Dynamic compaction is one of the effective methods to eliminate collapsibility of loess foundation. In order to study the mechanism of eliminating loess collapsibility by dynamic compaction, particle size test, collapsibility test, scanning electron microscope test and soil-water characteristic curve (SWCC) test were conducted on undistributed loess and compacted loess in Tongchuan City. The above experimental data was used for analyzing the effect of dynamic compaction on the particle size distribution, microstructural and unsaturated characteristic of loess, as well as the relation between these factors and collapsibility. It is shown that the clay content of the loess in Tongchuan area increases significantly under dynamic compaction. It is found that when the clay content is greater than 36.2%, the loess is no longer collapsible. It is observed that dynamic compaction leads to the formation of small and micro pores from collapsed macropores and mesopores. As a consequence, the density of particles increases and the collapsibility decreases. The slope of the SWCC curve desaturation section of compacted loess is greater than that for undistributed loess. This is because clay particles formed under dynamic compaction act as cementation materials, which is considered to increase the strength of cementation on the one hand, and to be filled in the pores on the other hand, increasing the density of loess. Finally, the results show that the SWCC curve fitting parameter a is related to the proportion of micro-pore area and the collapsibility coefficient. The collapsibility of loess can be judged indirectly from the characteristics of the SWCC curve.

To study the damage characteristics of rock masses in cold regions under the coupling effect of freeze-thaw cycles and fatigue loads, freeze-thaw cycle tests, nuclear magnetic resonance microscopic tests, and triaxial compression fatigue macroscopic tests under different confining pressures were carried out on single crack marble. The pore structure expansion characteristics of fissured marble after freeze-thaw cycles, as well as the mechanical properties and deformation failure characteristics of fissured marble under freeze-thaw cycles and fatigue loads were analyzed. A single crack marble fatigue damage constitutive model based on Nishihara creep model was established by introducing damage variables under freeze-thaw and fatigue loads. The results showed that with the increase of freeze-thaw cycles, the mass loss rate and longitudinal wave velocity loss rate of fissured marble gradually increased. The nuclear magnetic resonance T₂ curve showed a three peak characteristic, with the whole curve shifting to the right. The second peak gradually connected with the third peak, and the total peak area continued to increase. There was a positive correlation between confining pressure and the fatigue strength of fissured marble. With the increase of confining pressure, the fatigue resistance and ductility of fissured marble increased, and the failure mode of the rock sample gradually changed from local shear failure to overall shear failure. The theoretical curve of the established fatigue damage constitutive model was basically consistent with the experimental data. The research results could provide reference for the prevention and control of rock engineering disasters in cold regions.

Due to ignoring the influence of foundation pit unloading effect on the bearing properties of uprooted piles, the accuracy of in-situ test results needs to be studied when the excavation unloading area is large, and the current research on uplift piles mostly reflects the bearing properties of piles based on pile side friction resistance, and there are few studies on the normal pressure of pile-soil interface on pile sides. Compared with the frictional resistance of the pile side, the normal pressure of the pile-soil interface on the pile side can intuitively reflect the influence of foundation pit excavation and unloading on the bearing properties of the uprooted pile. In view of this, the combination of model test and numerical simulation was used to explore the stress response and deformation law of uplift piles under excavation and unloading conditions by changing the variables such as foundation pit excavation range and pile roughness, and then the bearing mechanism of uplift piles was revealed. The results show that the unloading effect of foundation pit excavation is related to the depth and width of the foundation pit, the effective pile length and the pile side roughness, according to the degree of influence: the effective pile length> the depth of the foundation pit> the roughness of the pile side > the width of the foundation pit. When the width of the foundation pit is greater than the critical value, the increase of the width of the foundation pit has little effect on the bearing characteristics of the uplift pile. Under the condition of the same effective pile length, the normal stress of the excavated pile side is proportional to the depth of the foundation pit and inversely proportional to the width of the foundation pit, and the relationship with the pile roughness is small. Under the condition of the same effective pile length, the frictional resistance of the pile after excavation is directly proportional to the depth of the foundation pit and the roughness of the pile, and inversely proportional to the width of the foundation pit.

