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En el lecho de la laguna de Altillo Chica, situada en el municipio manchego de Lillo, se observan trazas, a modo de surco, dejadas por materiales pétreos, de distintos tamaños, al desplazarse. El origen de estas estructuras de erosión (groove marks) en superficies tan llanas todavía es controvertido. En este trabajo se estudian las propiedades físicas, estructurales y resistentes del sedimento lagunar que pudieran justificar la formación de dichas estructuras. El sedimento, que se ha caracterizado como limo yesífero, presenta unos parámetros resistentes muy elevados que no justifican por sí solos los movimientos de los bloques en pendientes tan bajas. Los elevados valores de resistencia pueden deberse a la humedad higroscópica y capacidad de succión de estos depósitos Altillo Chica is a playa lake, located in Lillo (Central Spain), where long trails are left behind by rocks up to several centimetres in size, as they move across the bed. The mechanisms of formation of these sedimentary structures (groove marks) are still controversial. In this work the physical, structural and resistant properties of the sediment that could explain the formation of these structures are studied. The sediment, which is characterized as silt sized gypsum, has high resistance parameters that do not justify by themselves the movements of objects on surfaces with very low slopes. The high shear stress of these sediments can be related to the high hygroscopic humidity and suction

En el lecho de la laguna de Altillo Chica, situada en el municipio manchego de Lillo, se observan trazas, a modo de surco, dejadas por materiales pétreos, de distintos tamaños, al desplazarse. El origen de estas estructuras de erosión (groove marks) en superficies tan llanas todavía es controvertido. En este trabajo se estudian las propiedades físicas, estructurales y resistentes del sedimento lagunar que pudieran justificar la formación de dichas estructuras. El sedimento, que se ha caracterizado como limo yesífero, presenta unos parámetros resistentes muy elevados que no justifican por sí solos los movimientos de los bloques en pendientes tan bajas. Los elevados valores de resistencia pueden deberse a la humedad higroscópica y capacidad de succión de estos depósitos, Altillo Chica is a playa lake, located in Lillo (Central Spain), where long trails are left behind by rocks up to several centimetres in size, as they move across the bed. The mechanisms of formation of these sedimentary structures (groove marks) are still controversial. In this work the physical, structural and resistant properties of the sediment that could explain the formation of these structures are studied. The sediment, which is characterized as silt sized gypsum, has high resistance parameters that do not justify by themselves the movements of objects on surfaces with very low slopes. The high shear stress of these sediments can be related to the high hygroscopic humidity and suction

Reunión Ibérica sobre Fallas Activas y Paleosismología (3ª. 2018. Alicante). - Texto en español con resumen y palabras claves en inglés y español, El terremoto de Lorca de 2011 generó aceleraciones más altas de las esperadas debido a un fenómeno de directividad, condicionado por la velocidad de propagación de la ruptura cosismica en relación a la velocidad de las ondas de cizalla (Vs). En este trabajo se analizan los datos de dos tipos de ensayos realizados en el sondeo de investigación FAM-1, que atraviesa la fault gouge (FG): (1) testificación geofísica de velocidad de ondas acústicas (onda completa), y (2) ensayo down-hole (DH). La FG muestran valores de velocidades propias de rocas muy blandas o suelos rígidos. Dentro de la FG se observa una marcada anisotropía, con velocidades de propagación Vp más elevadas según la dirección de la zona de cizalla que aquellas según buzamiento. Los valores de Vs se encuentran por debajo de los 1000 m/s. Si además se considera la anisotropía, esto implicaría valores de Vs tan bajas como 680 ±25 m/s para las ondas de cizalla que viajan según buzamiento. = The Lorca earthquake (2011) generated larger ground acceleration than expected because of a directivity phenomenon. Directivity is influenced by the relationship between the velocity of the propagation of the coseismic rupture and the velocity of the shear waves (Vs). In this work, data from two different tests that were carried out inside the research borehole FAM-1 are analysed: (1) full waveform acoustic logging, and (2) Down-hole seismic testing. The FAM-1 borehole was drilled through more than 100 m of the fault gouge of the fault (FG). The FG shows low velocities, typical of a very weak rock or a stiff soil. A remarkable anisotropy in the velocity can be also observed within the FG, with higher velocities for Vp along the fault strike than those along fault dip. Vs values have been calculated below 1000 m/s. If we consider the anisotropy, the FG may have Vs as lower as 680 ±25 m/s propagating along dip., Departamento de Geodinámica, Estratigrafía y Paleontología, Universidad Complutense de Madrid, España, Instituto de Geociencias, Consejo Superior de Investigaciones Científicas, España, Instituto de Geociencias, Universidad Complutense de Madrid, España, Institut de Ciències de la Terra Jaume Almera, España, Análisis y Gestión del Subsuelo S.L., España, Departamento de Geología y Geoquímica, Universidad Autónoma de Madrid, España, Instituto Geológico y Minero de España, España

