Rock Slope Failures Research Articles

The Role of Water and Lithology on the Deformation and Failure of an Anaclinal Rock Slope in a Hydropower Reservoir

A series of settlement, cracking, and collapse of the Zhengjiaping slope has been increasingly developing since October 2015 during impoundment at the Dagangshan Hydropower Station. It is a dangerous signal, which means thatlandslide potential will be existed for the Zhengjiaping slope and poses greatthreat to the operation of hydropower station and traffic safety. Related slope protection measures and research studies have been implemented accordingly in the Zhengjiaping slope to prevent and control adverse influences on property security and human life in the reservoir area. In order to understand the geological and hydrological settings of the Zhengjiaping slope and its surroundings, a field investigation was carried out to determine the lithological composition and toppling/sliding deformation characteristics using exploratory adit and site boreholes. The large deformation process in the apparently deformed area was analyzed using borehole inclinometers and global navigation satellite systems (GNSS). It was found that the apparently deformed area zone was characterized by crushed rock masses, with only a small amount of slope deposits and the sliding deformation occurring in Zone I. The deformation process of the reservoir landslide was considered to be a complex integration of the geological effects of various adverse factors. Impoundment and heavy rainfall are the direct causes of sliding deformation. During the preparation of the basic conditions for sliding, lithology, tectonic activity, and artificial disturbances play an important role, including the sliding mass and the sliding surface zone.

UTILIZING A GEOMECHANICAL CLASSIFICATION TO PRELIMINARY ANALYSIS OF ROCK SLOPE STABILITY ALONG ROADWAY D340- 41.42, SOUTHWEST OF TURKEY: A CASE STUDY

Road construction is mostly passed through mountainous regions or hilly terrains in Turkey like in all world. In hence, roadway construction and widening are being constructed through blasting and excavation, leading to rock slope instabilities and failures then poses threats to life and property. The reasons for failure sometime after construction are likely due to the deterioration of rock masses in cut slopes. However, slope instability and failures mainly occur due to adverse slope geomorphological complexities, joint discontinuities, weathering, man-made activities, unloading; and several induced factors such as seasonal heavy rainfall events, snow coverage, etc. The objectives of this paper are therefore to identify the most significant parameters influencing the behavior of cut slope rock masses with employing SMR ,and to perform a preliminary slope instability assessment along roadway D340- 41.42, southwest of Turkey, where slopes located in a region of Taurus’s rugged terrains with known complex geometry, then propose a suitable control measures to mitigate potential failures of rock slope stability. In this study, 19 rock cuts are selected based on the observed failure mechanisms, slope geometry and materials. A systematic site investigation incorporating relevant engineering geological and geotechnical parameters were carried out in detail. Based on slope instability observations and SMR results rating, concluded that these slopes were widely controlled by discontinuities (structurally controlled failures). As well, SMR classification scheme was successfully used for failure classification in Taurus’s terrains. Finally, slope flattening with various angles method, wire mesh, toe support by detached rock blocks and drainage ditches redesign are proposed as a remedial measurement to protect road slope stability from failure.

Performance Evaluation of GFRP Rock Bolt Sensor for Rock Slope Monitoring by Double Shear Test

This study aims to evaluate the sensing performance of glass fiber‐reinforced polymer (GFRP) rock bolt sensors instrumented with strain gauges for monitoring rockslides. Experimental studies are conducted with four different types of GFRP rock bolt sensors and concrete blocks having central holes and two shear joints. Two GFRP rock bolt sensors are inserted into holes and then fixed in concrete blocks with cement grout and soil, respectively. The other two are coated with heat‐shrink tubes to protect strain gauges and wires, which are then fixed in concrete blocks with cement grout and soil, respectively. Double shear tests are performed to produce shear deformations of GFRP rock bolt sensors, and then strain change with shear displacement is monitored. The results manifest that the variation in strain with shear displacement is more sensitive in the GFRP rock bolt sensor fixed with soil than with cement grout. Also, strain gauge wires in the GFRP rock bolt sensor fixed with cement grout are broken earlier than with soil. Furthermore, it is confirmed that the heat‐shrink tube effectively protects strain gauges and wires, so that GFRP rock bolt sensors coated with heat‐shrink tubes work for a longer time than the uncoated sensors. The present study shows that the GFRP rock bolt sensor can be useful for monitoring rock slope failure.

