Transportation Geotechnics 44 (2024) 101171 Contents lists available at ScienceDirect Transportation Geotechnics journal homepage: www.elsevier.com/locate/trgeo A mechanical analysis model for tunnels under strike-slip faulting considering the fault zone width and nonlinear tunnel-stratum interaction Xiao Zhang a, b, c, Li Yu a, b, Mingnian Wang a, b, *, Henghong Yang a, b a School of Civil Engineering, Southwest Jiaotong University, Chengdu 610036, China Key Laboratory of Traffic Tunnel Engineering, Ministry of Education, Southwest Jiaotong University, Chengdu 610036, China c School of Transportation and Logistics, Southwest Jiaotong University, Chengdu 610036, China b A R T I C L E I N F O A B S T R A C T Keywords: Tunnel engineering Strike-slip fault Fault zone width Nonlinear tunnel-stratum interaction Mechanical response Tunnels crossing active fault zones are seriously damaged under the action of faulting. However, the influence of the fault zone width or nonlinear tunnel-stratum interaction is neglected in existing analytical models, resulting in incorrect estimation of the tunnel mechanical response. To aid in the seismic design of tunnels, a mechanical analysis model for tunnels under strike-slip faulting considering the effect of fault zone width and nonlinear tunnel-stratum interaction is first proposed in this work. The calculation results of the proposed model agree well with those obtained from the model test and numerical simulation, and the accuracy is obviously higher than that of the existing analytical methods. Compared with the FEM numerical model, the average errors of the peak bending moment, shear force and axial force calculated by the proposed model are 6.37 %, 11.00 % and 9.91 %, respectively. Neglecting the effect of fault zone width or nonlinear tunnel-stratum interaction, the tunnel response will be misestimated, e.g., when the fault displacement is 3 m and the crossing angle β is 90◦ , the overestimated value is approximately 40–110 %. Finally, the results of parameter analysis show that under the condition of 0◦ < β < 90◦ , the tunnel failure scope caused by the left-lateral strike-slip faulting is obviously larger than that caused by the right-lateral strike-slip faulting, while the conclusion is opposite under 90◦ < β < 180◦ ; the maximum strain within the tunnel correlates directly with fault displacement and the strength of the fault zone, exhibiting an inverse correlation with the width of the fault zone; meanwhile, the scope for tunnel failure is directly influenced by fault displacement, fault zone width, and the crossing angle (where 90◦ < β < 180◦ ), while inversely affected by the crossing angle (where 0◦ < β < 90◦ ) and the strength of the fault zone. t D C L n LF LH β V ux uy A E I Thickness Equivalent outer diameter Buried depth Length Number of elements Length in the footwall Length in the hanging wall Crossing angle Shear force Axial displacement Transverse displacement Cross-section area Young’s modulus Inertia moment l N M W WF WH Δf Δfx Δfy δx δy K0 Δx Δy χ Pxu Element length Axial force Bending moment Fault zone width Fault zone width in the footwall Fault zone width in the hanging wall Strike-slip displacement Axial displacement Transverse displacement Axial relative tunnel-stratum displacement Transverse relative tunnel-stratum displacement Lateral pressure coefficient Axial yield displacement Transverse yield displacement Axial bearing capacity * Corresponding author at: School of Civil Engineering, Southwest Jiaotong University, Chengdu 610036, China. E-mail addresses: xiao.zhang@swjtu.edu.cn (X. Zhang), yuli_1026@swjtu.edu.cn (L. Yu), 19910622@163.com (M. Wang). https://doi.org/10.1016/j.trgeo.2023.101171 Received 18 July 2023; Received in revised form 9 November 2023; Accepted 4 December 2023 Available online 10 December 2023 2214-3912/© 2023 Elsevier Ltd. All rights reserved. X. Zhang et al. Pχyu kχy Eχ Px Py f1 γχ cχ φχ kxx νχ Nch , Nqh χ χ Transportation Geotechnics 44 (2024) 101171 and cracking may occur. Additionally, Zhong et al. [21] pointed out that the increase in stratum stiffness in the fault zone reduces the extension but increases the severity of structural damage to the tunnel lining, which indicates that the fault zone width should be considered in tunnel response analysis. This point has also been widely recognized by many authors [17,22]. However, the numerical simulation of a tunnel crossing an active fault zone takes several hours even in a high-performance computer, which is not applicable to engineering design. Therefore, a series of analytical models have been proposed for the mechanical response analysis of a tunnel or pipeline under faulting. Newmark and Hall [23] first proposed a cable-like model for a pipeline under a strike-slip fault without considering the contribution of lateral stratum resistance. Kennedy [24] extended this model by considering stratum resistance, but the pipeline’s flexural stiffness is still not considered. Later, Wang and Yeh [25] partitioned the pipeline into four segments to compensate for the limitation of the cable-like models in neglecting the contribution of the pipeline’s flexural stiffness. In this model, the two high-curvature segments proximal to the fault are treated as circular arcs, while the two segments at the far ends are treated as elastic beams on an elastic foundation. After that, this model was improved and developed by many authors [26–31], and some shortcomings have been overcome. How­ ever, in these analytical models, the fault zone is simplified to a thin line, which is applicable to shallow buried pipelines (buried a few meters in the soft stratum), as shown in Fig. 3(a). The highway, railway and hy­ draulic tunnels crossing active fault zones are usually buried tens to hundreds of meters, and the fault zone width has a significant effect on the