Rock Slope Stability Assessment Research Articles

Stability Assessment of the Excavated Rock Slope at the Dagangshan Hydropower Station in China Based on Microseismic Monitoring

A high-resolution microseismic (MS) monitoring system was implemented at the right bank slope of the Dagangshan hydropower station in May 2010 to analyse the slope stability subjected to continuous excavation. The MS monitoring system could real-time capture a large number of seismic events occurring inside the rock slope. The identification and delineation of rock mass damage subject to excavation and consolidation grouting can be conducted based on the analysis of tempospatial distribution of MS events. However, how to qualitatively evaluate the stability of the rock slope by utilizing these MS data remains challenging. A damage model based on MS data was proposed to analyse the rock mass damage, and a 3D finite element method model of the rock slope was also established. The deteriorated mechanical parameters of rock mass were determined according to the model elements considering the effect of MS damage. With this method, we can explore the effect of MS activities, which are caused by rock mass damage subjected to excavation and strength degradation to the dynamic instability of the slope. When the MS damage effect was taken into account, the safety factor of the rock slope was reduced by 0.18 compared to the original rock slope model without considering the effect. The simulated results show that MS activities, which are subjected to excavation unloading, have only a limited effect on the stability of the right bank slope. The proposed method is proven to be a better approach for the dynamical assessment of rock slope stability and will provide valuable references for other similar rock slopes.

Assessment of rock slope stability with the effects of weathering and excavation by comparing deterministic methods and slope stability probability classification (SSPC)

Cut slopes are prone to fail due to the disturbance on original geometry and strength. In addition, because of these disturbances and stress relief, natural apertures which increase the weathering effects widen in engineering time. Owing to these reasons, slope stability assessment has a prominent role on these road cuts. Generally, slope stabilities are assessed by deterministic approaches with a significant engineering judgment. Because of this reason the reputation of probabilistic approaches is increasing. In this study, 20 road cuts located in North West Black Sea region of Turkey were evaluated using slope stability probability classification (SSPC). Considering this probabilistic approach, rock strength parameters and failure mechanisms were determined. Furthermore, slope mass rating (SMR) classification was applied for each road cut in order to compare with the results obtained from SSPC. These overall results were then evaluated with the field observations considering rockslope deterioration assessment (RDA) and Falling Rock Hazard Index (FRHI) for the disturbed/weathered zones, and failure mechanisms. According to these, SSPC is found to be more accurate for surficial degradations (raveling and fall) using samples taken from the disturbed/weathered zones rather than using relatively fresh samples beyond the disturbed zone. Moreover, despite strength differences between weathered and relatively fresh zones, SMR classification is identified to reveal the same stable probabilities. It is found that SSPC shows more detailed probabilistic results than SMR. Lastly, rockfall and raveling mechanisms determined by RDA and rockfall risk by FRHI were found to be coherent with SSPC and field observations.

Rock Slope Stability Assessment Using Geomechanical Classification and its Application for Specific Slopes along Kodaikkanal-Palani Hill Road, Western Ghats, India

ABSTRACT Linear infrastructure networks like roads play a vital role in the socio-economic development of hill towns centered on tourism. Stability of the slopes along the hill roads are therefore a major concern and slope failures lead to disruption of traffic and loss of property/life or both. This study analyses the stability of cut-slopes along the Kodaikkanal – Palani hill road in the Western Ghats, India using rock mass classification systems like rock mass rating (RMR), slope mass rating (SMR) and continuous slope mass rating (CSMR). These geomechanical classifications provide a preliminary assessment of rock quality based on rock strength, discontinuity properties, hydrogeological condition of the slopes and slope stability based on the inherent rock strength parameters, discontinuity orientation and method of excavation. The results showed that both rock quality and discontinuity orientation contribute to type of failure in rock slopes with RMR > 40. SMR results are conservative while CSMR classification is matches more closely to the failures obtained from the field survey. CSMR classification represents continuous slope stability conditions and hence are more suitable for development of spatial database. Cutting of roads, thereby, steepening slopes has a definite influence on the stability of slopes.

