C. Irigaray

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.

Geotechnical characterization of carbonate marls for the construction of impermeable dam cores

Abstract Fine-grained, more or less cohesive carbonate materials are extremely widespread in terms of surface area and are, therefore, commonly used as materials to construct impermeable cores for dams. However, it has not been adequately documented whether the carbonate content in fine-grained soils significantly affects their engineering behaviour. The present study shows that the carbonate content substantially influences the engineering behaviour of clayey material. For this, we subjected 32 samples to different laboratory tests, such as the normal Proctor, the Atterberg limits, granulometric analysis, oedometric and undrained triaxial tests. The resulting parameters were correlated with the carbonate content of the samples. The materials studied in this work had been used in the construction of the impermeable core of the San Clemente Dam, belonging to the hydrographic basin of the Guadalquivir River (southern Spain). These marls present, as their prime characteristic, a carbonate content of the fine fraction consistently exceeding 50%, giving them special importance in the study of this phenomenon. In this study, a direct relationship was found between the geotechnical properties of the soils studied and their degree of compaction, with the carbonate content and the type of minerals in the clay being the main factors determining the behaviour of these soils. Finally, we conclude that the percentage of carbonates should be used as a classification criterion for the soils used to construct the cores of earth-filled dams.

Engineering geological characterization of Neogene marls in the Southeastern Granada Basin, Spain

Analysis of 171 samples taken from the Neogene cohesive soils of the Southeastern edge of the Granada basin shows inverse correlation between carbonate content and dispersion index and swelling behaviour and direct correlations between carbonate content and shear strength. This paper shows that carbonate content and clay fraction activity have a great influence on the compaction characteristics of soils. Marls of the middle and upper Tortonian age (lower marls) are inadequate for use as subgrade because of their high plasticity. In addition, marls of lower and upper Messinian age (upper marls) are inadequate for use as subgrade because of their high carbonate content. The relationship between carbonate content and geotechnical properties is particularly important because the changes caused by pedogenic dissolution and precipitation processes lead to changes in mechanical behaviour.

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.

A multi-method approach for the characterization of landslides in an intramontane basin in the Andes (Loja, Ecuador)

In the last several decades, population growth in the cities of the Andes has caused urban areas to expand into landslide-prone areas. Fatal landslides affecting urban settlements are especially frequent in cities located in the Neogene intramontane basins of the Andes. These basins have similar situations and include geographical and geological features that frequently generate ground instabilities. We studied the characteristics of the mass movements observed in these basins by carrying out a detailed analysis of four landslides that have occurred in the Loja Basin (Ecuador). This multi-method study integrated geophysical, geotechnical methods, mineralogical studies and analyses of precipitation time series. Our study characterizes the slope movements as active, slow-moving, complex earthslide earthflows. According to Differential GPS measurements, these landslides move at velocities of up to several metres per year. Electrical resistivity tomography profiles show that most of the landslides are mainly surficial. Time-series analyses of precipitation reveal that rainfall events that are not exceptionally intensive can reactivate these landslides. This characteristic and the development of these landslides on low-gradient slopes are explained using the results obtained from the geotechnical and mineralogical analyses. We find that the smectite clay minerals detected in the mobilized geological formations, combined with the tropical climate of the northern Andean region, induce the observed weak slope stability conditions. The conceptual model for the studied landslides may aid in assessing landslide-prone areas in Loja and other Neogene intramontane basins of the Andes and can help to mitigate the associated risks.

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.

Application of Terrestrial Laser Scanner to the Assessment of the Evolution of Diachronic Landslides

During the diachronic evolution of landslides, slope-morphology changes may be detected and assessed by using high-resolution digital models. Slope deformation is detected by scanning sequences over a given time period. This paper presents the results found combining TLS digital models and Global Navigation Satellite Systems in the detection and assessment of reactivations and differential displacements of two slides located at the SW of Sierra Nevada (Spain) between 2008 and 2010. In the first landslide a maximum downward movement of 1.2 m at the top was measured, whereas below the middle part of the mass, 1.3 m of maximum advance was established with a maximum displacement gradient of 1.04 m/year. In the second landslide, downward displacements with gradients between 0.32 m and 0.56 m/year were found, corresponding to rupture movements in incipient to initial stages of evolution. The combined use of TLS and GNSS enabled a quantification and mapping of complementary terrain features which are considered useful in forecasting further activity and slope evolution of these landslides. The high resolution and accuracy of the techniques applied offer broad possibilities in the spatial location of the slope movement and also in forecasting its diachronic activity.

Factor Selection Procedures in a Google EarthTM Aided Landslide Susceptibility Model: Application to the Beiro River Basin (Spain)

A procedure to select the controlling factors connected to the slope instability has been defined. It allowed to assess the landslide susceptibility in the Rio Beiro basin (about 10 km2) over the north-eastern area of the city of Granada (Spain). Field and remote (Google EarthTM) recognition techniques allowed to generate a landslide inventory consisting in 127 phenomena. Univariate tests, using both association coefficients and validation results of single parameter susceptibility models, allowed to select among 15 controlling factors the ones that resulted as good predictor variables; these have been combined for unique conditions analysis and susceptibility maps were finally prepared. In order to verify both the goodness of fit and the prediction skill of the susceptibility models, two different validation procedures were applied and compared. Both procedures are based on a random partition splitting of the landslide archive for producing a test and a training subset. The relative error, considered between the intersected target landslides by the different susceptibility classes, was used to estimate the predictive skill of the maps.

The Calaiza landslide on the coast of Granada (Andalusia, Spain)

The Costa Tropical in Granada Province, in Southern Spain, was intensively developed during the 1980s and 90s. A complex of several residential communities was built on the eastern slope of the coastal Cerro Gordo hill (Almuñécar), on the pre-existing Calaiza landslide. This was not identified in the preliminary technical studies, thus giving rise to a set of incidents associated with this unforeseen unstable slope. To ensure sea views from all the houses, excavations and fillings were carried out, creating a stepped slope, on which the new foundations of structures and roads were located and subsequently damaged by an increasing number of cracks and deformations, leading to 42 houses becoming ruins in the period 2003–2016. Since 1990, annual and monthly rainfall has been variable in the area, and some rainfall peaks were eventually associated with damage proliferation, although more frequently damage was recorded during dry or low rainfall seasons, when water infiltrated from breaks in pipelines. This damage results from a combination of sliding and bad construction practices at increasing rates from dry to humid periods or during heavy rains. An overall perspective of the geotechnical and geomorphological features of the study area, the landslide reactivation, and its correlation with the damage evolution, as well as its legal consequences, is presented here.