A utility tunnel is an infrastructure that consolidates multiple municipal pipeline systems into a shared underground passage. As long linear structures inevitably cross different soils, this paper aims to accurately assess the seismic damage to a shallow-buried utility tunnel in a non-homogeneous zone by employing a viscous-spring artificial boundary and deriving the corresponding nodal force equations. The three-dimensional model of the utility tunnel-soil system is established using finite element software, and a plug-in is developed to simulate the three-dimensional oblique incidence of SV waves with a horizontal non-homogeneous field. In this study, the maximum interstory displacement angle of the utility tunnel is used as the damage indicator. Analysis of structural vulnerability based on IDA method using PGA as an indicator of seismic wave intensity, which considers the angle of oblique incidence of SV waves, the type of seismic waves, and the influence of the nonhomogeneous field on the seismic performance of the utility tunnel. The results indicate that the failure probability of the utility tunnel in different soil types increases with the incident angle and PGA. Additionally, the failure probability under the pulse wave is higher than that under the non-pulse wave; Particular attention is given to the states of severe damage (LS) and collapse (CP), particularly when the angle of incidence is 30 degrees and the PGA exceeds 0.6g, conditions under which the probability of failure is higher. Additionally, the failure probability of the non-homogeneous zone is greater than that of sand and clay; the maximum interlayer displacement angle increases with the incident angle, accompanied by greater PGA dispersion, indicating the seismic wave intensity. The maximum inter-layer displacement angle increases with the incident angle, and the dispersion of the seismic wave intensity indicator (PGA) becomes greater. This paper proposes vulnerability curves for different working conditions, which can serve as a reference for the seismic design of underground structures.

This paper establishes a novel full-process numerical simulation framework for analyzing the 3D seismic response of mountain tunnels induced by active faults. The framework employs a two-step approach to achieve wavefield transmission through equivalent seismic load: first, a highly efficient and accurate FMIBEM (Fast multipole indirect boundary element method) is used for large-scale 3D numerical simulations at the regional scale to generate broadband ground motions (1-5 Hz) for specific sites; subsequently, using the FEM (Finite element method), a refined simulation of the plastic deformation of surrounding rock and the elastoplastic behavior of the tunnel structure was conducted at the engineering scale. The accuracy of the framework has been validated. To further demonstrate its effectiveness, the framework is applied to analyze the impact of different fault movement mechanisms on the damage to mountain tunnels based on a scenario earthquake (Mw 6.7). By introducing tunnel structure damage classification and corresponding damage indicators, the structural damage levels of tunnels subjected to active fault movements are quantitatively evaluated. The findings demonstrate that the framework successfully simulates the entire process, from fault rupture and terrain amplification to the seismic response of tunnel structures. Furthermore, the severity of tunnel damage caused by different fault types is ranked as follows: reverse fault > normal fault > strike-slip fault.

Fiber reinforcement has been demonstrated to mitigate soil liquefaction, making it a promising approach for enhancing the seismic resilience of tunnels in liquefiable strata. This study investigates the seismic response of a tunnel embedded in a liquefiable foundation locally improved with carbon fibers (CFs). Consolidated undrained (CU), consolidated drained (CD), and undrained cyclic triaxial (UCT) tests were conducted to determine the optimal CFs parameters, identifying a fiber length of 10 mm and a volume content of 1 % as the most effective. A series of shake table tests were performed to evaluate the effects of CFs reinforcement on excess pore water pressure (EPWP), acceleration, displacement, and deformation characteristics of both the tunnel and surrounding soil. The results indicate that CFs reinforcement significantly alters soil-tunnel interaction dynamics. It effectively mitigates liquefaction by enhancing soil stability and slowing EPWP accumulation. Ground heave is reduced by 10 %, while tunnel uplift deformation decreases by 61 %, demonstrating the stabilizing effect of CFs on soil deformation. The fibers network interconnects soil particles, improving overall structural integrity. However, the increased shear strength and stiffness due to CFs reinforcement amplify acceleration responses and intensify soil-structure interaction, leading to more pronounced tunnel deformation compared to the unimproved case. Nevertheless, the maximum tunnel deformation remains within 3 mm (0.5 % of the tunnel diameter), posing no significant structural risk from the perspective of the experimental model. These findings provide valuable insights into the application of fibers reinforcement for improving tunnel stability in liquefiable foundations.

