Seasonal freezing and thawing significantly influence the migration and distribution of soil hydrothermal salts. Understanding the dynamics of hydrothermal salt forces in canal foundation soils is crucial for effective canal disease control and optimization. However, the impact on rectangular canals remains poorly understood. Therefore, field-scale studies on water-heat-salt-force-displacement monitoring were conducted for the canal. The study analyzed the changes and interaction mechanisms of water-heat-salt-force in the soil beneath the canal, along with the damage mechanisms and preventive measures. The results indicate that the most rapid changes in temperature, moisture, and salt occur in the subsoil on the canal side, with the greatest depth of freezing. Heat transfer efficiency provides an intuitive explanation for the sensitivity of ground temperature at the junction of the canal wall and subsoil to air temperature fluctuations, as well as the minimal moisture migration in this region under the subcooling effect. The temperature-moisture curve suggests that current waterheat-force and water-heat-salt-force models exhibit a delay in accurately predicting water migration within the subsoil. Rectangular canals are more susceptible to damage under peak freezing conditions, requiring a combined approach of freezing restraint and frost-heaving force to mitigate damage. These findings offer valuable insights for canal design, maintenance, and further research.

The foundation conditions of piers for multi-span long-distance heavy-haul railway bridges inevitably vary at different locations, which may lead to non-uniform ground motions at each pier position, potentially causing adverse effects on the bridge's seismic response. To investigate the seismic response of bridges and the running safety of heavy-haul trains as they cross the bridge during an earthquake, a three-dimensional heavy-haul railway train-track-bridge (HRTTB) coupled system model was developed using ANSYS/LS-DYNA. This model incorporates the nonlinear behavior of critical components such as bearings, lateral restrainers, piers, and wheel-rail contact interactions, and it has been validated against field-measured data to ensure reliable dynamics parameters for seismic analysis. A multi-span simply supported girder bridge from a heavy-haul railway (HHR) was employed as a case study, in which a spatially correlated non-stationary ground motion field was generated based on spectral representation harmonic theory. Comparative analyses of the seismic responses under spatially varying ground motions (SVGM) and uniform seismic excitation conditions were performed for the coupled system. The results indicate that the presence of heavy-haul trains prolongs the natural period of the HRTTB system, thereby appreciably altering its seismic response. At lower apparent wave velocities, more piers exhibit a low-response state, and some pier bases enter the elastic-plastic stage under local site effects. Compared with the piers, the bearings show higher sensitivity to seismic inputs; fixed bearings experience damage when subjected to traveling wave effects and local site effects, which is subsequently followed by the failure of lateral restrainers. Train running safety is markedly reduced when crossing local soft soil site conditions. The conclusions drawn from this study can be applied in the seismic design and running safety assessment of HHR bridge systems under SVGM.

A series of large-scale shaking table tests was conducted on a pile network composite-reinforced high-speed railway subgrade. The displacement, peak acceleration amplification factor, dynamic soil pressure, and geogrid strain data were used to investigate the dynamic characteristics. The Hilbert-Huang transform spectrum, marginal spectrum, and damping ratios were used to study the seismic energy dissipation characteristics and damage evolution mechanisms of the reinforced subgrade. The results indicate that the graded loading of seismic waves induces a global settlement phenomenon within the subgrade, the displacement phenomenon of the slope is more evident, and the reinforcement effectively mitigates the amplification effect of the peak acceleration along the elevation. The peak and cumulative residual dynamic soil pressures were most significant near the bedding layer, and the upper and middle parts of the subgrade exhibited superior stabilization performance. The geogrid reduced the local vibration variability and enhanced the overall stability. The damage evolution in the middle part of the subgrade was relatively gentle, whereas the slope exhibited a multistage development trend. The internal damage of the subgrade grows slowly at 0.1-0.2 g, faster at 0.2-0.6 g, and rapidly at 0.6-1.0 g.

The quest for clean, renewable energy resources has given a global rise in offshore wind turbine (OWT) construction. As OWTs are more exposed to harsh environmental conditions, the dynamic behavior of OWTs with jacket support structures under critical loading scenarios is crucial yet least understood, which becomes more convoluted with the consideration of soil-structure interaction (SSI) effects. In addition, the seismic characteristics of such systems heavily depend on the excitation characteristics like frequency content, a feature that is still ambiguous. This research aims to examine the influence of seismic frequency contents on the dynamic characteristics and damage modes of jacket-supported OWT systems including SSI effects. The numerical model is established and validated based on a previous study, which ensures the accuracy of the numerical modeling framework. Upon validation, extensive numerical analyses are performed under earthquakes with varying frequency contents. Results reveal the relationship among the ground motion frequency, SSI, and the dynamic and damage behavior of jacket-supported OWTs, offering important insights for the improved seismic design and analysis of jacket-supported OWTs.

