Rock Slope Failures Research Articles

Stochastic kinematic analysis of rock slope failure angle based on multi algorithm optimization, a case study of the proposed bridge project

ABSTRACT Due to the randomness and complexity of the discontinuity distribution, it is always complicated to analyse the three-dimensional stability problem of discontinuity-controlled rock slope in the field of engineering geology. Specifically, when restricted by poor sampling conditions, the discontinuity data obtained are very limited. To solve this problem, we propose a stochastic kinematic method to estimate the slope failure angle based on limited data. Taking the high-steep rock slope on the right bank of a proposed bridge as an example, the stochastic kinematic method based on multiple algorithms (Monte Carlo simulation, Latin hypercube, and Bayesian estimation) is used to analyse the failure angles of potentially unstable blocks in two modes of plane and wedge failure. After statistical optimisation, the slope failure angles are determined to be 65.69° (plane failure) and 58.65° (wedge failure); this approach is more objective than the empirical formula method and can be used as the basis for judging the slope stability. The method proposed in this study fully considers the randomness of discontinuity distribution and combination, and can use limited sample data to realise failure angle analysis and stability judgement. The result is important as a reference of significance for engineering construction and disaster prevention.

The Pretare-Piedilama Clastic Deposit: New Evidence of a Quaternary Rock Avalanche Event in Central Apennines (Italy)

This paper deals with the origin of the Pretare clastic deposit (PRA), which crops out along the Morricone fluvial valley in the Central Apennines of Italy. With the aim of deciphering the genesis of the PRA deposit, geological s.l. and geomorphological analyses were carried out allowing for the interpretation of the PRA deposit as a rock avalanche. Furthermore, geological cross sections constrained by well-log and field survey data, together with stratigraphic, sedimentologic, and morphometric analyses, allowed us to assign the deposit to a catastrophic rock slope failure, which occurred during a cold climate of the Late Pleistocene. Several issues concerning the propagation mechanisms were inferred from the mapping of 350 boulders over the entire accumulation area and from the measure of the morphometric parameters of the landslide body. We also performed a restoration of the potential source area by comparing the reconstructed pre- and post-failure DEMs. A missing volume of 8.41 × 106 m3 was estimated on the south-eastern side of the Vettore Mt., which is consistent with the deposit volume computed from the geological interpretation (10.56 × 106 m3). The outcomes of this study provide useful insights for a better understanding of the Quaternary morpho-evolution of the Central Apennines area where analogous rock avalanche events marked the recent evolution of the belt.

Failure mechanism and stability analysis of an open-pit slope under excavation unloading conditions

Excavation unloading significantly contributes to rock slope failure in an open-pit mine. At present, there is no relevant theoretical study on the failure mechanism of the rock slope under excavation unloading. Therefore, in this study, based on the theory of fracture mechanics, the expression of the stress intensity factor at the crack tip on the rock mass at the vertical distance, h, from the slope top under excavation unloading is derived, the calculation method of the crack initiation angle is given, the expression of the ultimate safe height of the slope under unloading is obtained, and the ratio of the fracture toughness of the slope rock mass to the composite stress intensity factor at the crack tip on the rock mass is defined as the slope stability factor, which is verified by an engineering example. The results show that the crack initiation angle decreased when crack inclination was increased, and the crack initiation angle increased when the side-pressure coefficient, slope angle, and friction coefficient were increased. The ultimate safety height of the slope decreased first and then increased with the increase in the crack angle, and it was approximately linear with the crack length and inversely proportional with the slope angle. The stability coefficient calculated by this method is the same as that calculated by the limit equilibrium method and is small, which indicates the accuracy and rationality of this method. Results in this study can provide a theoretical basis for understanding and controlling the slope collapse disaster induced by excavation unloading.

