Microstructural deformation mechanisms of unsaturated granular soils

A discrete model for unsaturated granular soils has been developed. Three discrete entities have been defined: particles, water menisci and pores. Local interaction forces and water transfer mechanisms have been integrated into a model through the appropriate equilibrium and balance equations. The results of several numerical tests using this model have been described and discussed. Simulations include wetting and drying under load tests, the application of suction cycles and the effect of a deviatoric stress ratio on wetting-induced collapse. The model reacts just as true granular soil samples behave in laboratory tests. The model provides a new insight into the internal mechanisms leading to large-scale features of behaviour such as wetting-induced collapse or the increase in soil strength provided by suction. The paper also stresses that matric suction changes acting on a granular structure are capable of explaining most of the macroscopic features of stress–strain behaviour.Peer Reviewe

Analysis of micro-properties for triaxial behaviour on coarse aggregates using DEM

This paper presents an analysis of the mechanical behaviour of coarse granular aggregates using the discrete element method. A background reference for the conducted study is the set of results of a few large scale triaxial tests performed at the UPC geotechnical laboratory. The basic tool used to simulate some of the tests is the computer code PFC3D. Rockfill particles (they have the size of gravels, typically ranging from 1 cm to 4 cm) were simulated as breakable clusters of 3D balls. Particle breakage occurs in time according to fracture mechanic’s laws. The relationship between stress intensity at a given particle, the size of an initial defect (crack) and the relative humidity could be established. This information was introduced in the numerical analysis to derive criteria for particle breakage in time. The paper describes the preliminary results of the work in progress. The influence of some properties such as particle shape, porosity, toughness, and friction coefficient was studied. The actual shape of rock gravels has been approximated by means of clusters of spherical particles. Several arrangements, comprising a different number of particles, have been tested, having always as reference validation criterion the results from triaxial tests performed. The results of the modelling exercise are encouraging and test results are reasonably well reproduced. The model is fairly general and it has a number of interesting capabilities

Multi-technique approach to rockfall monitoring in the Montserrat massif (Catalonia, NE Spain)

Montserrat Mountain is located near Barcelona in Catalonia, in the northeast of Spain, and its massif is formed by conglomerate interleaved by siltstone/sandstone with steep slopes very prone to rockfalls. The increasing number of visitors in the monastery area, reaching 2.4 million per year, has highlighted the risk derived from rockfalls for this building area and also for the terrestrial accesses, both roads and the rack railway. A risk mitigation plan has been launched, and its first phase during 2014-2016 has been focused largely on testing several monitoring techniques for their later implementation. The results of the pilot tests, performed as a development from previous sparse experiences and data, are presented together with the first insights obtained. These tests combine four monitoring techniques under different conditions of continuity in space and time domains, which are: displacement monitoring with Ground-based Synthetic Aperture Radar and characterization at slope scale, with an extremely non-uniform atmospheric phase screen due to the stepped topography and atmosphere stratification; Terrestrial Laser Scanner surveys quantifying the frequency of small or even previously unnoticed rockfalls, and monitoring rock block centimetre scale displacements; the monitoring of rock joints implemented through a wireless sensor network with an ad hoc design of ZigBee loggers developed by ICGC; and, finally, monitoring singular rock needles with Total Station.Peer ReviewedPostprint (author's final draft

Monitoring sea level by tide gauges and GPS at Barcelona and Estartit harbours

The presentation is directed to the description of the actual situation of the geodetic infrastructure of Barcelona and l’Estartit sites for sea level determination and contribution to regional sea level risePostprint (published version

