Y-shaped piles are a new type of pile whose cross-section is like the letter Y: they are often used in ground improvement for road or train subgrades in the eastern coastal region of China. To investigate the bearing behaviour of Y-shaped piles in saturated sand, a series of model tests under compressive and horizontal load for Y-shaped piles, circular pile (the same cross-sectional area of Y-shaped pile), and circular pile (the same perimeter of Y-shaped pile) were carried out. Comparative analysis was conducted on bearing capacity, axial force and side resistance distribution, load sharing ratio, bending moment, and lateral soil pressure distribution along the embedded length. The results show that the bearing capacity of a Y-shaped pile does not increase in proportion, and the shaft resistance is weakened to some extent in saturated sand; Y-shaped pile can effectively improve the compressive bearing capacity for the same amount of concrete. The lateral bearing capacity of a Y-shaped pile has directionality, and hanging a circular section into a Y-shaped section may improve the horizontal bearing capacity for the same amount concrete, but cannot give full play to the advantage of the larger side area for horizontal bearing capacity in saturated sand.

Limited research has been conducted on the failure mechanism of coal gangue railway subgrade structures during catastrophic flood disasters, including the impact of varying flood impact heights and load sizes. This study investigates the process and mechanism of coal gangue railway subgrade failure in the coal mining subsidence area, in conjunction with the “7.20” catastrophic flood in Zhengzhou. First, various factors such as impact forms, impact height, flow velocity, water depth, and wave height are considered, and a wave-water flow coupling calculation method is proposed to determine the catastrophic flood load acting on inclined slopes. The maximum impact load calculated is then applied to simulate the impact process of the catastrophic flood using Particle Flow Code 2D. As the flood-related parameters increase, the maximum impact load on the subgrade slope also increases, leading to the breakdown of the subgrade and causing fatal damage. Finally, the failure process of the coal gangue railway subgrade under the impact and scour of a catastrophic flood is divided into three stages: erosion weakening, potential failure surface formation, and overall failure. The main failure mechanisms of each stage are revealed. These research result findings offer valuable insights for the design of railway subgrade reinforcement under catastrophic flood conditions.

The construction and expansion of high-speed railway networks in China has been occurring at a fast pace, resulting in some lines crossing through coal mine goaf sites. However, the embankment and train loads may trigger the activation of the coal mine goaf ground, posing a threat to traffic safety. To ensure the safety of construction and railway lines, an evaluation model on the activation classification of coal mine goaf ground, taking into account the high-speed railway load, is proposed, which is mainly applicable for middle–deep and level goaf areas using a longwall mining method. Firstly, 12 influencing factors are selected as the underlying evaluation indexes, and the catastrophe progression method model for evaluating the coal mine goaf ground stability is constructed. The findings of the evaluation were found to align with the actual results, indicating the reliability of the model. Then, the additional stress calculation model for high-speed railway ground with different embankment heights, train speeds, and axle loads was established, and the train load disturbance depth with a 5% criterion was determined. The influence degree of load on high-speed railway was divided, and the weight of each factor was determined. Finally, the extension comprehensive evaluation method was used to unite the stability grade of the coal mine goaf site and the influence degree of the train, so the evaluation model on activation classification was proposed. The accurateness and reliability of the proposed model was verified using the Taijiao high-speed railway cases and the model test.

Coal-mining-induced goaf areas are widely distributed in China and pose potential risks to high-speed railways. Repeated train-induced cyclic loading may further disturb the already weakened ground and aggravate deformation of the subgrade. A study on the goaf ground soil along the Taijiao High-Speed Railway utilized a GDS dynamic triaxial apparatus and controlled variable method to examine how waveforms, cyclic stress ratios (CSRs), effective confining pressures, vibration frequencies and cycles affect soil dynamics. The results show that cumulative plastic strain and residual pore pressure ratio generally tended to stabilize after rapid early development; however, both responses increased markedly within the 2–3 Hz frequency range. Among the investigated variables, the cyclic stress ratio (CSR) exerted the most significant influence and showed an exponential relationship with cumulative plastic strain and residual pore pressure ratio, whereas effective confining pressure produced a nearly linear decreasing trend. A dynamic stress–strain backbone curve was constructed, and by introducing the influence of vibration cycles into the H-D framework, the modified model achieved better agreement with the experimental backbone curves than the conventional H-D model. Furthermore, ABAQUS simulations further demonstrated that train speed and subgrade form significantly influence the distribution of dynamic stress and vertical displacement in goaf ground, with a more severe response in the cutting section. The optimized constitutive model and numerical results provide theoretical support for foundation design, long-term stability assessment and settlement prediction of high-speed railways constructed over goaf ground.

There are significant safety risks associated with the construction and operation of wind turbines in goaf sites. Investigating the catastrophic mechanisms underlying wind turbine foundations is crucial for addressing these scientific challenges. This study employs the empirical formula method to quantitatively evaluate and analyze the stability of a goaf site. Additionally, the disaster mechanisms of wind turbine foundations in these areas are examined through similar model tests and numerical simulations. The findings indicate that the settlement deformation of the wind turbine foundation is closely related to the magnitude of the applied load. Upon completion of the loading, the maximum settlement of the foundation under rated and extreme wind speed conditions was recorded at 0.16 mm and 0.26 mm, respectively, while the maximum inclination angles were 0.04° and 0.18°, respectively. At the conclusion of the loading process, the soil pressure differences between the leeward and windward sides of the base were measured at 95.3 kPa and 139 kPa under rated and extreme wind speed conditions, respectively. This data suggests that extreme wind speeds significantly influence the distribution of base pressure, resulting in an increased uneven settlement of the foundation.