Ground Investigations and Detection and Monitoring of Landslides Using SAR Interferometry in Gangtok, Sikkim Himalaya

The Himalayan state of Sikkim is prone to some of the world’s largest landslides, which have caused catastrophic damage to lives, properties, and infrastructures in the region. The settlements along the steep valley sides are particularly subject to frequent rainfall-triggered landslide events during the monsoon season. The region has also experienced smaller rock slope failures (RSF) after the 2011 Sikkim earthquake. The surface displacement field is a critical observable for determining landslide depth and constraining failure mechanisms to develop effective mitigation techniques that minimise landslide damage. In the present study, the persistent scatterers InSAR (PSI) method is employed to process the series of Sentinel 1-A/B synthetic aperture radar (SAR) images acquired between 2015 and 2021 along ascending and descending orbits for the selected areas in Gangtok, Sikkim, to detect potentially active, landslide-prone areas. InSAR-derived ground surface displacements and their spatio-temporal evolutions are combined with field investigations to better understand the state of activity and landslide risk assessment. Field investigations confirm the ongoing ground surface displacements revealed by the InSAR results. Some urban areas have been completely abandoned due to the structural damage to residential housing, schools, and office buildings caused by displacement. This paper relates the geotechnical investigations carried out on the ground to the data obtained through interferometric synthetic aperture radar (InSAR), focusing on the triggering mechanisms. A strong correlation between seasonal rainfall and landslide acceleration, as well as predisposing geological-structural setting, suggest a causative mechanism of the landslides.

Effect of Inclined Tension Crack on Rock Slope Stability by SSR Technique

The tension cracks and joints in rock or soil slopes affect their failure stability. Prediction of rock or soil slope failure is one of the most challenging tasks in the earth sciences. The actual slopes consist of inhomogeneous materials, complex morphology, and erratic joints. Most studies concerning the failure of rock slopes primarily focused on determining Factor of Safety (FoS) and Critical Slip Surface (CSS). In this article, the effect of inclined tension crack on a rock slope failure is studied numerically with Shear Strength Reduction Factor (SRF) method. An inclined Tension Crack (TC) influences the magnitude and location of the rock slope’s Critical Shear Strength Reduction Factor (CSRF). Certainly, inclined cracks are more prone to cause the failure of the slope than the vertical TC. Yet, all tension cracks do not lead to failure of the slope mass. The effect of the crest distance of the tension crack is also investigated. The numerical results do not show any significant change in the magnitude of CSRF unless the tip of the TC is very near to the crest of the slope. A TC is also replaced with a joint, and the results differ from the corresponding TC. These results are discussed regarding shear stress and Critical Slip Surface (CSS).

Some thoughts on rock slope stability issues in Mars

In this study, the author outlines rock slope stability issues in Mars through the images provided by Mars Rovers of NASA and investigates the rock slope stability issues with the consideration of the various conditions such as layering, discontinuous nature of rock mass, overhanging, impact, vibrations as well as precarious rock blocks. Rock slope failures in Mars are categorized with references to those on Earth and the fundamental mechanisms are summarized. It is shown that. the methods developed for rock slopes can be utilized with due considerations of environmental and gravitational differences using the principles of Rock Mechanics. The outcomes of these investigations are presented and discussed in this contribution.

Field Investigation and Numerical Analysis of Shear Failure in Mudstone-Shale Interbedded Antidip Rock Slopes

Field Investigation and Numerical Analysis of Shear Failure in Mudstone-Shale Interbedded Antidip Rock Slopes

Litho-structural control on rock slope failures at Garmaksla, Billefjorden coastline, Svalbard

The eastern slope of Garmaksla, a flat-topped mountain at the western margin of Billefjorden, Svalbard, is affected by mass movements of different types. Rotational rock slides, rock fall and a rock avalanche affecting the coastal cliff are shallow surface expressions covering a larger rock mass instability that is bordered to the west by the Balliolbreen Fault. This structural feature is part of the Billefjorden Fault Zone and accommodated multi-phase deformation since Devonian time. Based on a comprehensive morpho-structural analysis, the mapped surface features and rock slope failures are explained by a compound rock slide model that reveals a litho-structural control on the type and mechanism of slope instability. The Balliolbreen Fault serves as an inherited zone of weakness that is reactivated as the rear rupture surface of the rock slide. In addition, favourably oriented bedding planes and pre-existing fault zones serve as prime conditioning factors for the compound rock slide. A postglacial age of at least 6 ka is derived from 14 C dated sediments of Garmaksla Lake, a perennial sag pond along the main scarp. Although the current state of activity of the compound rock slide is unclear, an increase of shallow slope instabilities is expected owing to climate warming.