Grouting pavements are susceptible to cracking, which can significantly reduce their service life. For this reason, water-borne epoxy resin (WER) was added to the grouting materials to improve the performance of grouting asphalt mixtures. Grouting materials with different levels of WER were prepared and characterised for their flow properties, setting time, mechanical strength and micromorphology. The road performance of the grouting asphalt mixtures was evaluated through wheel tracking test, low-temperature bending test and water immersion Marshall test. The results show that, WER can form a membrane structure on the surface of hydration products, improving the flexibility of grouting materials. However, it also delays the setting time of grouting materials. The addition of WER slightly diminishes the high-temperature performance of grouting asphalt mixtures, but improves the low-temperature cracking resistance and water stability of grouting asphalt mixtures. In particular, 7.5% WER increases the low-temperature destructive strain of grouting asphalt mixtures by 29.2%.

To meet the increasingly refined individual-level traffic management and travel service needs in the new era, a vehicle travel destination prediction method that comprehensively considers temporal and spatial correlation was proposed based on the traditional prediction method based on historical trajectories. Using data from video AI recognition and vehicle satellite positioning, the vehicle stopping points were identified to segment the vehicle's full-day travel trajectories and establish a historical vehicle travel trajectory database. By studying the temporal and spatial characteristics of vehicle travel, a calculation method for the temporal and spatial correlation of vehicle travel trajectories was proposed, and a vehicle travel destination prediction model was constructed using temporal and spatial correlation as weights. Taking the vehicle travel in Futian Central District of Shenzhen as an example, four typical vehicle travel trajectories including private cars and taxis were selected to establish a model prediction accuracy evaluation function. The prediction accuracy of travel destinations for different types of travel and different degrees of trajectory completion was analyzed and compared with the historical trajectory-based prediction method. The results show that the prediction accuracy of travel destinations for different types of vehicles is basically positively correlated with the degree of trajectory completion. When the trajectory completion rate reaches 80%, the accuracy of travel prediction basically reaches over 80%. Compared with the traditional prediction method based on historical trajectories, the prediction method considering temporal and spatial correlation has higher prediction accuracy, especially for taxis services with no fixed commuting travel characteristics. The prediction accuracy of travel destinations has been improved by more than 16%. The research results can better meet the needs of global traffic management.

To investigate driving workload on mountainous expressways, a naturalistic driving study was conducted utilizing an eye tracker to capture drivers' eye movement data in a realistic driving environment. Employing the change rate of pupil area, average saccade time, blink frequency, and fixation time ratio as primary indicators, a quantitative driving workload model was formulated through a combined weighting approach. This model aimed to reveal the driving workload evolution mechanism in typical scenarios of mountain expressways such as bridge and tunnel clusters, tunnel clusters, and short distances between tunnels and intersections. A clustering algorithm was applied to determine the classification thresholds for driving workload, thereby identifying high-risk scenarios characterized by heightened workload. The results show that the types of bridges within bridge-tunnel groups, the length of connection sections between tunnel groups, and the proximity of tunnels to interchanges significantly influence driving workload. A positive correlation was observed between driving workload and bridge size, whereas driving workload exhibited a negative correlation with the length of connection sections between tunnel groups and the distance from tunnels to interchanges. The thresholds of high, medium and low intensity levels of driving workload on mountain expressway are 0.54 and 0.26. Scenarios with bridge-tunnel groups composed of large or super-large bridges, tunnel groups with distances less than 300 m, and tunnel-to-interchange sections with distances less than 400 m were classified as high-risk driving workload scenarios. It is advisable to implement an intelligent lighting system within expressway tunnels, establish light-reducing structures at tunnel entrances, and in scenarios where tunnels are located in close proximity to interchanges, consider installing designated lane-changing zones within suitable tunnel sections to facilitate smooth lane transitions.

Under the context of the rapid rise of smart airports, the widespread deployment of autonomous vehicles requires an efficient safety operation system. In order to develop a collision warning method based on collision probability for airport unmanned driving vehicles, using ADS-B data as a foundation, considering the interaction between aircraft and vehicles at taxiway segments and intersections. The collision probability analysis was conducted for these two types of interactive environments. Through the analysis of single-vehicle warning simulation diagrams, different levels of warning thresholds were set. When the collision probability was 0.3≤p(c)≤0.5, the following vehicle entered the secondary warning state, and the vehicle braking acceleration took a value range of 0.5~1.5 m/s². When p(c)＞0.5, the following vehicle entered the primary warning state, and the vehicle braking acceleration took the maximum value of 2 m/s², and carrying out simulation analysis for the same taxiway and intersection according to the set warning threshold, the simulation test showed that the collision warning method based on collision probability could calculate the probability of collisions occurring during vehicle movement on the taxiway, and perform deceleration braking according to the corresponding warning threshold, effectively reducing the possibility of collision accidents. Through Monte Carlo random simulation experiments, the collision probability change diagram under different driving modes at crossroads was obtained, and the effectiveness of the warning algorithm was verified by using hierarchical warnings for simulation analysis. The simulation experiment proved that regardless of the driving mode, the warning algorithm could effectively avoid collision conflicts, further proving that the proposed method had high adaptability. A collision probability-based collision warning method was constructs for airport unmanned driving vehicles, which can effectively avoid the occurrence of airport field collision conflicts. Meanwhile, it can significantly improve the safety of unmanned driving vehicles in the airport environment.