Numerical Simulation of Slide-Toe-Toppling Failure Using Distinct Element Method and Finite Element Method

In blocky and layered rock slopes, toppling failure is a conventional type of instability which may occur in mining and civil engineering. If this kind of slope failure happens as a consequence of another type of failure, it is mentioned to as secondary toppling failure. “slide-toe-toppling” is a kind of secondary toppling failures, where the toe part of the slope is toppled as a consequence of a semi or non-circular sliding failure at the upper of the slope. This failure has been studied using physical modelling and analytical method. In the present study, firstly a brief review of the toppling failure in rock slopes is summarized, and the mechanism of slide-toe-toppling failure is described. Then, this failure is examined through a series of numerical modelling. Distinct element method (UDEC software) and finite element method (Phase2 software) were used in this research. Three types of slide-toe-toppling failures, including flexural, blocky, and block-flexural, are simulated. Comparison between two numerical modellings (distinct element and finite element methods) with the result of pre-existing physical models and analytical solution, illustrates that UDEC software has a better agreement than Phase2 software. This accordance indicates that this numerical code is well capable to analyze the behavior of slide-toe-toppling failure.

An analytical solution for analysis of toppling-slumping failure in rock slopes

When a slope consists of a horizontal weak rock or soil overlaid by some vertical strong slender rock columns, the slope is prone to a secondary toppling failure which is known as “toppling-slumping” failure. In the slope, rock columns impose pressure on the lower continuous weak rock or soil mass which leads to a differential settlement at the base of each rock column or a circular shear failure in the continuous mass. If the differential settlements reach a special threshold, rock column overturn and toppling-slumping will happen. However, the circular shear failure of the soil or weak rock mass which is a well-recognized failure mechanism will occur when shear stress in the slope exceeds its shear strength. In this paper, an attempt has been made to better understanding of the “toppling-slumping” failure mechanism through developing an analytical solution. For this purpose, first an Airy stress function is acquired for the lower continuous soil mass and its stress distribution and displacement are accordingly determined analytically due to the overlaid rock columns loads. Then, differential settlements at the base of all rock columns and shear stresses in the soil or weak rock mass are computed and compared with the toppling and shear failure criteria to assess slope failure. Finally, several design-charts are developed that determine the stability of a slope against toppling-slumping failure mechanism based on geometric characteristics of the slope and shear strength of its constituent material. Also, a Mathematica package code was developed to evaluate the stress distribution within the slope, and the safety factor. The results show that the vertical stress distribution plays a significant role in the settlement of the rock columns. Results also manifested that at a certain distance from the slope crest, the set of rock columns will act like a single column on a half-plane. The shear or toppling failure of the slope not only depends on the material's strength but also on the geometry and the normalized column distance.

Direct observations of a three million cubic meter rock-slope collapse with almost immediate initiation of ensuing debris flows

Catastrophic collapse of large rock slopes ranks as one of the most hazardous natural phenomena in mountain landscapes. The cascade of events, from rock-slope failure, to rock avalanche and the near-immediate release of debris flows has not previously been described from direct observations. We report on the 2017, 3.0×106m3 failure on Pizzo Cengalo in Switzerland, which led to human casualties and significant damage to infrastructure. Based on remote sensing and field investigations, we find a change in critical slope stability prior to failure for which permafrost may have played a destabilizing role. The resulting rock avalanche traveled for 3.2km and removed over one million m3 of glacier ice and debris deposits from a previous rock avalanche in 2011. Whereas this entrainment did not lead to an unusually large runout distance, it favored debris flow activity from the 2017 rock avalanche deposits: the first debris flow occurred with a delay of 30s followed by ten debris flows within 9.5h and two additional events two days later, notably in the absence of rainfall. We hypothesize that entrainment and impact loading of saturated sediments explain the initial mobility of the 2017 rock avalanche deposits leading to a near-immediate initiation of debris flows. This explains why an earlier rock avalanche at the same site in 2011 was not directly followed by debris flows and underlines the importance of considering sediment saturation in a rock avalanche’s runout path for Alpine hazard assessments.