An Ms 7.4 earthquake struck China Maduo County in 2021, and it was a typical strike-slip rupture earthquake with clear directionality. A near-fault bridge named the Yematan No.2 Bridge suffered severe seismic damage in the Maduo earthquake. To analyze the seismic damage mechanism of the Yematan No.2 Bridge, the detailed finite element model of the bridge upline and downline was established in this study. To analyze the coupled effects of soil liquefaction, traveling wave effects, and seismic inertial forces, and to make the numerical simulation results better reflect structural seismic responses under real-site liquefaction conditions, this paper proposes a simplified method for simulating ground motions in liquefiable sites. This method integrates key effects induced by liquefaction into the ground motion simulation process. The detailed finite element model of the bridge upline and downline was established in this study. Then, the near-fault seismic bedrock motion of three directional components was synthesized by using the velocity pulse method to simulate the low-frequency pulse component and the stochastic finite-fault method to simulate the high-frequency component. The seismic ground motion was inversely computed by the equivalent linear method, and the field residual displacement measurement was used to optimize the seismic ground motion amplitude. Furthermore, to study the soil liquefaction effect on the bridge seismic damage, a simplified model based on planar one-dimensional wave theory was employed, and the seismic ground motion on the soil liquefaction site was computed through the site transfer function by using the inverse Fourier transform. Finally, the bridge seismic response analysis was conducted under non-uniform seismic excitation to consider the seismic traveling wave effect. The results show that the bridge's severe seismic damage is caused by the following multiple factors: (i) the fault rupture directionality of the near-fault earthquake results in the significant girder displacement along the bridge; (ii) the differential displacements between the upline and downline are also attributed to the soil liquefaction effect; (iii) the seismic traveling wave effect of strong seismic motion exacerbates the bridge seismic damage.

The freeze-thaw damage of cementitious coarse grained fillings (CCGFs) significantly affects the firmness, stability, and durability of high-speed railway subgrades. It is favorable to employ geopolymer binders to improve the engineering performance of coarse grained fillings (CGFs), further ensure the safety of high-speed railway subgrades in cold regions due to their excellent mechanical and environmental-friendly performances. This study conducted a series of freeze-thaw and mechanical tests on geopolymer stabilized coarse grained fillings (GSCGFs). The influence of gradation, compaction degree, and freeze-thaw cycles on the integrity, strength, and stiffness of GSCGFs was investigated. The evolution law of their freeze-thaw damage was discussed quantitatively based on an improved damage factor. The results show that the mass loss rate of Group B GSCGFs with a fine-grained particle content of less than 15% was lower than that of Group A GSCGFs with a fine particle content between 15% and 30% overall. When other conditions remain unchanged, the mass loss rate of GSCGFs decreased with the increase of compaction degree but increased nonlinearly with the freeze-thaw cycles. The strength and stiffness of GSCGFs decrease nonlinearly with the freeze-thaw cycles and presented a first fast and then slow-down change trend, their stiffness evolution at different compaction degrees revealed a big difference due to the weakening bite effect and enhancing overhead structure among rock blocks. The strength reduction of Group A GSCGFs was less than that of Group B under the high compaction degree. The stiffness deterioration of Group A GSCGFs was about twice that of Group B. There seemed to be no absolute correlation that the strength of GSCGFs was positively correlated with their stiffness. By building an exponential relationship between the compressive strength of GSCGFs and the freeze-thaw cycles that followed the findings of previous several studies, an improved exponential damage evaluation model was proposed to represent the performance degradation of GSCGFs. The outcomes of this study can provide theoretical support for understanding the physical and mechanical behaviors of GSCGFs and applying them in engineering practices.

The artificial ground freezing (AGF) method is a frequently-used reinforcement method for underground engineering that has a good effect on supporting and water-sealing. When employing the AGF method, the mesoscopic damage reduces the strength of the frozen sandy gravel and consequently affects the bearing capacity of the frozen curtain. However, a few studies have been conducted on the mesoscopic damage of artificial frozen sandy gravel, which differs from fine-grained soil due to its larger gravel size. Therefore, based on triaxial compression tests and CT scanning tests, this paper investigates both the mesoscopic damage mechanism and variations in artificial frozen sandy gravels. The findings indicate that there are contact pressures between gravel tips within the frozen sandy gravel, with damage primarily concentrated around these gravels during incompatible deformation within a four-phase medium consisting of ice, water, soil, and gravel. Furthermore, numerical simulation validates that failure typically initiates at delicate contact surfaces between gravel and soil particles. For instance, when the axial strain reaches 8%, the plastic strain at the location of gravel contact reaches 4.6, which significantly surpasses most of the surrounding plastic strain zones measuring around 1.3. Additionally, the maximum local stress within the soil sample is as high as 48 MPa. This failure event is distinct from viscoplastic failure observed in frozen fine-grained soil or brittle failure seen in frozen rock. The findings also indicate that the mesoscopic damage is about 0.3 when the axial strain is 10%. The study's findings can serve as a valuable guide for developing finite element models to assess damage caused by freezing in sandy gravel using AGF method.