Tectonic deformation and landscape evolution inducing mass rock creep driven landslides: the Loumar case-study (Zagros Fold and Thrust Belt, Iran)

Several landscape evolution models have been proposed so far to explain the dynamic feedback between Earth surface processes and tectonics in the Zagros Mountains. Nevertheless, the relationship among time-dependent rock mass deformations, landscape evolution rates, and tectonics in triggering large rock landslides is still poorly studied in this region and worldwide.To fill this gap, here we focus on the previously unknown Loumar landslide affecting the NE flank of the Gavar anticline (Zagros Mountains) through a multi-perspective methodology which includes SAR Interferometry, geomorphometry, linear temporal inversion of river profiles and field survey for independent OSL dating of geomorphic markers of landscape evolution.We estimated that at 93 +21/−16 ka the backlimb of the Gavar fault-propagation fold reached limit equilibrium conditions for the slope failure, caused by an acceleration in the fold growth. The growth of a minor fold also induced the abandonment of a meandering canyon and the river migration to a new narrow gorge. The fluvial downcutting kinetically released the limestone strata that started to deform through Mass Rock Creep (MRC). The MRC process accumulated inelastic strain until 5.52 ± 0.36 ka, when the slope evolved into a failure causing the partial occlusion of the valley and the generation of a pond.The obtained creep timespan of 104–105 years since the initiation of the MRC process is consistent with the typical lifespan of gravity-induced slope deformations in non-glaciated regions. For this reason, such an approach can be used for the reconstruction of slow deforming slope evolution to predict the hazard of slopes prone to massive rock slope failure, linking it to the MRC stages.

Geophysical evidence of massive hyperconcentrated push waves with embedded toma hills caused by the Flims rockslide, Switzerland

Abstract. Rockslides and rock avalanches are amongst the most destructive natural hazards in the alpine environment. The Flims rockslide is the largest known rock-slope failure in the Alps, which provides excellent outcrops and has fascinated researchers since the early 20th century. The postulated impact of the Flims rockslide on Lake Bonaduz caused intensely fluidized rock material, which formed the Bonaduz Formation and toma hills, probably accompanied by a catastrophic impact wave. So far, this hypothesized sequence of events is based only on sedimentological and geomorphic analyses. We present electrical resistivity tomography (ERT) profiles, which we correlated with the sedimentological information obtained from outcrops and drill logs. Here, geophysical evidence on a metre and decametre scale complements prior outcrop and sample intervals with much smaller representativeness. Our study provides new insights into the distribution, thickness, and internal structure of the Bonaduz Formation and the toma hills as well as other flood deposits around the Ils Aults, where we studied the sediment to a depth of up to 160 m. There is geophysical evidence that the Bonaduz Formation formed an onlap onto the Ils Aults and is thus the stratigraphically younger unit. The toma hills consist of blocky cores with an agglomeration of smaller mixed sediments, which drift and override the toma core, causing their smoothly shaped top. We consider simultaneous transport of the hills within the Bonaduz Formation but a slightly slower movement at the front due to a bulldozing effect. This study contributes to an improved understanding of (i) the complex stratigraphical context of the Tamins and Flims deposits, (ii) water-rich entrainment in rock avalanches, and (iii) the genesis and transport of toma hills.

Theoretical and numerical analysis of flexural toppling failure in soft-hard interbedded anti-dip rock slopes

