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Expansive soils are characterized by repeated swelling and shrinkage. They cause great damage to engineering projects because of their expansiveness, over-consolidation and propensity to crack. However, the impact of cracks on the stability of an expansive soil slope during loading and irrigation is not yet fully understood. This study aimed to investigate the relationship between slope state and crack development in fissured expansive soils. A series of physical model tests with different types of cracks were conducted, in which the fissured expansive soil slopes were subjected to different loadings (1.6, 3.2, 4.8, 6.4, 16 MPa), and irrigated at a flow rate of 25 mL/min. The VIC-2d software, which utilizes the digital image correlation principle, was used to quantitatively obtain the horizontal and vertical strain data of the slope model. The closure and opening of cracks, and the slope state after loading and irrigation were monitored by strain data analysis using VIC-2d software. The results indicate that the excessive overlying stress revives the existing cracks and produces sliding along the crack interface. The sliding surface of the fissured expansive soil slope became shallower due to the water infiltration. It was demonstrated that the middle and foot of the fissured expansive soil slope were the key positions for reinforcement from the perspective of the mutual transformation of tensile strain and compressive strain on the surface of the slope. It is of great importance to study the relationship between the crack strain state and deformation trend of a slope subjected to loading and infiltration to understand the progressive surface- or shallow-layer sliding mechanisms, and reinforce key areas of the slopes in areas containing moderately or strongly expansive soils with abundant cracks.

Soil&ndash, rock mixtures (SRM) have the characteristics of distinct heterogeneity and an obvious structural effect, which make their physical and mechanical properties very complex. This study aimed to investigate the deformation properties and failure mode of the shear zone as well as the movement of block stones in SRM experimentally, not only considering SRM shear strength. The particle composition and proportion of specimens were based on field samples from an SRM slope along national highway 318 in Xigaze, Tibet. Shear zone deformation tests were carried out using an SRM-1000 large-sized geotechnical apparatus controlled by a motor servo, considering the effects of different stone contents by mass (0, 30%, 50%, 70%), vertical pressures (50, 100, 200, 300, and 400 kPa), and block stone sizes (9.5&ndash, 19.0, 19.0&ndash, 31.5, and 31.5&ndash, 53.0 mm). The characteristics of the shear zone deformation and block stone interactions were monitored by placing aluminum wires and dry ash in holes in the specimens. The results showed that the stone content 30% and 70% were two critical thresholds to determine the deformation characteristics of SRM. Under the conditions of high stone content and large particle size, the stones throughout the shear surface tended to extrude and roll during the shear process. The block stones around the shear surface were mainly affected by dilatancy and exhibited extrusion, particle breakage, and redistribution. The deformation pattern could be considered as be analogous to push-type shear deformation from the back to front or composite shear deformation from the front and back to the middle of the slope. It is of great importance to study the shear characteristics and deformation evolution of SRM to understand the progressive shear process of the sliding zone and the failure mode of landslides.

Swelling tests of Mengzi remolded expansive soil inundated with different types of wetting fluids (distilled water, saline water and acidic water) were carried out using advanced consolidometer. Swelling characteristics of expansive soil under different initial conditions were studied. The dose–response model was used to fit the rules of swelling time interval for expansive soil with water immersion. The quantitative relationships between the swelling deformation and initial conditions (initial water content, initial dry density and overburden pressure) were attained using 3D regression analyses. The differences in deformation rules of expansive soil with water immersion in each region are bigger for the differences of genetic types, mineral compositions, chemical characteristics of soils and sample preparation techniques and instrument error. The expansion deformation rules of soil immersed in salt and acid solution are the same as the rules of soaked soil. The important indices obtained can be provided to the engineering design, construction and stability evaluation of expansive soil slopes.

According to Mengzi expansive soil, consolidated drained tests and undrained tests are carried on under saturated and remoulded conditions. The stress-strain characteristics of saturated soil are researched systematically under different confining pressure, initial dry density, initial water content, shearing rate and drainage condition. The inherent unity of diversity of shearing strength for the same samples measured by different experimental methods is indicated according to the normalization of critical state test results. And the failure lines inp‘-q- ν space of remoulded saturated expansive soil under consolidated drained and undrained conditions are attained. The hyperbolic curve model can fit well the weak hardening stress-strain curves and the exponential curve model can fit the weak softening stress-strain curves. The test results can provide technical parameters and theoretical help for shearing strength variation of slope during rainfall and strength state of soil structure in normal water level.