Expansive soil is a source of risk to the foundations or subgrade engineering. Stabilization of expansive soil is imperative for practical engineering. A series of laboratory experiments were performed to analyze the physical‐mechanical properties and microstructures of stabilized soil. Three stabilizers used in this study are fly ash, sand, and basalt fiber. Different percentages of fly ash (0, 5, 10, 15, and 20%), sand (0, 8, 16, and 24%), and basalt fiber (0 and 0.4%) were added by weight into natural soil. Experimental results indicate that the optimum moisture content of stabilized soil increases with the increase of fly ash content for a given sand content, whereas the maximum dry density shows a decreasing trend. The variation trend of optimum moisture content and maximum dry density turns reverse with the increase of sand content for a given fly ash content. Plasticity index is decreased by both increasing fly ash content and sand content. It is found that the maximum unconfined compressive strength and optimum growth rate of strength are obtained by selected mixtures of 10% fly ash, 8% sand, and 0.4% basalt fiber contents. As the analysis of complementary effect suggests, most of the mixt treatments applied in this study have produced good results associated with the strength enhancement of expansive soil. In line with the results of SEM tests, the connection among clay particles has been enhanced through the generation of hydration products (C‐S‐H and AFt) of fly ash. The filling effect of sand has increased the integrality and compactness of stabilized soil. Moreover, the gripping effect between fibers and soil particles notably improves the strength of stabilized soil. The effect of sand on reinforced soil with 0.4% basalt fiber increases the interfacial force between fibers and soil particles.

Dynamic compressive tests are performed in three frozen soil types under different stress states at freezing temperatures of −5°C and −15°C with impact loading pressures from 0.3 MPa to 0.6 MPa. The effects of frozen soil type, freezing temperature, impact loading pressures, and stress states on incident energy and energy absorption characteristics, such as absorbed energy and energy absorbency rate, are investigated. The experimental results show that most of the incident energy is reflected back to the incident bar, and incident energy linearly increases with the increase of impact loading pressures. Both absorbed energy and energy absorbency rate are found to be negatively correlated with freezing temperature, and there values under confining pressure state are larger than that under uniaxial condition. The effects of confining pressure on absorbed energy are quite different at different freezing temperatures. In addition, frozen soil type also affects absorbed energy and energy absorbency rate. Meanwhile, impact loading pressure shows an increased effect on the absorbed energy, but it has little effect on energy absorbency rate in the research.

Considering the periodical moisture variation in deep rock masses, cyclic wetting and drying under high geothermal condition is a vital issue for the safety and stability of deep rock engineering. To investigate the coupled effect of water temperature and cyclic wetting and drying on dynamic mechanical characteristics of sandstone, dynamic uniaxial compressive tests were carried out under the same loading condition for sandstone specimens subjected to cyclic wetting and drying treatment. When the temperature was 60°C in both wetting and drying processes, cyclic wetting and drying treatment presents a detrimental effect on the tested sandstone. Both physical and dynamic uniaxial compressive characteristics deteriorate in an exponential function with the increase of wetting and drying cycles. Based on SEM image analyses, the initiation and propagation of microcracks is mainly the result of cyclic loading and unloading of tensile stresses induced by water absorption and desorption of kaolinite within sandstone during cyclic wetting and drying treatment. After 15 cycles of wetting and drying, the deterioration of both physical and dynamic uniaxial compressive characteristics first increase then decrease with water temperature in wetting process elevating from 20°C to 98°C. SEM images indicate that more microcracks generate when water temperatures increase from 20°C to 60°C, while the micromorphology is changed and fewer microcracks display due to kaolinite mobilization when water temperature increases from 60°C to 98°C. The threshold value for the effect of water temperature on cyclic wetting and drying is found to be about 60°C for the tested sandstone.

The dynamic stress‐strain relationship of artificial frozen silty clay under one‐dimensional coupled static and dynamic loads is obtained using modified split Hopkinson pressure bar (SHPB) equipment. The variation in dynamic compressive strength, dynamic deformation modulus, energy dissipation, and failure mode of artificial frozen silty clay with axial precompressive stress ratio are studied in this research. Experimental results indicate that the dynamic stress‐strain curves under uniaxial state and one‐dimensional coupled static and dynamic loads can be divided into four stages, i.e., compaction stage, elastic stage, plastic stage, and failure stage. The dynamic compressive strength, first‐stage deformation modulus, second‐stage deformation modulus, and absorbed energy density of artificial frozen silty clay present a trend of first increase and then decrease with the increase of axial compressive stress ratio, and the axial compressive stress ratio corresponding to the peak value is 0.7 in this test. In addition, there is a very similar effect of axial precompressive stress ratio on dynamic compressive strength and second‐stage deformation modulus of artificial frozen silty clay. At 0.4 axial compressive stress ratio, spall phenomenon appears at circumferential direction and center position of the frozen soil specimen has no obvious failure. Shear failure appears at 0.7 to 0.9 axial compressive stress ratio, and the larger the axial compressive stress ratio applies, the more obvious the shearing surface appears; moreover, comminution failure mode appears at 1.0 axial compressive stress ratio.

To investigate the influence of nonparallel end‐surface on stress uniformity during loading process in rock SHPB test, SHPB numerical simulations have been carried out by LS‐DYNA when end‐face nonparallelism is within 0.40% and Young’s modulus ranges from 14 GPa to 42 GPa. Isotropic linear elastic model is applied for elastic steel pressure bar, and HJC constitutive model is chosen for rock specimen. Numerical simulation results indicate that fluctuation effect exists in both reflected stress waves and transmitted stress waves, and it is enhanced with the increase of end‐surface nonparallelism. The stress nonuniformity coefficient attenuates in a serrated fluctuation. With the increase of end‐surface nonparallelism, the amplitude of transmitted stress wave gradually reduces, while stress nonuniformity coefficient increases. Stress equilibrium time first decreases slightly then increases in a step type. Therefore, nonparallel end‐surface leads to two reverse results for stress uniformity during SHPB loading process, extending stress equilibrium time and shortening stress equilibrium time. And the influence on shortening stress equilibrium time is weak, while the influence on extending stress equilibrium time is great. When end‐surface nonparallelism is 0.10%, stress equilibrium time achieves its lowest value whatever Young’s modulus is. Hence, end‐surface nonparallelism of the rock specimen is suggested to be controlled within 0.10% when conducting SHPB tests.

Freeze-thaw cycle and moisture content are important factors for structural strength degradation in cold areas. Using coal gangue and slag to prepare alkali slag ceramsite concrete (ASCC) can implement the reuse of solid waste of coal gangue and slag. To study the influence of ceramsite content and moisture content on compressive strength and energy characteristics under freeze-thaw cycles (FTCs), uniaxial compression tests were conducted for ASCC with different moisture contents (dry, 4%, 5%, and 6%) and ceramsite contents (0%, 25%, 50%, 75%, and 100%) after 20 FTCs. The results show that the stress-strain curves of ASCC with different moisture contents and ceramsite contents all undergo four stages under FTCs, namely initial compaction, elastic deformation, crack development, and post-peak failure. The addition of coal gangue ceramsite makes concrete failure show certain ductility characteristics. Both compressive strength and ultrasonic pulse velocity decrease with the moisture content, and elastic energy utilization rate of wet ASCC is better than that of dry ASCC. The compressive strength, ultrasonic pulse velocity, and energy characteristics all decrease with the increase of ceramsite content.