J. D. Jiménez-Perálvarez

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.

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.

Landslide-risk mapping in a developing hilly area with limited information on landslide occurrence

Landslide risk was assessed at the basin scale, in terms of specific landslide risk, in a region with limited information on landslide occurrence. Specific landslide risk was mapped by combining the landslide-hazard map and vulnerability of the elements at risk. The assessment of landslide hazard was based both on the spatial-temporal probability of landslide occurrence and on landslide intensity. In this regard, a major problem to resolve was the landslide-occurrence probability. Thus, several procedures were performed, including remote-sensing-based techniques, photointerpretation, dendrochronology, and press news. On the other hand, vulnerability was studied based empirically on the inferred relationship between the hazard class and the likely damage that the landslide would cause. In this way, vulnerability was shown in terms of expected degree of loss by using property-loss criteria. The results reveal that specific landslide risk in the area is mainly low, since just 2.26% of zone showed either a possible or a likely specific landslide risk. Buildings, irrigation structures, and main roads cover 2.6% of the study zone while representing approximately 80% of the specific landslide risk. By contrast, croplands cover almost 50% of the area but represent only 7.1% of specific landslide risk. The results indicate that, although this empirical methodology is subject to some level of uncertainty, it can provide reasonable estimates of specific landslide risk over a large area despite lacking information on landslide occurrence.

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.