The flexible joints and segmental lining serve as effective seismic measures for tunnel in high-intensity seismic area. However, the tunnel axial deformation at flexible joints has not been fully incorporated into analytical models. This study presents a novel mechanical model for flexible joints that considers tension (compression)shear-rotation deformations, replacing the traditional shear-rotation springs model. An improved semi-analytical solution has been developed for the longitudinal response of a tunnel featuring a three-way flexible joint mechanical model subjected to fault movement. The nonlinear elastic-plastic foundation spring, the soil-lining tangential interaction, and the axial force of tunnel lining have been considered to improve the applicability and precision of proposed method. The proposed solution is compared with existing models, such as short beams connected by shear and rotation springs, by examining the predictions against numerical simulations. The results indicate that the predictions of the proposed model align much more closely with the outcomes of the numerical simulations than those of the existing models. For the working conditions selected in 4, neglecting the tension-compression deformation at flexible joints an 81.8% error in the peak axial force of the tunnel and a 20.2% error in the peak bending moment. The reason is that ignoring the axial deformation of these joints results in a larger calculated axial force on the lining, which subsequently leads to increased bending moment and shear force. Finally, a parameter sensitivity analysis is conducted to investigate the effect of various factors, including flexible joint stiffness, segmental lining length, and the length of the tunnel fortification zone.

The transfer process of vertical stress of strata is affected by local soil arching effect, to address the limitation of differential soil layer method in overestimating the transferred stress, a method for calculating average vertical stress based on stress transfer ratio was proposed. This approach integrates numerical simulation results on the relationship between the rotation angle of principal stress and the average vertical compressive and shear stresses. Additionally, the shear stress distribution and the transmission behavior of vertical stress in both the equal settlement zone and the arching zone were verified. The results indicate that the stress transfer ratio can be used to define the boundary between the equal settlement plane and the soil arching zone of the tunnel. As the final stress transfer ratio increases, the path of principle stress gradually evolves into a closed arch trace, the proportion of transition before the peak of the average vertical stress curve decreases, while both the inflection point of the stress curve and the boundary of the equal settlement zone shift upward, and the transferred stress of strata with unit thickness increases accordingly. The transferred stress increases with gradual rotation of the principal stress, once the principal stress path forms a closed arch, the stress transfer function exhibits a sharp rise. The rate of change of the stress transfer ratio also increases in tandem with the rotation angle of the principal stress. These findings reveal the vertical stress transfer mechanism in the local soil arching zone and clarify the influence of the principal stress path on this process.

Tunnels that cross active faults will inevitably be severely damaged, and there are mainly five fault types. There are five main fault types: strike-slip fault, normal fault, reverse fault, and oblique-slip fault (normal or reverse strike-slip fault). However, there is no calculation method of tunnel longitudinal mechanical analysis for all fault types, and the calculation accuracy is reduced by the assumptions used in the existing calculation models to simplify the solution of complex differential equations. In pursuit of this objective, this study presents a novel semi-analytical model that accounts for five distinct types of faults and analyzes complex mathematical problems via the finite difference method, thereby circumventing the need to derive intricate analytical solutions. Additionally, an unconventional iterative approach is suggested for the computation of the nonlinear interaction between the tunnel and soil. This method exhibits exceptional efficiency, requiring less than one second per calculation on a laptop. Furthermore, when compared to a numerical model based on finite elements and varying fault displacements, this model demonstrates that the longitudinal forces and displacements are quantitatively in good approval, even when massive fault displacements are considered. Finally, this model is utilized to assess the longitudinal displacements, forces, and safety factors of the Daliang tunnel under faulting, and the failure range and failure modes are consistent with the actual situation. The suggested approach addresses a gap in the existing literature and is valuable for quickly, cost-effectively, and stably analyzing and designing tunnels intersecting with active faults.