Application of rock mass classification systems to rock slope stability assessment: A case study

The stability of rock slopes is considered crucial to public safety in highways passing through rock cuts, as well as to personnel and equipment safety in open pit mines. Slope instability and failures occur due to many factors such as adverse slope geometries, geological discontinuities, weak or weathered slope materials as well as severe weather conditions. External loads like heavy precipitation and seismicity could play a significant role in slope failure. In this paper, several rock mass classification systems developed for rock slope stability assessment are evaluated against known rock slope conditions in a region of Saudi Arabia, where slopes located in rugged terrains with complex geometry serve as highway road cuts. Selected empirical methods have been applied to 22 rock cuts that are selected based on their failure mechanisms and slope materials. The stability conditions are identified, and the results of each rock slope classification system are compared. The paper also highlights the limitations of the empirical classification methods used in the study and proposes future research directions.

Assessment of rock slope stability by slope mass rating (SMR): A case study for the gas flare site in Assalouyeh, South of Iran

Slope mass rating (SMR) is commonly used for the geomechanical classification of rock masses in an attempt to evaluate the stability of slopes. SMR is calculated from the RMR89-basic (basic rock mass rating) and from the characteristic features of discontinuities, and may be applied to slope stability analysis as well as to slope support recommendations. This study attempts to utilize the SMR classification system for slope stability analysis and to investigate the engineering geological conditions of the slopes and the slope stability analysis of the Gas Flare site in phases 6, 7 and 8 of the South Pars Gas Complex in Assalouyeh, south of Iran. After studying a total of twelve slopes, the results of the SMR classification system indicated that three slope failure modes, namely, wedge, plane and mass failure were possible along the slopes. In addition, the stability analyses conducted by a number of computer programs indicated that three of the slopes were stable, three of the slopes were unstable and the remaining six slopes were categorized as \'needs attention\' classes.

Weak foliated rock slope stability analysis with ultra-close-range terrestrial digital photogrammetry

This paper presents a review of the data acquisition procedures of geotechnical parameters for rock slope stability assessment and the proposal of some new improvements. For this purpose, a piece of research based on the slope mass rating classification system using close-range terrestrial digital photogrammetry (CR-TDP) has led to improvements in quality and timing of discontinuity data acquisition, and analyzes the suitability of each one of the parameters when applied to weak foliated rocks. TDP allows rapid 3D image acquisition of a rock slope, which can be analyzed using software to determine the geometrical parameters that affect stability. A fast procedure to perform the photogrammetric, non-contact survey in order to obtain the 3D images is shown in this paper. Being a rapid and single-person task, this procedure provides enough precision to be applied to weak foliated rock slopes with non-well-defined geometry. Furthermore, the study has focused on highly foliated rock outcrops, in which high resolution in the 3D images is very desirable. This research was applied to mountain road cuts, in which the use of TDP with a very close range was necessary. Through an application on weak rocks in the Alpujarras (Andalusia, Spain), this work analyzes the bias when applying TDP to materials such as these, under progressive weathering processes.

Comparing manual and remote sensing field discontinuity collection used in kinematic stability assessment of failed rock slopes

This work was supported by the University of Alicante, within the framework of project GRE14-04. Additional funding was obtained from the Spanish Government, project number TIN2014-55413-C2-2-P.

Assessment of discontinuous rock slope stability with block theory and numerical modeling: a case study for the South Pars Gas Complex, Assalouyeh, Iran

In this study, a geotechnical model has been used to analyze the stability of a discontinuous rock slope. The main idea behind block theory is that it disregards many different combinations of discontinuities and directly identifies and considers critical rock blocks known as “key blocks”. The rock slope used as a case study herein is situated in the sixth phase of the gas flare site of the South Pars Gas Complex, Assalouyeh, Iran. In order to analyze the stability of discontinuous rock slopes, geotechnical modeling which was divided into geometrical sub-modeling and mechanical sub-modeling has been utilized. This model has been established upon the KGM (key-group method) algorithm which was based on the limit equilibrium method and block theory and prepared and coded by the Mathematica software. According to the results of the stability analysis, the analyzed slope was determined to be in the category of “needs attention,” and the security level, calculated through the FORM (first-order reliability method) analysis, was estimated to be 1.16. In order to verify the model, the results obtained from the model were compared with those of the UDEC software, which is a numerical method based on distinct components. As a conclusion, it was determined that the results of the model agreed well with those of the numerical method.

