The cumulative deformation properties of subgrade soil under cyclic traffic loads are critical for optimizing pavement structure design and ensuring long-term highway structural performance. This study aims to investigate the coupling effect of freeze-thaw cycles and cyclic loads on the cumulative deformation behaviors and meso-structure of coarse-grained saline soil (CGSS) subgrade filling in high-cold areas. Dynamic triaxial tests and computed tomography (CT) scanning were conducted to analyze the CGSS under different working conditions. The research focused on the dynamic deformation development and damage evolution under varying freeze-thaw cycles and load amplitudes. The research results show that the cumulative deformation behavior of CGSS under cyclic loading is relatively sensitive to the freeze-thaw process. The cumulative dynamic strain increases as the freeze-thaw cycles, with a critical freeze-thaw cycle number of five. The stable cumulative dynamic strain curve exhibits clear three-stage characteristics when plotted in semi-log coordination, with critical loading cycles at 20 and 1,000. After 10–100 loading cycles, the cumulative strain curve quickly shows failure. The CGSS’s low density and pore regions greatly increase after a freeze-thaw cycle. The rise in dynamic stress amplitude notably affects the bonding between soil particles and crystalline salts. The coupling effect of the freeze-thaw cycle and dynamic activity exacerbates the deterioration of soil structure, resulting in variations in CT values within the scanning layer in the final state.

A hybrid control method based on sliding mode observer and predictive functional control is proposed to improve the performance of the linear motor servo system, which is usually characterized by nonlinearity, uncertainty and disturbances. Firstly, the mathematical model of linear motor servo system is established. Then, the sliding mode observer is designed to compensate for the parameter changes and external disturbances, and the disturbance information is fed back to the predictive function controller, and a prediction model with disturbances is established, so as to optimize the control method and improve the control effect of servo system. The simulation results show that the controller based on the sliding mode observer and predictive functional controller can effectively suppress the disturbances and improve the rapid response and steady-state accuracy of the system. As the controller shows strong robustness and anti-disturbance, it can be used to effectively control the servo systems.

This paper investigates hazard assessment and mitigation measures for rainfall-induced debris flow at a highway tunnel portal in Guangdong, China. The tunnel is situated at the outlet of a steep gully with a channel length of 2.38 km, an elevation difference of 682 m, and a gradient of 23.4%. Under extreme rainfall conditions, the portal faces severe risks of scouring and inundation that threaten the structural safety and operational stability of the highway. A high-resolution digital elevation model was established via UAV oblique photogrammetry, and debris flow processes were simulated using HEC-RAS 6.4. The hydrologic behavior under 20-year, 50-year, and 100-year recurrence intervals is first investigated in the research area. After that, the Bingham flow model is used for the debris flow simulation. Results show that as the return period increases from 20 to 100 years, the maximum flow depth at the tunnel portal rises from 1.92 to 2.21 m and the maximum flow velocity rises from 5.8 to 7.8 m/s, indicating that flow velocity is more sensitive to rainfall intensity than flow depth. These simulated flow depths far exceed the 0.5 m flood level stipulated in the Chinese highway tunnel design code, indicating a serious threat to tunnel safety. Based on a quantitative comparison between single-dam and multi-dam schemes, a multi-dam combination with different heights at four positions along the gully is proposed for segmented interception. This multi-dam scheme successfully reduces the flow depth at the tunnel portal to zero without requiring any individual dam to exceed 10 m in height, demonstrating a favorable balance between engineering feasibility and disaster mitigation effectiveness.