Compared to traditional tunnel construction, artificial freezing involves two distinct stages: freezing and thawing. However, this process can pose a risk to the surrounding environment if it is not possible to accurately analyze the frost heave and thawing settlement during the freezing process. The thermomechanical coupled mathematical model of formation frost heave was established by considering boundary conditions, such as formation temperature and convective heat transfer, and introducing the parameters of instantaneous volumetric strain and denaturation characteristic coefficient. In addition, the numerical analysis method for the whole construction process of the tunnel by the horizontal freezing method was established by programming the user subroutine that takes into account the characteristic coefficients of frozen soil relying on the secondary development technology of ABAQUS (version 2022). Then, the method was applied to the horizontal freezing engineering of a double-line tunnel, and the distribution laws of the freezing temperature field and frost heave displacement field were obtained and compared with the field measurement results. The numerical analysis method for determining the deformation law of the ground surface has been shown to be reliable through comparison with field measurements. This method can serve as a reference for designing effective ground surface heaving control schemes during the freezing construction period of tunnels in complex environments.

This paper addresses stability challenges at excavation faces in shield tunneling through water-rich soil-rock formations, particularly focusing on partial failure caused by significant strength differences between soil and rock layers. A three-dimensional discrete rotational failure mechanism model is developed under the limit analysis upper-bound theorem, considering the influence of pore water pressure. This model leads to a novel method for calculating ultimate support pressure in complex strata, with its reliability confirmed through comparison with existing solutions. Key findings reveal a roughly linear positive correlation between soil layer proportion, water level, soil saturation weight, and ultimate support pressure. Conversely, cohesion, tunnel depth and friction angle demonstrate an inverse correlation. Notably, the relationship between soil layer proportion and ultimate support pressure exhibits significant nonlinearity. Cohesion and water level exert the most significant effects on ultimate support pressure, while the impact of soil layer proportion is notably complex. Additionally, a normalized design method is established using tunnel diameter and soil saturation weight, supported by design charts for varying normalized cohesion, normalized water level, and friction angles. A detailed example of a classic case is provided to illustrate the use of these design charts, aiding practical engineering applications.

Compound large deformation in tunnel has been a challenging issue influenced by complex geological conditions such as weak surrounding rock, high ground stress and groundwater. This paper summarizes the characteristics of compound large deformation in Gaopo tunnel, which passes through a weak coal-bearing stratum. Mechanical and swelling tests were conducted, alongside in-situ stress tests, to analyze the potential for squeezing and swelling deformations. A numerical simulation using an elastoplastic damage model, coupled with a method that calculates the humidity field based on the temperature field, was carried out to quantitatively analyze the mechanisms of compound large deformation. It was found that ground stress emerges as the primary determinant of the compound large deformation in Gaopo tunnel, followed by weakened surrounding rock and the humidity field. To address these problems, a new support scheme primarily based on double primary support was proposed. Field monitoring was conducted to evaluate the mechanical and deformation characteristics of support structure during the construction process. The results indicate that the new support scheme effectively controlled the compound large deformation, and the timing of the second primary support installation was found to be satisfactory. The treatment experience provides valuable insights for support design in tunnels experiencing compound large deformation issues.

When a tunnel passes through the silty clay stratum, disasters such as initial support failure and sudden instability of the face are prone to occur, which seriously affects construction safety and geo-ecology. To find the causes of tunnel deformation failure and propose effective solution measures, this study takes a highway tunnel crossing a powdery clay stratum as the research object. Firstly, the tunnel disaster characteristics were scrutinized through comprehensive on-site research. Subsequently, soil specimens were subjected to triaxial testing and microscopic analysis to discern the underlying causes of initial support damage. Furthermore, various reinforcement strategies were evaluated via numerical simulations. Subsequent to this, the identified reinforcement measures were implemented in the field, and their efficacy was assessed through on-site deformation and force monitoring. The findings reveal that the increased water content of the silty clay and its accumulation at the foot of the arch leads to a lack of load-bearing capacity, while the earth in the arch appears to slip and cut, which is the main cause of the initial support misalignment disaster. After optimization, a reinforcement solution of advanced large pipe shed +1.0 m large arch foot + 6 m of double feet-lock anchor pipes at 70 degrees and 0 degrees is determined. Site deformation and stress tests demonstrated maximum deformation of 13.4 cm, maximum surrounding rock pressure of 164 kPa, and maximum stress in the steel frame of 28.31 MPa, validating the effectiveness of the reinforcement solution.

