Rock Slope Failures Research Articles

Fracture Failure of Consequent Bedding Rock Slopes After Underground Mining in Mountainous Area

Underground coal mining in the southwestern mountainous area of China causes potential large-scale landslides. To prevent the geohazards of consequent bedding rock slopes after underground mining, the deformation and failure configuration were determined by two landslides caused by underground mining. Then, a prediction model for the fracture failure of the consequent bedding rock slopes was established and validated by physical modeling. The prediction model can analyze the stress and bending moment in the consequent bedding rock slope caused by underground mining and predict the location of fracture failure of the slope. The prediction results for the Masangwan landslide showed that the fracture was at 103.5 m as compared to the actual slip length of 114 m, with an error of 10.5 m, and the relative error at 9.21%. The prediction model has good prediction effect. Physical modeling showed that the crack locations from a similar model appeared at specific intervals in the further advancement of underground mining. The rock mass at a distance from the boundary of the separation zone of the slope surface reached the tensile limit when the length of the separation reached the maximum threshold value, producing tensile cracks. The crack locations from a similar model appeared at specific intervals in the further advancement of underground mining. In addition, the error between the crack location and the prediction result was found to be only 0.0352 m, and the relative error was 5.79%. A comparison between the physical and proposed models showed that the predicted fracture failure is consistent with the laboratory results. The prediction and physical model neglect the impact of environmental factors on fracture development, such as the complex geological structure and the physical and chemical transport of water in the rock mass, resulting in a small error in the prediction results. Therefore, the prediction results can effectively reflect the deformation and failure of consequent bedding rock slopes caused by underground mining. The proposed model can serve as a theoretical basis to predict the geological disasters of consequent bedding rock slopes caused by underground mining.

Probabilistic analysis of potential planar-type rock slope failure of selected Malaysian rock slopes

Probabilistic analysis of potential planar-type rock slope failure of selected Malaysian rock slopes

Modelling the flexural buckling failure of stratified rock slopes based on the multilayer beam model

The buckling failure of stratified rock slopes intersected by a set of steep discontinuities that are approximately parallel to the slope surface is frequently encountered while constructing railways and roadways in mountainous areas. In this study, an analytical approach based on the energy equilibrium principle is presented to solve the flexural buckling stability of stratified rock slopes within the framework of multilayer beam theory. The generalized Hoek-Brown failure criterion is introduced to reflect the influences of slope size (scale effects) on the buckling stability. Subsequently, numerical and physical modellings from previous literatures are employed to validate the proposed approach. Furthermore, a practical case of Bawang Mountain landslide is also used for the comparative analysis. The study shows that the present analytical approach is capable to provide a more reasonable assessment for the buckling failure of stratified rock slopes, compared with several existing analytical approaches. Finally, a detailed parametric study is implemented, and the results indicate that the effects of rock strength, rock deformation modulus, geological strength index, layer thickness and disturbance degree of rock mass on the buckling failure of stratified rock slopes are more significant than that of rock type and slope angle.

Analysis of Seismic Stability of an Obsequent Rock Slope Using Time–Frequency Method

Obsequent rock slopes are often thought to be more stable than consequent slopes and passive sliding is unlikely to occur under earthquake loading. However, failures in obsequent rock slopes were indeed observed in recent large earthquakes. This paper presents a time–frequency solution to the seismic stability of obsequent rock slopes fully considering the time–frequency characteristics of earthquake waves. Large-scale shaking table tests were conducted to illustrate the application of the time–frequency method to an obsequent rock slope containing multiple weak layers with a small dip angle. The seismic stability of the obsequent rock slope is analyzed combining the time–frequency method, outcomes from the shaking table test, and conventional pseudo-static and dynamic numerical analyses. The results show that passive sliding can develop in the obsequent rock slope when taking the time–frequency components of the earthquake waves and the vertical seismic force into account. The middle–upper part of the obsequent rock slope is more vulnerable to seismic damage. The slope bulges under the earthquake loading; the maximum permanent surface displacement occurs at the middle–upper part of the slope, rather than the slope crest. Additionally, the response of seismic safety factor lags behind the responses of acceleration and surface displacement.