tunnel response [21], as shown in Fig. 3(b). Therefore, these models are not applicable to tunnels crossing active fault zones due to the neglect of the influence of fault zone width. Additionally, to assess the tunnel response under the action of fault zone displacement, a series of analytical models have been developed [32–37], and the effect of fault zone width is considered based on the elastic foundation beam theory. In these models, a tunnel crossing an active fault zone is simplified as an elastic beam acting on an elastic foundation, and the tunnel-stratum interaction is assumed to be linear. However, the relevant model tests [38] and numerical simulations [39] showed that the tunnel-stratum interaction stress increases nonlinearly with increasing fault displacement, indicating that the tunnel-stratum interaction has obvious nonlinearity. Therefore, this assumption is un­ realistic and can lead to incorrect estimation of the internal force of the tunnel under faulting. To this end, a mechanical analysis model for tunnels under strike-slip faulting considering the fault zone width and nonlinear tunnel-stratum interaction is proposed in this work, and the above weaknesses have been fixed. Transverse bearing capacity Transverse stiffness Young’s modulus Axial stratum stress Transverse stratum stress Coating dependent factor Unit weight Cohesion Friction angle Axial stiffness Poisson’s ratio Bearing capacity factor Note: Considering the stratum parameters of the fault zone and host rock, the parameter variable χ is introduced. The parameters of the fault zone for χ = f and host rock for χ = h. Introduction Active fault zones are widely distributed around the world, espe­ cially in China, the USA, Turkey and Japan. Generally, a fault zone consists of a fault core and a damage zone, and its width varies from tens to hundreds of meters [1,2], as shown in Fig. 1. With the development of infrastructure construction, it is inevitable that some tunnels will cross active fault zones, especially in seismically active regions. However, the displacement of the active fault zone would result in severe damage to tunnels, i.e., the 1906 San Francisco earth­ quake caused severe damage to two tunnels crossing the San Andreas fault [3]; the 1999 Chi-Chi earthquake in Taiwan caused significant damage to many nearby tunnels due to the displacement of the Che­ longpu fault [4]; the 2008 Wenchuan earthquake in China resulted in severe damage to several tunnels along the Duwen expressway [5]; and the 2016 Kumamoto earthquake in Japan severely damaged the Toyama tunnel near the fault [6]. Most notably, during the 2022 Menyuan earthquake in China, the Daliang tunnel suffered severe damage due to a 3 m strike-slip fault displacement [7,8], as plotted in Fig. 2. Therefore, the mechanical response of tunnels under faulting has been widely investigated. A series of model tests [9–14] and numerical simulations [15–20] have been conducted to investigate the tunnel response under faulting. The results show that the tunnel is subjected to a combination of tensile (compressive), bending and shearing and experiences an elongated ‘S’shaped deformation along the tunnel axis; the tunnel internal forces increase with increasing fault displacement, stratum stiffness and tunnel stiffness; under the action of fault zone displacement, the tunnel will be severely damaged, especially near the fault zone, where tunnel collapse Establishment of the proposed model Outline The proposed model is plotted in Fig. 4, where the strike-slip displacement is Δf, the crossing angle is β (0◦ < β < 180◦ ), the tunnel equivalent diameter is D (i.e., the diameter of a circular tunnel with the same area as the prototype tunnel), the lining thickness is t, the burial depth is C, the fault zone width is W (WF in the footwall and WH in the hanging wall) and the tunnel length is L (LF in the footwall and LH in the hanging wall). Note that the fault core is simplified to a fault plane, as the width of the fault core is much smaller than that of the damage zone. This simplification has been widely employed in previous works [17]. The left- and right-lateral strike-slip faults and crossing angles β are considered in this work, as shown in Fig. 4(a) and (b). As plotted in Fig. 4, the axial and transverse fault displacements Δfx and Δfy acting on the tunnel can be calculated by Eq. (1) and Eq. (2). The value of Δf is positive (+) for left-lateral strike-slip faults and negative (-) for right-lateral strike-slip faults. Fig. 1. Conceptual model of a fault zone illustrating the main architectural elements: damage zone and fault core. 2 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 Fig. 2. Daliang tunnel damaged due to strike-slip faulting in the 2022 Menyuan earthquake [7,8]: (a) circumferential crack; (b) collapsed lining; (c) bulging invert; (d) spalling lining. Fig. 3. Schematic diagram of (a) a shallow pipeline and (b) a deep tunnel crossing an active fault zone. Δfx = Δf cosβ (1) Δfy = Δf sinβ (2) where N is the axial force caused by the combined action of axial and transverse displacements, which will be discussed later. Based on Eq. (3), the following equation of moment equilibrium is obtained: Derivation of the governing equation Based on previous studies [31,40], a tunnel crossing an active fault zone is simplified as a large-deformed beam acting on a nonlinear foundation, as shown in Fig. 5. The tunnel-stratum interaction is described by a series of nonlinear springs, and the fault displacements are applied at the ends of the springs. The different mechanical char­ acteristics of the fault zone and host rock are reflected by different stratum stiffnesses. Considering the different stratum parameters of the fault zone and host rock, the parameter variable χ is introduced. The parameters of the fault zone for χ = f and host rock