Biaxial compression tests with the same specimen size and different maximum grain sizes were simulated for coarse‐grained soils using the discrete element method to study the influence of grain size on the mechanical properties and force chain. The maximum grain sizes were 40, 20, 10, and 5 mm, respectively. The grading with self‐similar fractal structure in mass is designed to ensure the same pore structure for soils. The shear strength increased with the increase in maximum grain size. Evident increase in shear strength and significant size effect were observed when the ratio of the specimen diameter to maximum grain size was less than five. The shear dilation of coarse‐grained soils increases with the increase in maximum grain size. The contact force distribution was uniform when maximum grain size was small but tends to be uneven with the increase in maximum grain size, thereby causing the increase in shear strength by stable strong force chains. This finding demonstrates size effect on the mechanical properties and force chain of cohesionless coarse‐grained soils under the biaxial compression condition.

Landslide dam is one of the main types of barrier dams, whose structure is loose and stability is poor. Once seepage failure occurs, it will threaten the life and property safety of downstream people. The particle composition and depositing characteristics of the dam are key influence factors in evaluating the seepage safety of landslide dams, which are also the primary considerations to carry out model tests. Based on previous studies, combined with the results of field investigations and indoor model tests, the depositing characteristics of landslide dams and advances in model tests for seepage failure are summarized, and the existing problems are discussed. Results show that the depositing characteristics of the landslide dam are related to the lithology of landslides, sliding path, bank slope structure, etc. The failure modes and processes of landslide dams are varied from depositing characteristics, particle size compositions to hydraulic conditions. For the landslide dams with high permeability zones, their failure can be attributed to the progressive cycle of piping and downstream dam slope collapse. While designing a model test, experimenters should not only consider the dynamic flow similarity but also determine the particle size distribution of the dam soils according to the relationship between particle size and particle movement. Finally, it is proved that the grading entropy can comprehensively reflect the gradation characteristics of the landslide dam as well as the change in gradation in the fine particle erosion process, which can be used to predict the permeability and internal stability of dam particles. Combined with other information, the failure mode and process of landslide dam can be predicted. The research results can provide references for the experimental research of landslide dam.

Gravel content is an important factor affecting the mechanical properties of clay-gravel mixtures. To study the effects of gravel content on the shear strength of clay-gravel mixtures, constant-strain-rate drained triaxial compression tests were conducted for various mixtures. The gravel contents were 30%, 40%, 50% and 70%. The confining pressures were varied from 50kPa to 300kPa. Test results indicate that the deviator stress at failure under the same confining pressure increases with the increase in gravel content. As the gravel content in the mixtures is between 30% and 50%, the shear strength is jointly attributed by clay and gravel. An increase in gravel content results in slight increases in both the cohesion intercept and internal friction angle. At gravel content of up to 70%, the shear strength of the mixture is controlled by that of the gravel, and the cohesion intercept and the internal friction angle increase sharply.

The gradation of rockfill affects creep behaviour, but indoor testing apparatus does not allow a field maximum particle size of the rockfill of 1000 mm. To investigate the creep behaviour of rockfill with different maximum particle sizes and establish a creep model for the rockfill material, oedometer creep tests for slate rockfill material with different maximum particle sizes were conducted to explore the effect of gradation on the creep behaviour of rockfill materials. The test results showed that the creep strain increases and the rate of increase decreases with the increase in vertical stress. The creep strain increases with the decrease in maximum particle size under all vertical stresses. Furthermore, a particle size ratio R_dwas defined to establish the creep model. An empirical creep model was proposed to calculate the creep strain for rockfill with oversized particles that are not allowed by the experimental apparatus. Three groups of test data were used to determine the model parameters, and one group of test data was used to verify the predictive capacity of the model. The results showed that the model can satisfactorily predict the creep behaviour of slate rockfill with oversized particles.

A study has been conducted to investigate the mechanical properties of cement-mixed gravel using the unconfined compression test and the tensile test. Basic factors including the curing period, the water-binder ratio, the cement content, and the strain rate were evaluated. Ordinary Portland cement with fly ash was employed as the cementation agent for preparing cemented samples. The results indicate that the unconfined compressive strength, the deformation modulus, and the tensile strength increase with the increase in the curing period. The ratio of tensile strength to unconfined compressive strength has no distinct change after 7 days. An optimum water-binder ratio can be obtained. The unconfined compressive strength and deformation modulus decrease as the water-binder ratio decreases and increase from the optimum water-binder ratio. With the increasing of the cement content, the unconfined compressive strength increases distinctly, the deformation modulus increases significantly when the cement content is less than 4% and then increased slowly, and the failure strain increases to a peak value and then decreases. With the increasing of the strain rate, the unconfined compressive strength increases slightly and the deformation modulus increases slowly. The failure strain decreases with an increase in the strain rate.