En este trabajo se presenta el estudio de los parámetros mecánicos de la roca de falla (fault gouge) de la falla de Alhama de Murcia (FAM) próxima al bloque levantado. Esta falla es una de las más activas de la Península Ibérica y destaca por tener segmentos con un espesor de roca de falla (FG) exhumada de 50-80 m de espesor en régimen frágil. Su composición mineralógica se compone mayoritariamente por minerales del grupo de la mica (moscovita y paragonita) y cuarzo; en la fracción arcillosa predomina la ¡Hita acompañada por caolinita. Muestra una marcada fábrica tectónica caracterizada por la orientación preferente de los minerales laminares según una textura anastomosada que controla la resistencia mecánica de la falla. Para este estudio se han tomado muestras inalteradas procedentes de dos sondeos sobre los que se han realizado distintos ensayos de esfuerzo-deformación considerando diferentes orientaciones de los esfuerzos respecto a la fábrica. El ángulo de fricción (50°) para los planos orientados desfavorablemente. Estos elevados valores fueron obtenidos también en muestras remoldeadas de FG sin orientaciones preferentes We present the results of the mechanical parameters of natural clay rich fault-rock (fault gouge) from one of the most active faults in the Iberian Peninsula, Alhama de Murcia Fault (FAM). FAM shows segments partially formed by exhumed fine grained fault gouge (FG) with a 50-80 m thickness developed mainly in a brittle regime. It is composed mainly by mica (muscovite and paragonite) and quartz, the clay minerals are mainly illite with some caolinite. The FG shows a notable tectonic fabric characterized by the preferred orientation of plate -like minerals arranged in an anastom osing texture which controls the mechanical behavior of the fault. Undisturbed samples, taken from two fault observatory boreholes, have been used for laboratory tests. The result of the study shows that there is important variability in strength properties depending on the stress orientation in relation to fabric. The friction angle (rp) varies between very low values (16°-26°) for planes oriented favorably to the tectonic fabric to very high values (>50°) for planes unfavorably oriented. This high value of friction angle was a lso obtained in reconstructed and not oriented FG samples

En este trabajo se presenta el estudio de los parámetros mecánicos de la roca de falla (fault gouge) de la falla de Alhama de Murcia (FAM) próxima al bloque levantado. Esta falla es una de las más activas de la Península Ibérica y destaca por tener segmentos con un espesor de roca de falla (FG) exhumada de 50-80 m de espesor en régimen frágil. Su composición mineralógica se compone mayoritariamente por minerales del grupo de la mica (moscovita y paragonita) y cuarzo; en la fracción arcillosa predomina la ¡Hita acompañada por caolinita. Muestra una marcada fábrica tectónica caracterizada por la orientación preferente de los minerales laminares según una textura anastomosada que controla la resistencia mecánica de la falla. Para este estudio se han tomado muestras inalteradas procedentes de dos sondeos sobre los que se han realizado distintos ensayos de esfuerzo-deformación considerando diferentes orientaciones de los esfuerzos respecto a la fábrica. El ángulo de fricción (50°) para los planos orientados desfavorablemente. Estos elevados valores fueron obtenidos también en muestras remoldeadas de FG sin orientaciones preferentes, We present the results of the mechanical parameters of natural clay rich fault-rock (fault gouge) from one of the most active faults in the Iberian Peninsula, Alhama de Murcia Fault (FAM). FAM shows segments partially formed by exhumed fine grained fault gouge (FG) with a 50-80 m thickness developed mainly in a brittle regime. It is composed mainly by mica (muscovite and paragonite) and quartz, the clay minerals are mainly illite with some caolinite. The FG shows a notable tectonic fabric characterized by the preferred orientation of plate -like minerals arranged in an anastom osing texture which controls the mechanical behavior of the fault. Undisturbed samples, taken from two fault observatory boreholes, have been used for laboratory tests. The result of the study shows that there is important variability in strength properties depending on the stress orientation in relation to fabric. The friction angle (rp) varies between very low values (16°-26°) for planes oriented favorably to the tectonic fabric to very high values (>50°) for planes unfavorably oriented. This high value of friction angle was a lso obtained in reconstructed and not oriented FG samples