Nivelación hidrostática entre dos mareógrafos situados en el Puerto de Barcelona

Este estudio pretende relacionar los registros (marzo de 2013 a febrero de 2014) de dos mareógrafos situados en el Puerto de Barcelona y que se han denominado BCN2 y BCN3. El mareógrafo BCN2 pertenece a la RED de MAReógrafos de Puertos del Estado (REDMAR) y refiere los datos al NMMA1995 mientras que BCN3, propiedad de la Autoridad Portuaria de Barcelona, los refiere a la Red Topográfica del Puerto de Barcelona observada mediante técnicas GNSS. Ambos mareógrafos están separados unos 3Km. en línea recta y unos 8Km. por tierra. El objetivo ha sido determinar la diferencia existente entre los ceros de referencia de los dos mareógrafos. El nivel de mar observado por los mareógrafos, sin tener en cuenta la acción del oleaje, está afectado por la marea astronómica y la marea meteorológica. La marea meteorológica es de tipo aleatorio, por el contrario la marea astronómica es de carácter determinista y se puede resolver realizando el análisis de armónicos. Para ello, una vez realizado el control de calidad de los datos brutos, se utilizó la aplicación T_TIDE en MATLAB obteniendo como resultado para cada mareógrafo tres gráficas y dos ficheros. Las gráficas representan respectivamente el nivel del mar observado, la marea astronómica y la meteorológica o residuo y de los dos ficheros, uno corresponde al cálculo de los componentes armónicos, del que nos interesa la componente Z0 (nivel medio del mar) y el segundo contiene la componente meteorológica. Se puede concluir en que el cero de referencia de BCN3 está situado 0,096 metros por encima del NMMA 1995.Peer ReviewedPostprint (published version

Landslide monitoring using multi-temporal SAR interferometry with advanced persistent scatterers identification methods and super high-spatial resolution terraSAR-X Images

Landslides are one of the most common and dangerous threats in the world that generate considerable damage and economic losses. An efficient landslide monitoring tool is the Differential Synthetic Aperture Radar Interferometry (DInSAR) or Persistent Scatter Interferometry (PSI). However, landslides are usually located in mountainous areas and the area of interest can be partially or even heavily vegetated. The inherent temporal decorrelation that dramatically reduces the number of Persistent Scatters (PSs) of the scene limits in practice the application of this technique. Thus, it is crucial to be able to detect as much PSs as possible that can be usually embedded in decorrelated areas. High resolution imagery combined with efficient pixel selection methods can make possible the application of DInSAR techniques in landslide monitoring. In this paper, different strategies to identify PS Candidates (PSCs) have been employed together with 32 super high-spatial resolution (SHR) TerraSAR-X (TSX) images, staring-spotlight mode, to monitor the Canillo landslide (Andorra). The results show that advanced PSI strategies (i.e., the temporal sub-look coherence (TSC) and temporal phase coherence (TPC) methods) are able to obtain much more valid PSs than the classical amplitude dispersion (DA) method. In addition, the TPC method presents the best performance among all three full-resolution strategies employed. The SHR TSX data allows for obtaining much higher densities of PSs compared with a lower-spatial resolution SAR data set (Sentinel-1A in this study). Thanks to the huge amount of valid PSs obtained by the TPC method with SHR TSX images, the complexity of the structure of the Canillo landslide has been highlighted and three different slide units have been identified. The results of this study indicate that the TPC approach together with SHR SAR images can be a powerful tool to characterize displacement rates and extension of complex landslides in challenging areasPeer ReviewedPostprint (published version

Two decades of GPS/GNSS and DInSAR monitoring of Cardona salt mines (NE of Spain) – natural and mining-induced mechanisms and processes

Cardona area presents surface rising and subsidence active movements. In 1999 a series of sinkholes appeared due to the infiltration of Cardener River water into the mine tunnels, damaging surface infrastructures. Since then, high precision GNSS/GPS was used annually to position a network of 40 points spread over the area. GNSS/GPS work is carried out with the Fast-Static (FS) method. Additionally the surface movements have been monitored with satellite Differential Interferometry Synthetic Aperture Radar (DInSAR). Results indicate that the movement has a complex spatial distribution although consistent along time. Some areas show surface rising during the last two decades, while other areas show subsidence. The use of the two techniques allowed to determine the most plausible causes of these movements generated by a set of interwoven natural and human-induced complex processes.Peer ReviewedPostprint (published version