for χ = h. For − (4) where uy is the transverse displacement of the tunnel. The bending moment of the tunnel is [41]: M = − EI d2 uy dx2 (5) where I and E are the inertia moment and Young’s modulus of the tunnel, respectively. Based on Eq. (4) and Eq. (5), yields: f instance, the nonlinear transverse stiffness of the fault zone is ky , and the nonlinear stiffness of the host rock is khy . Under the action of fault dis­ EI placements (Δfx and Δfy) and stratum stresses (Px and Py), the tunnel is subjected to axial force N, shear force V and bending moment M, as plotted in Fig. 5. According to Fig. 5, the microelement equilibrium of moment yields: Py dM + M + Vdx + Ntanθdx = M + (dx)2 2 dM duy =N +V dx dx d3 uy duy =N +V dx3 dx (6) By taking the derivative from both sides of Eq. (6), yields: EI (3) d4 uy dN duy d2 uy dV = +N 2 + dx dx dx dx4 dx (7) From the microelement equilibrium of forces in the y-direction, 3 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 Fig. 4. (a) A tunnel crossing an active fault zone, (b) left-lateral strike-slip fault with 0◦ < β < 90◦ , (c) left-lateral strike-slip fault with 90◦ < β < 180◦ , (d) rightlateral strike-slip fault with 0◦ < β < 90◦ and (e) right-lateral strike-slip fault with 90◦ < β < 180◦ . yields: dV = Py dx δy = Δfy − uy (8) Based on Eq. (4) ~ Eq. (10) yields the governing equation of trans­ verse tunnel displacement uy: The nonlinear transverse stratum stress Py is proportional to the value of the relative transverse tunnel-stratum displacements δy and nonlinear stratum stiffnesses kχy : Py = kyχ δy (10) EI d4 uy N d2 uy 1 dN duy − − + uy = Δfy kyχ dx4 kxχ dx2 kxχ dx dx (9) (11) Derivation of the axial force equation Based on previous studies [31,40], the axial force N of a large deformed tunnel consists of a frictional axial force Na (caused by fric­ tional axial tunnel-stratum interaction) and a membrane axial force Nb The relative transverse tunnel-stratum displacements δy can be calculated by 4 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 Fig. 5. Schematic diagram of a tunnel in bending, tension and shearing. (caused by large transverse deflection). Neglecting the term Nb leads to erroneous results of tunnel response under faulting [27,31,40]. N = Na + Nb = EA(εa + εb ) The membrane axial strain εb of the tunnel owing to this large transverse deflection is derived as [31,40]: √̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅ du (18) εb = 1 + ( y )2 − 1 dx (12) where A is the lining cross-sectional area; εa and εb are the axial strains caused by frictional axial tunnel-stratum interaction and trans­ verse deflection, respectively. Using the following series expansion yields: √̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅ du 1 du 1 du εb = 1 + ( y )2 = 1 + ( y )2 − ( y )4 … 2 dx 8 dx dx (1) The frictional axial force Na The higher-order terms in Eq. (19) are deleted under the premise of ensuring the calculation accuracy. Therefore, the membrane axial strain εb and axial force Nb can be calculated by In the axial direction, the tunnel is subjected to the axial fault displacement Δfx and frictional stress Px, resulting in axial tunnel displacement ux and axial force Na, as shown in Fig. 6. The axial force Na of the tunnel is [41]: Na = EAεa = EA dux dx 1 duy 2 ) 2 dx (13) Nb = EAεb = by (14) Due to the nonlinear stratum stiffnesses kχx and kχy , it is difficult to obtain the analytical solution of tunnel displacements ux and uy. Therefore, the finite difference method is used to solve the governing equations Eq. (11) and Eq. (17). As shown in Fig. 7, a tunnel with a length of L is discretized along the axial direction into n + 5 node ele­ ments (including four virtual node elements), and the element length is l = L/n. (15) (16) Based on Eq. (14) ~ Eq. (16), the differential equation of axial tunnel displacement ux is: − EA d2 ux + ux = Δfx kxχ dx2 (21) Solution of the governing equations The relative axial tunnel-stratum displacements δx can be calculated δx = Δfx − ux ( )2 EA duy 2 dx Note that the key problem in analysing the tunnel response under faulting is to solve the governing equations of the axial and transverse tunnel displacements ux and uy, i.e., Eq. (11) and Eq. (17). The nonlinear axial stratum stress Px is a function of the relative axial tunnel-stratum displacement δx and nonlinear stratum stiffnesses kχx : Px = kxχ δx (20) εb = ( According to Eq. (13), the axial tunnel displacement ux must be ob­ tained to calculate the axial force Na. Therefore, the governing equation of the axial tunnel displacement ux is derived herein. From the free body equilibrium of forces in the x-direction in Fig. 6, yields Na = Na + Px dx + dNa (19) (17) (2) Membrane axial force Nb Fig. 7. Discretization of the tunnel. Fig. 6. The frictional axial tunnel-stratum interaction. 5 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 Solution of the axial tunnel displacement ux According to the finite difference method, the difference expression of Eq. (17) is: ) EA ( − χ 2 ux,i+1 − 2ux,i + ux,i− 1 + ux,i = Δfx,i kx,i l (22) where kχx,i , ux,i and Δfx,i are the axial stratum stiffness, tunnel displacement and fault displacement of node i, respectively. The frictional axial force Na at both ends of the tunnel is zero, i.e., Na,0 = Na,n = 0. According to the finite difference method and Eq. (13), the difference expressions of the boundary conditions are: Na,0 = ) EA ( ux,1 − ux,− 1 = 0 2l ux,n+1 = ux,n− 1 (26) (39) (41) [ [A](n+1)×(n+1) = [A2 ](n+1)×(n+1) − [A1 ](n+1)×(n+1) (28) ... ux,n ]Tn+1 (29) ... Δfx,i ... ux,i ]T Δfx,n n+1 ] [ Δfy = Δfy,0 (30) Solution of the transverse tunnel displacement uy According to the finite difference method, the difference expression of Eq. (11) is: kxχ = ) ) EI ( Ni ( χ 4 uy,i+2 − 4uy,i+1 + 6uy,i − 4uy,i− 1 + uy,i− 2 − χ 2 uy,i+1 − 2uy,i + uy,i− 1 ky,i l ky,i l kyχ = (31) where