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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.

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. e 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. erefore, 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.

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.