Rock avalanche mobility: optimal characterization and the effects of confinement

A Central Asia rock avalanche (rockslide) inventory that includes about 600 case studies with measured parameters is used to present a quantitative characterization of rock avalanche mobility and its dependence on the controlling parameters such as volume and height drop. The mobility can be characterized by runout and angle of reach, as well as by the affected area. The database was analyzed after dividing the rock avalanches into three confinement categories—frontally confined, laterally confined, and unconfined. In addition to the traditionally used slope failure volume and height drop, we correlated mobility parameters with their product that is proportional to the potential energy released during rock avalanche emplacement. It was found that coefficients of determination of the regressions of the affected area with volume and, especially, with its product with maximal height drop are higher than those of volume with runout and much higher than those of volume with angle of reach for all confinement conditions. Thus, these relationships provide an optimal characterization of the rock avalanche mobility. Relative influence of failure volume and height drop on rock avalanche mobility was also analyzed. The regression equations obtained in this study were successfully applied to several case studies from other mountain regions. The proposed regression equations can be used to predict the exposure of elements at risk threatened by anticipated rock avalanches. They can also be used to estimate the parameters of rockslide dams that might originate at the sites with anticipated large-scale rock slope failures, if their volumes and height drops can be assessed. The confinement conditions are statistically proved to influence the rock avalanche mobility and must be taken into consideration during hazard and risk assessment.

Rock slope failure in the British mountains

In this first full review of extant Quaternary Rock Slope Failure (RSF) in the British mountains, we provide a near-complete inventory of 1082 sites, 40% being rock slope deformations, 40% arrested rockslides, and 20% rock avalanches. Current RSF activity is negligible, and this relict population is predominantly paraglacial, with a parafluvial minority. Its spatial distribution is perplexing, with RSF density varying greatly, both regionally and locally. In the Scottish Highlands, eight main clusters account for 76% of RSF area in 15% of the montane area. Local concentrations occur in all the British ranges, across high and low relief, in core and peripheral locations, and on varied geological and glaciological domains; as conversely do extensive areas of sparsity, even in similar lithologies. Generic interpretations are thus precluded. Geology is only a secondary control. An association with Concentrated Erosion of Bedrock (CEB) is proposed, as a driver of intensified slope stresses. CEB is most evident at those glacial breaches of main divides where the most vigorous recent incision is inferred, and also in some trough-heads. A clear association between RSFs and these ‘late-developing’ breaches is demonstrated in the Highlands, in 42 localities, with sparsity away from them. It is also seen in seven Lake District localities. Glaciological models identify ice sheet volatility capable of driving breach ramification. High-magnitude paleoseismic events are generally unlikely to have provoked RSF clusters; a few candidates are considered. RSF has been underrated as an agent of mountain landscape evolution in Britain; its spatio-temporal incidence may assist in calibrating regional ice sheet models, and in assessing climate change impacts. We argue that the CEB:RSF association has global relevance in identifying primary drivers of mass movement in bedrock.

Scottish landform examples 45: Sgriob na Caillich: a landslide-sourced medial moraine on the Isle of Jura

ABSTRACTMedial moraines deposited by former glaciers and ice sheets are rare in Scotland. The most prominent example is the Sgriob na Caillich moraine, which consists of two to four parallel belts of angular quartzite boulders that extend northwestwards for over 3.5 km from the SW flank of Beinn an Oir on the Isle of Jura. The boulder belts extend to within 300 m of the present coastline, where they are truncated by a low bluff and raised marine terrace. The source of the moraine coincides with bedrock gullies and cliffs that represent the scars of former rock-slope failure(s), indicating that the moraine debris was sourced by one or more rockfalls or rockslides onto the ice surface after Beinn an Oir had emerged from the thinning ice cover as a nunatak. Exposure dating of boulders on the moraine indicate that it formed at 16.6 ± 0.8 ka, consistent with the timing of ice-sheet retreat in this sector. The alignment of the moraine indicates ice-margin retreat to the SE; as regional ice-sheet retreat across the adjacent offshore shelf was to the NE, this anomaly implies that a residual icefield became stranded on Jura during ice-sheet retreat.