Ni, kχy,i , uy,i and Δfy,i are the axial force, transverse stratum stiffness, transverse tunnel displacement and transverse fault displace­ ment of node i, respectively. The axial force N, bending moment M and shear force V at both ends of the tunnel are zero. According to the finite difference method and the elastic beam theory, the difference expressions of the boundary condi­ tions are: M0 = − ) EI ( uy,1 − 2uy,0 + uy,− 1 = 0 l2 ) EI ( Mn = − 2 uy,n+1 − 2uy,n + uy,n− 1 = 0 l (34) Vn = − ) EI ( uy,n+2 − 2uy,n+1 + 2uy,n− 1 − uy,n− 2 = 0 2l3 (35) Δfy,1 Δfy,2 ⎧P x ⎪ ⎪ ⎨ |δ | ... uy,n ]Tn+1 ]T ... Δfy,n n+1 ... Δfy,i Δx⩽|δx | χ ⎪ ⎪ ⎩ Pxu Δx 0⩽|δx | < Δx (42) (43) ⎧ Py ⎪ ⎪ ⎪ ⃒⃒δ ⃒⃒ ⎨ ⃒ ⃒ Δy⩽⃒δy ⃒ ⎪ Pχ ⎪ ⎪ ⎩ yu Δy ⃒ ⃒ 0⩽⃒δy ⃒ < Δy (44) x y Pχxu = παχ cχ D + πCDγχ (33) ) EI ( uy,2 − 2uy,1 + 2uy,− 1 − uy,− 2 = 0 2l3 ... uy,i (45) where Pχxu and Pχyu are the bearing capacities of the axial and trans­ verse stratum, respectively; Δx and Δy are the corresponding yield displacements of the tunnel-stratum interaction; and the relative axial and transverse tunnel-stratum displacements δx and δy can be calculated by Eq. (16) and Eq. (10), respectively. χ χ The axial and transverse stratum bearing capacity Pxu and Pyu can be calculated by [42]: (32) V0 = − uy,2 Nonlinear tunnel-stratum interaction To solve the equations of tunnel displacements, Eq. (27) and Eq. (40), χ χ the key point is to calculate the nonlinear stratum stiffnesses kx and ky . The widely recognized nonlinear structure-stratum interaction curves recommended by design guideline [42] are employed in this work as an example, see Fig. 8. In addition, to assess the tunnel response under both left- and right- lateral strike-slip faulting (see Fig. 4) with uniform governing equations, it is assumed that these springs can withstand compression and tension. Otherwise, it is necessary to establish different calculation models for different situations. The force vector applied to the tunnel by these springs is shown in Fig. 8. According to Fig. 8, the axial and transverse stratum stiffnesses kχx and kχy can be calculated by The calculation of matrix [A] is detailed in Appendix A. ) ( 1 − χ 2 (Ni+1 − Ni− 1 ) uy,i+1 − uy,i− 1 + uy,i = Δfy,i 4ky,i l uy,1 The calculation of matrix [B] is detailed in Appendix B. where Δfx,2 uy,n+2 = 4uy,n − 4uy,n− 1 + uy,n− 2 [ ] uy = [ uy,0 (27) [A][ux ] = [Δfx ] Δfx,1 (38) where According to Eq. (22) ~ Eq. (26), the axial tunnel displacement ux can be calculated by [ [Δfx ] = Δfx,0 uy,n+1 = 2uy,n − uy,n− 1 (24) (25) ... (37) [B](n+1)×(n+1) = [B1 ](n+1)×(n+1) − [B2 ](n+1)×(n+1) − [B3 ](n+1)×(n+1) + [B4 ](n+1)×(n+1) ux,− 1 = ux,1 ux,2 uy,− 2 = 4uy,0 − 4uy,1 + uy,2 According to Eq. (31) ~ Eq. (39), the transverse tunnel displacement uy can be calculated by [ ] [ ] (40) [B] uy = Δfy Therefore, the axial tunnel displacement ux of nodes − 1 and n + 1 can be obtained as follows: ux,1 (36) (23) ) EA ( Na,n = ux,n+1 − ux,n− 1 = 0 2l [ux ] = [ ux,0 uy,− 1 = 2uy,0 − uy,1 1 + K0 tan(f1 φχ ) 2 (46) (47) χ χ χ χ Pχyu = Nch c D + Nqh γ CD where c is the stratum cohesion, γ is the stratum unit weight, K0 is the lateral pressure coefficient, αχ is the adhesion factor, φχ is the stra­ tum friction angle, f1 is the coating dependent factor, and the bearing χ χ capacity factors Nch and Nqh can be interpreted from design charts [42]. χ Therefore, the transverse tunnel displacement uy of nodes − 1, − 2, n + 1 and n + 2 can be obtained as follows: 6 χ X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 Fig. 8. Nonlinear tunnel-stratum interaction curves [42] in the (a) axial and (b) transverse directions. Calculation process To obtain the values of the nonlinear stratum stiffnesses kχx and kχy , a novel iterative method is proposed in this section. In short, the stratum stiffnesses kχx and kχy are continuously decreased until the tunnel dis­ placements and axial force N converge. The specific calculation process is as follows (see Fig. 9): f f (2) The 1st iteration calculation. • Calculate the initial tunnel displacements ux,i,1 and uy,i,1 by Eq. (27) and Eq. (40). • Calculate the initial relative tunnel-stratum displacements δx,i,1 and δy,i,1by Eq. (16) and Eq. (10). Ni Mi (D − t) + A 2I (51) Ni Mi (D − t) − 2I A (52) σ i,left (53) E σ i,right E (54) Note that the positive strain indicates the tensile state, and the negative strain represents the compressive state. f Comparison with the model test Parameters f the j-1th stratum stiffnesses khx,i,j− 1 , khy,i,j− 1 , kx,i,j− 1 and ky,i,j− 1 into Eq. (27) and Eq. (40). • Calculate the jth relative tunnel-stratum displacements δx,i,j and δy,i,j by Eq. (16) and Eq. (10). Wang et al. [43] conducted 1 g model tests to investigate the me­ chanical response of a tunnel subjected to right-lateral strike-slip fault­ ing, as shown in Fig. 10. The detailed testing parameters are shown in Table 1. In the theoretical model analysis, the tunnel-stratum interaction properties are calculated by the guideline [42], as shown in Table 2. Note that the coating-dependent factor f1 of the tunnel-stratum interface is 0.7, as smooth gypsum is used to simulate the tunnel in the model tests. f • Calculate the jth stratum stiffnesses khx,i,j , khy,i,j , kx,i,j and ky,i,j by Eq. (44) and Eq. (45). • Calculate the jth membrane axial forceNb,i,j by Eq. (21). Equations of the tunnel forces and stresses The tunnel axial force Ni, bending moment Mi and shear force Vi of node i can be calculated according to the finite difference method in difference form: ) EA( )2 EA ( ux,i+1 − ux,i− 1 + 2 uy,i+1 − uy,i− 1 2l 8l (50) εi,right = Eq. (44) and Eq. (45). • Calculate the initial membrane axial force Nb,i,1 by Eq. (21). (3) The j (j > 1)th iteration calculation. • Calculate the jth tunnel displacements ux,i,j and uy,i,j by substituting Ni = ) Ni ( ) EI ( uy,i+2 − 2uy,i+1 + 2uy,i− 1 − uy,i− 2 − uy,n+1 − uy,n− 1 2l3 2l