J. Chacón

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.

Isotopic dating of the mylonitization of the Azuaga Group in the Badajóz-Córdoba belt, SW Spain

ZusammenfassungAufgrund von Rb-Sr-Datierungen in Muskoviten ist für die M1Metamorphose und die damit verbundene Mylonitisierung der Ultramylonite der Las Grullas-Formation in der Azuaga-Gruppe, Badajóz-Córdoba-Gürtel, ein Alter von ca. 355 Ma (Spätes Tournais/Frühes Visé) festgestellt worden. Dieses Alter könnte mit dem Akkretionsproze\ (Sutur der Ossa-Morena-Zone zur Zentral-Iberischen-Zone) verbunden sein, der für Metamorphose und Mylonitisierung verantwortlich gemacht wird.Muskovit der Valencia de Las Torres-Formation spiegelt ein etwas geringeres Rb-Sr-Alter von ca. 337 Ma wieder. Die entsprechenden K-Ar-Alter zeigen, da\ es nach dem Ende der Metamorphose einige 20 Ma gedauert hat, bis die Gesteine unter die Schlie\ungstemperatur des Muskovits für K-Ar abgekühlt waren. Rb-Sr-Daten von Gesamtgesteinsproben zeigen, da\ die Las Grullas-Ultramylonite wahrscheinlich aus ordovizischen Granitoiden entstanden sind.AbstractOn the basis of Rb-Sr muscovite dating an age of about 355 Ma (Late Tournaisian/Early Visean) is assigned to the M1 metamorphism and associated mylonitization of the ultramylonites of the Las Grullas Formation in the Azuaga Group, Badajóz-Córdoba belt. This age may possibly be related to the accretion process (suturing of the Ossa-Morena Zone to the Central Iberian Zone) thought to be responsible for the metamorphism and mylonitization. Muscovite from the Valencia de Las Torres Formation displays a somewhat lower Rb-Sr age of about 337 Ma. The corresponding K-Ar ages indicate that after the termination of the metamorphism it took some 20 Ma before the rocks had cooled below the closure temperature of muscovite to K-Ar. Whole-rock Rb-Sr data indicate that the Las Grullas ultramylonites were probably derived from Ordovician granitoids.ResumenDataciones Rb-Sr en moscovitas de alrededor de 355 Ma (Tournaisiense tardío a Viseense) se asignan al metamorfismo M1 y se asocian a la milonitización de ultramilonitas de la Formación Las Grullas en el Grupo de Azuaga, Eje Badajóz-Córdoba. Esta edad podría posiblemente datar el proceso de acreción (sutura de la Zona de Ossa-Morena a la Zona Centro-Ibérica) interpretado como responsable del metamorfismo y milonitización. Moscovita de la Formación Valencia de Las Torres indice una edad Rb-Sr un poco más bajo de cerca de 337 Ma. Las correspondientes edades K-Ar indican que después de la terminación del metamorfismo, se tardó cerca de 20 Ma antes que las rocas se enfriaran por debajo de la temperatura de cierre de la moscovita para K-Ar. Datos Rb-Sr de roca total indican que las ultramilonitas de Las Grullas posiblemente se deriven de granitoides ordovicicos.кРАткОЕ сОДЕРжАНИЕс пОМОЩьУ МЕтОДА Rb/Sr ОпР ЕДЕлИлИ ВОжРАст m1 МЕтАМОРФИжМА пО МУскОВИтАМ И сВьжА ННОИ с НИМ МИлОНИжАцИ И УльтРАМИлОНИтОВ ФОР МАцИИ Las Grullas гРУппы Azuaga, пОьсА Badajoz-Cordiba В пРИМЕРНО 355 М ИллИОНОВ лЕт — пОжДНИИ тУРНЕИс кИИ/РАННИИ ВИжЕИскИИ ВЕкА/-. пРОцЕссы МЕтАМОРФИж МА И МИлУНИжАцИИ пРЕД ОпРЕДЕлИлИ ВОжРАст ЁтИх пОРОД. с п ОМОЩьУ МЕтОДА Rb/Sr УДАлОсь ОпРЕДЕлИть, Ч тО ВОжРАст ФОРМАцИИ Valencia de Las Torres пО МУскОВИтУ, кАк НЕс кОлькО БОлЕЕ МОлОДОИ, И сОстАВльЕт пРИМЕРН О тОлькО 337 МИллИОНОВ л Ет. ОДНАкО, ВОжРАст, ОпРЕДЕлЕННы И пО МЕтОДУ кАлИь/АРгО НА, жАстАВльЕт пРЕДпОлА гАть, ЧтО пОслЕ жАВЕРш ЕНИь МЕтАМОРФжМА пРОшлО ЕЩЕ НЕскОлькО ДЕсьткОВ МИллИОНОВ лЕт, пОкА пОРОДы НЕ Охл АДИлИсь НИжЕ тЕМпЕРА тУРы ОБРАжОВАНИь МУскОВИ тОВ, пОДхОДьЩИх Дль Оп РЕДЕлЕНИь пО k/Ar МЕтОДУ. пРИ ИсслЕД ОВАНИИ ОБЩЕИ пРОБы с пОМОЩьУ МЕтОДА Rb/Sr Уст АНОВИлИ, ЧтО УльтРАМИ лОНИты Las Grallas, ВЕРОьтНО, ОБРАжОВАл Ись Иж гРАНИтОИДОВ ОРДОВИкА.