Permafrost distribution in steep rock slopes in Norway: measurements, statistical modelling and implications for geomorphological processes

Abstract. Permafrost in steep rock slopes has been increasingly studied since the early 2000s in conjunction with a growing number of rock slope failures, which likely resulted from permafrost degradation. In Norway, rock slope destabilization is a widespread phenomenon and a major source of risk for the population and infrastructure. However, a lack of precise knowledge of the permafrost distribution in steep slopes hinders the assessment of its role in these destabilizations. This study proposes the first nationwide permafrost probability map for the steep slopes of Norway (CryoWall map). It is based on a multiple linear regression model fitted with multi-annual rock surface temperature (RST) measurements, collected at 25 rock slope sites, spread across a latitudinal transect (59–69∘ N) over mainland Norway. The CryoWall map suggests that discontinuous permafrost widely occurs above 1300–1400 and 1600–1700 m a.s.l. in the north and south rock faces of southern Norway (59∘ N), respectively. This lower altitudinal limit decreases in northern Norway (70∘ N) by about 500±50 m, with a more pronounced decrease for south faces, as a result of the insolation patterns largely driven by midnight sun in summer and polar night in winter. Similarly, the mean annual RST differences between north and south faces of similar elevation range around 1.5 ∘C in northern Norway and 3.5 ∘C in southern Norway. The CryoWall map is evaluated against direct ice observations in steep slopes and discussed in the context of former permafrost studies in various types of terrain in Norway. We show that permafrost can occur at much lower elevations in steep rock slopes than in other terrains, especially in north faces. We demonstrate that the CryoWall map is a valuable basis for further investigations related to permafrost in steep slopes in terms of both practical concerns and fundamental science.

Theoretical and numerical study on the block-flexure toppling failure of rock slopes

Block-flexure toppling failure is frequently encountered in rock slopes. In this paper, we first proposed two theoretical models to calculate the factor of safety against block-flexure toppling, namely, step by step analysis model (LEM-SSAM) and overall analysis model (LEM-OAM). Then, we developed two special MATLAB codes for a quick stability estimation based on the proposed methods, respectively. Next, the universal distinct element code (UDEC) was used to study the failure mechanisms of block-flexure toppling. In order to realistically simulate the excavation of slope and obtain the detailed damage information of joints, we developed two FISH functions in UDEC. Finally, we conducted a comparative analysis of the limit equilibrium method and the numerical simulations through twelve theoretical models. The results show that many aspects of block-flexure toppling failure have been captured using UDEC combined with the developed FISH functions. The LEM-OAM and UDEC agree well while a larger factor of safety is obtained using the LEM-SSAM. It is found that the dip angles and friction angles of the joints dipping steeply into face have a great influence on block-flexure toppling failure while the influence of the cross joint spacing is less significant.

Reconstruction of river valley evolution before and after the emplacement of the giant Seymareh rock avalanche (Zagros Mts., Iran)

Abstract. The Seymareh landslide, detached ∼10 ka from the northeastern flank of the Kabir-kuh fold (Zagros Mts., Iran), is recognized worldwide as the largest rock slope failure (44 Gm3) ever recorded on the exposed Earth surface. Detailed studies have been performed that have described the landslide mechanism and different scenarios have been proposed for explaining the induced landscape changes. The purpose of this study is to provide still missing time constraints on the evolution of the Seymareh River valley, before and after the emplacement of the Seymareh landslide, to highlight the role of geomorphic processes both as predisposing factors and as response to the landslide debris emplacement. We used optically stimulated luminescence (OSL) to date lacustrine and fluvial terrace sediments, whose plano-altimetric distribution has been correlated to the detectable knickpoints along the Seymareh River longitudinal profile, allowing the reconstruction of the evolutionary model of the fluvial valley. We infer that the knickpoint migration along the main river and the erosion wave propagation upstream through the whole drainage network caused the stress release and the ultimate failure of the rock mass involved in the landslide. We estimated that the stress release activated a mass rock creep (MRC) process with gravity-driven deformation processes occurring over an elapsed time-to-failure value on the order of 102 kyr. We estimated also that the Seymareh damming lake persisted for ∼3500 years before starting to empty ∼6.6 ka due to lake overflow. A sedimentation rate of 10 mm yr−1 was estimated for the lacustrine deposits, which increased up to 17 mm yr−1 during the early stage of lake emptying due to the increased sediment yield from the lake tributaries. We calculated an erosion rate of 1.8 cm yr−1 since the initiation of dam breaching by the Seymareh River, which propagated through the drainage system up to the landslide source area. The evolutionary model of the Seymareh River valley can provide the necessary constraints for future stress–strain numerical modeling of the landslide slope to reproduce the MRC and demonstrate the possible role of seismic triggering in prematurely terminating the creep-controlled time-to-failure pathway for such an extremely large case study.