εi,left = • Calculate the initial stratum stiffnesses khx,i,1 , khy,i,1 , kx,i,1 and ky,i,1 by f Vi = − σ i,right = f f (49) σ i,left = kx,i,0 = Pxu /Δx and ky,i,0 = Pyu /Δy. f ) EI ( uy,i+1 − 2uy,i + uy,i− 1 l2 Under strike-slip faulting, the maximum stress occurs at the tunnel hances, as shown in Fig. 4. The stress σi and strain εi at the left and right tunnel hances of node i are respectively: (1) Pretreatment • Input parameters. • Calculate Δfx,i and Δfy,i by Eq. (1) and Eq. (2). • Assume the membrane axial force Nb,i,0=0.. • Assume the the stratum stiffnesses khx,i,0 = Phxu /Δx, khy,i,0 = Phyu /Δy, f Mi = − Results The longitudinal strain and transverse displacement at the right hance obtained by the proposed model and model test are plotted in Fig. 11. Note that, in the condition of only considering the nonlincar (48) 7 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 tunnel-stratum interaction (i.e., analytical model II), the parameters of the host rock are employed in the entire model; in the condition of only considering the fault zone width (i.e., analytical model III), the linear stratum stiffnesses are calculated by the equations listed in Appendix C [44]. Specifically, the strain is symmetric about the fault plane, first increases and then decreases as the fault distance increases and finally reaches zero at both ends of the tunnel. The value of longitudinal strain at the fault plane is zero, and the maximum value is located near the fault. Under strike-slip faulting, the transverse displacement of the tunnel shows an ‘S’ shape. In addition, the results of the proposed model agree well with the 1 g model test, but ignoring the influence of fault zone width or nonlinear tunnel-stratum interaction will result in obvi­ ously larger results. Comparison with the 3D FEM numerical model To comprehensively verify the proposed model, the calculation re­ sults of tunnel displacements and forces obtained by the proposed model are compared with the results from the 3D FEM numerical model. Establishment of the FEM numerical model As shown in Fig. 12, an FEM numerical model with a geometry of Table 1 Model testing parameters [43]. Parameter Tunnel Fault Stratum Value D t C L LF LH β E ν W WF WH Δf γf cf φf Ef νf γh ch φh Eh Fig. 9. Calculation flow chart. νh Fig. 10. Model testing equipment [43]. 8 Width Thickness Buried depth Length Length in the footwall Length in the hanging wall Crossing angle Young’s modulus Poisson’s ratio Width Width in the footwall Width in the hanging wall Fault displacement Unit weight of the fault zone Cohesion of the fault zone Friction angle of the fault zone Young’s modulus of the fault zone Poisson’s ratio of the fault zone Unit weight of the host rock Cohesion of the host rock Friction angle of the host rock Young’s modulus of the host rock Poisson’s ratio of the host rock 0.24 m 0.015 m 0.72 m 2.8 m 1.4 m 1.4 m 90◦ 0.5 GPa 0.25 0.72 m 0.36 m 0.36 m − 0.013 m 16.3 kN/m3 3.2 kPa 26◦ 17 MPa 0.45 16.8 kN/m3 11.4 kPa 38◦ 108 MPa 0.35 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 Table 2 Tunnel-stratum interaction parameters[42]. Parameter Phxu Value Axial bearing capacity of the host rock αh = 0.608 − 0.123 ch 0.274 0.695 11.4 0.274 0.695 − ( +( = 0.608 − 0.123 × +( − ) ) )3 100 100 ( ch )2 11.4 2 11.4 3 ch +1 +1 +1 +1 100 100 100 100 = 1.018 ) ( 1 + K0 Phxu = παh ch D + πDCγh tan f1 φh 2 = 3.14 × 1.018 × 11.4 × 0.24 + 3.14 × 0.24 × 0.72 × 16.8 × f Pxu Axial bearing capacity of the fault zone = 13.306kN/m cf 0.274 0.695 3.2 0.274 0.695 − ( α = 0.608 − 0.123 − +( = 0.608 − 0.123 × +( ) ) )3 100 ( cf )2 100 3.2 2 3.2 3 cf + 1 +1 +1 +1 100 100 100 100 f Pfxu = παf cf D + πDCγf = 1.025 ) 1 + K0 ( tan f1 φf 2 = 3.14 × 1.025 × 3.2 × 0.24 + 3.14 × 0.24 × 0.72 × 16.3 × Phyu Transverse bearing capacity of the host rock 1+1 × tan(0.7 × 38◦ ) 2 [ Nhch = min = 5.380kN/m 1+1 × tan(0.7 × 26◦ ) 2 0.72 11.063 7.119 − ( 6.752 + 0.065 × )2 + ( )3 , 9 0.24 0.72 0.72 +1 +1 0.24 0.24 0.72 Nhqh = 6.816 + 2.019 × − 0.24 = 6.367 ( 0.146 × ] ) ) ) ( ( 0.72 2 0.72 3 0.72 4 + 7.651 × 10− 3 × − 1.683 × 10− 4 × 0.24 0.24 0.24 = 11.752 Phyu = Nhch ch D + Nhqh γh CD = 6.367 × 11.4 × 0.24 + 5.180 × 16.8 × 0.72 × 0.24 f Pyu Transverse bearing capacity of the fault zone [ Nfch = min = 51.536kN/m 0.72 11.063 7.119 − ( 6.752 + 0.065 × )2 + ( )3 , 9 0.24 0.72 0.72 +1 +1 0.24 0.24 0.72 Nfqh = 3.332 + 0.839 × − 0.24 = 6.367 0.090 × ( ] ) ) ) ( ( 0.72 2 0.72 3 0.72 4 + 5.606 × 10− 3 × − 1.319 × 10− 4 × 0.24 0.24 0.24 = 5.180 Pfyu = Nfch cf D + Nfqh γf CD = 6.367 × 3.2 × 0.24 + 5.180 × 16.3 × 0.72 × 0.24 Δx Δy K0 f1 Axial yield displacement Transverse yield displacement Lateral pressure coefficient Coating dependent factor = 17.479kN/m 0.01 m 0.015 m 1 0.7 Fig. 11. Tunnel response comparison with the 1 g model test [43]: (a) longitudinal strain and (b) vertical displacement. tangential friction coefficients are tan(φf) and tan(0.6φχ) [42], respec­ tively, because there is usually a plastic waterproof plate between the tunnel and the stratum. 