Rock Mass Classification and Assessment of Stability of Critical Slopes on National Highway-22 in Himachal Pradesh

ABSTRACT Rock slopes require geo-engineering evaluation to assess the instability of critical slopes leading to landslides particularly in Himalayan terrain where rocks are highly jointed, fractured and weathering prone. Interplay of discontinuities in the rocks coupled with other parameters is one of the prime causes of failure of slopes. Engineering rock mass classification, such as, rock mass rating (RMR) and slope mass rating (SMR) along with geological strength index (GSI) have widely been used for stability assessment of rock slopes above tunnel portals, and these classifications are employed here for assessment of stability of slopes of critical nature along Rampur-Powari highway in Himachal Pradesh. In the present study, out of 154 numbers of slopes, a total of 29 have been selected for assessment of their criticality by employing RMR, SMR and GSI.

Quantifying irreversible movement in steep, fractured bedrock permafrost on Matterhorn (CH)

Abstract. Understanding rock slope kinematics in steep, fractured bedrock permafrost is a challenging task. Recent laboratory studies have provided enhanced understanding of rock fatigue and fracturing in cold environments but were not successfully confirmed by field studies. This study presents a unique time series of fracture kinematics, rock temperatures and environmental conditions at 3500 m a. s. l. on the steep, strongly fractured Hörnligrat of the Matterhorn (Swiss Alps). Thanks to 8 years of continuous data, the longer-term evolution of fracture kinematics in permafrost can be analyzed with an unprecedented level of detail. Evidence for common trends in spatiotemporal pattern of fracture kinematics could be found: a partly reversible seasonal movement can be observed at all locations, with variable amplitudes. In the wider context of rock slope stability assessment, we propose separating reversible (elastic) components of fracture kinematics, caused by thermoelastic strains, from the irreversible (plastic) component due to other processes. A regression analysis between temperature and fracture displacement shows that all instrumented fractures exhibit reversible displacements that dominate fracture kinematics in winter. Furthermore, removing this reversible component from the observed displacement enables us to quantify the irreversible component. From this, a new metric – termed index of irreversibility – is proposed to quantify relative irreversibility of fracture kinematics. This new index can identify periods when fracture displacements are dominated by irreversible processes. For many sensors, irreversible enhanced fracture displacement is observed in summer and its initiation coincides with the onset of positive rock temperatures. This likely indicates thawing-related processes, such as meltwater percolation into fractures, as a forcing mechanism for irreversible displacements. For a few instrumented fractures, irreversible displacements were found at the onset of the freezing period, suggesting that cryogenic processes act as a driving factor through increasing ice pressure. The proposed analysis provides a tool for investigating and better understanding processes related to irreversible kinematics.

Rock Slope Stability Assessment of Limestone Hills in Northern Kinta Valley, Ipoh, Perak, Malaysia