Mejoras introducidas en la red local de monitorización de movimientos de Cardona al trabajar con doble constelación GNSS

Alrededor de la localidad de Cardona (Barcelona, España) la explotación minera ha provocado subsidencias y otros desórdenes en superficie. En 1997 se estableció en la zona una red local de unos 40 puntos, para control de movimientos mediante GPS (método Estático-Rápido), con campañas anuales. En la última campaña de campo (octubre de 2008) se ha tenido ocasión de emplear cuatro receptores de doble frecuencia y de doble constelación, capaces de registrar y procesar las portadoras de los satélites GPS americanos y de los GLONASS rusos. Se han procesado las baselíneas de dos maneras diferentes: con todos los observables o bien sólo con los de GPS. Como era de esperar, el procesado con la doble constelación introduce una muy ligera mejora operativa de precisión al disponer de mayor número de satélites. La desviación típica de una serie de 34 cierres de triángulos observados pasa de 4 mm (GPS) a 3 mm (GPS+GLONASS) en planimetría, y de 6 mm (GPS) a 4 mm (GPS+GLONASS) para la componente altimétrica.Postprint (published version

Estudio del geoide en el parque nacional de Doñana

En el marco de los proyectos de la DGICyT “Procesos hidrogeológicos y geomorfológicos en los humedales del área de Doñana” y “Análisis de la dinámica del sistema acuífero de Doñana y sus relaciones con la evolución reciente del modelado dunar y con los usos del terreno y del acuífero” (Madre I y Madre II, respectivamente), se ha establecido una red GPS enlazada con la red REGENTE y dotada de cota ortométrica en todos sus puntos mediante nivelación geométrica y medidas de gravedad. Uno de los objetivos de estas redes es el de analizar y ajustar los modelos de geoide existente IBERGEO95 y EGG97, así como de calcular un nuevo modelo que se adapte a la zona y que permita facilitar el establecimiento de un modelo hidrogeológico para este área. Un modelo de geoide de precisión permitirá convertir las cotas de los posicionamientos GPS de elipsoidales a ortométricas. Esto es fundamental para los trabajos de modelado hidrológico superficial y subterráneo que se están llevando a cabo en el entorno del Parque Nacional de Doñana. Contar con un modelo de geoide bien escalado localmente también ha sido un punto clave para el adecuado ajuste de un MDT de la marisma obtenido mediante Láser Escáner Aerotransportado por encargo de la Confederación Hidrográfica del Guadalquivir. Por otra parte, las singularidades del campo gravitatorio podrán corroborar la existencia de algunas estructuras geológicas tipo falla regional. En esta comunicación se resumen los trabajos realizados hasta la fecha y se presenta el estado actual del modelo de geoide.Peer ReviewedPostprint (published version

RockGIS: a GIS-based model for the analysis of fragmentation in rockfalls

A rockfall is a mass instability event frequently observed in road cuts, open pit mines and quarries, steep slopes and cliffs. After its detachment, the rock mass may disaggregate and break due to the impact with the ground surface, thus producing new rock fragments. The consideration of the fragmentation of the rockfall mass is critical for the calculation of the trajectories of the blocks and the impact energies and for the assessment of the potential damage and the design of protective structures. In this paper, we present RockGIS, a GIS-based tool that simulates stochastically the fragmentation of the rockfall, based on a lumped mass approach. In RockGIS, the fragmentation is triggered by the disaggregation of the detached rock mass through the pre-existing discontinuities just before the impact with the ground. An energy threshold is defined in order to determine whether the impacting blocks break or not. The distribution of the initial mass between a set of newly generated rock fragments is carried out stochastically following a power law. The trajectories of the new rock fragments are distributed within a cone. The fragmentation model has been calibrated and tested with a 10,000 m3 rockfall that took place in 2011 near Vilanova de Banat, Eastern Pyrenees, Spain.Peer ReviewedPostprint (author's final draft