100 m × 200 m × 85 m is established using ABAQUS to simulate the tunnel’s response under strike-slip faulting. Both the stratum and the tunnel are modelled by 3D solid continuum elements. The stratum is an ideal elastic-plastic material conforming to the Mohr–Coulomb strength criterion, and the elastic model is adopted for the tunnel. The normal contact behavior between the hanging wall and footwall, as well as between the stratum and tunnel, is defined as hard contact, while the tangential behavior is set as penalty contact. The corresponding Parameters Note that a large strike-slip displacement of 3 m is considered, and the calculation includes three simplified steps: 9 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 Fig. 12. Geometry and mesh of the FEM numerical model. (1) The initial ground stress balance. (2) The installation of tunnel lining. (3) The strike-slip displacement Δf is applied to the model bound­ aries to simulate fault dislocation, as shown in Fig. 13. The detailed calculation parameters are listed in Table 3. Note that the host rock has a larger unit weight than the fault zone, and this paper takes 21 kN/m3 and 19 kN/m3 as an example. The tunnel-stratum interaction parameters employed in the pro­ posed analysis model are obtained by Eq. (46) and Eq. (47), as listed in Table 4. Note that since the normal and tangential contact behaviors between the stratum and the tunnel are set as hard and penalty contact, respectively, the value of αχ equals 0. Table 3 Calculation parameters. Parameter Tunnel Fault Results Stratum As plotted in Fig. 14, the transverse tunnel displacement and forces (bending moment, axial force and shear force) are symmetric about the fault. The bending moment is almost zero at the tunnel-stratum crossing point (at x = 0 m) and increases with increasing fault distance. The axial and shear forces reach their peak value at the tunnel-stratum crossing point and decrease with increasing fault distance. The maximum value of the bending moment is reached approximately 25 m away from the Value W t H C L LF LH β E ν W WF WH Ef νf γf cf φf Eh νh γh ch φh Width Thickness Height Buried depth Length Length in the footwall Length in the hanging wall Crossing angle Young’s modulus Poisson’s ratio Width Width in the footwall Width in the hanging wall Young’s modulus of the fault zone Poisson’s ratio of the fault zone Unit weight of the fault zone Cohesion of the fault zone Friction angle of the fault zone Young’s modulus of the host rock Poisson’s ratio of the host rock Unit weight of the host rock Cohesion of the host rock Friction angle of the host rock 10 m 0.35 m 10 m 30 m 200 m 100 m 100 m 90◦ 31.5 GPa 0.2 50 25 25 0.5 GPa 0.4 19 kN/m3 100 kPa 18◦ 1.2 GPa 0.33 21 kN/m3 400 kPa 28◦ fault plane and finally converges to zero at approximately 50 m away from the fault plane. In addition, the comparisons also show that the calculation results of the theoretical model (i.e., analytical model I) considering the influence of fault zone width and nonlinear tunnelstratum interaction are in good agreement with the numerical simula­ tion results. Otherwise, the tunnel response will be highly enhanced by approximately 40 %~110 % (i.e., analytical models II and III) under this condition. The peak axial force, shear force and bending moment calculated by the proposed model and the 3D FEM model are plotted in Fig. 15. Compared with the numerical model, the relative errors of the peak bending moment, shear force and axial force calculated by analytical model I (considering the fault zone width and nonlinear tunnel-stratum Fig. 13. Numerical model boundary conditions. 10 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 Table 4 Tunnel-stratum interaction parameters. Parameter Phxu value Axial bearing capacity of the host rock αh = 0 Phxu = παh ch D + πDCγh f Pxu Axial bearing capacity of the fault zone αf = 0 ) 1 + K0 ( 1+1 × tan(0.6 × 28◦ ) tan f1 φh = 0 + 3.14 × 10 × 30 × 21 × 2 2 = 5972.538kN/m ) 1 + K0 ( 1+1 × tan(0.6 × 18◦ ) tan f1 φf = 0 + 3.14 × 10 × 30 × 19 × 2 2 = 3414.226kN/m [ ] 30 11.063 7.119 Nhch = min 6.752 + 0.065 × − ( )2 + ( )3 , 9 10 30 30 +1 +1 10 10 Pfxu = παf cf D + πDCγf Phyu Transverse bearing capacity of the host rock Nhqh = 4.565 + 1.234 × = 6.340 ( )2 ( )3 ( )4 30 30 30 30 − 0.089 × + 4.275 × 10− 3 × − 9.159 × 10− 5 × 10 10 10 10 = 7.574 Phyu = Nhch ch D + Nhqh γh CD = 6.340 × 400 × 10 + 7.574 × 21 × 30 × 10 f Pyu Transverse bearing capacity of the fault zone [ = 73075.427kN/m Nfch = min 6.752 + 0.065 × Nfqh = 2.399 + 0.439 × 30 11.063 7.119 − ( )2 + ( )3 , 9 10 30 30 +1 +1 10 10 ] = 6.340 ( )2 ( )3 ( )4 30 30 30 30 − 0.030 × + 1.059 × 10− 3 × − 1.754 × 10− 5 × 10 10 10 10 = 3.473 Pfyu = Nfch cf D + Nfqh γf CD = 6.340 × 100 × 10 + 3.473 × 19 × 30 × 10 Δx Δy K0 f1 Axial yield displacement Transverse yield displacement Lateral pressure coefficient Coating dependent factor 0.01 m 0.1 m 1.0 0.6 = 26136.879kN/m Fig. 14. Tunnel response comparison with the 3D FEM numerical model. 11 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 16000 2500 2000 12000 1500 8000 1000 4000 500 0 0 Fig. 15. Comparison of the tunnel peak forces with different analytical models. interaction) are 6.37 %, 11.00 % and 9.91 %, respectively; the relative errors of the peak bending moment, shear force and axial force calcu­ lated by analytical model II (only considering the nonlinear tunnelstratum interaction) are 31.67 %, 60.01 % and 31.32 %, respectively; and the relative errors of the peak bending moment, shear force and axial force calculated by analytical model III (only considering the fault zone width) are 63.00 %, 199.92 % and 77.36 %, respectively. In addition, the average errors of analytical model I, analytical model II and analytical model III are 9.09 %, 41.02 % and 113.43 %, respectively. Parameter analysis In previous tunnel and pipeline analytical models [26–36], the ulti­ mate strain of the corresponding materials is usually employed as the criterion of structural safety. Therefore, to assess the safety of tunnels crossing active strike-slip fault zones, the strains at tunnel hances and Fig. 16. Strain distribution of tunnel hances under left- and right- lateral strike-slip faulting. 