Transonic fan rotor blades will suffer from morphological decay problems such as leading edge erosion in actual operation, and the flow field structure in the tip zone will change and then induce aerodynamic performance degradation. The effects of leading edge erosion on the tip leakage flow of the fan rotor were investigated from constant numerical computation in this paper. The results show that at the stall point of the eroded blade, its isentropic efficiency, total pressure ratio and mass flow rate decrease by 4.3%, 0.43% and 5.63%, respectively, and the leading-edge erosion also causes a decrease in the stabilized operating margin by 0.69%. For the flow in the tip zone, the leading-edge erosion causes an increase in the entropy increase area and intensity in the flow surface of S1 at the tip zone and the flow surface of S3 in the exit region, and the formation of a low Mach Number flow region in different blade heights; the leakage flow structure under the leading edge erosion undergoes malignant changes, the demarcation point of the main leakage flow and the secondary leakage flow is advanced, carrying more fluid for secondary leakage, and the leakage vortex deflection angle of the eroded blade reaches 30° from 15°, hitting the leading edge of the blade directly and causing flow blockage.

To address the issue of land and capital waste caused by suboptimal site selection and construction models for urban drone landing and takeoff sites, the maximum coverage model is initially used for site selection. However, due to the uneven distribution of demand points and overly simplistic coverage determination criteria, the results show low coverage rates and overly concentrated site selection. To solve this problem, a method based on spatially continuous demand for the maximum coverage model of drone landing and takeoff site selection was proposed, considering factors such as no-fly zones and application scenarios. Demand objects were determined using a regular grid, and candidate sites were identified using the PIPS(polygon intersection point set) method. The feasibility of the improved model was validated through a case study of site selection for urban drone landing and takeoff sites in Binhai New Area, Tianjin. When the number of landing and takeoff sites was fixed at 14, the improved model increased the actual service area coverage rate from 62.03% to 88.61%. The results indicate that this method better meets the practical requirements for drone landing and takeoff site selection, resulting in more evenly distributed and rational site layouts, and significantly enhancing the service coverage rate of the drone landing and takeoff sites.

The transformation of sludge into biochar adsorbents for the removal of tetracycline contaminants in water bodies represents one of the effective approaches for the resource utilization of sludge and enables the realization of the circular economy concept of “treating waste with waste”. Municipal sludge was employed as the raw material, and sludge biochar was fabricated through pyrolysis for the adsorption and removal of tetracycline. The adsorption and removal efficacy of tetracycline was investigated, and the preparation conditions of sludge biochar and adsorption environmental conditions were optimized. Additionally, by combining methods such as scanning electron microscopy, infrared spectroscopy, and BET(Brunauer,Emmett,Teller) specific surface area testing, the structural characteristics of sludge biochar and the underlying mechanism of its adsorption behavior towards tetracycline were explored. The results indicate that the sludge biochar prepared under a pyrolysis temperature of 800 ℃ and a pyrolysis duration of 4 hours exhibits the optimal adsorption performance for tetracycline. The pH value exerts a significant influence on the adsorption effect. In a weakly acidic environment, the adsorption effect of sludge biochar on tetracycline is the most favorable, with a maximum adsorption capacity reaching 45.33 mg/g. Thermodynamic and kinetic analyses demonstrate that the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model can appropriately fit the adsorption process of tetracycline by sludge biochar. The adsorption process is primarily monolayer adsorption, dominated by surface chemical adsorption. In conjunction with the analysis of characterization test results, the chemical adsorption mainly involves processes such as electrostatic attraction, cation exchange, complex precipitation, π-π conjugation, and hydrogen bonding. Simultaneously, the pore structure characteristics of sludge biochar result in the adsorption process of tetracycline also encompassing pore filling and Van der Waals force.