Failure mechanisms in two-layer undrained slopes

This note presents results of stability analyses of two-layer undrained slopes by the finite element method. The study focuses on the circumstances under which either deep or shallow failure mechanisms occur, as a function of the strength ratio of the layers, slope angle, and foundation depth ratio. Improved knowledge of the location of the critical failure mechanism(s) in two-layer systems will give engineers better insight into where to focus their attention in terms or remediation or reinforcement to preserve stability.

Pull-Out Capacity and Failure Mechanisms of Strip Anchors in Clay

Plate anchors are a well-established solution for supporting the efforts of floating platforms for wind and marine renewable energies. The behavior of ultrathin rigid plate anchors buried in purely cohesive soils under undrained and plane-strain conditions is analyzed. As already known, a dimensional analysis shows that the pull-out capacity of the anchor may be expressed using a weightless break-out factor (Nc0) that only depends on the ratio between the depth and the anchor width (H/B). Using finite element analyses, tabulated values of the weightless break-out factor are provided in this paper and three different failure mechanisms are identified, namely very shallow (quasi-vertical), shallow or intermediate (semi-vertical), and deep (rotational). For very shallow failure mechanisms, the studied problem is completely equivalent to the trapdoor problem because immediate breakaway at the bottom part of the anchor is considered (vented conditions). The existing analytical solutions for the very shallow (Nc0 = 1.956 H/B) and deep cases (Nc = 3π + 2) using the slip-line method are reviewed and an analytical limit is proposed for the first time for the very shallow mechanism (H/B = 1.314). For shallow (intermediate) cases, the failure mechanism is identified and the angle of the main slip lines is numerically evaluated.

Analysis of Factors Triggering Shallow Failure and Deep-Seated Landslides Induced by Single Rainfall Events

Earthquakes, rainfall, or a combination of both can trigger landslides, which can be classified into shallow and deep-seated types according to scale. Landslide risk potential can be charted according to the spatiotemporal characteristics of a combination of triggering factors that can be collated for similar historical events by various methods. The geographic information system (GIS) and the instability index method are two approaches commonly used to perform such a task; however, the nature of the event and the quality of imported data affect the degree of bias of model predictions against real-time values. To identify the differences between shallow and deep-seated landslides, 324 cases of landslides triggered by single rainfall events in Taiwan are analyzed in this study. It is determined that the principal factor governing shallow failure for rainfall-induced landslides is slope and that deep-seated failure is controlled by the amount of accumulated rainfall. By arranging the weighting, these factors could predict 93% and 75% of the occurrences of shallow and deep-seated landslides, respectively, based on a pre-event digital terrain model.