Early Warning of Rock Slope Failure Based on Bolt Axial Force Monitoring

The selection of appropriate monitoring methods is necessary to realize the early warning of slope stability. In this study, a new monitoring method was proposed on the basis of bolt stress variation with reduction factors. Numerical simulation was conducted to construct a rock slope model with joint, and the monitoring bolt was placed at the joint. The relationship between bolt axial force and slope stability was investigated. Moreover, the position and inclination of the bolt were investigated thoroughly. A comprehensive comparison was conducted using an existing displacement monitoring method. Results show that (1) a single peak distribution of the bolt axial force occurs along the length, and the peak appears at the location of the joint and bolt intersection with bolt axial force saltation, which is considered the optimal axial force monitoring position. (2) Regardless of the bolt inclination, the axial force saltation constantly exists, and the internal slope stress can be monitored, except when the angle is 90°. (3) The bolt position does not influence the monitoring effects provided that the bolt penetrates the joint. (4) The axial force saltation of the bolt is earlier than the displacement saltation of the slope; this phenomenon can achieve remarkable monitoring effects appropriately for slope stability early warning.

Detection and geometric characterization of rock mass discontinuities using a 3D high-resolution digital outcrop model generated from RPAS imagery – Ormea rock slope, Italy

The use of a remotely piloted aircraft system (RPAS) and digital photogrammetry is valuable for the detection of discontinuities in areas where field mapping and terrestrial photogrammetry or laser scanner surveys cannot be employed because the slope is unsafe, inaccessible, or characterized by a complex geometry with areas not visible from the ground. Using the Structure-from-Motion method, the acquired images can be used to create a 3D texturized digital outcrop model (TDOM) and a detailed point cloud representing the rock outcrop. Discontinuity orientations in a complex rock outcrop in Italy were mapped in the field using a geological compass and by manual and automated techniques using a TDOM and point cloud generated from RPAS imagery. There was a good agreement between the field measurements and manual mapping in the TDOM. Semi-automated discontinuity mapping using the point cloud was performed using the DSE, qFacet FM, and qFacet KD-tree methods applied to the same 3D model. Significant discrepancies were found between the semi-automatic and manual methods. In particular, the automatic methods did not adequately detect discontinuities that are perpendicular to the slope face (bedding planes in the case study). These differences in detection of discontinuities can adversely influence the kinematic analysis of potential rock slope failure mechanisms. We use the case study to demonstrate a workflow that can accurately map discontinuities with results comparable to field measurements. The combined use of TDOM and RPAS dramatically increases the discontinuity data because RPAS can supply a good coverage of inaccessible or hidden portions of the slope and TDOM is a powerful representation of the reality that can be used to map discontinuity orientations including those that are oriented perpendicular to the slope.

Multi-stage structural and kinematic analysis of a retrogressive rock slope instability complex (Preonzo, Switzerland)

Large catastrophic rock slope failures are difficult to predict because the underlying mechanisms causing slope accelerations are difficult to study under in-situ conditions. For slope failures with compound basal rupture planes, not only fracture propagation and slip in the basal rupture surface, but also within the landslide body control the displacement evolution and time-to-failure. The Preonzo instability complex in southern Switzerland failed several times since 2002 and offers a unique opportunity to study these mechanisms under in-situ conditions. The largest failure at Preonzo occurred in May 2012 and was conditioned by large slope parallel (NNE-SSW) fracture zones, which are intersected by NE and SW and E-W striking faults creating diverging lateral boundaries. Whereas in the head scarp region oblique and flexural toppling along pre-existing fracture sets is the prevailing mechanism, sliding of either planar or wedge type is the preferred kinematic mode facilitated by the new discontinuities developed within the basal rupture surfaces. These dominating mechanisms, leading to a classical rock slope collapse, could only be revealed in retrospect. We compare fracture patterns in stable ground (tectonic and unloading fractures) with new fractures related to rock slope failure observed on basal rupture surfaces and in the head scarp. Simplified mechanical and kinematic analyses show that old pre-existing tectonic fractures cannot accommodate substantial deformations under the in-situ stress conditions and propagate/connect through curved wing cracks forming at high angles. This situation favors the development of new nearly slope parallel fractures, which are interpreted as synthetic P-shears along localized shear zones. Fractographic markings on these fractures indicate a continuous and relatively fast formation, which presumably has taken place during a period of about 60 years prior to catastrophic failure. This detailed description of the multi-stage evolution of slope failure at Preonzo represents a unique data set for future numerical studies of progressive failure in crystalline rocks.

