In the past 30 years, research on rainfall-induced landslides has grown remarkably. The contribution of matric suction to soil strength and the physics of water flow in unsaturated soils are widely accepted phenomena among researchers. However, the adoption of unsaturated soil mechanics in geotechnical engineering practice has been relatively slow, in part due to the practicality of design solutions available to the engineer. This paper conducts a parametric study on unsaturated silty slopes under a vertical steady flow rate to identify the suitable slope and hydrologic conditions to incorporate unsaturated conditions for preliminary stability analysis. Notably, the contribution of suction is most significant for silt/clay slopes with a water table located below the mid-height of the slope. For slopes with slope height ≥20 m and a fairly high water table, the slope height is a primary controlling factor of slope stability. Two case studies based on distinct failure mechanisms are presented to review the application of common geotechnical software in rainfall seepage and stability analyses of unsaturated slopes. Focus is placed on the pre-failure and failure stages of each case study. The slip surface search method, failure mode, and coupling approach integrated into each computer program caused notable differences in output results.

The settlements and corresponding soil reactions of a surface raft foundation subjected to vertically uniform load at the sites of granular or cohesive soils have been qualitatively introduced to engineers in the past. This study intends to verify the foundation load-response mechanism using three-dimensional finite-element analyses. The Mohr–Coulomb soil model was used to simulate the nonlinear effects of the granular and cohesive soils. The coefficients of subgrade reactions of the soil were back-calculated and compared to those obtained from the rigid foundation model. For all the square surface rafts studied, non-uniform settlements with the largest value at the center can be found. For the smallest rafts located in clay, the soil reactions were found to be rather consistent. For larger rafts in clay, the soil reactions would be changed according to the soil stiffness and raft dimensions. For surface rafts in sand, the effects of soil stiffness on soil reactions appeared to be insignificant. The soil reactions were generally higher at the center and varied with raft dimensions. For the smallest raft in sand, large soil reactions can be found at the edge. The coefficients of subgrade reactions were found to be more consistent with the smallest values occurring at the center. The results of this study indicate that the load-response mechanism of the raft foundation is rather complicated. Such load-response mechanisms are strongly affected by the relative rigidity of the foundation depending on soil stiffness and foundation dimensions.

River slopes can be changed due to an extreme event, e.g., a large-scale earthquake. This can uplift a riverbed greatly and thereby change the behavior of the river flow into a free or submerged overfall. Corresponding damage, including extreme erosion, on bridge piers located in the river can take place due to the aforementioned flow conditions. A reconstructed bridge pier in the same location would also experience a similar impact if the flow condition is not changed. It is important to identify these phenomena and research the mechanism in the interaction between overfall types and scour at bridge piers. Therefore, this paper is aimed at studying a mechanism of free and submerged overfall flow impacts on bridge piers with different distances by a series of moving-bed experiments. The experiment results showed clearly that bridge pier protection requires attention particularly when the pier is located in the maximum scour hole induced by the submerged overfall due to the z directional flow eddies. In many other cases, such as when the location of the bridge pier was at the upstream slope of a scour hole induced by a flow drop, a deposition mound could be observed at the back of the pier. This indicates that, while a pier is at this location, an additional protection takes place on the bridge pier.

This paper presents a study on bridge pier protection with a single porous basket (SPB) in clear-water experiments. The SPB is a type of combined flow-altering countermeasure. The SPB was installed at a distance ahead of the protected pier. After a series of tests, the results showed that appropriate installation of the SPB was able to effectively adjust the flow pattern to reduce the down-flow motion and horseshoe vortex ahead of the pier. Dominant factors for the pier protection—considered for all tests—included the distance between the basket and pier, submerged depth of the basket, basket length, pier diameter, basket diameter, hole size, porosity, and the flow approaching angle. After evaluating these parameters through laboratory tests, the results of protection were optimized. In optimal conditions, the SPB was able to provide maximum pier protection and decrease the maximum scour depth by as much as 75.53%.