Rachid El Hamdouni

Verification of landslide susceptibility mapping: a case study

A methodology is proposed for mapping susceptibility to landsliding and validating the results. Heavy rains in late 1996 and early 1997 led to a large number of landslids in the Rute sector (Cordoba, Southern Spain), where landslide susceptibility mapping had previously been carried out using a ‘matrix’ method developed with a Geographical Information System (GIS). Analysis of the distribution of the new landslides (or reactivated earlier ones) enabled the methodology to be validated by calculating association coefficients and determining the closeness of the match between subsequent field evidence and the previously defined susceptibility levels. From the data obtained, it can be concluded that the susceptibility mapping effectively explained the spatial distribution of landslides, thus providing valuable information on stability conditions over a widespread area. Copyright

The importance of the precipitation and the susceptibility of the slopes for the triggering of landslides along the roads

In order to characterise the influence of the heavyrains on the observed landslides during the 1996–1997hydrological cycle, rainfall records for the last 100years are analysed from 104 stations in easternAndalusia. Regarding the amounts of rain recordedbetween October 1996 and March 1997 in the 104stations studied, 31 presented new all-time records;15 presented values that were 80–100% of thepre-1995 record; 49 stations, 80–50%; and 9stations, < 50%. A map has been devised of thesusceptibility of the materials through which thesouth-eastern Andalusian road network crosses,together with an inventory of the damage caused byinstability phenomena on banks and cuttings of theroad network during the winter of 1996–1997. Therelationships between the rainfall during the studyperiod, the damage caused to the road network and thesusceptibility of the materials affected are analysed.The results indicate that there is a clearcorrespondence between the rainfall recorded and thesusceptibility of the materials with the inventorieddamage. It is concluded that the widespread seriousdamage caused in early 1997 to the roads andsurrounding areas in the Alpujarra region and thecoast of the Province of Granada was mainly caused bythe extraordinarily heavy rains. However, considerablyless damage was observed where the susceptibility ofthe terrain is low, thus highlighting the extremeusefulness of terrain-susceptibility maps for riskprevention and territorial planning.

Improvement of the JRC Calculation Using Different Parameters Obtained Through a New Survey Method Applied to Rock Discontinuities

Abstract This paper presents a new, fast and economical method for digitizing a rock surface profile to determine its joint roughness coefficient (JRC) value (Barton and Choubey, Rock Mech Rock Eng 10:1–54, 1977) using a set of existing parameters, the appropriateness of which has been tested. The new procedure was applied to four rock road cuts in the Alpujarra area of Granada province (Andalusia, Spain), supported by 117 digitized profiles. The method avoids any personal subjectivity bias. The usual subjectivity in the visualization and assessment of the JRC value is estimated here by a survey test answered by 90 trained users. The survey test consisted of a set of JRC visual comparisons of 12 roughness profiles, selected from the 117 profiles surveyed during the field research in the Alpujarra region, with the Barton typical profiles. The results of the survey clearly show systematic inaccuracies in the traditional procedure that are reduced if the advice presented in the conclusions of this paper is taken in account when performing the visual estimation.

Methodology for Landslide Susceptibility and Hazard Mapping Using GIS and SDI

In this work a methodology for preparing landslides susceptibility and hazard maps is presented, based in a bivariate analysis between past movements and determinant factors. The methodology for determining the susceptibility is an adaptation of the matrix method to a GIS, and it has been tested and validated in different zones and environments of Andalusia (southern Spain). The text also discusses the availability of information layers in Spanish SDI to developing these susceptibility maps. For the hazard evaluation, we propose a methodology of determining the susceptibility in different return periods from inventories of landslides that show activity in these considered periods. The activity was estimated from stereoscopic and monoscopic analysis of aerial photographs from different dates, using geological and geomorphic criteria, and the study of rainfall time series. Since all, four periods were considered in a logarithmic scale of 10 years (approximate return period of rainfall generating instability in the area), 100, 1000 and 10000 years. After determining the susceptibility, it was transformed into annual hazard dividing by the number of years of the return period. Finally, a total hazard map was obtained by determining at each point the maximum value of hazard of the different periods and it is expressed in several intervals.

Urban Landslides at the South of Sierra Nevada and Coastal Areas of the Granada Province (Spain)

The Southern flank of Sierra Nevada and coastal Mediterranean areas of South Spain, in the Andalusian Granada Province, a high number of urban settlements and roads have been affected by landslides and instability problems since the fifties. In this period, a very quick economic development with an intense annual increase of touristic demand gave place to rapid enlargements of formerly small villages, and the widespread land-use change from agricultural to urban not only around the pre-existing urban centres, but also in many new developed lands along the coast for urbanization or leisure services. This Mediterranean coast, in the uplifting section of the Eurasia an African plates, is mainly excavated on metapelites of the Betic Cordillera Internal Zone, showing very inclined if not vertical slopes on Lower Triassic to Paleozoic series of marble, schist, phyliite and quartzite units, very deformed and weathered, so giving place to instability problems which are described in this paper.

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.

Combined effects of blasting and geological structure on rock mass stability???a case study from the Marrakech???Agadir highway, Morocco

The Marrakech–Agadir highway crosses mountainous areas of the Western High Atlas of Morocco with a high risk of slope instability. The use of explosives as an excavation method, especially at kilometric point 33 on the Imintanout–Argana section, has triggered major ruptures. The regional geological setting, together with the lithological and structural characteristics of the rock mass, represent the major factors influencing this operation where the degree of disturbance is estimated as 0.82. The studied slope is located along the trajectory of a submeridian fault corridor remobilised because of blasting during excavation works. This slope reveals instabilities associated with tectonic planes (F1 and F2) and/or bedding (S0) and the presence of argillites and siltstones that coincide with bedding. These unconsolidated layers, inclined in the direction of excavation, act as slide planes. Structurally, the Pk33 slope can be subdivided into three zones depending on the displacement type being recorded and may be a fortiori related to the geomechanical properties of the substrate. The rheological characteristics of zones B and C, highly fractured and with low competence, respectively, explain their relatively different displacement patterns from that of zone A. The maximum instantaneous explosive load used for offloading the upper part of the sliding mass has been estimated in order to increase the safety factor for the instable slope.