In cold regions, freeze‐thaw action poses a significant hazard to road engineering. In order to avoid the adverse effects of inorganic materials on soil modification, we applied lignin, which is an environmentally friendly and organic polymer, to improve the silt sand from cold regions. The significance of this study is to facilitate the better application of lignin. The macroscopic engineering properties of the soil showed that, before freeze‐thaw, as the lignin content increased, thermal conductivity and permeability decreased, pH first increased rapidly and then stabilized between 10 and 11, and dynamic resilient modulus first increased then decreased; after freeze‐thaw, as lignin content increased, thermal conductivity and permeability decreased, and dynamic resilient modulus first increased then decreased. The freeze‐thaw action reduced the thermal conductivity and dynamic resilient modulus of silt sand treated with lignin and increased its permeability. The test results of soil microstructure indicated that, before freeze‐thaw, the silt sand and silt sand treated with lignin were structurally compact; after freeze‐thaw, the silt sand showed numerous cracks and pores and had a loose soil structure, whereas the silt sand treated with lignin showed fewer cracks and pores, and its soil structure was more compact under the encapsulation and filling action of cementitious materials. No new chemical elements, mineral components, or functional groups were produced when lignin was mixed with silt sand. The mechanism by which lignin improved the macroengineering properties of silt sand involved the cementitious material produced by the interaction between lignin and soil minerals, which encapsulated the soil particles and filled the interparticle pores. Research results can provide a theoretical reference for engineering application of lignin in cold regions.

Asphalt-treated base (ATB-25) is a widely used flexible base material. The composition and gradation of mineral aggregate are important factors affecting pavement performance of asphalt treated base. In this study, two new methods were proposed to address the problems of existing aggregate proportion calculation for asphalt mixtures: (1) the combination of generalized inverse solution of the normal equation and spreadsheet trial and (2) quadratic programming. Both methods can calculate mass ratios of various aggregates in a quick and accurate manner. The orthogonal test was used to design nine aggregate gradations within the range of asphalt treated base (ATB-25) stated in the industrial standard. The aggregate proportion was calculated by two new methods. The Marshall test, water weight test, rutting test, and water-soaked Marshall test were carried out on the asphalt mixture specimens. The pavement performance test results were fuzzified using the fuzzy mathematics method, and the weights of pavement performance evaluation indexes were determined through the analytic hierarchy process. Taking the fuzzy comprehensive evaluation values as the objective function, test results were analyzed and evaluated. Finally, the optimal aggregate gradation was determined considering factors of compactness, high-temperature rutting resistance, and water stability.

Based on the unified strength theory, a new method to calculate the plane soil slope safety factor was derived that considers the effect of intermediate principal stress σ₂ and at‐rest lateral pressure coefficient K₀. Calculation examples from the literature were used to compare the new calculation method and the current slice method; the results showed that both provided good consistency. The new method can provide a reference for slope stability evaluation. The new method was used to calculate the soil slope safety factors for different values of intermediate principal stress parameter b, double shear stress parameters , and static lateral pressure coefficient K₀. The results showed that the safety factor F_s increased when b was increased; F_s first increased and then decreased when was increased; and F_s increased when K₀ was increased. These results show that the intermediate principal stress as well as the stress state and its changes cannot be ignored during soil slope stability analysis. The slope soil characteristics and stress state should be considered to determine the unified strength theoretical parameters and static lateral pressure coefficient, maximize the potential of slope soil strength, and effectively reduce the costs of soil slope engineering.

Aiming at the problem that the existing stopping sight distance model is out of sync with the development of the times, this paper puts forward a new stopping sight distance model considering the fuzziness and randomness of design parameters, and deduces the calculation method of fuzzy reliability of stopping sight distance. Firstly, the actual braking process of vehicle is divided into three stages: driver’s reaction stage, braking force rising stage and continuous braking stage. Based on MATLAB/Simulink software, the calculation model of complete braking stage is simulated and analyzed, and then the calculation model of stopping sight distance of ESC system is proposed. Secondly, considering the fuzziness of operating speed, the fuzzy reliability theory is introduced to establish the function of the fuzzy reliability of the stopping sight distance. Using the Gaussian fuzzy number and the center point method, the reliability index and failure probability of stopping sight distance are obtained, and the safety and reliability of stopping sight distance are described. Finally, according to the “Unified Standard for Reliability Design of Highway Engineering Structures”, the traditional reliability calculation method and fuzzy reliability calculation method are respectively used to calculate the stopping sight distance value corresponding to the highway safety level. Taking the calculated value of ESC system stopping sight distance model at the design speed of 120 km/h as a reference, the reliability index and failure probability of the two reliability calculation methods are calculated. The results show that the new stopping sight distance model is closer to reality than the existing stopping sight distance model in the continuous braking stage. Compared with the traditional reliability calculation method, the fuzzy reliability calculation method has high reliability index, low failure probability and high calculation accuracy. Implementing road design based on the stopping sight distance value calculated by the new stopping sight distance model and fuzzy reliability theory can improve road safety.

The service performance of chromium-free zinc–aluminum coatings exhibits characteristics from multiple perspectives. Fully considering the physical properties, corrosion resistance, and economic viability of the coatings, this study incorporates the concepts of “domain” and “degree” from extenics theory into the analytic hierarchy process to optimize the formulation of chromium-free zinc–aluminum coatings. The findings reveal that the extension analytic hierarchy process takes into account the diversity of evaluation indicators, enhancing the objectivity and accuracy of the comprehensive evaluation results. Nine formulations were developed using a four-factor, three-level orthogonal experiment to evaluate the effects of metal powder, PEG-400, KH-560, and sodium molybdate on the service performance of chromium-free zinc–aluminum coatings. Utilizing an extensible hierarchical sorting weight system alongside a performance index grading and scoring method, 3# emerged with the highest score, indicating the best overall performance. The research outcomes offer innovative insights and technical support for optimizing the formulations of chromium-free zinc–aluminum coatings and other coatings.