[EN] We present the results of the mechanical parameters of natural clay rich fault-rock (fault gouge) from one of the most active faults in the Iberian Peninsula, Alhama de Murcia Fault (FAM). FAM shows segments partially formed by exhumed fine grained fault gouge (FG) with a 50-80 m thickness developed mainly in a brittle regime. It is composed mainly by mica (muscovite and paragonite) and quartz, the clay minerals are mainly illite with some caolinite. The FG shows a notable tectonic fabric characterized by the preferred orientation of plate-like minerals arranged in an anastomosing texture which controls the mechanical behavior of the fault. Undisturbed samples, taken from two fault observatory boreholes, have been used for laboratory tests. The result of the study shows that there is important variability in strength properties depending on the stress orientation in relation to fabric. The friction angle (φ) varies between very low values (16ᵒ-26ᵒ) for planes oriented favorably to the tectonic fabric to very high values (>50ᵒ) for planes unfavorably oriented. This high value of friction angle was also obtained in reconstructed and not oriented FG samples., [ES] En este trabajo se presenta el estudio de los parámetros mecánicos de la roca de falla (fault gouge) de la falla de Alhama de Murcia (FAM) próxima al bloque levantado. Esta falla es una de las más activas de la Península Ibérica y destaca por tener segmentos con un espesor de roca de falla (FG) exhumada de 50-80 m de espesor en régimen frágil. Su composición mineralógica se compone mayoritariamente por minerales del grupo de la mica (moscovita y paragonita) y cuarzo; en la fracción arcillosa predomina la illita acompañada por caolinita. Muestra una marcada fábrica tectónica caracterizada por la orientación preferente de los minerales laminares según una textura anastomosada que controla la resistencia mecánica de la falla. Para este estudio se han tomado muestras inalteradas procedentes de dos sondeos sobre los que se han realizado distintos ensayos de esfuerzo-deformación considerando diferentes orientaciones de los esfuerzos respecto a la fábrica. El ángulo de fricción (φ) varía desde valores mínimos (16ᵒ-26ᵒ) para los planos de rotura orientados favorablemente a la fábrica tectónica hasta valores máximos (>50ᵒ) para los planos orientados desfavorablemente. Estos elevados valores fueron obtenidos también en muestras remoldeadas de FG sin orientaciones preferentes., Este trabajo ha sido financiado por el proyecto INTERGEO (CGL2013-47412-C2- 1-P).

Se ha estudiado la composición mineralógica de los depósitos terciarios de la Cuenca del Guadiana a partir del análisis mediante Difracción de rayos X de 137 muestras. Los depósitos de la Cuenca del Guadiana presentan una gran homogeneidad mineralógica al estudiar la roca total. Están formados por filosilicatos, cuarzo y feldespato en menor proporción Esta aparente homogeneidad en la sucesión terciaria desaparece al analizar la fracción, The mineralogical composition of 137 samples collected from the tertiary sediments in the Guadiana Basin has been studied by X-Ray Diffractometry. The mineralogical composition for the whole-rock samples is remarkably homogeneous being rich in phyilosilicates, quartz, with minor feldspars. However, this homogeneity disappears when studying the fraction

The RISNAV project, financed by the Civil Defence Department of Navarre (Northern Spain), aims at assessing seismic risk of the entire region. The final goal of the project is the definition of emergency plans for future earthquakes. With this purpose, four main topics are covered: seismic hazard characterization, geotechnical classification, vulnerability assessment and damage estimation. In this work, the seismic hazard and vulnerability assessment studies are presented.

