3D stability analysis method for toppling failure on rock slopes

In this paper, an optimized solution method is proposed for the 3D stability analysis of rock slopes subject to toppling failure based on their geometric and mechanical properties. It was verified by a 3D block system that focused on the geometric properties of toppling slopes as a research object, considering the force and its action point on the interface of the block system as unknown variables, as well as introducing the definition of a safety factor considering both tension and shear strength reduction. The proposed method implied setting constraints, such as the balance equation corresponding to block force and moment, as well as non-violation of the yield criterion, considering the minimum value of the safety factor as the objective function. It was applied to the analysis of two typical 3D models simulating toppling failure on slopes. The example of a 3D spherical toppling slope was reconstructed and corroborated by calculations. The experimental results demonstrated that the proposed method could appropriately reflect the mechanical properties and stability behavior of a 3D toppling slope, thereby facilitating the analysis of the stability of 3D toppling rock slope model.

A Study on Evaluation of Slope Stability and Range of Rockfall Hazard of Daljeon-ri Columnar Joint in Pohang, Korea

In this study, we evaluated the slope stability of the Pohang Daljeon-ri columnar joint (Natural Monuments # 415) and calculated the maximum energy, jumping height and moving distance of rockfalls using a simulation. Based on the results, we established the range of rockfall risk. The slopes of the Pohang Daljeon-ri columnar joint have dip directions of 93.79°, 131.99°, 165.54° and 259.84° from left (SW) to right (NE). Furthermore, they have a fan-like shape. The Pohang Daljeon-ri columnar joints are divided into four sections depending on the dip direction. The measurement results of the discontinuous face show that zone 1 is 125, zone 2 is 261, zone 3 is 262, zone 4 is 43. The results of slope stability analyses for each section using a stereographic projection method correspond to the range of planar and toppling failure. Although it is difficult to diagnose the type of failure, risk evaluation of currently falling rocks requires further focus. The maximum movement distance of a rockfall in the simulation was approximately 66 m and the rockfall risk range was the entire area under slope. In addition, it is difficult to forecast where a rock will fall as it rolls in various directions due to topographic factors. Thus, the installation of measures to prevent falling is suggested to secure the stability based on the results of the rockfall simulations and its probabilistic analysis.

Analysis of Flexural Toppling Failure in Rock Slopes Using Discrete Element Method

Flexural toppling failure is a common failure mode of natural and artificial rock slopes, which has caused serious damage to human life and property. In this work, an advanced numerical method called the Universal Distinct Element Code (UDEC) was used to study the mechanism of flexural toppling failure. In total, more than twenty slope models were built and analyzed. Two new parameters (displacement discontinuity and transition coefficient of failure surface) were introduced to present a further understanding of flexural toppling. The results show the failure zone of rock slopes subjected to flexural toppling includes two parts: the first-order instability part (FOIP) and the independent toppling zone (ITZ). The FOIP can be further divided into two subzones: the sliding zone (SZ) and the superimposed toppling zone (STZ). The occurrence of surface deformation discontinuities is the precursor to flexural toppling failure. The first displacement discontinuity occurs on the boundary between the FOIP and the ITZ. The angle, spacing, and angle of the joints, the angle of the slope has a significant influence on the stability of anti-dip bedding rock slopes. However, they do not affect the deformation and failure pattern of the slope.

The Southwell Topple – reassessment of a very large coastal toppling failure on the Isle of Portland, UK

The Southwell Topple is a spectacular example of a toppling failure on the southeastern coastline of the Isle of Portland, on the south coast of England. Types of mass movements, which occur around almost the entire coastline of Portland and include some other much smaller but well-known topples, vary depending on local geological and topographic contexts. The ‘Southwell Landslide’ of 1734 (i.e. the Southwell Topple), differs in most respects from all the others, not least in its size. We examine the historical and geological contexts of the Southwell Topple in order to explain its origins and characteristics. The recently published bathymetric data from the DORIS project reveals the tectonic context for the landslide, particularly the frequent transform faults parallel to the southeastern coastline of Portland and the axis of the Shambles Syncline forming Portland's ‘central depression’. It appears that the Southwell Topple resulted from coast-parallel tectonic discontinuities – probably a single joint and/or transform fault – through the Portland Stone combined with preferential marine erosion of the underlying weaker Portland Sand.