In this paper, through extensive on-site research of the plain concrete composite foundation for the Jiuma Expressway, the study conducted proportional scaling tests. This study focused on the temperature, moisture, pile-soil stress, and deformation of this foundation under freeze-thaw conditions. The findings indicate that the temperature of the plain concrete pile composite foundation fluctuates sinusoidally with atmospheric temperature changes. As the depth increases, both temperature and lag time increase, while the fluctuation range decreases. Furthermore, the effect of atmospheric temperature on the shoulder and slope foot is more significant than on the interior of the road. During the freeze-thaw cycle, the water content and pore-water pressure in the foundation fluctuate periodically. The pile-soil stress fluctuates periodically with the freeze-thaw cycle, with the shoulder position exhibiting the most significant changes. Finally, the road displays pronounced freeze-thaw deformations at the side ditch and slope toe. This study provides a valuable basis for the construction of highway projects in cold regions.

Dam safety is critical for protecting downstream lives, property, ecosystems, and socio-economic stability. Investigating dam breach mechanisms and establishing safety warning thresholds hold significant scientific and practical value. This study conducted dam breach model tests under diverse conditions and developed a monitoring and warning system using high-precision inclinometers to elucidate deformation characteristics and failure mechanisms. Experimental results revealed three distinct failure stages: tension cracking, localized soil flow/collapse, and catastrophic collapse/landsliding. Precursor phenomena such as seepage and cracking were observed prior to soil flow failure, suggesting that rapid infiltration line reduction during this phase could mitigate large-scale failures. Tilting deformation of the downstream slope was identified as a viable early warning indicator. An improved tangent angle method subdivided the rapid deformation stage into three substages (early, middle, and late) using thresholds of 45 degrees, 80 degrees, and 85 degrees, respectively, to establish tiered warning criteria. Additionally, a reciprocal velocity method was proposed to predict breach timing by characterizing the relationship between the inverse rate of slope angle change and time, demonstrating effective breach time prediction.

The construction of a power grillage is of great significance for promoting local economic development. Identifying the characteristics of foundation damage is a prerequisite for ensuring the normal service of the power grillage. To investigate the bearing mechanism and failure mode of the grillage root foundations, a novel research method with a transparent soil material was used to conduct model tests on different types of foundations using particle image velocimetry (PIV) technology. The results indicate that, compared to traditional foundations, the uplift and horizontal bearing capacities of grillage root foundations increased by 34.35% to 38.89% and by 10.76% to 14.29%, respectively. Furthermore, increasing the base plate size and burial depth can further enhance the extent of the soil displacement field. Additionally, PIV analysis revealed that the roots improve pile-soil interactions, transferring the load to the surrounding undisturbed soil and creating a parabolic displacement field during the uplift process, which significantly suppresses foundation displacement. Lastly, based on experimental data, an Elman neural network was employed to construct a load-bearing capacity prediction model, which was optimized using genetic algorithms (GAs) and the whale optimization algorithm (WOA), maintaining a prediction error within 3%. This research demonstrates that root arrangement enhances the bearing capacity and stability of foundations, while optimized neural networks can accurately predict the bearing capacity of grillage root foundations, thus broadening the application scope of transparent soil materials and offering novel insights into the application of artificial intelligence technology in geotechnical engineering. For stakeholders in the bearing manufacturing industry, this study provides important insights on how to improve load-bearing capacity and stability through the optimization of the basic design, which can help reduce material costs and construction challenges, and enhance the reliability of power grillage infrastructure.

To accurately simulate the three-dimensional stress state and service performance of subgrade under long-term traffic loads, a subgrade service performance test system was developed. The test system consists of the loading system, a fully digital servo control system, and a data acquisition system. Based on the time-history characteristics of total stress components (three normal stresses and three shear stresses) of subgrade soil elements under traffic loads, the loading system was designed with four dynamic actuators and three static actuators. The loading system can simulate the rotation of principal stress axis in any subgrade soil elements through coordinated dynamic and static loading. The calculation method of load system was established to achieve the threedimensional stress state of subgrade soil element under traffic loads. Furthermore, the model tests were conducted on the developed test system to verify the three-dimensional stress state of subgrade under the typical traffic loads, such as highways, railways and airports. Results shows that the actual output load deviation of each dynamic and static servo actuator is under 1%. The time-history curves of dynamic stress components and the attenuation of vertical dynamic stress are in good fit with the theoretical calculations. Besides, the vertical dynamic stress in the subgrade decreases progressively with depth, and the stress path of the soil element is approximately heart-shaped. The above validated results indicate that the test system accurately simulates the three-dimensional stress state of subgrade under different traffic loads. Therefore, the subgrade service performance test system developed in this study offers a new concept, method, and technology for investigating the evolution of subgrade service performance under long-term traffic loads.

Damage to buried gas pipelines caused by mining activities has been frequently reported. Based on a case study from the Central China coal mining area, this research employs a scaled model experiment to investigate the movement of overlying strata in a room-and-pillar mining goaf. Distributed optical fiber strain sensors and thin-film pressure sensors were used to simultaneously measure the stress variations in the pipeline and changes in the soil pressure surrounding it. As the mining recovery rate increased from 50% to 86%, the maximum displacement of the overburden sharply escalated from 33.55 mm to 79.19 mm. During surface subsidence, separation between the pipeline and surrounding soil was observed, leading to the formation of a soil-arching effect. The development of the soil-arching effect increased soil pressure on the top of the pipeline, while soil pressure at the bottom of the pipeline increased on the outer side of the subsidence area and decreased on the inner side. Three critical sections of the pipeline were identified, with the maximum stress reaching 1908.41 kPa. After the completion of mining activities, pipeline collapse occurred, leading to a weakening of the soil-arching effect. Consequently, both stress concentration in the pipeline and soil pressure decreased. The probability integral method was corrected by incorporating the fracture angle, which enabled the determination of the location of maximum surface subsidence curvature, found to be close to the three failure sections of the pipeline.

Seismic retrofitting of existing bridges has been in practice for years to meet the stringent seismic requirements set forward by revised design codes. For retrofitting, however, bridge piers are often prioritized while less attention is given to the bridge foundations, which are equally prone to damage under seismic loadings. The current work presents a series of experimental studies in assessing the performance of 2 x 2 pile groups reinforced with micropiles in terms of head-level stiffness and damping under low-to-high levels of static and dynamic loadings, encompassing the influence of loading-induced soil nonlinearity. Practical micropiles inclinations of 0 degrees, 5 degrees, and 10 degrees with respect to the vertical are studied. Experimental results reveal that the head-level stiffnesses of pile groups reinforced with micropiles, contrary to the general expectations, become smaller than the pile group without micropiles at higher levels of applied loading. To elucidate the governing mechanism for such experimentally obtained results, three-dimensional nonlinear finite-element analyses were carried out. Results from the numerical analyses support the experimental results, suggesting that the presence of micropiles may not always increase the head-level stiffness of soil-foundation systems, particularly at higher levels of applied loading where the soil nonlinearity generated at the vicinity of piles and micropiles governs the overall head-level stiffnesses.