In this paper a geotechnical-siesmic amplification classification based on geological data is proposed for the Murcia region, (SE Spain). The structural damages caused during earthquake are controlled by local geological condition especially surface geology conditions and topography. The presence of some kind of soil type could produce increase in the intensity as a consequence of seismic wave amplification. The factor of amplification which can duplicate or triplicate the seismic waves is directly related to the geotechnical (dynamic) properties of geological materials. Regarding this fact, we have carried out geotechnical classification of the geological materials, in order to see their possible contribution to this local ground amplification. According to this classification the amplification effect in the earthquake area varies from nil, where bedrock is exposed to high where Plio-Quaternary fluvial and alluvial sediments are present

In this paper a geotechnical-siesmic amplification classification based on geological data is proposed for the Murcia region, (SE Spain). The structural damages caused during earthquake are controlled by local geological condition especially surface geology conditions and topography. The presence of some kind of soil type could produce increase in the intensity as a consequence of seismic wave amplification. The factor of amplification which can duplicate or triplicate the seismic waves is directly related to the geotechnical (dynamic) properties of geological materials. Regarding this fact, we have carried out geotechnical classification of the geological materials, in order to see their possible contribution to this local ground amplification. According to this classification the amplification effect in the earthquake area varies from nil, where bedrock is exposed to high where Plio-Quaternary fluvial and alluvial sediments are present

This work analyzes the geological source of the Mw 4.8 February 4 2002, Gérgal earthquake. The interpretation of local geological data, the relocation of the aftershocks sequence using a local velocity model, the focal mechanism calculation and the interferometric study of the area using RADAR images give evidences that support a tensional stress source with a rupture plane oriented NW-SE to NNE-SSW

This work analyzes the geological source of the Mw 4.8 February 4 2002, Gérgal earthquake. The interpretation of local geological data, the relocation of the aftershocks sequence using a local velocity model, the focal mechanism calculation and the interferometric study of the area using RADAR images give evidences that support a tensional stress source with a rupture plane oriented NW-SE to NNE-SSW

The illite crystallinity index of Kubler (1C) has been studied to establish the conditions of the last deformation stages in the Santa María de la Alameda shear zone. For this study, it has been used mainly the fine grained fraction of the samples (less than 2 mm) which is concentrated along small brittle fractures and zones of protocataclasitic material. The studied rocks give "illite crystallinity index" values between 0.35 D°2q and 0.25 D°2q, pointing to deformation conditions at temperatures which denotes a retrograde metamorphismo zone belonging to the epizone and anquizone. These results indicate a a rétrogradation condition for the late brittle deformation stage of the Santa Maria de alameda fault, in temperatures range between 255 and 200° C

Principles of fractal geometry have been applied to the description of quartz grain borders and to the assessment of deformation temperature in milonitic rocks at the Santa Maria de la Alameda Ductile Shear Zone (Central System). This shear zone have evolved during late variscan tectonic period in a large temperature range, which goes from regional metamorphic pick conditions (Amphibolite facies) to temperatures lower than for Greenschists facies. Using fractal dimension analysis techniques and the temperature calibration performed by Kruhl y Nega (1996), have been established a temperature sequence, diminishing from around 490°C to 325°C during the simultaneous processes of milonitization and retrogressive metamorphism. These results are in agreement with temperatures obtained from deformation mechanisms in quartz and potassium feldspar showming the validity of fractal geometry method to deformation temperature assessment

The RADAR interferometry (INSAR) is a modern technique that offers the possibility to identify and quantify surface displacements using phase differences from two different RADAR images (Massonnet and Feigl, 1998). The result of an interferometric study applied to the February 1 999 (Mb: 4.8) Mula (Murcia) earthquake is shown in this work. The available seismological data for this earthquake give different focal mechanisms (reverse or strike-slip mechanism) depending on the applied method. The five coseismic interferograms show that the Mula mainshock produced a very small surface deformation, less than expected for a pure reverse and swallow source. This evidence and the surface geological data support a NE-SO strike-slip fault (probably the Crevillente fault) to be the seismogenetic source

The RADAR interferometry (INSAR) is a modern technique that offers the possibility to identify and quantify surface displacements using phase differences from two different RADAR images (Massonnet and Feigl, 1998). The result of an interferometric study applied to the February 1 999 (Mb: 4.8) Mula (Murcia) earthquake is shown in this work. The available seismological data for this earthquake give different focal mechanisms (reverse or strike-slip mechanism) depending on the applied method. The five coseismic interferograms show that the Mula mainshock produced a very small surface deformation, less than expected for a pure reverse and swallow source. This evidence and the surface geological data support a NE-SO strike-slip fault (probably the Crevillente fault) to be the seismogenetic source