Traditional inorganic curing agents have long been utilized to improve the mechanical properties of loess for engineering applications in regions abundant with loess. However, the unique climatic conditions in northwest China, marked by low temperatures and substantial temperature variations, make improved loess prone to structural degradation, which can result in brittle failure and subsequent engineering challenges. This study combines the principles of reinforced soil mechanics with conventional soil improvement techniques to conduct unconfined compressive (UC) tests, freeze-thaw (F-T) cycle tests, triaxial shear tests, and microstructure analyses under various initial conditions using cement and polypropylene fiber composite improved loess (CFIL) as the test material. The research aimed to examine the mechanical properties and the internal damage mechanisms of CFIL subjected to F-T environments. Results indicated that an increase in the length and content of polypropylene fibers significantly improved the unconfined compressive strength (UCS) of CFIL. This enhancement initially showed a rapid rate of improvement before experiencing a subsequent decrease. The addition of fibers significantly mitigates the degree of strength attenuation in the specimens subjected to F-T cycles compared to cementimproved loess. This effect is attributed to the overlapping and interweaving of polypropylene fibers in CFIL, which, along with loess particles embedded in cement hydrates enveloped by the fibers form a robust skeleton that enhances both strength and deformation resistance. Based on the variations in strength across different fiber lengths (Lf), fiber contents (Cf), and cement contents (Cc) before and after F-T cycles, the optimal Lf is identified as 12 mm, while the optimal Cf and Cc are 0.3 % and 2 %, respectively. The stress-strain curve of CFIL displays strain-softening behavior, although this behavior is notably less pronounced than in cement-improved loess. Furthermore, the initial tangent modulus and triaxial strength of CFIL decrease nonlinearly as the number of F-T cycles (NF-T) increases, with the rate of decrease gradually slowing over time. A decrease in freezing temperature (T) exacerbates the deterioration of the mechanical properties of improved soil. Microstructural test results indicate that as the NF-T increases, the porosity (n) of CFIL rises, accompanied by an increase in the proportion of macropores and mesopores, while the proportion of micropores and small pores diminishes. Utilizing the binary medium theory, the F-T damage mechanism of CFIL was investigated, and a damage equation that captures the dual impacts of F-T cycles and loading was formulated. Building on the Lemaitre equivalent strain principle and the nonuniform medium homogenization theory, a binary medium model for CFIL considering F-T cycles was developed. The proposed constitutive model effectively characterizes the stress-strain relationship of CFIL under F-T conditions, as demonstrated by the comparison between experimental results and calculated data.

The growth of rock structural surfaces makes the deformation and stability analysis of rock pits more complex and challenging than that of soil pits. To investigate the damage mechanism of this foundation and provide ideas for foundation support, the paper constructed a simplified model by approximate plane analysis and dimensionless analysis of the similarity principle. The physical model was constructed from a mixture of materials, and then foundation excavation and loading tests were completed. The strain value of the strain gauges increased in stages in the range of 0-250. Excavation of the structural surface resulted in an increased number of deformation mutations. This type of rocky foundation damage underwent three stages: overburden crack development, cumulative deformation of the S-S, and collapse of the sliding body. Furthermore, numerical simulations corresponding to the physical model tests were set and used to validate and complement the physical tests. When the line loads reached 70.83 kN/m and 127.5 kN/m, the plastic zone of the structural surface was completely penetrated and the sliding body collapsed. The results of the studies can serve as a useful reference and guide for the excavation and support design of real-world rock foundation projects that are similar.

A fault is a geological structure characterized by significant displacement of rock masses along a fault plane within the Earth's crust. The Yunnan Tabaiyi Tunnel intersects multiple fault zones, making tunnel construction in fault-prone areas particularly vulnerable to the effects of fault activity due to the complexities of the surrounding geological environment. To investigate the dynamic response characteristics of tunnel structures under varying surrounding rock conditions, a three-dimensional large-scale shaking table physical model test was conducted. This study also aimed to explore the damage mechanisms associated with the Tabaiyi Tunnel under seismic loading. The results demonstrate that poor quality surrounding rock enhances the seismic response of the tunnel. This effect is primarily attributed to the distribution characteristics of acceleration, dynamic strain, and dynamic soil pressure. A comparison between unidirectional and multi-directional (including vertical) seismic motions reveals that vertical seismic motion has a more significant impact on specific tunnel locations. Specifically, the maximum tensile stress is observed at the arch shoulder, with values ranging from 60 to 100 kPa. Moreover, NPR (Non-Prestressed Reinforced) anchor cables exhibit a substantial constant resistance effect under low-amplitude seismic waves. However, when the input earthquake amplitude reaches 0.8g, local sliding occurs at the arch shoulder region of the NPR anchor cable. These findings underscore the importance of focusing on seismic mitigation measures in fault zones and reinforcing critical areas, such as the arch shoulders, in practical engineering applications.