Safety assessment of ductile iron (DI) pipelines under fault rupture is a crucial aspect for underground pipeline design. Previous studies delved into the response of DI pipelines to strike-slip faults, but all existing theoretical methods for DI pipelines under strike-slip faults are not suitable for normal fault conditions due to the difference in soil resistance distribution. In this study, analytical solutions considering asymmetric soil resistance and pipe deflection are developed to analyze the behavior of DI pipelines under normal faulting. Results indicate that DI pipelines with a longer segment length are more vulnerable to pipe bending damage, while exhibiting a lower sensitivity to joint rotation failure. For the conditions of pipe segment length L = 1.5 m at all burial depths and L = 3 m at a shallow burial depth, when the fault-pipe crossing position shifts from a joint to a quarter of the segment length (rp = 0 similar to 0.25), DI pipelines are more prone to joint rotation failure. However, in the cases of L = 3 m at a moderate to deep burial depth and L = 6 m at all burial depths, the most unfavorable position is rp = 0.75, dominated by the mode of pipe bending failure.

Pipes and tunnels are prone to longitudinal deformation under normal faulting. Predicting the active length, defined as the major deformed length, is crucial for the seismic design of pipes and tunnels. However, an accurate prediction method is hard to develop due to a limited number of experimental data. In this study, a large number of numerical simulations are conducted based on a three-dimensional beam-spring model validated by centrifuge tests. The results are fed to XGBoost models to develop a robust prediction method. For ease of application, only the friction angle of soil, burial depth, diameter, and thickness of pipes or tunnels are incorporated as features. A hyperparameter tuning approach integrating grid search and Bayesian optimization was employed in the training process to establish optimal models with comparatively low complexity and high accuracy. A comparison of predictions from the XGBoost models and curves fitted on relative structure-soil stiffness demonstrates that XGBoost models are much superior. The effects of each feature on the predictions were analyzed by employing the SHAP method. The proposed XGBoost models can effectively and efficiently predict the active length of pipes and tunnels with minimal inputs.

Damage to the overlying soil caused by fault misalignment poses a significant threat to the structural safety of buried pipelines crossing faults, which is a non-negligible factor in the design of underground pipelines in complex environments. Existing research rarely involves analytical solutions for the force and deformation of pipeline structures under normal and reverse fault movements, and theoretical studies on fault-pipeline interactions often treat the pipeline structure as continuous, with little consideration for the influence of pipeline joints. Firstly, soil displacement curves for both normal and reverse faults are derived using the erf and erfc functions, based on a simplified SSR (stationary zone, shearing zone, rigid body zone) soil deformation model. Secondly, the deformation and internal force of the buried pipeline structure are solved using the two-parameter Pasternak foundation model and the finite difference method. Finally, the theoretical analytical solution is compared with existing experimental and 3D numerical simulation results, showing good agreement. In addition, sensitivity analyses are conducted for key physical parameters, including fault dip, fault-pipeline inter location, and joint rotation stiffness. The results show that fault dip will change the position of the pipeline displacement curve and axial stress curve, but the maximum displacement and maximum axial stress are basically identical. The inter of the fault and the pipeline will not only change the shape of the pipeline displacement curve and axial stress curve, but also alter the maximum axial stress. With the increase of joint rotation stiffness, the maximum axial stress value of the pipeline increases. When the joint rotation stiffness is large enough, the jointed pipeline can be calculated as if it is continuous.

Multiple fault planes often coexist within a fault zone during fault dislocation. However, all the previous analytical models assume that there is only one fault plane during a fault dislocation, which is inconsistent with the actual engineering conditions. In this paper, theoretical analysis and numerical simulations are used to investigate the mechanical response and damage characteristics of tunnels subjected to multiple normal faulting. A nonlinear theoretical model is established for analyzing the mechanical response of tunnels subjected to multiple normal faulting. The number of fault planes, the shear effect of the soil and the tunnel, the fault zone width, and the nonlinear soil-tunnel interaction are applied inside the theoretical model, significantly improving the analysis accuracy and applied range. The corresponding numerical simulation based on the Concrete Damaged Plasticity (CDP) Model is carried out to study the damage characteristics of the tunnel. The proposed theoretical model is verified by model tests and numerical simulations, which exhibit consistency in both qualitative and quantitative aspects. A parametric analysis is presented, wherein the impacts of varying numbers of fault planes, fault plane distances ( d ), fault displacement ratios ( xi ), and buried depths ( C ) on the tunnel response are investigated. The results show that an increasing number of fault planes leads to a reduced peak bending moment ( M max ) and shear force ( V max ). As the number of fault planes increased from one to four, M max and V max decreased by 1.57 times and 3.31 times, respectively. Expanding d corresponds to a reduction in both M max and V max . The minimum V max within the tunnel materializes at xi 4 ( Delta f d1 = Delta f d2 = Delta f d3 ), and the tunnel ' s V max appears at the fault plane of maximum fault displacement. Moreover, with the augmentation of C , an increase in both M max and V max was observed. Additionally, upon attaining a normal fault displacement of 0.2 m, the tunnel lining undergoes both tensile and compressive failure at the fault plane. As the normal fault displacement surpasses 0.4 m, the failure range of the tunnel at the fault plane undergoes a precipitous escalation, marked by a maximum increase of 68.8 % in tensile failure and a 29.6 % increase in compressive failure.

Fault movement during earthquakes is a geotechnical phenomenon threatening buried pipelines and with the potential to cause severe damage to critical infrastructures. Therefore, effective prediction of pipe displacement is crucial for preventive management strategies. This study aims to develop a fast, hybrid model for predicting vertical displacement of pipe networks when they experience faulting. In this study, the complex behavior of soil and a buried pipeline system subjected to a normal fault is analyzed by using an artificial neural network (ANN) to generate predictions the behavior of the soil when different parameters of it are changed. For this purpose, a finite element model is developed for a pipeline subjected to normal fault displacements. The data bank used for training the ANN includes all the critical soil parameters (cohesion, internal friction angle, Young's modulus, and faulting). Furthermore, a mathematical formula is presented, based on biases and weights of the ANN model. Experimental results show that the maximum error of the presented formula is 2.03%, which makes the proposed technique efficiently predict the vertical displacement of buried pipelines and hence, helps to optimize the upcoming pipeline projects.