Principles of fractal geometry have been applied to the description of quartz grain borders and to the assessment of deformation temperature in milonitic rocks at the Santa Maria de la Alameda Ductile Shear Zone (Central System). This shear zone have evolved during late variscan tectonic period in a large temperature range, which goes from regional metamorphic pick conditions (Amphibolite facies) to temperatures lower than for Greenschists facies. Using fractal dimension analysis techniques and the temperature calibration performed by Kruhl y Nega (1996), have been established a temperature sequence, diminishing from around 490°C to 325°C during the simultaneous processes of milonitization and retrogressive metamorphism. These results are in agreement with temperatures obtained from deformation mechanisms in quartz and potassium feldspar showming the validity of fractal geometry method to deformation temperature assessment

In this work is shown how an active fold (the Sierra de Cartama fault) is marked by the drainage pattern and topography, besides of structural data. The Sierra de Cartama fold is an asymmetric fold with double plunge and determines the shape of an elongated saw in the Western Betic Chains (South of Spain). Watching the drainage patterns, it can be noticed how streams and creeks round the saw. The uplift of the saw raise the valleys steeply, even leaving a hanging valley ("wind gap ") at the western part of the structure. Regarding to these observations, the lateral propagation of the fold seems to be toward the west. The proposed structure implies the existence of a compressive neotectonic activity in the zone. The compressive horizontal direction is N10e-30eW, perpendicular to the fold axis. In this tectonic environment it could be possible to interpret a reverse fault in deep associated with the fold growth

The Santa Maria de Alameda (Madrid) Ductile Shear Zone is a complex mylonitic belt trending east -West and dipping 30°-60° southward. The hanging wall block sinks towards the South-Southeast. Its kinematics is in relation to an extensional tectonic regime with North-south stretching direction. This large structure belongs to the early stages of the Malagon tectonic period, where important faulting and dike emplacement were produced. The shearing process was developed in retrograde metamorphic conditions in a wide range of temperature, which goes from 400° C to 150° C. The age of this deformation is constrained by the variscan regional metamorphic peak and the intrusion of late variscan granitoids (Las Navas del Marques adamellites), being therefore, between early Namurian and Stephanian

The Santa Maria de Alameda (Madrid) Ductile Shear Zone is a complex mylonitic belt trending east -West and dipping 30°-60° southward. The hanging wall block sinks towards the South-Southeast. Its kinematics is in relation to an extensional tectonic regime with North-south stretching direction. This large structure belongs to the early stages of the Malagon tectonic period, where important faulting and dike emplacement were produced. The shearing process was developed in retrograde metamorphic conditions in a wide range of temperature, which goes from 400° C to 150° C. The age of this deformation is constrained by the variscan regional metamorphic peak and the intrusion of late variscan granitoids (Las Navas del Marques adamellites), being therefore, between early Namurian and Stephanian

Signs of recent tectonic activity are found at the Extremadura sector of Alentejo-Plasencia fault. This fault was active during the alpine compressional period as a sinistraI strike-slip fault at the foreland of a collisional zone and presents some activity from the Miocene to the Quaternary. Upper «Raña» deposits of Early Villafranquian age, present an around-2-meter-vertical-displacement at the north border of Alburquerque granitic massif. Close to this point old fluvial terraces of unknown age are folded and faulted, and low terraces (3 m above present river course) are jointed. In the tertiary Cañaveral pull-apart basin , at the Alcantara reservoir border, the fault disrupts a Tagus river fluvial terrace, which lies 80 m above the river course and has a probable Middle Pleistocene age. All these observations imply a vertical displacement which could be related to a slip rate less than 0.007 mm/year. If this fault is compared with other active faults of the Hesperian Massif, such as the Braganga-Manteigas one, it becomes clear that Alentejo-Plasencia fault is less active. There are though paleoseismicity structures associated to the Alentejo-Plasencia fault, such as liquefaction feature