Soft-hard interbedded structures are commonly found in anti-dip rock slopes and endow the slopes with special properties. In this work, a simple two-beam model was first used to discuss the possible failure modes of rock layers with different lithology. The exact failure sequence of rock layers depends on their tensile strengths, elastic moduli, and thicknesses. Then, based on the deformation compatibility of rock layers, a novel theoretical method called the DCM for assessing the stability of soft-hard interbedded anti-dip rock slopes was proposed. A centrifuge test and a numerical model were used to verify the feasibility of the DCM. The calculated critical g-level of 47 g for the centrifuge model and a safety factor of 0.96 for the numerical model agree well with the results of the centrifuge test (45 g) and numerical simulation (0.98). Moreover, the traditional limit equilibrium method (LEM) was also adopted to explore these two models. The calculated results of 68 g and 1.79 using the traditional LEM were found to be much larger than the validated values, with deviations of more than 50%. This finding implies that the traditional LEM is not suitable for assessing the stability of soft-hard interbedded anti-dip rock slopes. In addition, the failure evolution of toppling failure in soft-hard interbedded anti-dip rock slopes was investigated using numerical modelling. The results show that the soft and hard rock layers do not fail at the same time; the rock layers of one type of lithology are destabilized first, then the other rock layers begin to fail until the entire slope undergoes flexural toppling.

Preliminary analysis of rock mass weathering grade using image analysis of CIELAB color space with the validation of Schmidt hammer: A case study

Rock slope instability causes rock slope failure with intense weathering processes in tropical regions. In addition to the various advanced numerical rock slope stability assessment techniques that have been developed thus far, simple evaluation techniques characterizing the rock slope weathering degree based on color changes of the rock surface remain one of the main techniques used by most geologists onto the rock slope stability assessment. The present study proposed a new evaluation method for weathering assessment of the limestone rock slope with computer-assisted image processing technologies to reduce human-induced errors based on a manual characterization process. The color changes of the limestone rock referring the CIELAB color space, which indirectly indicated the differential weathering of the rock mass, were measured in-situ using the FRU colorimeter with a 40 mm aperture. The Schmidt hammer was used to determine the intact rock strength and validate the color changes of the limestone rock to the International Society For Rock Mechanics (ISRM) weathering grade standard. Results indicated that a* and b* correlated strongly with R2 = 0.7404, underscoring the consistency of the CIEL*a*b color space data obtained in situ. The a* and b* correlated strongly with the uniaxial compressive strength result obtained via the rock Schmidt hammer test, with R2 of 0.7058 and 0.7011, respectively. The results were verified with the weathering grades analyzed using image analysis technique. In conclusion, the CIELAB color space is an effective tool in the preliminary assessment of rock mass weathering, particularly for slightly vegetated rock slope outcrops.

Rock Endpoints and Barriers Estimation of Slope Failure in Pinousuk Gravel Slopes using Rocfall Simulation

The research is conducted to simulate the possibility of rock fall occurrences in the study area. The study area is located at highland area in Mesilou, Kundasang, Sabah which consists of Late Pleistocene age of tilloid deposits namely Pinousuk Gravel. Four slopes of Pinousuk Gravel were selected to estimate the distance of rock endpoints and the locations of barriers to minimize the damage when slope failure occurs by using ‘Rocfall’ simulation software. The software is commonly used for risk assessment of potential rock slope failure. The result of analysis shows the rock endpoints distance ranges from the 3.1 meters to 4.9 meters from the foot of the slope with bounce height from 0.6 meters to 2.2 meters during downfall. Based on total amount of kinetic energy on each slope, the location of the proposed barrier is within 1 meter to 4 meters from the slope foot. As a conclusion, the rock endpoints depend on slope height and angle, while the proposed location for barrier is based on its ability to withstand the kinetic energy released during slope failure.

Modelling the pre- and post-failure behaviour of faulted rock slopes based on the particle finite element method with a damage mechanics model

We develop a novel numerical model incorporating a damage mechanics formulation into the particle finite element method for analysing the pre- and post-failure behaviour of faulted rock slopes. In this computational framework, the stress-driven strain localisation and damage evolution are modelled based on an isotropic damage model; discontinuity structures like fault zones are represented as thin continuum layers with equivalent mechanical properties; the particle finite element method is used to solve and track the large deformation of rock masses. In the paper, we first present the mathematical formulation of the proposed model in the context of the Hellinger-Reissner variational principle. We conduct a thorough validation of our model for simulating the damage of brittle materials against well-documented experimental datasets of different failure scenarios. We then apply the model to simulate the deformation and failure phenomena of faulted rock slopes including both the pre-failure progressive damage and post-failure transient runout, demonstrating the strong capability of our model in physically capturing the initiation, evolution, and consequence of catastrophic rock slope failure across multiple temporal scales. In addition, our simulations can realistically reproduce the slope displacement time series with the interplay between rock damage and fault reactivation explored. The present work has important implications for understanding the physical mechanisms that drive the progressive destabilisation and catastrophic failure phenomena of rock slopes in nature.