The ground movement during the construction of shallow loess tunnels can easily cause deformation damage to surface buildings. Most the current studies focus on the damage soft soil and rock tunnels to independent buildings, and there are few studies on the case of building groups in loess areas. Using the new Xi 'Yan Railway Luochuan Tunnel as a case study, we conducted on -site testing to study building settlement and crack development characteristics. Three-dimensional numerical simulations were carried out to analyze settlement, flexure deformation, and main tensile strain distribution characteristics of the buildings at different buried depths. The study determines the extent of damage resulting from differential settlement and tension cracks. The results show that construction during the upper, middle, and lower bench stages results in significant ground volume loss, leading to a 'wide and steep ' settlement pattern with a maximum settlement value of 567 mm. Building cracks exhibit positive and inverted splayed shapes, with lengths ranging from 0.5 to 6.0 m and widths between 0 to 170 mm. As buried depth increases, maximum settlement, flexure deformation, and main tensile strain of buildings also increase. The severe damage range of buildings initially increases and then stabilizes, with the maximum range caused by differential settlement and tensile cracks being 34 m and 29 m from the tunnel axis, respectively. Based on the analysis of building damage characteristics, it was determined that a combination of surface measures and measures within the tunnel should be used to control building damage caused by tunnel construction. These research findings can serve as valuable references for similar projects.

Tunnels subjected to active fault dislocation may experience significant damage. This paper establishes a novel methodology and solution procedure for analyzing the mechanical response and failure characteristics of tunnels subjected to active fault dislocation based on an elastic foundation beam model. The proposed methodology includes axial, transverse, and vertical soil-tunnel interaction terms, in addition to geometrical nonlinearity and axial force terms in the governing equation. This approach has a significantly extended application range, effectively addressing the problems encountered in tunnels crossing active faults with diverse crossing angles, dip angles, and fault types. The proposed methodology is verified by comparison to a 3D FEM model with various fault types, experimental tests, and on-site case, and the results are in excellent quantitative and qualitative agreement with the numerical, experimental, and on-site results. When fault displacement is below 0.5 m, disregarding geometric nonlinearity results in calculation errors of approximately 10% to 17% for peak axial force (Nmax), 18% to 22% for peak shear force (Vmax), and 20% to 30% for peak bending moment (Mmax). Finally, the responses caused by different factors, i.e., fault type, fault displacement, tunnel stiffness, and tunnel diameter, are investigated in detail to better understand tunnels crossing active faults. The results show that amongst the various fault types, the Vmax and the Mmax experienced by tunnels subjected to oblique slip-fault dislocation surpass those of other fault types, accompanied by the most extensive failure range. The augmentation of fault displacement, tunnel stiffness, and tunnel diameter precipitates a corresponding escalation in the Nmax, Vmax, Mmax, and failure range. Under oblique-slip fault dislocation, the tunnel undergoes an initial phase of shear failure, followed by tension-bending failure, delineated by distinct fault displacement thresholds of 0.1 m and 0.2 m, respectively. The proposed methodology provides the advantage of reliable stability analysis and design of tunnels crossing active faults.

Affected by the near-fault pulse-like ground motions, the tunnels emerged in adverse geology, especially in an inhomogeneous strata are more vulnerable. However, the quantitative index effects on tunnel response during pulse identification are unclear and the propagation features of the near-fault pulse-like waves in a soft soil interlayer site are seldom revealed. In view of this, an improved energy-based pulse identification was used in this study to quantitatively extract the potential pulse energies emerged in velocity time-histories of ground motions. Subsequently, a series of numerical simulations were carried out to consider the critical parameters of soft soil layer and input ground motions. Finally, the dynamic response of the tunnel and interaction differences of soil and tunnel subjected to three types of ground motions were revealed. The result showed that the near-fault pulse-like ground motions pose a commonly severe damage to the tunnel, especially in the high pulse period ground motions based on the energy-based pulse identification method. The pulse energy of ground motions is an effective pulse index to analyze the seismic effects on tunnel when pulse periods of two different ground motions are uniform, and the index affects the tunnel in dynamic internal forces. More importantly, the existence of soft soil layer severely affects the propagation of input ground motions. At frequency domain, the ground response increases at high frequency component in the near-fault pulse-like ground motion, while the response shows a decreasing at low frequency component.