A review on the development of rock slope stability assessment in Malaysia

Rock mass classification systems are commonly used in the design and construction of rock engineering, and have seen widespread modifications and validations by various researchers over the last few decades. In Malaysia, several methods for large-and medium-scale slope assessment systems have been developed for prediction of landslide risk. Most of the methods however were found to be unsatisfactory in actual prediction of slope failures. The rock mass classification, in particular the slope mass rating (SMR), continues to be the preferred preliminary method in small-scale assessment of rock slope stability. Kinematic analysis is also widely used for predicting potential failure in structurally-controlled rock slope, and has been used independent or as compliment to rock mass classification systems. These methods are not entirely adequate in incorporating the local condition of rock mass: as a result, several works have modified the parameters of slope stability assessment methods to consider the condition of the rock mass such as the effect of heterogeneous rock units and weathering of rocks. In addition to these conventional methods, geophysical methods such as electrical resistivity, and remote sensing methods such as light detection and ranging (LiDAR), are increasingly being used in both preliminary and post-slope failure analysis. This paper reviews the development of rock slope stability assessment methods in Malaysia, as well as covering the viability of integrating geophysical and laser scanning methods with conventional methods to develop a more comprehensive rock slope assessment.

A paraglacial rock-slope failure origin for cirques: a case study from Northern Iceland

The contribution of paraglacial rock-slope failure (RSF) to the excavation of cirques in glacial landscapes is explored in the Tindastóll Mountain, Skagi peninsula, northern Iceland. We analyze 8 cirques that developed during the Quaternary and 13 paraglacial RSF cavities that developed during the Holocene in this paleo-plateau. From a reconstruction of the pre-Quaternary surface of the plateau, we calculate the excavated volumes of the cirques and RSF cavities and quantify the contribution of Holocene RSF to cirque growth. By extrapolating this contribution to the whole Quaternary, we find that paraglacial RSF is a first-order contributor to the development of cirques. This contribution is twofold: first, paraglacial RSF creates cavities along valley slopes, in which cirque glaciers can develop during subsequent glaciations; second, paraglacial RSF along pre-existing cirque walls promotes cirque widening and deepening. Our results also reveal that Quaternary glacial/paraglacial erosion rates range from 0.02 to 0.17 mm yr‑¹ in the studied cirques. We infer that glaciers are (i) efficient preparatory factors for the destabilization of slopes by paraglacial RSF, (ii) efficient conveyors to evacuate deposits produced by paraglacial RSF in cirques, but (iii) not necessarily predominant agents in the excavation of cirque bedrocks.

A strength reduction method based on the Generalized Hoek-Brown (GHB) criterion for rock slope stability analysis

The strength reduction method (SRM) combining with the Generalized Hoek-Brown (GHB) criterion has become a widely used means to assess the stability of rock slopes. Therefore, various efforts have been made to establish a standard reduction strategy for strength parameters. This paper presents a new nonlinear SRM based on the GHB criterion, and the core novelty of the proposed method is to provide a reduction strategy with precise physical meaning to find an optimal set of parameters that trigger rock slope failure. To verify the validity of the proposed method, two illustrative examples are analyzed. The results show that the proposed method could lead to a reasonable safety factor, and the critical sliding surface obtained by the proposed method can reflect the tensile crack in the steep slope. Finally, to distinguish the computational results and efficiency among the proposed method and other preexisting reduction methods, other more 8 slopes selected from the literature are used for research objects. The results show that the safety factors resulted from the proposed method are very close to those acquired by the most accurate method available at present (Hammah’s method), however, its computational efficiency is comparatively higher than that of Hammah’s method.

Summary of Study on Toppling Deformation of Rock Slope

The toppling of anti-dip layered rock slope is a typical mode of rock slope failure. Because this kind of deformation phenomenon is very common in hydraulic engineering and highway engineering, it has been paid more and more attention by the engineering community. The deformation mode, factors affecting toppling rock slope and dumping deformation mechanism were described in this paper.