The uniqueness of the karst topography of Kinta Valley is the result of the spectacular shaped steep-sided limestone towers. The instability of these hillslopes however, may affect the vulnerability of the surrounding area. This paper presents the results of slope stability assessment by using kinematic analysis to investigate the possible failure modes of 7 slopes in Gua Naga Mas (GNM1, GNM2 and GNM3), Gua Kandu (GK1, GK2 and GK3) and Gua Tempurung (GT) located in the southern part of the Kinta Valley, Ipoh, Perak. From the results of the slope stability assessment, it was determined that planar failure and wedge failure were the main failure modes. The GNM1 slope of Gua Naga Mas consist of four wedge failures and a planar failure with dip directions/dip angles of 005°/54°, 354°/59°, 124°/52°, 360°/50° and 063°/70° respectively. The GNM2 slope consists of a wedge failure with the dip direction/dip angle of 021°/64°. Two wedge failures and a planar failure were identified on slope GNM3 with the respective dip directions/dip angles of 336°/49°, 301°/68° and 270°/71°. The GK1 slope for Gua Kandu consists of wedge and planar failures with dip directions/dip angles of 231°/49° and 217°/49° respectively. The mode of failure at GK2 slope was identified as wedge failure with the dip direction/dip angle of 154°/44°. No mode of failure was identified on slope of GK3. Slope GT of Gua Tempurung was identified to have two wedge failures with dip directions/dip angles of 011°/49° and 321°/48° respectively.

Cut slope stability assessment along ghat road section of Kolli hills, India

In the present study, cut slope stability assessment along ghat road section of Kolli hills was carried out by using various geotechnical parameters of rock and soil slope sections and structural kinematics of major discontinuities is presented. The rock slope (RS) stability assessment was carried out using Rock Mass Rating basic (RMRbasic) and Slope Mass Rating (SMR) classification systems. The type of failure and their Factor of Safety (FOS) for individual RS was calculated using Hoek and Bray method. In the case of soil slopes (SS), the FOS was calculated using Circular Failure Chart (CFC) and Limit Equilibrium (LE) methods. The input data for the slope stability analyses were collected through extensive field work followed by stereonet plotting and laboratory test. There are six rock slope sections, and five soil slope sections were taken into consideration for the cut slope stability analyses. The area depicts class II (RS-1, 2, & 6) and class III (RS-3, 4, & 5) of RMR classes. The SMR result depicts for RS-1, RS-2, and RS-6 are 64.40, 60.02, and 60.70, respectively, and falls in class II stable condition. The SMR values of RS-3 and RS-5 were 44.33 and 57, respectively, and come under the class III partially stable condition. The RS-4 with SMR value of 17.33 falls under the class I completely unstable condition. The FOS of planar failure case indicates that RS-3 (FOS = 0.22) is more unstable, while all other sections are having greater than 1 FOS. The calculated FOS values using CFC method reveals that the FOS is very close to 1 for all the SS sections that fall under completely saturated condition which indicates that these slope sections may fail during heavy rainfall. In LE method, the sections SS-3 and SS-4 are unsafe under partially and completely saturated (natural slope) condition. In average slope condition, all the SS sections are unsafe under partially or completely saturated conditions. The facets 2, 3, 4, and 5 required mitigation measures, to improve the stability of slopes. Site-specific mitigation measures were suggested for partially or completely unstable rock and soil cut slopes.

Recent advances in the stability assessment of natural and engineered rock slopes

Science’s understanding of the failure mechanisms of large natural and engineered slopes has been improved considerably over the past 15 years. Significant improvements have been realized in innovative methods of data acquisition through field measurement and monitoring, as well as numerical modelling techniques. However, inadequate understanding of complex geology and landslide processes means that any interpretation of landslide data remains mostly subjective. This causes major uncertainty in landslide risk assessment.
 Over the past decade, Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO; http://www.csiro.au/) has developed novel techniques to facilitate efficient assessment of rock slope stability. These include SirovisionTM, Siromodel, and three CSIRO numerical codes: CSIRO‑SPH, CSIRO‑DEM and CSIRO‑COSFLOW.
 SirovisionTM is a geological/geotechnical mapping and analysis system that generates accurate, scaled 3D images of rock faces from stereo photographs of exposed rock surfaces, allowing for rapid rock mass structural mapping. Siromodel is a polyhedral modelling system that reads the SirovisionTM data, generates discrete fracture networks (DFN) and performs polyhedral (rock block) modelling and a first‑pass stability analysis.
 CSIRO‑SPH, CSIRO‑DEM and CSIRO‑COSFLOW are all used for detailed stress‑deformation analysis of rock slopes; however, each code has its own problem‑specific advantage. CSIRO‑SPH is suited for large deformation problems, and can simulate large scale fluid flow problems, such as modelling a dam breakage. CSIRO‑DEM is suited for rock breakage process analysis, and assessment of the runout distance of failure debris. CSIRO‑COSFLOW is designed specifically for efficient, accurate stress‑deformation analysis of stability of structures on bedded sedimentary rocks, where failures along the preexisting bedding planes and through the intact rock layers occur simultaneously.

