Risk evaluation of rock mass sliding in El-Deir El-Bahary valley, Luxor, Egypt (original) (raw)
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Comparing rockfall scar volumes and kinematically detachable rock masses
Scenario-based risk assessment for rockfalls, requires assumptions for different scenarios of magnitude (volume). The magnitude of such instabilities is related to the properties of the jointed rock mass, with the characteristics of the existing unfavourably dipping joint sets playing a major role. The critical factors for the determination of the maximum credible rockfall volume in a study site, the Forat Negre in Andorra, are investigated. The results from two previous analyses for the rockfall size distribution at this site are discussed. The first analysis provides the observed size distribution of the rockfall scars, and it is an empirical evidence of past rockfalls. The second one, calculates the kinematically detachable rock masses, indicating hypothetical rockfalls that might occur in the future. The later gives a maximum rockfall volume, which is one order of magnitude higher, because the persistence of the basal planes is overestimated. The tension cracks and lateral planes interrupt systematically the basal planes, exerting a control over their persistence, and restricting the formation of extensive planes and large rockfall failures. Nonetheless, the formation of basal planes across more than one spacings of tension cracks is possible and small step-path failures have been observed too. Concluding, the key factor for the determination of the maximum credible volume at the study-site is the maximum realistic length of the basal planes, penetrating into the rock mass, their spacing, and, if applied, the contribution of the rock bridges to the overall rock mass resistance.
Rock Fall Failure Model practical example of Umm Sid Plateau-Sharm El Sheikh area, Egypt
A severe rock fall in the upper jointed Reefal Limestone unit which represents the main foundation rock bed of Umm Sid plateau .The main causative factors of rock fall is the movement of the limestone blocks under the effect of deferential erosion (undercut ) of the underneath sandstone unit. Photogeologic mapping and Geological Field measurements have been carried out for the Umm Sid plateau to investigate the factors controlling the rock fall of the uppermost layers of the plateau. The geological field measurements as well as geological disk studies are used to produce a model representing the joint orientations, stability model and failure mechanism geologic model. Kinematic analysis of the acquired data indicated that the topmost unit of the plateau is affected by three main sets of joints E-W, NE-SW and NW-SW trends. The hard Reefal Limestone unit is underlying with relatively soft sandstone unit. The sand stone unit is intercalated with marl and clays that increase the potentiality of deferential erosion. Kinematic analyses of the measured joints were studied by using Hoek and Bray failure methods (2004), Dips program Version 5.1.8 and RocPlane Version 2.0. The site observation and measurements indicated that the rock falls is seriously active and accordingly the scarp edge retreat and that may lead to a dangerous impact on the existing hotels and resorts located at this plateau. Index Terms-Sharm El Sheikh (Umm Sid Plateau), Kinematic analyses, Rock fall and Failure model. ---------- ----------
Rock fall hazard assessment: from qualitative to quantitative failure probability
A new method (HGP) is proposed to estimate the failure probability of potentially unstable rock masses in a homogenous area, as a function of time. It is based on both geomechanical and historical approaches: the first one is aimed to classify the rock masses according to their relative failure probability, but the time factor can not be approached by a mechanical analysis; the second one to estimate the mean expected rock fall number in the studied area, for the considered period and for different volume classes. This rock fall frequency can be estimated from a rock fall inventory, directly or indirectly using a power law for the volume distribution. A relation between these frequencies and the erosion rate is established, which allows to approach the former from a paleogeographical study. The failure probabilities can be calculated from the expected total rock fall number in the area, and the numbers of potential rock falls with different relative probabilities. The method is appl...
Comparing kinematically detachable rock masses and rockfall scar volumes
IOP Conference Series: Earth and Environmental Science, 2015
In rockfall prone areas the evaluation of the risk due to worst case scenarios requires the establishment of maximum thresholds for the expected rockfall volumes. The magnitude of such instabilities is often related to the properties of the jointed rock mass, with the characteristics of the existing unfavorably dipping joint sets playing a major role. The studysite here is the chute of Forat Negre in Andorra. The size distribution of the missing volumes from the scars was calculated using terrestrial laser scanner point cloud data and reaches up to few thousands of m 3. On the other hand, the application of Markland criteria on a Digital Elevation Model of the zone indicated the kinematically detachable rock masses to be up to tens of thousands of m 3. As the size of the scar areas does not indicate the occurrence of such events in the past, the effect of the joint persistence as assumed for the two analyses is discussed here. The areas of the exposed joint surfaces belonging to each discontinuity set are obtained and their use as a measure of the relative persistence of each set is proposed. The average and median length of the sets F3 and F5 (sliding planes) are found to be similar to the average and median spacing of the intersecting set F7 (tension crack), suggesting that the F7 set exerts a control over the persistence of the former ones. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Journal of Geophysics and Engineering, 2008
Stability assessment of a cliff strongly depends on the fracture pattern and the face topography. Geological observations as well as classical geodetic measurements are difficult to perform on high nearly vertical cliffs like the ones surrounding the town of Grenoble (French Alps). In this study we combine remote and ground imaging techniques for characterizing the geometry and the fracture pattern of potential unstable cliff sites. A Dense Digital Surface Model (DDSM) of the rock face can now be obtained from laser scanning (Lidar) or photogrammetry. These techniques are safer and quicker than direct measurements. They offer the possibility to collect structural data and to sample the shape of the outcrop at a centimetric resolution. We applied these two techniques to a potential unstable site (the "Roche du Midi", Vercors massif) for determining the main fracture families affecting the rock mass and we obtained results similar to direct measurements performed on the nearby outcrops and on the cliff face itself. The laser scanning data suffers a bias in the illumination of the site. Geophysical experiments were also conducted on the plateau and on the cliff face in order to delineate the fracture pattern inside the rock mass. ERT (Electrical Resistivity Tomography) and GPR (Ground Penetrating Radar) profiles were performed on the plateau and allowed near-vertical open fractures to be located in the vicinity of the surface. Best geophysical results in terms of penetration and resolution were however obtained from GPR profiles conducted directly on the cliff face. Laser scanning data were combined with GPR data in order to take into account the shape of the sampled profiles. The combination of vertical and short horizontal profiles allowed the strike and dip of the discontinuities to be determined. The two main families were imaged, as well as a major continuous inward dipping reflector which was not shown during the initial reconnaissance. Further investigation inside the mass effectively showed the existence of this fracture. These results highlight the power of the GPR technique in characterizing the discontinuity pattern inside rock mass for improving the model in view of hazard assessment.