12 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 failure scope with different parameters are analysed in this section. The failure scope is determined by the ultimate tensile and compressive strain of the concrete. Additionally, the ultimate compressive strain εcu of C35 concrete is 3300 με, and the ultimate tensile strain εtu is 100 με [45]. The tunnel length L is 1000 m, the fault displacement Δf is 2 m, the crossing angle β is 80◦ or 100◦ , and the other parameters are the same as in Table 3. strike-slip faulting both linearly increase with increasing fault displacement. The maximum strains are 6220, 8158, 9985, 11,730 and 13,356 με for 1.0, 1.5, 2.0, 2.5 and 3.0 m of fault displacement, respectively. Additionally, the tunnel failure scope also linearly in­ creases as the fault displacement increases. Specifically, when the fault displacement is 1.0–3.0 m, the tunnel failure scope is 208–352 m and 79–97 m under left- and right- lateral strike-slip faulting, respectively. Longitudinal strain distribution along the tunnel Effect of the fault zone width W As shown in Fig. 16, the strain distribution of the left and right tunnel hances is symmetrical about the fault plane under strike-slip faulting. The maximum strain is located around the fault plane, and when the fault plane distance is greater than 150 m, the tunnel strain tends to zero. Under left-lateral strike-slip faulting with a crossing angle β = 80◦ , the maximum tensile strain occurs at the right tunnel hance of the hanging wall and left tunnel hance of the footwall, while the maximum compressive strain occurs at the left tunnel hance of the hanging wall and right tunnel hance of the footwall; under left-lateral strike-slip faulting with β = 100◦ , the tunnel response is symmetric with that of leftlateral strike-slip faulting-. In addition, under left-lateral strike-slip faulting with β = 80◦ , the failure scope is governed by the tensile strain, which is 290 m; under left-lateral strike-slip faulting with β = 100◦ , the failure scope is governed by the compressive strain, which is 86 m. In addition, under right-lateral strike-slip faulting, the tunnel response is symmetric with that of left-lateral strike-slip faulting. The results show that the failure scope under left-lateral strike-slip faulting is obviously larger than that under right-lateral strike-slip faulting under the condi­ tion of 0◦ < β < 90◦ because the ultimate tensile strain of concrete is much smaller than its ultimate compressive strain. However, under the condition of 90◦ < β < 180◦ , the opposite conclusion is obtained. Then, the effect of fault displacement Δf, fault zone width W, fault zone cohesion cf and crossing angle β on the maximum strain and failure scope of the tunnel is discussed under the condition of 0◦ < β < 90◦ . The tunnel response under the condition of 90◦ < β < 180◦ can be obtained based on Fig. 16. The effect of the fault zone width W on the tunnel response is investigated by changing the fault zone width as W = 0, 10, 25, 50 and 100 m. In Fig. 18, the maximum tunnel compressive and tensile strains under left- and right- lateral strike-slip faulting both decrease with increasing fault zone width until W > 50 m, and the maximum strain is 14224–9148 με for different fault zone widths. The tunnel failure scope increases with increasing fault zone width. For instance, when the fault zone width is 0–100 m, the failure scope is 282–295 m and 79–93 m under left- and right- lateral strike-slip faulting, respectively. Effect of the fault displacement Δf To investigate the influence of the crossing angle β on the mechanical responses of the tunnel, a parametric analysis is performed where the crossing angle β is 20◦ , 40◦ , 60◦ and 80◦ . As shown in Fig. 20, the maximum compressive strain under left- lateral strike-slip faulting and the maximum tensile strain under right- lateral strike-slip faulting in­ crease with increasing crossing angle, while the maximum tensile strain Effect of the fault zone cohesion cf To investigate the influence of the fault zone cohesion cf on the tunnel responses, five cases with different fault zone cohesion cf are investigated, with values increasing from 50 kPa to 400 kPa. Fig. 19 shows that the maximum tension and compressive strains monotonically increase with increasing fault zone cohesion, and the maximum strain is 9748–11702 με for different fault zone cohesions. In contrast, the failure scope decreases with increasing fault zone cohesion. For instance, when the fault zone cohesion is 50–400 kPa, the failure scope is 292–281 m and 89–78 m under left- and right- lateral strike-slip faulting, respec­ tively. This conclusion is also obtained by Zhong et al. [21], which is because the stratum bearing capacity and stiffness increase with increasing cohesion according to Eq. (44) ~ Eq. (47). Effect of the crossing angle β To investigate the influence of the fault displacement Δf on the tunnel responses, a parametric analysis is performed where the fault displacement Δf is 1.0, 1.5, 2.0, 2.5 and 3.0 m. In Fig. 17, the maximum tunnel compressive and tensile strains under left- and right- lateral 400 130 120 300 200 110 100 90 100 0 Fig. 17. Tunnel response under strike-slip faulting with different fault displacements. 13 80 70 0.0 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 300 295 290 285 110 100 90 280 275 270 265 80 70 260 60 0.00 0.0 Fig. 18. Tunnel response under strike-slip faulting with different fault zone widths. 300 100 295 95 290 90 285 280 85 275 80 270 75 265 260 70 0.0 0.0 Fig. 19. Tunnel response under strike-slip faulting with different fault zone strengths. 700 350 600 300 500 250 400 200 300 150 200 100 100 50 0 0 Fig. 20. Tunnel response under strike-slip faulting with different crossing angles. 