Some considerations on the role of joint spacing in rock slope stability analyses using a 3D discrete element approach

Stability assessment of potential wedge failures in rock slopes is usually carried out based on stereographic projection techniques and limit equilibrium analyses. Nevertheless, this methodology presents several limitations (i.e., lack of information on joint mechanical properties, oversimplification of the structure, etc.) that could lead to poorly accurate conclusions. In line with this idea, the main objective of this work is to evaluate the effect of joint spacing in the estimation of the factor of safety of rock slopes affected by potential wedge failures. For this purpose, a 3D numerical distinct element code (3DEC) was selected to carry out a substantial number of simulations in which the factor of safety of two types of slopes, affected by different discontinuity sets, was studied by using the shear strength reduction (SSR) method. Different values of joint spacing, cohesion, and friction angles were considered, combined with two angles of the slope face under study. A discrete fracture network (DFN) model was also implemented, with the aim of benchmarking results with those obtained from the original models. The joint spacing has been found to relevantly affect the values of the factor of safety of the slope, which showed variations of up to 40% in comparison with those obtained from limit equilibrium methods. This work provides an insight to a more realistic interpretation of rock slope analyses against wedge failures, particularly to better estimations of the factor of safety.

Late Holocene initiation of a deep rock slope failure in an alpine valley revealed by 10Be surface exposure dating (Chamonix, France)

We studied a newly identified, multiple-kilometer-long rock slope failure in the Aiguilles Rouges massif (Chamonix valley, France). Owing to a high-resolution light detection and ranging (LiDAR) digital elevation model (DEM) and field work, we mapped morphostructures, including scarps, open fractures, and counterscarps. In some places, vertical offsets can reach tens of meters and crevasses can be meters wide. The evidence of gravitational activity (boulder displacements from analyses of archival satellite images) and the sharpness of the scarp outcrops together suggest very recent movements. These observations agree with ground displacement rates of a few millimeters per year estimated by interferometric synthetic aperture radar (InSAR) time series between 2014 and 2018.We sampled two vertical profiles along the top scarps to define the chronology of the slope failure using beryllium-10 (10Be) surface exposure dating. Glacially polished surfaces cut by these gravitational scarps were also sampled to determine glacial retreat timing as well as to constrain the pre-exposure 10Be inheritance. In total, 11 samples were studied.Our results highlight a significant time lag (approximately 15 ka) between the first evidence of nonglacial activity and the initiation of the slope failure that happened 1.3–2.5 ka ago, depending on the inheritance schemes. This suggests that the delayed opening of the crevasse is only one stage of a process that began when the valley was deepened and the glacial debuttressing is not the unique driving factor. This process of progressive failure of an excessively steep slope may continue, and the evolution of this slope failure may constitute a hazard for the upper part of the Chamonix valley.

Model tests and numerical simulations on hydraulic fracturing and failure mechanism of rock landslides

Hydraulic fracturing (HF) is an important reason for inducing rock landslides. The impacts of the angle between the transverse pressure stress and the initial fracture, the transverse pressure stress, the length and aperture of the initial fracture on the critical water pressure stress of HF were analyzed based on the model tests of cement mortar specimens. The HF numerical simulations were carried out and the fracture aperture, pore pressure, strain and stiffness degradation index were analyzed, and the HF mechanism of rock was revealed. Taking a rock slope along G205 in China as an example, the landslide stability under high groundwater pressure was studied by numerical simulations, and the whole processes of the expansion, propagation, penetration and the rock slope failure were reproduced. The results showed that when HF occurred on the cement mortar specimens, a large amount of water seeped from the fracture and made a dull sound of failure, the water pressure on the fracture plane decreased rapidly, but not completely penetrated, and there was still a certain residual strength of the specimen. The HF of rock is a quasi-brittle failure, including static stage, micro fracture propagation stage and macro fracture formation stage. There are 3 dangerous rocks on the rock slope, among which WYT3 is in a stable state under the natural condition and in an unstable state under the rainstorm condition and seismic condition. The fracture propagation of WYT3 under the action of high groundwater pressure experienced slow development stage, rapid development stage and penetration stage, among which the slow development stage lasted the longest, and the slope failure occurred immediately after the fracture penetrated.