This computational study focuses on the thermo-hydro-mechanical simulations of the behaviors of freezing soils used for artificial ground freezing (AGF) in a metro project. Leveraging the experimental and field data available in the literature, we simulate the sequential freezing and excavation of a twin tunneling that occurred in months during the actual construction of the tunnel. A thermo-hydro-mechanical model is developed to capture the multi-physical rate-dependent behaviors triggered by phase transitions, as well as the creeping and secondary consolidation of the soil skeleton and the ice crystals. We then calibrate the material models and establish the THM finite element model coupled with the rate-dependent multi-physical models, which may accurately predict the surface heave induced by ground freezing throughout the project. To showcase the potential of using simulations to guide the AGF, we simulate the scenario where a simultaneous freezing scheme is employed as an alternative to the actual sequential scheme design. We then compared the simulated performance with the recorded results obtained from the sequential scheme. Finally, parametric studies on the effect of ground temperature, the porosity of the frozen soil, and the intrinsic elastic modulus of the solid skeleton are conducted. The maximum surface heave is inferred from finite element simulations to quantify the sensitivity and the impact on the safety of AGF operations.

This study presents a hierarchical multiscale approach that combines the finite-element method (FEM) and the discrete-element method (DEM) to investigate tunneling-induced ground responses in coarse-grained soils. The approach considers both particle-scale physical characteristics and engineering-scale boundary value problems (BVPs) simultaneously, accurately reproducing typical tunneling-induced mechanical responses in coarsegrained soils, including soil arching and ground movement characteristics observed in laboratory tests and engineering practice. The study also unveils particle-scale mechanisms responsible for the evolution of soil arching through the underlying DEM-based RVEs. The results show that the rearrangement of microstructures and the deflection of strong contact force chains drive the rotation of macroscopic principal stress and the formation of soil arch. The microscopic fabric anisotropy direction can serve as a quantitative indicator for characterizing soil arching zones. Moreover, the effects of particle size distributions (PSD) and soil densities on ground deformation patterns are interpreted based on the stress-strain responses and contact network characteristics of DEM RVEs. These multiscale insights enrich the knowledge of tunneling-induced ground responses and the same approach can be applied to other geotechnical engineering analyses in coarse-grained soils.

Large-span corrugated steel utility tunnels are widely used owing to their large spatial spans and excellent mechanical properties. However, under seismic forces, they may experience significant deformation, making repair challenging and posing a serious threat to personal safety. To study the seismic performance of corrugated steel utility tunnels, an equivalent orthotropic plate was introduced, and a simplified three-dimensional refined finite element model was proposed and established. Considering the site conditions of the structure, the structural parameters, and different seismic input conditions, a detailed analysis was conducted using the endurance time analysis method. The results indicated that the simplified model agreed well with the experimental results. The seismic input conditions significantly affected the relative deformation of the structure. Under the action of P waves (compression waves) and P + SV waves (compression and shear waves), the deformation of the upper part of the structure was relatively uniform, whereas under the action of SV waves (shear waves), the deformation of the crown was more evident. The greater the burial depth of the structure, the stronger the soil-structure interaction, and the smaller the increase in relative deformation. In soft soil, the structure was more likely to be damaged and should be carefully observed. Additionally, increasing the corrugation profile of the steel plates during the design process was highly effective in enhancing the overall stiffness of the structure. Based on the above calculation results, the relative deformation rate was proposed as a quantitative index of the seismic performance of the structure, and corresponding values were recommended.