14 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 under left- lateral strike-slip faulting and the maximum compressive strain under right- lateral strike-slip faulting first increase and then decrease with increasing crossing angle. Note that under the condition of 90◦ < β < 180◦ , the opposite conclusion is obtained. Because the axial component of the fault displacement Δfx decreases with increasing crossing angle in the condition of 0◦ < β < 90◦ and decreasing crossing angle in the condition of 0◦ < β < 90◦ , resulting in the reduction of axial force N. the maximum strain is located around the fault plane. Under leftlateral strike-slip faulting with 0◦ < β < 90◦ , the failure scope is governed by the tensile strain. Under right-lateral strike-slip faulting with 0◦ < β < 90◦ , the failure scope is governed by the compressive strain. The failure scope under left-lateral strike-slip faulting is obviously larger than that under right-lateral strikeslip faulting because the tensile strength of concrete is much smaller than its compressive strength. However, under the con­ dition of 90◦ < β < 180◦ , the opposite conclusion is obtained. (4) The value of the tunnel maximum strain is directly related to the fault displacement Δf and fault zone cohesion cf and has an in­ verse relationship with the fault zone width Wf; the tunnel failure scope is directly related to the fault displacement Δf, fault zone width Wf, and crossing angle β (0◦ < β < 90◦ ) and has an inverse relationship with the crossing angle β (90◦ < β < 180◦ ) and fault zone cohesion cf. Conclusion In this work, a mechanical analysis model for tunnels under strikeslip faulting considering the fault zone width and nonlinear tunnelstratum interaction is first established. More specifically, tunnels crossing active fault zones are simplified as an elastic beam acting on a nonlinear foundation; the nonlinear tunnel-stratum interaction is considered by a series of nonlinear axial and transverse nonlinear springs; the different mechanical characteristics of the fault zone and host rock are described by different spring stiffnesses; and the nonlinear tunnel-stratum interaction is analysed by the finite difference method and a novel iterative method for nonlinear spring stiffness. The con­ clusions are summarized as follows: Additionally, the range of application of this proposed model and its limitations should be noted as follows: • The proposed model applies to strike-slip faults but does not extend to dip-slip faults. • In this model, the tunnel is assumed to possess elastic properties, while disregarding the elastic-plastic characteristics of concrete. • The proposed model only compares the strain and displacement of the tunnel with the model tests. The stratum pressure and tunnel failure scope should be considered in future works. (1) The displacement, bending moment, shear force and axial force of the proposed model agree well with the results obtained from model tests and numerical simulations. Compared with the nu­ merical model, the relative errors of the peak bending moment, shear force and axial force calculated by the proposed model are 6.37 %, 11.00 % and 9.91 %, respectively, and the average relative error is 9.09 %. (2) The proposed model significantly improves the accuracy of existing analytical models. More specifically, neglecting the ef­ fect of the fault zone width or nonlinear tunnel-stratum interac­ tion, the tunnel response will be misestimated, e.g., when the fault displacement is 3 m and the crossing angle is 90◦ , the overestimated value is approximately 40 % to 110 %. The relative average errors of analytical model I (considering the fault zone width and nonlinear tunnel-stratum interaction), analytical model II (only considering the nonlinear tunnel-stratum inter­ action) and analytical model III (only considering the fault zone width) are 9.09 %, 41.02 % and 113.43 %, respectively. (3) The strain distribution of the left and right tunnel hances is symmetrical about the fault plane under strike-slip faulting, and Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data availability No data was used for the research described in the article. Acknowledgement The authors are grateful for the support from the National Natural Science Foundation of China (52378411 and 52208404). Appendix A ⎡ − 2 ⎢ χ ⎢ kx,0 ⎢ ⎢ 1 ⎢ ⎢ χ ⎢ kx,1 ⎢ ⎢ EA ⎢ ⎢ [A1 ] = 2 ⎢ 0 l ⎢ ⎢ ⎢ ⎢ 0 ⎢ ⎢ ⎢ ... ⎢ ⎢ ⎣ 0 ⎤ 2 χ kx,0 0 0 ... − 2 χ kx,1 1 χ kx,1 0 ... 1 χ kx,2 − 2 χ kx,2 − 1 χ kx,2 ... ... 1 χ kx,3 ... − 2 χ kx,3 ... 0 0 0 0 ... ... ... 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ... ⎥ ⎥ ⎥ − 2⎦ χ kx,n (A1) (n+1)×(n+1) 15 X. Zhang et al. ⎡ 1 ⎢0 ⎢ ⎢0 [A2 ] = ⎢ ⎢0 ⎢ ⎣ ... 0 Transportation Geotechnics 44 (2024) 101171 0 0 1 0 0 1 0 0 ... ... 0 0 0 0 0 1 ... 0 ⎤ 0 0⎥ ⎥ 0⎥ ⎥ 0⎥ ⎥ ... ⎦ 1 (n+1)×(n+1) ... ... ... ... ... ... (A2) Appendix B ⎡ 2 ⎢ kχ ⎢ y,0 ⎢ ⎢− 2 ⎢ ⎢ χ ⎢ ky,1 ⎢ ⎢ 1 EI ⎢ ⎢ [B1 ] = 4 ⎢ kχ l ⎢ y,2 ⎢ ⎢ ⎢ 0 ⎢ ⎢ ⎢ ... ⎢ ⎢ ⎣ 0 2 χ ky,0 0 ... 5 χ ky,1 − 4 χ ky,1 1 χ ky,1 ... − 4 χ ky,2 6 χ ky,2 4 χ ky,2 ... 1 χ ky,3 ... − 4 χ ky,3 ... 6 χ ky,3 ... 0 0 0 ⎡ − 2N0 ⎢ kχ ⎢ y,0 ⎢ ⎢ N ⎢ 1 ⎢ χ ⎢ ky,1 ⎢ ⎢ 1⎢ ⎢ [B2 ] = 2 ⎢ 0 l ⎢ ⎢ ⎢ ⎢ 0 ⎢ ⎢ ⎢ ... ⎢ ⎢ ⎣ 0 ⎤ − 4 χ ky,0 − ... ... ... 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ... ⎥ ⎥ ⎥ 2 ⎦ χ ky,n (B1) (n+1)×(n+1) ⎤ 2N0 χ ky,0 0 0 ... − 2N1 χ ky,1 N1 χ ky,1 0 ... N2 χ ky,2 − 2N2 χ ky,2 N2 χ ky,2 ... ... N3 χ ky,3 ... − 2N3 χ ky,3 ... 0 0 0 0 ... ... ... 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ... ⎥ ⎥ ⎥ − 2Nn ⎦ χ ky,n (B2) (n+1)×(n+1) ⎡ ⎤ 0 ⎢ ⎢ − (N2 − N0 ) ⎢ χ ⎢ ky,1 ⎢ ⎢ ⎢ 0 1 ⎢ ⎢ [B3 ] = 2 ⎢ 4l ⎢ ⎢ ⎢ ⎢ 0 ⎢ ⎢ ⎢ ... ⎣ 0 ⎡ 1 0 ⎢0 1 ⎢ ⎢0 0 [B4 ] = ⎢ ⎢0 0 ⎢ ⎣ ... ... 0 0 0 0 0 0 1 0 0 1 ... ... 0 0 0 0 N2 − N0 χ ky,1 0 − (N3 − N1 ) χ ky,2 0 0 ... 0 ... (N3 − N1 ) χ ky,2 ... 0 ... ... − (N4 − N2 ) χ ky,3 ... ... ... 0 0 0 ... 0 0 ⎥ ⎥ 0 ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ 0 ⎥ ⎥ ⎥ ... ⎥ ⎦ 0 (B3) (n+1)×(n+1) ⎤ ... 0 ... 0 ⎥ ⎥ ... 0 ⎥ ⎥ ... 0 ⎥ ⎥ ... ... ⎦ ... 1 (n+1)×(n+1) (B4) Appendix C. [44] √̅̅̅̅̅̅̅̅̅̅̅ Eχ D4 ky = [ ] EI D 1 − (νχ )2 χ 1.3Eχ (C1) 12 16 X. Zhang et al. Transportation Geotechnics 44 (2024) 101171 References [21] Zhong ZL, Wang Z, Zhao M, Du XL. Structural damage assessment of mountain tunnels in fault fracture zone subjected to multiple strike-slip fault movement [J]. Tunn Undergr Space Technol 2020;104:103527. [22] Shen YS, Gao B, Yang XM, Tao SJ. 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