The tensile strength of the soil predicted by the classical Mohr-Coulomb (M-C) yield criterion is suspicious, because it is determined from the extrapolation of the test results in the compressive regime. In this case, the classical M-C yield criterion is modified by reducing the tensile strength in the tensile regime. An analytical approach under the framework of limit analysis is carried out incorporating with the modified yield criterion to obtain the upper-bound solutions of the slope stability. Stability charts for slopes with tensile strength cut-off under different seismic accelerations are provided. It is revealed that considering the effects of tension cut-off, the stability factor is reduced by 55% for vertical slopes subjected to seismic loads.

Snow cover melting leads to a release of stored winter-time precipitation over a relatively short period of time and thus affects the stability of embankment and cut slopes. Capturing the patterns of pore water pressure responses against the snow melt water infiltration and reflecting them into seepage flow analysis and mechanical stability analysis may lead to more precise assessment of the spring-time instability peculiar to snowy cold regions. This paper describes lessons from the authors’ experience in monitoring snow and ground conditions in three sites in Hokkaido, which were with limited access during winter. From long-term observation spanning up to 5 years, patterns and features in the snow cover evolution and ground responses are summarised. A correlation was found between the peak snow cover depth and the delay in slope surface pore water pressure responses, which represents the significant time required for melted snow to travel through the snow beneath. Reflecting this delay could lead to more precise spring-time pore water pressure assessment in slopes.

This study investigates the shear behaviors of unsaturated structured loess in direct shear test by the discrete element method (DEM). A bond contact model characterized by the consideration of inter-particle attraction and van der Waals force was used. The direct shear tests were simulated under different suctions and vertical pressures. The simulation results were analyzed in terms of stress–strain relationships, volumetric responses, bond breakages and contact fabric. It is shown that: 1) The shear strength of structural loess samples can be enhanced by decreasing water content and increasing vertical pressure; the strain softening and dilatancy behaviors of structural loess enhance with the decrease of water content and vertical stress, respectively. 2) The bond breakage rate in shear band is related to the macroscopic mechanical response. 3) The anisotropy of the contact fabric changes more significantly in the shear band during shearing, it is of great significance to study the microcosmic properties of particles in shear band.

In 2013, a number of shallow landslides triggered by heavy rainfall affected a mountainous area which located on Izu-Oshima island (Eastern Japan). These slopes are consist of fine soil layers and coarse soil layers which have different permeability coefficient and soil water characteristic curves. To clarify the characteristics of water infiltration in such unsaturated multi-layered slope and to assess the influence of the water content distribution on slope failure, 4 groups of slope model experiments were conducted. Silica No 1(D50=3.10 mm) and silica No 7(D50=0.16 mm) were used as the slope materials. The results indicated that wetting front apparently stopped at the interface between the silica No 7 layer and silica No 1 since the capillary barrier works and then lateral water flow occurred along with the interface and infiltrate into next layer when soil approaches saturation. It was found that lower water content in fine and coarse layer, unsaturated permeability coefficient K in coarse layer (5.54E-06 cm/s) is smaller than fine layer (1.08E-04 cm/s) since matric suction is 2.5 kPa, which result that capillary barrier works. In addition, higher water zone still exists at the bottom of the fine layer after drainage for a long period which results in the failure in this zone firstly when second rainfall was applied. Piping occurred at the bottom of the model when amount of water exists inside the slope.

A method is proposed that the changes of elastic wave velocities are a function of normal stress, soil moisture, shear stress and shear displacement, can be expressed as ΔV =a*(Δ〖σ)〗^(m/2)+b*ΔVWC+c*Δτ+d*Δx , Where σ is normal stress, VWC is volumetric water content, τ is shear stress, x is the shear displacement. This study aims at investigating the elastic wave propagation in soil, to find out the method using the changes of elastic waves in the slope surface layer and applied to an early warning system. A series of experiments were conducted, the first one was a laboratory experiment using multi-layer shear model to determine the coefficient of normal stress, soil moisture content, the shear stress, and the displacement. The elastic wave velocities calculated by the coefficient and the input soil moisture and shear stress were compared to the measured velocities, the results show they were the similar trend. The second one was elastic wave monitoring on-site. The results of on-site also showed that the elastic wave velocities changes with the soil moisture. It is similar to the result of laboratory experiment. Monitoring elastic wave in the surface layer of slope can detect its instabilities. Slope failure may be predicted based on the historical record of elastic wave propagation in soil.