The role of a bentonitic layer on slope stability in bedded limestone: the case study of the December 2004 Ca' Madonna Quarry rock slide (Umbria-Marche Apennines, Central Italy)

This work describes and analyses the December 2004 rockslide that affected the working face of the Ca’ Madonna quarry (Municipality of Urbania, Province of Pesaro and Urbino, Italy), where limestones are extensively quarried for aggregates. The landslide occurred along an unsurveyed, approximately 10-cm thick clayey intra-bed layer that mainly consists of smectite-group clayey minerals. Laboratory analyses indicate that it is very active and shows a high capacity to absorb water until reaching a swelling pressure of up to 1200 kPa. Mining activities reduced lithostatic load and facilitated rainwater infiltration down to this bentonitic layer, which led to fully softened conditions with a resulting severe reduction in the shear strength parameters. Under such conditions, the slope stability back-analysis was performed by the limit equilibrium method, considering a planar rock slope failure with tension cracks and with different water level heights. The results show that a small increase of water pressure was sufficient to exceed the factor of safety. Stratigraphically, this layer can be correlated with the Lower Campanian Bentonitic Layer already reported in other sites of Central Italy. Therefore, the potentially great spatial extent of this layer and the possibility that the reported conditions may occur in other similar settings, make it important to identify its presence in order to prevent analogous situations.

Extended finite element simulation of step-path brittle failure in rock slopes with non-persistent en-echelon joints

The aim of this paper is to investigate the brittle failure mechanism of rock slopes with non-persistent en-echelon joints using the extended finite element method (XFEM). In the research, a novel geometrical method distinguished from the conventional level set method is proposed to describe the cracks in the XFEM. The numerical form of the J-integral considering the effect of the bode force and the frictional contact force is provided. Moreover, a refined coalescence method is proposed. Then, the state function employed to define the state of the crack and the method used to define the crack growth increment are introduced. Next, some numerical tests are carried out to validate the feasibility of the XFEM. Finally, two typical rock slope modes are provided to illustrate the mechanism of the step-path brittle failure of rock slopes.

Kinematic Analysis and Rock Mass Classifications for Rock Slope Failure at USAID Highways

Rock slope kinematic analysis and rock mass classifications has been conducted at the 17^th km to 26^th km of USAID (United States Agency for International Development) highway in Indonesia. This research aimed to examine the type of rock slope failures and the quality of rock mass as well. The scan-line method was performed in six slopes by using a geological compass to determine rock mass structure on the rock slope, and the condition of joints such as persistence, aperture, roughness, infilling material, weathering and groundwater conditions. Slope kinematic analysis was performed employing a stereographic projection. The rock slope quality and stability were investigated based on RMR (rock mass rating) and SMR (slope mass rating) parameters. The rock slope kinematic analysis revealed that planar failure was likely to occur in Slope 1, 3, and 4, the wedge failure in Slope 1 and 6, and toppling failure in Slope 2, 5, and 6. The RMR rating is ranging from 57 to 64 and can be categorized as Fair to Good rock. The SMR rating revealed that the failure probability of Slope 3 was 90%, while it was from 40% to 60% for others. Despite the uniform RMR for all slopes, the SMR was significantly different. The detailed quantitative consideration of orientation of joint sets and geometry of the slope contributed to such differences in outcomes.