The Effect of some discontinuities on rock Slope Failure in Some Selected Sites in Bammo Anticline

Field studies of the slopes of Bammo anticline, in Northeast of Iraq, was carried out in five selects stations, where rock slopes and the discontinuities were surveyed in these stations and its relationships with failures were determined. The field work was revealed the abundance of rock slope failures, the dominant types are rock fall and toppling. 
 Slope stability assessment was carried out by stereographic projection was made using software (GEOrient 9.5.0), the slopes were classified according to (Al-Saadi, 1981), and the rocks were described in engineering terms according to (Anon, 1972) depending on field data. The study also revealed that the factors affecting slope stability in the study area were slope angle, height, dip of strata, and discontinuities. Some remedial measures are suggested for the unstable slopes, and the most important removal of the detached block.

Mineralogical Characteristics of Hydrothermally-altered Andesite in Kalirejo Village and The Surrounding Areas, Indonesia

Type and intensity of hydrothermal alterations affect rock engineering properties and slope stability. Identification of mineralogical characteristics of rocks is essential in determination of rock slope failure mechanism in a hydrothermal alteration zone.This research was conducted to identify mineralogical characteristics of hydrothermallyaltered andesite in Kalirejo Village and surrounding areas, Indonesia. The research was conducted by field observation and laboratory analyses involving petrographic and X-ray Powder Diffraction (XRD) analyses. The results showed that the research area was dominated by argillic alteration type and high alteration intensity implying high susceptibility to slope failures

The 2016 Lamplugh rock avalanche, Alaska: deposit structures and emplacement dynamics

Supraglacial landslides result from the catastrophic failure of periglacial rock slopes and deposit large volumes of rock and ice onto the glacier surface. The most remarkable features of these landslides are their prominent long flowbands and a high mobility that exceeds that of their counterparts in other environments. Based on field surveys, high-resolution digital elevation models, and continuous seismic data, we show that the emplacement dynamics of the 2016 rock avalanche on Lamplugh Glacier were characterized by two distinct stages. During the first stage, the debris traveled about 5 km from the base of the slope. Clear long-period seismic signals during this stage record strong interactions of the rock avalanche debris with the ground, suggesting dynamic processes such as grain collisions and fragmentation. The second stage was essentially aseismic at long periods and dominated by low-friction sliding at slow deceleration rates. A higher density of flowbands and increased entrainment of snow from the runout path characterize the morphology of this second-stage distal deposition. Around the margins, lobes are offset by up to 400 m along major strike-slip faults, whereas within individual lobes, offsets between flowbands are much less pronounced (0 to < 10 m). The two-stage emplacement model may explain the higher apparent mobility of supraglacial landslides.

Numerical and theoretical study of bi-planar failure in footwall slopes

Bi-planar failure is the commonest type of failure in steep and high footwall slopes. This paper presents an investigation of the bi-planar failure mechanism and a stability analysis model for footwall slopes based on the study of eleven diabase mines in Hunyuan County, Shanxi Province, China. First, a detailed investigation of the site and tests were carried out to obtain a geological model and calculation parameters for the slope. Then, the failure process in footwall slopes was investigated by a trigon approach performed using the Universal Distinct Element Code (UDEC) software package. A mechanism was then obtained for bi-planar compression–shear failure by combining the results obtained for the stress, displacement, and crack development. Subsequently, based on the limit equilibrium and frictional plasticity theories, a new columnar mechanical model was proposed for bi-planar footwall slope failure. The results demonstrate that the UDEC trigon approach was well suited to simulating bi-planar failure in steep and high footwall slopes. Employing this approach, a sliding failure surface that initiates, develops, and propagates in the discontinuity and intact rock could be correctly captured and the evolution of the damage in the toe of the slope could be quantitatively investigated. The results also indicate that shear failure first occurs at persistent discontinuities and then compression–shear failure occurs in the intact rocks. In addition, the failure surface of the rock emanates from the toe of the slope, is oriented upwards at an angle to the persistent discontinuity thus forming the through sliding surface (this angle can be determined using frictional plasticity theory). The critical heights and safety factors of footwall slopes could be readily obtained by employing this new columnar mechanical model giving results that are consistent with the results of numerical simulations. Furthermore, the results of a parameter-sensitivity analysis show that the dip angle of the toe breakout surface increases as the slope angle increases. However, the angle between the toe breakout and internal shear surfaces remains unchanged as the slope angle increases. Moreover, the critical height of the footwall slope decreases linearly as the slope angle increases. The method proposed provides theoretical guidance for the stability analysis of steep and high footwall slopes. The results produced should also help engineers to gain a better understanding of the mechanisms of bi-planar failure in such rock slopes.