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.

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.

Weathering, swelling behaviour and index properties of neogene marls from the Granada basin (South Spain)

The geotechnical features of the three members of the Neogene of the Grenade basin (South Spain) are described from 170 samples. The upper member shows 30 meters of soil with 46–90% silt, 5–52% clays (34 to 82% smectitic), high durability-high plasticity and high swelling potential. In the upper 10 meters, some very local layers of silts and gypsum are observed and at the bottom 20 meters of detritic deposits. The middle member is composed by 80 to 250 meters of marly soils with 40–92% of silt fraction, 5 to 60% of clay fraction (40 to 100% illitic), high weathering index and low swelling potential. Some turbiditic and evaporitic deposits, several tens of meters thick, are also locally interlayered. The upper member is composed by 100 meters of detritic-carbonated soils with 0–88% of sand fraction and 5–57% of clay fraction (30–80% smectitic). The weathering index and the swelling potential are similar to the middle member, even with its higher smectitic contain and because of the swelling inhibition derived from the higher carbonate and sulfate proportions.

Soil liquefaction potential induced by the Andalusian earthquake of 25 December 1884

On 25 December 1884, an earthquake of epicentral intensityI0 = IX in the MSK scale caused great damage ‘in a large area in the provinces of Granada and Málaga, in the south of Spain. The reports of the Spanish, Italian and French Commissions that studied the earthquake described ground phenomena in seven different sites which can be identified as soil liquefaction.By means of dynamic penetration tests carried out in the above sites, the corresponding soil profiles (based on SPT data and water table depth) were established, and the occurrence of liquefaction was proved in five out of seven of these sites. Also, the intensities at such locations and the magnitude of the earthquake were estimated.From the geotechnical data and the cyclic stress ratio induced by the earthquake, liquefaction conditions were confirmed in all the five sites which presumably liquefied. Then, possible values of the minimum ground surface accelerations necessary for the onset of liquefaction at each location were calculated. The results obtained were completed with data reported in six liquefaction case studies from Japan and the United States, from which design charts relating soil acceleration with normalized SPT values for different intensity levels were drawn.Finally, by using standard attenuation curves, the above data were translated into epicentral distances, and good agreement with the known epicentral area was found. As a result, a consistent approach for liquefaction hazard and source location problems has been developed. The proposed method combines in its formulation historical evidence and earthquake engineering techniques.