Slope Mass Rating (SMR) Classification for Rock Slope Stability and Geohazard Vulnerability Assessment

Quantitative classification from the Slope Mass Rating (SMR) has introduced an empirical assessment for rock slope stability rating. This stability classification enables us to foreseethe magnitude and susceptibility of rock mass failure towards adjacent infrastructure and human life. In this study, the stability of quarry rock slope was classified using SMR classification system and kinematic stability analysis before being correlatedwith geohazard vulnerability assessment. Geological formation study with site geographical survey from aerial photogrammetry technique provided comprehensive data for the study area. Fieldwork to evaluate the SMR assessment parameters was conducted by discontinuity mapping using scanline method. In-situ evaluation of rock mass such as rebound surface hardness and discontinuity characterization was carried out with rock material sampling for laboratory testing. Kinematic stability analysis presented an estimation for the direction and mode of rock slope failure. The SMR classification that constitutes geomechanics attributes had introduced the global stability rating of rock mass structure, thus facilitating the prediction of potential failure magnitude. Hence, the integration of these stability indications provides sufficient empiricalestimation for geohazard vulnerability zoning for the studied area.

Rock slope failure in the Southern Carpathians (Romania): Range-wide inventory and links with long-term mountain landscape evolution

Rock slope failure (RSF) is now widely recognised as a significant contributor to the denudation of mountain ranges. Its spatial incidence can consequently be a valuable indicator of prevailing process domains, tectonic regimes and climatic variations, whether active or past. Here we provide the first systematic inventory of RSF in the Southern Carpathians, a mountain range marginally glaciated during the Pleistocene, cut by valleys up to 1.3 km deep, and displaying low-gradient summit erosion surfaces that suggest late Neogene uplift and incision of an extensive plateau. We discuss the spatial distribution of RSF in terms of process interactions and landscape evolution scenarios. Widespread metamorphic bedrock outcrops are confirmed as highly susceptible to RSF, particularly to large-scale slope deformation, but RSF also occurs on other lithologies as smaller rockslides and avalanches. Substantial spatial densities of RSF cluster around the residual, plateau-like range-top surface rims. We ascribe this to the ‘raised plateau’ features of the mountain range, where its fat, flat massifs engender greater slope stresses than would thin, serrated ones where arêtes and pyramidal peaks are gravitationally more stable. A large minority (42 %) of RSFs are spatially associated with glacial cirques and trough flanks. While these nominally qualify as paraglacial RSFs, glacial erosion may not be the main driver because the majority of RSFs occur along ridgetops and upper hillslopes in previously unglaciated fluvial contexts. Many of them thus qualify as parafluvial RSFs – i.e., occurring within a fluvial catchment but not directly generated by stream undercutting. We introduce the concept of fluvial–parafluvial and periglacial–parafluvial cycles as complementary to the recognised glacial–paraglacial cycle. All three process regimes may have prevailed concurrently or in succession, emphasising that cirque glaciation was probably not a principal agent in shrinking range-top erosion surfaces during the Quaternary. We point to post-orogenic (Neogene) tectonic uplift as the overarching driver of RSF in the Southern Carpathians, with pervasive fluvial incision keeping slopes close to failure thresholds. The role of RSF (extant and in earlier cycles) as a primary agent in perimeter scarp retreat and massif dissection here offers a ‘Transylvanian model’ of global interest whether as a comparator or a contrast for other ranges.

Blockslopes Caused by Large to Meso-scale Rock Slope Failures in the Upper Okumatajirodani Valley on the Eastern Side of Mount Maehotaka-dake North Ridge, Northern Japanese Alps

Blockslopes Caused by Large to Meso-scale Rock Slope Failures in the Upper Okumatajirodani Valley on the Eastern Side of Mount Maehotaka-dake North Ridge, Northern Japanese Alps