2013
the northern border of the Pyramids Plateau is an attractive location for new touristic resorts and developing settle- ments. This area suffers from extensive extension cracks that have resulted from uncontrolled blasting in limestone quarrying. The old quarrying activities resulted in unstable high rock cuts which impose safety risks during the construction activities in this area. The geological conditions of the rock units and the discontinuity patterns have been mapped and measured in detail. A ste- reonet failure envelope technique is used to evaluate the instability of the existing rock cuts. The geotechnical parameters of the existing rock units are studied based on some boreholes drilled in the area of study. The discontinuities failure envelope analysis, geotechnical parameters of rock cuts as well as survey of the extension cracks, slope stability models are used to study the stability and to develop optimum engineering solutions for protection and stabilization measures o...
An alternative rock mass classification system for rock slopes
Bulletin of Engineering Geology and the Environment, 2009
A system for the quantification of the failure hazard of rock cuttings structured in the form of rating tables is proposed. Rock cuttings are classified according to their failure hazard taking into account both their drained condition and the influence that climatic conditions have on stability; the latter being the most common landslide-triggering factor. The system deals with seven types of failure including slides, topples and falls. Where possible and convenient, parameters are amalgamated using wellestablished expressions of safety factor increasing the objectivity of the system. In addition to triggering mechanisms, site-specific parameters related to the mean and critical precipitation height, as well as the potential for the development of adverse, water-related conditions are taken into account to arrive at a Hazard Index value. Keywords Rock mass rating Á Rock falls Á RMR Á SMR Á Rock cutting failure Á Quantitative risk assessment Résumé Un système sur la quantification du risque d'échec des déblais rocheux structuré sous la forme des tableaux d'évaluation est proposé. Les déblais rocheux sont classifiés selon leur risque d'échec prenant en compte leur condition asséchée et l'influence des conditions climatiques sur la stabilité; le dernier facteur déclenchement des glissements de terrain est le plus commun. Le système traite avec sept types d'échec, glissements, renversements et éboulements rocheux sont compris. Lorsque cela est possible et pratique, les paramètres sont fusionnés en utilisant des expressions du facteur de sécurité connues, qui accroissent l'objectivité du système. En outre des mécanismes de déclenchement, les paramètres relatifs à la moyenne et à la hauteur critique de la précipitation du site spécifique, ainsi que la possibilité du développement des conditions négatives et relatives à l'eau, sont prises en considération pour arriver au Valeur du Risque. Mots clés Classification du massif rocheux Á Eboulements rocheux Á RMR, SMR, Echec des déblais rocheux Á Evaluation quantitative de risque L. Pantelidis (&) Civil Engineering,
The use of fracture mechanics for the study of the progressive failure in geomaterials
2008
Keywords: rock fracture mechanics, progressive failure, displacement discontinuity method ABSTRACT: This paper presents some basic concepts of linear and non linear fracture mechanics, with particular attention to some aspects related to hard soils and rocks such as the behaviour of cracks in compression. A non-linear method is presented in particular, which allows to simulate the process zone at the crack tip as a cohesive crack, where shear resistance decays from the peak to the residual value as a function of the relative slip. A numerical methodology is also presented, based on the BEM technique of the Displacement Discontinuity Method. Finally, two examples of application to the study of the progressive failure in geomaterials are presented. The first is the back analysis of the triggering phase of the Ranc rockfall, occurred in the Vercors massif (F) in 2004. A linear elastic analysis allowed to simulate a toppling failure mechanism due to the progressive failure of surveyed r...
The RockRisk project: rockfall risk quantification and prevention
2017
Rockfalls are frequent instability processes in road cuts, open pit mines and quarries, steep slopes and cliffs. The orientation and persistence of joints within the rock mass define the size of the kinematically unstable rock volumes and determine the way how the detached mass be-comes fragmented upon the impact on the ground surface. Knowledge of the size and trajectory of the blocks resulting from fragmentation is critical for calculating the impact probability and intensity, the vulnerability the exposed elements and the performance of protection structures. In this contribution we summarize the main goals and achievements of the RockRisk project. We focused on the characterization of the rockfall fragmentation by means of the analysis of the fracture pattern of intact rock masses, the development of a fragmentation model and its integration into rockfall propagation analysis. The ultimate goal of the project is to quantify risk due to rockfalls and develop tools for the improve...