Two-Dimensional Stability Assessment of Rock Slopes Based on Random Field

AbstractGeotechnical engineering is dominated mostly by uncertainties, because it always deals with highly variable natural materials. Reliability-analysis approaches emerge as a more reasonable and rigorous way of handling uncertainties. Two-dimensional stability assessment of rock slopes is performed, and the probability of failure of rock slopes against planar sliding is determined using the random fields. Both cohesion and friction coefficient along a discontinuity are treated as a normal random field and are represented by the mean values, standard deviations, spatial correlation lengths, correlation coefficient, and cross-correlation length, which account for the cross correlation between cohesion and coefficient of friction. Several examples are used to verify the proposed approach. The numerical results obtained from the proposed method are in good agreement with the numerical results obtained from Monte Carlo simulations. Moreover, the proposed method provides a new approach to study two-dimensio...

Assessment of rock slope stability by probabilistic-based Slope Stability Probability Classification method along highway cut slopes in Adilcevaz-Bitlis (Turkey)

Rock slope stability is of great concern along highway routes as stability problems on cut slopes may cause fatal events as well as loss of property. In rock slope engineering, stability evaluations are commonly performed by means of analytical or numerical analyses, principally considering the factor of safety concept. As a matter of fact, the probabilistic assessment of slope stability is progressively getting popularity due to difficulties in assigning the most appropriate values to design parameters in analytical or numerical methods. Additionally, the effect of heterogeneities in rock masses and discontinuities on the analysis results is minimized through the probabilistic concept. In this study, slope stability of high and steep sedimentary rock cut slopes along a state highway in Adilcevaz-Bitlis (Turkey) was evaluated on the basis of probabilistic approach using the Slope Stability Probability Classification (SSPC) system. The probabilistic assessment indicates major slope stability problems because of discontinuity controlled and discontinuity orientation independent mass movements. Almost all studied cut slopes suffer from orientation-independent stability problems with very low stability probabilities. Additionally, the probability of planar and toppling failures is significantly high with respect to the SSPC system. The stability problems along the investigated rock slopes were also verified by field reconnaissance. Remedial measures such as slope re-design and reinforcement at the studied locations should be taken to prevent hazardous events along the highway. On the other hand, the probabilistic approach may be a useful tool during rock slope engineering to overcome numerous uncertainties when probabilistic and analytic results are compared.

Assessment of rock slope stability at Cham-Shir Dam Power Plant pit using the limit equilibrium method and numerical modeling

There is global concern about the stability of rock slopes in open pit mines while the limit equilibrium technique used for modeling complex geometries and forces fails to provide a complete understanding of the behavior of rock slopes due to its inherent shortcomings. However, numerical approaches to modeling complex rock structures have improved the general understanding of these slope structures. In this study, geological and geotechnical data were obtained from both exploration drill holes and laboratory tests using face mapping and scanline surveys to reveal three major joint sets related to the regional tectonic history at the Cham-Shir dam power plant pit in Iran. The joints play an important role in the slope stability of the open pit, notably in terms of planar and wedge failures. Moreover, both the limit equilibrium technique and the discrete element method were employed to analyze the stability of the Cham-Shir dam power plant pit in an attempt to evaluate its behavior under both supported and unsupported conditions in the three modes of continuous rock mass, rock mass with two joint sets, and rock mass with three joint sets. Results show that the rock mass is stable in the continuous mode. The possible failure must, therefore, be due to the structure type and the joint sets at the site. To address the requirements and to resolve the problem, a simulation study was conducted. Based on the findings, stage by stage excavations are recommended for the study site.

