Boulders mixed with debris flows roll downstream under interactions with debris flow slurry, which poses a great threat to the people, houses, bridges, and other infrastructure encountered during their movement. The catastrophic debris flow in Zhouqu County, which occurred on 7 August 2010, was used as an example to study the motion and accumulation characteristics of boulders in debris flows. In this study, a fluid–solid coupling model utilizing the general moving objects collision model and the renormalization group turbulent model was used in the FLOW-3D software, treating boulders with different shapes in the Zhouqu debris flow as rigid bodies and the debris flow as a viscous flow. Numerical simulation results show that this method can be used to determine the motion parameters of boulders submerged in debris flows at different times, such as the centroid velocity, angular velocity, kinetic energy, and motion coordinates. The research method employed herein can provide a reference for studying debris flow movement mechanisms, impact force calculations, and aid in designing engineering control structures.

Preferential flow is widely developed in varieties of voids (such as macropores and fissures) in loess areas, affecting slope hydrology and stability and even leading to geological disasters. However, the model of seepage evolution with dynamic preferential flow is not clear, which obstructs the disclosure of the mechanism of landslides induced by the preferential flow. This study aimed to capture the seepage and occurrence status of water in loess voids, explain the variability characteristics of the loess pore structure, and reveal the seepage evolution model of dynamic preferential flow. Preferential infiltration experiments were conducted by combining X-ray computed tomography (X-ray CT) nondestructive detection with contrast techniques under dynamic seepage conditions. Three-dimensional (3D) visualized reconstruction, digital image correlation (DIC), image processing, and quantitative analyses were performed in AVIZO 2019.1, including two-dimensional (2D) and 3D characteristics of preferential flow distribution and macropore changing, dynamic variation of the porosity, pore number, volume, dip angle, and connectivity. Results showed that (1) preferential flow exists under saturated and unsaturated conditions in loess with strong uniformity and anisotropy; (2) preferential flow not only migrates into existing connected macropores, but also connects the original isolated pores into channels and forms larger percolation groups of contrast medium under the gradually increased high pressure; (3) the seepage develops with the evolution model of ‘preferential flow–piston flow–preferential piston mixture flow–piston flow’ in the dynamic process. The new insights into the characteristics of the seepage evolution in undisturbed loess under dynamic preferential flow will enrich the understanding of loess seepage and provided an important reference for future research on the slope instability of the loess induced by preferential flow.

To address the cracking problem caused by the weak tensile performance of concrete, this study investigates the failure mechanisms of basalt fiber-reinforced concrete under different fiber contents, single-blend, and mixed-blend schemes through splitting tensile tests and discrete element method (DEM) simulations. The tests employ 0.1–0.3% of 18 mm single-blend fibers and 6 mm:12 mm:18 mm (3:4:3) mixed-blend schemes, and PFC software is used to simulate crack propagation in fiber-reinforced concrete. The results show that the optimal 0.2% content of 18 mm single-blend fibers enhances the splitting tensile strength by 10.8%, whereas excessive 0.3% content reduces the strength by 7.8% due to poor dispersion. The mixed-blend scheme, via gradient crack-resisting effects of multi-scale fibers, increases the strength by 7.43% compared with the single-blend group at the same fiber content. DEM simulations reveal that fibers delay crack propagation through stress concentration transfer: single-blend fibers render tortuous crack paths, while mixed-blend fibers form three-dimensional crack networks, transforming the failure energy dissipation mode from single pull-out to multi-stage consumption. This research provides theoretical basis and optimization strategies for the anti-cracking design of basalt fiber-reinforced concrete.

Extreme climate events are occurring frequently under global warming. Previous studies primarily focused on isolated extreme climate events, whereas research on the synergistic changes between extreme cold (EC) and extreme warm (EW) events remains limited. This study conducted trend, correlation, and dispersion analyses on EC and EW, as well as their synergistic changes, in the Sanjiang Plain from 1960 to 2019, using inverse distance weighting, statistical methods, and the Mann–Kendall test. The results indicated that cold-to-warm (C2W) and warm-to-cold (W2C) events were significantly and positively correlated with elevation, with correlation coefficients (r) of 0.76 and 0.84, respectively. Meanwhile, C2W showed a significant negative correlation with latitude (r = −0.55), while W2C also exhibited a significant negative correlation with latitude (r = −0.71). However, there was a significant positive correlation between (EC) and latitude (r = 0.65). After 1980, both the declining trend of EC and the increasing trend of EW slowed down, and the trends in C2W and W2C changed from decline to increase. The dispersion of EC and EW shows an increasing trend, while the dispersion of C2W and W2C exhibits a decreasing trend. This study provides important references for studying temperature fluctuations and addressing extreme climate changes.

The finite volume method (FVM) is used to numerically investigate the sloshing behaviors of dual liquid tanks with gas inflow in this study. The sloshing process of a single liquid tank is simulated to verify the feasibility of the numerical method. Three different inlet boundary conditions are then discussed in order to obtain a reasonable gas flow rate. The sloshing process of a dual liquid tank with the gas inflow is simulated, and the effects of three different factors on the sloshing behaviors are investigated. The results indicate that the overload, flow rate, and filling ratio can affect the peak value of the impact force acting on the tank wall. The impact force is positively proportional to the overload (1G, 3G, or 5G). An increase in flow rate (50 g/s, 1000 g/s, or 5000 g/s) or a decrease in filling ratio (99.52%, 75.64%, or 63.69%) can increase the size and number of bubbles, leading to intensified sloshing behavior and increased impact force.