An analogue Toma Hill formation model for the Tyrolian Fernpass rockslide

The Fernpass rockslide occurred about 4100 years ago and is one of the largest rock slope failures in the Alps, the run-out area being characterized by a hummocky surface with Toma Hills that were formed after the rockslide event. These hills, characterized by a cone-like shape with a flattened top, are typical for many rockslides, and the name “Toma” is derived from local dialects in Switzerland and Tyrol, Austria. So far, five hypotheses have been proposed for the formation of Toma Hills, the two relating to glacial activity being outdated meanwhile. These hypotheses cannot explain all features observed on site. Therefore, to investigate one of these hypotheses, a qualitative laboratory-scale analogue groundwater flow model with the size 1.5 × 1 × 0.8 m was used to investigate the contribution of internal erosion by suffosion to forming Toma Hills. From the model, hydrogeological calculations of Darcy velocity and hydraulic conductivity were determined to help understand the present study. The average hydraulic gradient of the experiments was close to that in reality. Hydraulic conductivities in the five experiments were comparable to the calculated field hydraulic conductivity (Bialas and Seelheim equations). A limnokrene like one south-west of Biberwier developed in all experiments. Development of lateral and transversal cracks, water-filled lateral depressions of the material in the model and discharge of finer material implicated that internal erosion is a substantial contribution to the Toma Hill formation. Based on the experimental results, we deduce that Toma Hill formation took between 140 and 580 years.

Classification of Red-Bed Rock Mass Structures and Slope Failure Modes in South China

Red beds are Meso–Cenozoic continental sedimentary strata that are mainly composed of gravel stone, sandstone, siltstone, mudstone, and shale and occasionally have interlayers of limestone, halite, and gypsum. As a typical rock mass, red beds are widely distributed throughout South China. In a typical tropical and subtropical continental environment, red beds are the product of multiple sedimentary cycles, which have resulted in complicated rock mass structures that play an important role in rock mass stability. It is thus of great significance to investigate the influence of different rock mass structures on the stability of red-bed slopes. In this paper, the geological formation history of red beds in South China is described. The main features of red-bed rock mass slopes in South China are discussed. The main combinations of inner geomechanical structures comprise: (1) mega-thick soft rock structures; (2) mega-thick hard rock structures; (3) thick hard rock structures with weak intercalation; and (4) soft–hard interbedded structures. In addition, the features of slope failure are analyzed, and four common failure modes are identified from the statistical data: (a) weathering spalling and scouring; (b) rock falls; (c) landslides; and (d) tensile dumping.

Natural Frequency Characteristics of Rock Masses Containing a Complex Geological Structure and Their Effects on the Dynamic Stability of Slopes

The seismic failure of rock slopes is commonly a cumulative damage process; in particular, local slope damage usually occurs before the occurrence of landslides. The local damage in rock slopes is often caused by the high-frequency components of the waves. Special attention should be paid to the relationship between the local damage and the dynamic failure of landslides, which is of great significance to the study of the cumulative failure evolution of landslides. Based on a numerical modal analysis and dynamic characteristics determined using shaking-table tests, the relationship between the local damage and the dynamic failure of a rock slope with discontinuous joints and its failure mechanism is investigated in the frequency domain. The modal analysis clarifies the natural frequencies and vibration modes of the slope. The tests investigate the effects of the natural frequencies on the slope dynamic characteristics. The numerical and test results show that the high- and low-frequency components mainly induce local and overall deformation of the surface slope, respectively. The analyses of the peak Fourier spectrum amplitude (PFSA) suggest that the dynamic failure process of the slope includes a local damage stage ( 0.297 g). The high-frequency components play a major role in the slope cumulative deformation process, and the low-frequency components determine the failure mode of the landslide. The local damage induced by high-frequency components first occurs and progressively develops; then, when the damage is accumulated to a certain extent, the surface slope fails because of the low-frequency components.