Rock slope stability analyses using extreme learning neural network and terminal steepest descent algorithm

The analysis of rock slope stability is a classical problem for geotechnical engineers. However, for practicing engineers, proper software is not usually user friendly, and additional resources capable of providing information useful for decision-making are required. This study developed a convenient tool that can provide a prompt assessment of rock slope stability. A nonlinear input–output mapping of the rock slope system was constructed using a neural network trained by an extreme learning algorithm. The training data was obtained by using finite element upper and lower bound limit analysis methods. The newly developed techniques in this study can either estimate the factor of safety for a rock slope or obtain the implicit parameters through back analyses. Back analysis parameter identification was performed using a terminal steepest descent algorithm based on the finite-time stability theory. This algorithm not only guarantees finite-time error convergence but also achieves exact zero convergence, unlike the conventional steepest descent algorithm in which the training error never reaches zero.

Systematic Approach to Sustainable Rock Slope Stability Evaluation

Geological discontinuities play an important role in the evaluation of rock slope stability. Romana's Slope Mass Rating (SMR) system provides a methodology to quantify rock slope stability. Employing Bieniawski's Rock Mass Rating (RMR) to classify the rock mass of an investigated slope, SMR enables an objective determination of the rating adjustment values based on discontinuity orientation-slope orientation, respective dips angles and slope excavation methods. However the surface roughness of the discontinuities and their peak friction angles (αp) that are fundamental in determining rock slope stability are not directly considered in this evaluation. A more sustainable approach to rock slope stability assessment proposed here combines the SMR determination with the determination of the peak friction angle, αp of the discontinuity surfaces. Based on this proposal, the potential for slope failure can be quantified as follows: if SMR predicts failure and dip angle of the discontinuity (βi) > the peak friction angle (αp) the slope has a very high failure potential; if SMR predicts failure and βi < αp, the slope has intermediate failure potential; if the slope is stable according to SMR & βi > αp, the slope has low failure potential and if stable according to SMR and βi < αp, the slope can be considered as stable.

ROCK SLOPE ASSESSMENT USING KINEMATIC AND NUMERICAL ANALYSES

This paper presents stability assessment of rock slopes at Jalan Kuari, Cheras, Kuala Lumpur. The site is a disused quarry slope where a low cost residential area of Pangsapuri Intan was built very close to it, frequent instability at the rock slope have been reported. A detailed discontinuity assessment was carried at the site, then, the kinematic and numerical analyses were performed in order to determine the stability of the rock slope. The kinematic analysis was carried out using DIPS 5.0 software and the results showed that about 19% is the percentage of the wedge failure that is encountered for the rock slope. Meanwhile, the finite element method of analysis in Phase2 showed that the slope is in stable condition, with the Strength Reduction Factor (SRF) of 2.0. The difference between the results of the kinematic and the finite element analyses is because, the kinematic analysis considered the discontinuities volume and orientations with regards to the slope face, while the finite element, analysed the slope with respect to strength properties. Since the slope is a disused quarry, where previous blasting work had produced fractures on the rock face, these discontinuities and fractures are more influencing the instability and the result from kinematic analysis shows a good agreement with the field observation.

Application of the SSPC method in the stability assessment of highway rock slopes in the Yunnan province of China

Assessing the stability of rock slopes is an important and difficult problem. Rock mass classification systems have become a suitable tool for fast assessment of rock slope stability. In contrast to other slope stability classification systems, the slope stability probability classification (SSPC) method has made obvious progress. In this study, numerous excavation slopes were surveyed along the Wentian and Xiaolan highways in the Yunnan province, China and their basic data were collected in the field. From the slopes, we choose some typical excavation slopes with different structure types, such as cataclastic, granular, layered and blocked structures. According to the three-step analysis method in the SSPC system, failure probability of the excavation slopes were assessed based on the possible failure mechanisms and modes of the slopes. The results show that the SSPC method exhibited an accuracy of 70 % in the stability assessment of the highway slopes in the Yunnan province.