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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.

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.