Based on the deficiencies of the generalized response displacement method and the integral response displacement method for longitudinal seismic analysis of the shield tunnel, the dynamic sub-str1cture analysis method for longitudinal seismic response of a large-diameter shield tunnel crossing the complex soil layer is proposed. The feasibility and superiority of the dynamic sub-structure analysis method are explored by comparing it with the calculation results of the three-dimensional (3D) soil-underground structure interaction model. Then, a finite element refined 3D model of the 2.7 km Suai submarine shield tunnel is established by using the proposed method, and the longitudinal seismic response of the large-diameter shield tunnel crossing complex soil layers is simulated and analyzed. The research results indicate that the proposed dynamic sub-structure method has clear concepts, accurate calculation results and high efficiency to simulate the dynamic soil-tunnel interaction, which can avoid the error effect of the equivalent soil spring used in the generalized response displacement method. At the same time, this method can consider the seismic effect of the complex soil layers which has been avoided by the generalized response displacement method and the integral response displacement method. Also, the calculation results by the proposed method can comprehensively present the typical earthquake damages of shield tunnels crossing the wide river valley or the strait. It proves that it is not appropriate to simplify the longitudinally of the shield tunnel into a straight line, as doing so would neglect the influence of the longitudinal slope of complex river valleys or the straits. Also, the longitudinal seismic response of the shield tunnel is more sensitive to low-frequency seismic waves and the bolts are more susceptible to seismic damage compared to the segment opening.

In view of the pollution of unpaved road dust in the current mines, this study demonstrated the excellent dust suppression performance of the dust suppressant by testing the dynamic viscosity, penetration depth and mechanical properties of the dust suppressant, and apply molecular dynamics simulations to reveal the interactions between substances. The results showed that the maximum dust suppression rate was 97.75 % with a dust suppressant formulation of 0.1 wt% SPI + 0.03 wt% Paas + NaOH. The addition of NaOH disrupts the hydrogen bonds between SPI molecules, which allows the SPN to better penetrate the soil particles and form effective bonding networks. The SPI molecules rapidly absorb onto the surface of soil particles through electrostatic interactions and hydrogen bonds. The crosslinking between SPI molecules connects multiple soil particles, forming larger agglomerates. The polar side chain groups in the SPN interact with soil particles through dipole-dipole interactions, further stabilizing the agglomerates and resulting in an enhanced dust suppression effect. Soil samples treated with SPN exhibited higher compressive strength values. This is primarily attributed to the stable network structure formed by the SPN dust suppressant within the soil. Additionally, the SPI molecules and sodium polyacrylate (Paas) molecules in SPN contain multiple active groups, which interact under the influence of NaOH, restricting the rotation and movement of molecular chains. From a microscopic perspective, the SPN dust suppressant further strengthens the interactions between soil particles through mechanisms such as liquid bridge forces, which contribute to the superior dust suppression effect at the macroscopic level.

In urban subway construction, shield tunneling near pile groups is common, where additional loads may threaten existing structures. This study establishes multiple 3D nonlinear FDM models with fluid-solid coupling to investigate how tunnel-pile clearances (Hc) affect the mechanical response of low-cap pile groups (2 x2) during side-by-side twin tunneling in composite strata. The advanced CYSoil model, incorporating nonlinearity, strain path dependency, and small strain behavior, is employed to simulate soil response. Results show that tunneling induces up to a similar to 66.7 % reduction in pore water pressure, forming a funnel-shaped seepage pattern. As Hc increases from 0.8D to 2.6D, the low-pressure zone shifts from sidewalls to vault and invert, while maximum displacements reduce by up to 14.04 mm (lateral), 5.28 mm (transverse), and 19.68 mm (vertical). Axial force evolution in piles follows a three-stage decline, i.e., rapid, slow, and moderate, with peak shaft resistance concentrated near the tunnel axis. These findings aid in optimizing tunnel-pile configurations and mitigating geotechnical risks.

The coupled thermo-hydro-mechanical response caused by fire temperature transfer to surrounding rock/soil has a significant impact on tunnel safety. This study developed a numerical simulation model to evaluate the effects of fire on tunnel structures across different geological conditions. The heat transfer behavior varied with the mechanical properties and permeability of the geotechnics, concentrating within 1.0 m outside the tunnel lining and lasted for 10 days. Significant differences in pore water pressure changes were observed, with less permeable geologies experiencing greater pressure increases. Tunnel deformation was more pronounced in weaker geotechnics, though some tunnels in stronger geologies showed partial recovery post-fire. During the fire, thermal expansion created a bending moment, while a negative bending moment occurred after the fire due to tunnel damage and geotechnical coupling. The entire process led to irreversible changes in the bending moment. The depth of tunnel burial showed varying sensitivity to fire across different geological settings. This study provides important references for fire protection design and post-fire rehabilitation of tunnels under diverse geological conditions.