Guadalquivir blue clays are strongly afected by physical weathering which Is responsible of considerable geotechnical problems in engineering works associated with landslides. Microfabric and mineralogy properties have been studied using the XRD and SEM, to asses possible changes in their internal properties with the weathering process. Different weathering profiles of this clays have been described using field criteria, on which mineralogical composition and microfabric aspects were assesed. The results have indicated that, the geotechnical problems are not caused by a change in mineralogical and chemical aspects, but rather a combination of slaking, brittleness and disaggregation, resulting from stress release. It has been shown also that these processes are stimulated by the presence of expansive type clay minerals in the sediment. However the interlaminar cation is Ca, where by the osmotic expansion is not determinative but rather the interlaminar one developed mostly between the aggregates.The most important element affected by this process Is the microfabric feature represented by discontinuios day matrix microfabric type, and existance of floculated aggregates in FE arrangement of clay plates. These arrengements favours fragmentation of the sediment into small aggregates with dessication and humectation cycle accelerated with the clay nature.

Signs of recent tectonic activity are found at the Extremadura sector of Alentejo-Plasencia fault. This fault was active during the alpine compressional period as a sinistraI strike-slip fault at the foreland of a collisional zone and presents some activity from the Miocene to the Quaternary. Upper «Raña» deposits of Early Villafranquian age, present an around-2-meter-vertical-displacement at the north border of Alburquerque granitic massif. Close to this point old fluvial terraces of unknown age are folded and faulted, and low terraces (3 m above present river course) are jointed. In the tertiary Cañaveral pull-apart basin , at the Alcantara reservoir border, the fault disrupts a Tagus river fluvial terrace, which lies 80 m above the river course and has a probable Middle Pleistocene age. All these observations imply a vertical displacement which could be related to a slip rate less than 0.007 mm/year. If this fault is compared with other active faults of the Hesperian Massif, such as the Braganga-Manteigas one, it becomes clear that Alentejo-Plasencia fault is less active. There are though paleoseismicity structures associated to the Alentejo-Plasencia fault, such as liquefaction feature

Alentejo-Plasencia fault was active during the alpine compressional phases with a sinistral strike-slip movement in two main stages. The fault geometry was straight and no important bendings formed during Paleogene, when the maximum shortening direction was close to N-S or NNE-SSW. During Miocene (Middle Aragonian) and related to the Neocastellana tectonic phase, the Alentejo-Plasencia fault still moved as a sinistraI strike-slip due to a NW-SE compression, but the Extremadura sector of the fault curved and bends formed along the fault at certain points where important lithologic changes were present. Several restraining and releasing bends formed; these latter creating pull-apart basins, some of them filled with continental clastic sediments. Most of the fault displacement (about 3 Km.) seems to be related to the alpine tectonics. The small displacement compared with the fault length is coherent with its location on a co//s/ona/ area foreland

Alentejo-Plasencia fault was active during the alpine compressional phases with a sinistral strike-slip movement in two main stages. The fault geometry was straight and no important bendings formed during Paleogene, when the maximum shortening direction was close to N-S or NNE-SSW. During Miocene (Middle Aragonian) and related to the Neocastellana tectonic phase, the Alentejo-Plasencia fault still moved as a sinistraI strike-slip due to a NW-SE compression, but the Extremadura sector of the fault curved and bends formed along the fault at certain points where important lithologic changes were present. Several restraining and releasing bends formed; these latter creating pull-apart basins, some of them filled with continental clastic sediments. Most of the fault displacement (about 3 Km.) seems to be related to the alpine tectonics. The small displacement compared with the fault length is coherent with its location on a co//s/ona/ area foreland

Guadalquivir blue clays are strongly afected by physical weathering which Is responsible of considerable geotechnical problems in engineering works associated with landslides. Microfabric and mineralogy properties have been studied using the XRD and SEM, to asses possible changes in their internal properties with the weathering process. Different weathering profiles of this clays have been described using field criteria, on which mineralogical composition and microfabric aspects were assesed. The results have indicated that, the geotechnical problems are not caused by a change in mineralogical and chemical aspects, but rather a combination of slaking, brittleness and disaggregation, resulting from stress release. It has been shown also that these processes are stimulated by the presence of expansive type clay minerals in the sediment. However the interlaminar cation is Ca, where by the osmotic expansion is not determinative but rather the interlaminar one developed mostly between the aggregates.The most important element affected by this process Is the microfabric feature represented by discontinuios day matrix microfabric type, and existance of floculated aggregates in FE arrangement of clay plates. These arrengements favours fragmentation of the sediment into small aggregates with dessication and humectation cycle accelerated with the clay nature.