Ice -wedges are periglacial landforms that develop as a result of thermal contraction -cracking in continuous permafrost regions, which appear as polygonal networks on the ground surface. Given their complex thermomechanical loading history, very few related numerical models have so far been developed. In this study, 2-D eXtended finite element simulations are employed to represent the formation process of ice -wedges and to investigate the effect of select environmental controls on crack initiation and growth. Seventeen combinations of soil type and temperature-time series are used in four case studies addressing model testing, the permafrost stress regime, the freezing volumetric expansion of porewater, and a new remeshing process introduced to simulate ice -wedge growth over multiple years. The model testing shows good agreement with field observations from the Arctic and demonstrates the ability of the modelling procedure to reproduce the salient features of thermal contraction -cracking. The permafrost stress regime is found to be strongly affected by soil type and climate, with coarse -grained soils and cold climates leading to higher tensile stresses than fine-grained soils and warm climates. Higher tensile stress are also predicted for saturated soils due to the freezing volumetric expansion of porewater.

Tunnels subjected to reverse fault dislocation undergo severe structural damage, and their mechanical response and failure characteristics play a key role in seismic fortification efforts. This paper investigates the mechanical responses and failure characteristics exhibited by tunnels subjected to reverse faulting using theoretical analysis and numerical simulations. A theoretical model is established for analysing the bending moment, shear force, and safety factor of the tunnels under reverse fault dislocation. The nonuniform fault displacement, fault zone width, and nonlinear soil-tunnel interaction is applied in the proposed theoretical model, significantly improving the analysis accuracy and range of applicability. The corresponding numerical simulation based on the XFEM (extended finite element method) is carried out, and the proposed theoretical model is verified by the numerical results. The theoretical results demonstrate excellent agreement with the numerical results when nonuniform fault displacement is considered. A parametric analysis is presented in which the effects of the maximum fault displacement, fault zone width, and ratio of the maximum fault displacement of the footwall to the hanging wall are investigated. The results show that the ultimate fault displacement for compression-bending failure of the tunnel subjected to reverse fault dislocation is estimated to be approximately 30 cm, while the ultimate displacement for shear failure stands at 20 cm. Variations in the fault displacement ratio yield alterations in the distribution pattern and peak values of internal forces, together with shifts in the potential failure ranges of the footwall and hanging wall. Additionally, an initial crack emerged on the tunnel crown near the fault plane, followed by a second crack on the tunnel invert. Upon reaching a fault displacement of approximately 40 cm, the crack fully traverses the entire tunnel lining.

Buried pipelines are subjected to various types of loads, including external pressure from soil overburden and internal pressure from pressurized fluids. These loads can induce axial and hoop stresses, which are the primary factors leading to the formation of integrity threats, such as cracks. The presence of cracks can render a pipeline susceptible to failure, posing a significant threat to its operation, safety, and the environment. This underscores the importance of promptly detecting and evaluating even seemingly minor surface defects, as they can significantly damage the structural integrity of the pipeline. It is also crucial to accurately predict the failure pressures of pipelines with cracks to ensure that the operating pressure remains below this critical limit with an adequate margin of safety. A variety of approaches exist for assessing cracks in pipes, including empirical approaches such as MAT-8, Ln-Sec and CorLASTM models, as well as numerical approaches like the extended finite element method (XFEM). XFEM is a powerful tool to estimate the failure pressures of pipelines containing cracks. It extends the capabilities of the traditional Finite Element Method (FEM) and offers a more effective means of simulating crack propagation. In ABAQUS, initial cracks can be modelled in either sharp or blunted shapes. However, it is uncertain whether the shape of the crack affects the failure pressures of cracked pipelines. For this purpose, detailed parametric studies are necessary to investigate the implications of pre-existing cracking shapes on the ductile fracture response of pipes subjected to pure mode I loading.