Landslide susceptibility mapping based on triggering factors using a multi-modal approach

Landslide susceptibility mapping has been done using statistical and physically-based assessment techniques with limited focus on mode-specific models to identify failure modes and runout patterns. Because each failure mode has different consequences, it is essential to identify the failure mode associated with each slope inclination category, triggering factor, and geological setting. This paper presents a multimodal regionalscale assessment procedure for rainfall and earthquake-induced landslides, in the country of Lebanon, where landslide inventories are not available. Three failure modes are studied: debris flows, rock-slope failures, and coherent rotational slides. Areas prone to each mode of failure are identified based on geology and topography, then, using mode-specific models, their susceptibility to landslides is assessed. A runout assessment approach is then presented to identify the influence area of each predicted landslide and to obtain comprehensive susceptibility maps. Field assessment validated the proposed model which was in good agreement with actual slope failures across Lebanon. Therefore, the multimodal approach may be used to assess rainfall-induced landslide susceptibility, especially when landslide inventories are unavailable.

Rock slope stability analysis by approximation of geological strength index and finite element method

As a part of natural geography systems, rock slopes have treasured amount of natural resources potential. The rock materials could be utilized to fulfill several needs, especially to construct buildings. However, society sometimes have taken advantages from the slope’s existence in wrong ways. The exploitations toward rock materials, either through manual or modern way (blasting) have caused some cracks occurred. These cracks have reduced the stability of rock slopes and easily triggered failures on rock slopes. In this paper, the stability of a rock slope will be precisely discussed by using Geological Strength Index (GSI) and was analyzed by using finite element method. The rock samples were taken from Pangkalan (West Sumatera, Indonesia), which this location is also vulnerable to rock slope failures. Geological Strength Index was obtained by doing manual observations on rock sample’s properties, i.e. joint, cracks, and discontinuity. The result was consisted of rock’s properties. Meanwhile, the analysis by using finite element method produced an outcome in form of safety factor. This result could be made as a reference for pre-disaster mitigation in Pangkalan.

Modelling of rock slope failures due to geological discontinuties to minimize risk from road cut failures

Rock slope failures are common issues on road cuts. Geological discontinuities are one of main causal factors for the occurrence of rock slope failures and most rocks exposed in road cuts show slope failures as rock falls. Most of the roads constructed across hilly areas have risk from such slope failures resulting in adverse effects on road uses. The aim of the present study is to model rock slope failures which can be used at the design stage to reduce the risk from structural geological features especially planer structures (foliation and joint planes). Two road traces which run across Sri Lankan mountain terrains (Avissawella – Hatton and Balangoda – Haputale roads) were used for the study. Field data on orientation of structural geological features and the type of rock involved in rock falls were collected from 44 locations along both road stretches. Dip Anlysist 2.0 was used for modelling the slope failures. Wedge failure, Toppling and Plane failure modes were considered. Wedge failure is the most common rock slope failure observed. When compared with field observations, the model shows 64% precision from 44 locations studied. The model revealed that the risk from road cut failures can be minimized by optimising existing road orientation and slope angle of the cut. The slope failures can be reduced by using this type of model analysis during the design stage of new roads.

Correction to: Seismic wave propagation characteristic and its effects on the failure of steep jointed anti-dip rock slope

The published version of this article, unfortunately, contained error. A compass went unconverted in the upper-right corner of Fig. 1. Given in this article is the correct image.

Quantitative hazard assessment system (Has-Q) for open pit mine slopes

Rock slope hazard assessment is an important part of risk analysis for open pit mines. The main parameters that can lead to rock slope failures are the parameters traditionally used in geomechanical classifications, the slope geometrical parameters and external factors like rainfall and blasting. This paper presents a methodology for a hazard assessment system for open pit mine slopes based on 88 cases collated around the world using principal components analysis, discriminant analysis and confidence ellipses. The historical cases used in this study included copper, gold, iron, diamond, lead and zinc, platinum and claystone mines. The variables used in the assessment methodology are uniaxial compressive strength of intact rock; spacing, persistence, opening, roughness, infilling and orientation of the main discontinuity set; weathering of the rock mass; groundwater; blasting method; and height and inclination of the pit. While principal component analysis was used to quantify the data, the discriminant analysis was used to establish a rule to classify new slopes about its stability condition. To provide a practical hazard assessment system, confidence ellipses were used to propose a hazard graph and generate the HAS-Q. The discriminant rule developed in this research has a high discrimination capacity with an error rate of 11.36%.

