The current formula of critical hydraulic gradient is not adapted to solve critical hydraulic gradient of cohesive soil. Assume that the seepage failure mode of the cohesive soil foundation was cylindrical or inverted circular truncated cone, based on the calculation formula of the critical hydraulic gradient of Terzaghi, the analytical formula of the critical hydraulic gradient considering the influence of the shear strength of the soil was derived. Then, the seepage failure process of the clay layer was simulated numerically, and the effects of the clay layer thickness, failure radius, and shear strength indexes on the critical hydraulic slope were analyzed. The comparison results show that the numerical test results are in good agreement with the calculated results of the new formula. In addition, the critical hydraulic gradient of sandy loam and loess under different working conditions was studied severally by a self-made permeation failure instrument. The results show that the critical hydraulic gradient decreases with the increase of soil thickness and failure radius, and the maximum error between the test and the corresponding formula results is no more than 16%.

In order to study the compressive deformation and energy evolution characteristics of concrete under dynamic loading, impact compression tests with impact velocities of 5, 6, and 7 m/s were carried out on concrete samples with aggregate volume ratios of 0, 32%, 37%, and 42%, respectively, using a split Hopkinson pressure bar test apparatus. The broken concrete pieces after destruction were collected and arranged. The fractal characteristics of fragmentation distribution of concrete specimens with different aggregate rates under impact were discussed, and the roughness of the fragment surface was characterized by the fractal dimension of the broken fragment and the crack surface energy was calculated. In addition, the analytical equation of the fractal dimension of the broken fragment and the crack surface energy was established. The relationship between the specimen energy absorption and the crack surface energy was compared and analyzed. The results show that the concrete specimens are mainly tensile split failure modes under different impact speeds. The fractal dimension, absorption energy, and crack surface energy all increase with the increase in impact speed and decrease with the increase in the aggregate rate. When the aggregate rate is different, the effective utilization rate of the absorbed energy is the largest when the aggregate content is 37%. The surface energy of the crack can be used to estimate the concrete dynamic intensity.

In order to study the permeability characteristics of cohesive soil in the consolidation process more accurately, in this work, the pores occupied by the combined water were defined as invalid pores, and the effective pores and ineffective pores were decoupled to study the relationship between effective pores and permeability coefficient. The widely used empirical formulas of the permeability coefficient were modified, and the empirical formulas of the permeability coefficient suitable for the consolidation process of cohesive soil were obtained. Combined with the e − lg σ relationships of normally consolidated soil, underconsolidated soil, and overconsolidated soil, the formulas of permeability coefficient, which considering the influence of initial consolidation state and consolidation stress, in the consolidation process of cohesive soil, were proposed. Finally, the rationality of the new formulas proposed in this paper was analyzed by indoor consolidation-permeability test and existing research. The results showed that the permeability coefficient of cohesive soil in the consolidation process predicted by the new formulas were more consistent with the measured average value. This study possesses practical engineering significance to solve the problem of foundation consolidation settlement.