic Elastoplastic Model for Soft Clays" Canadian Geotechnical Journal 40, pp , (2003). 6. Lee K. M., Manjunath A., and Dewaiker D. M., "Numerical and Model Studies of Strip Footing Support by a Reinforced Granular Fill Soft Soil System" Canadian Geotechnical Journal 36, pp , (1999). 7. Zhang L., "Settlement Patterns of Soft Soil Foundations Under Embankments" Canadian Geotechnical Journal 36, pp , (1999). 8. Hasan, H. A., El-Nahhas, F. and Belal, A.M. "Analysis of Rock-Lining Interaction for CircularTunnels using the Finite Element Simulation" Eleventh International Colloquium on Structural and Geotechnical Engineering, ICSGE, Ain Shams, Egypt, (2005). 9. Mansour, M., "Three Dimensional Numerical Modelling of Hydroshield tunneling" Ph. D. Thesis, University of Innsbruck, Austria, (1996). تأثير وجود طبقة من الطين اللين على ينشأ سلوك نفق في تربة مكونة من طبقات نظرر للكثافة ررسل كيرراةناسل ك ةكاررسل رر ل كمرر ال كارارر للمفررةلم انررسل كظررة للدنظرر للكد ىررةال ك رر ا ل رر لديررة ةل كمدصالتلممةلقر لارى ال كر لان رةول جردجل ار للكألنفرةق.لت ترر ل يرسل فنفرةقلمرال كمدتردلةتل كتر ل تهال كمهن ياال إلن ة ااالدمهن ي ل كت جاجلدنظ للكد رد ل ر ال فنفرةقلليرفةليرجضل ف لممرةلقر لانرت ل لنهةلر ل كم ةاةل كنةت سلمراللمثارسلتنفار ل فنفرةق لدكىةكرسل كتر لكهرةل ارر ل ففر للنر مةلارتالىفر ل كنفرقل رر لت رررسلمادنررسلمررالجرظررةتلم تثفررسلدف جرر لمررال كررطلا ل ىترردتل رر ال كجرظررةتللثرر لجرظررسلمررال كجرراال كثاا.لدنظ للفالمفةل ل كندعلمال كت رسلا تر لمال كندعل ك يلايربلافا لمال كم ةاةللن مةلاادال ر ل

17 ل( EFFECT OF SOFT CLAY LAYER ON BEHAVIOR OF TUNNEL 1117 لدلق ابلمالمنجظسل إلن ةو لممةلا ةلمال كت د لل كمثىسلل لمفةل ال كجرظسل ل اللترة للن ل يسل دتىثاةلمفةل ال كمن آت.لللل ل مالل ال ل ال كم ةاةل كت لا بللالتى ل ل اللترة للال كهردجل كنةت لمالىف ل كنفقلنتا سلد د لجرظرسل كجاال كثاالدا كطل كظدال ك ثاسل كمتدك لل ل يال كنفرقلنتا رسل نتر ةجل ر ال كجرظرسللتارداللارر لرافار ل مال كىةالتل ف ال كت لاللتىتديللث لمفةل ال كجرظسل كت افس لد لاتدقر للثر للر للمت ار تلمنهرةل مدتعلجرظسل كجاال كثاالرةكنيرسلكفتىسل كنفقل ةلللالاللدل لميتد اللدلليفثهلدا كطليمطلجرظسل كجاال كثاالمظة نسلمعل كظج ل ك ث لكثنفق.ل ل لالتتد ل كرىثلتال يسليتلىةالتلكمدتعلديمطلجرظسل كجاال كثاالكتمفةلم تث ل كىةالتل كت لاتدقعل لدتالمظة نسل ال كىةالتلرةكىةكسل فصثاسل كت لاللتىترديللثر لجرظرسل كجراال كثراا.لدت رمةلتثرطل كىةالتللن مةلتادالجرظسل كجاال كثاالللث ل كنفقلداللت ت طلم هل لليل ولدىةكرسللنر مةلتاردالللثر ل دت ت طلمعل كنفقل ل ولدل اللن مةلتاردال ر لنفرسلميرتدال كنفرقلدكاراليرماهةللقرةلمرالقجر ل كنفرق ل دتال يسلىةكسللن مةلتاردالجرظرسل كجراال كثراالليرفةل كنفرقلدت رت طلم رهل ر ل ر و لفرالىةكرسللنر مةلتاردال ليرفةل كنفررقلداللت ررت طلمررعل كنفرقل رر لليل رر ولدل رر اللنر مةلتاردال رر لنفررسلميررتدال كنفررقلدكارراليررماهةل لار لمالقج ل كنفق.ل ل دمالل ال كنتة ل كت لتال كتدصةلاكاهةلمال ل كرىثل دل اة لل لمظ ل كظدال ك ثاسلكرر ل كىرةالتل لال كىةكسل فصثاسلد ف ج لمال كطل دلت ا لندعل كظردال كمىد ارسل ك ثارسل ر ل يرال كنفرقللمرالتر جل ج د ر للنرهل ر ل اك ل لدك اس لدمالمد بلاك ليةكبلدك اسل لىةكسلقردال كظرولدلر دال النىنرةو لامرةل ىةكسل كظدال كمىد اسلدك دال كمتدك لل إالنظةجل كظمسلدكظةعلدف نةبل) Spring Crown, Invert, and lines لافر لتراف للرجرظرسل كجراال كثرااللرالررةق ل كنظرةج ل ر لىرااللنرهل ر لىةكرسلقردال كظرول رإال فاترة ل د ك ابل) Knees Shoulders (للاف لتاف and لللال ف ا.لامةلتال يتنتةجللاللار لترافا للنر مةلتاردال جرظررسل كجرراال كثرراال رر لنفررسلميررتدال كنفررقلدارر ل كررطل كتررافا لر اررة لليررمطلتثررطل كجرظررس لداارردالتافا ررةل ت ا لك سلاماالا مةكهلا لاةنتلجرظسل كجاال كثاالر ا للفلث للدلفيرفةللرالميرتدالم ار ل كنفرق.ل دلثاهل إالد رد لجرظرسلمرال كجراال كثراالق اررسلمرالم ار ل كنفرقلا ربللال ج اى ر لتافا رةلر راال اللتررة للنر ل تىثاةلدتصماال كنفق.للل ل