Mechanics of the earthquake-induced Hongshiyan landslide in the 2014 Mw 6.2 Ludian earthquake, Yunnan, China

The Hongshiyan landslide, the largest landslide (volume ~ 12.24 Mm3) triggered by 2014 Mw 6.2 Ludian earthquake, blocked the Niulan river forming a rockslide dam; the failure potential of the dam created an elevated risk to population and infrastructure downstream. We provide insight into the failure mechanics of the Hongshiyan landslide using data obtained by means of remote sensing techniques and traditional in-situ surveys. Geological data obtained by these methods was then used for kinematic and numerical analyses. Our study shows that failure of the Hongshiyan landslide involved a high rock slope with an average slope of 55° and aspect of 185° SSW, in which the geological setting consists of an upper strong limestone slab and an underlying weak silty mudstone. The geological setting allowed the landslide to develop, as follows: i) the silty mudstone, due to its poor mechanical properties, was subject to ductile deformation under the compressive loading from the overlying strong limestone slabs; ii) a large number of release fractures in the limestone developed as a consequence of pre-failure progressive deformation in the underlying weak mudstone; iii) the oxidation and solution along steep joint walls in the upper limestone indicates that the joints are pathways that allow water ingress into the mudstone, further promoting the degradation of shear strength in this layer. Distinct element modelling (UDEC) was used to back analyse the failure mechanism and develop the geological model that best reproduced the Hongshiyan failure geometry. Results show that the failure surface consisted of two elements. The upper steeply dipping release surface formed along the slope-parallel steep cross joints defining a jointed, strong limestone slab, and the toe of the failure formed a curved failure surface through the ductile weak silty mudstone, underlying the limestone slab, independent of any discontinuities within it. The pre-failure observations and numerical analysis suggest that the Hongshiyan slope was in a state of marginal static stability prior to the earthquake as a result of pre-failure progressive deformation controlled by the shear strength of the underlying mudstone. Overall, the marginal pre-earthquake stability of the Hongshiyan slope, coupled with the strongest seismic loading, which the Hongshiyan slope has been historically subjected to, are the reasons why this moderate earthquake induced a large-scale catastrophic rock slope failure.

Crack Propagation and Coalescence of Step-Path Failure in Rocks

To provide insight into the understanding of step-path failure in rocks, gypsum specimens containing various configurations of preexisting flaws are used to investigate the crack behaviors of step-path failure in rock slopes under compression in terms of the inclination angle and number of flaws. The results show that step-path failure is usually caused by wing cracks (or tensile cracks) when the preexisting flaws are isolated or when two preexisting flaws are adjacent. Additionally, with an increase in the number of flaws, step-path failure is more likely to be caused by mixed wing-secondary crack formation (or tensile–shear crack formation), indicating that the mechanism of step-path failure is associated with the characteristics of the flaw (including the number of flaws, flaw inclination angle, flaw spacing, etc.). In the process of step-path cracking and failure, wing cracks can initiate at or near the middle of a preexisting flaw when the preexisting flaw has a small inclination angle (e.g., 0° or 15°), and secondary cracks usually propagate in three directions: (1) in the horizontal direction of the specimen; (2) coplanar or quasi-coplanar to the preexisting flaw; (3) in the direction perpendicular to that of wing crack propagation. Additionally, the closer the inclination angle is to 90°, the harder the secondary crack initiates. In addition, four types of coalescence cracks are identified from the specimens containing two preexisting flaws. The peak load of the specimen is influenced by the inclination angle; the closer the inclination angle is to 90°, the greater the peak load of the specimen. Furthermore, the equation describing the wing crack path of an isolated flaw, two types of spalling formations and the characteristics of the wing and secondary crack surfaces are determined and discussed.