Radar interferometry techniques for the study of ground subsidence phenomena: a review of practical issues through cases in Spain

Subsidence related to multiple natural and human-induced processes affects an increasing number of areas worldwide. Although this phenomenon may involve surface deformation with 3D displacement components, negative vertical movement, either progressive or episodic, tends to dominate. Over the last decades, differential SAR interferometry (DInSAR) has become a very useful remote sensing tool for accurately measuring the spatial and temporal evolution of surface displacements over broad areas. This work discusses the main advantages and limitations of addressing active subsidence phenomena by means of DInSAR techniques from an end-user point of view. Special attention is paid to the spatial and temporal resolution, the precision of the measurements, and the usefulness of the data. The presented analysis is focused on DInSAR results exploitation of various ground subsidence phenomena (groundwater withdrawal, soil compaction, mining subsidence, evaporite dissolution subsidence, and volcanic deformation) with different displacement patterns in a selection of subsidence areas in Spain. Finally, a cost comparative study is performed for the different techniques applied.

A new approach for semi-automatic rock mass joints recognition from 3D point clouds

Rock mass characterization requires a deep geometric understanding of the discontinuity sets affecting rock exposures. Recent advances in Light Detection and Ranging (LiDAR) instrumentation currently allow quick and accurate 3D data acquisition, yielding on the development of new methodologies for the automatic characterization of rock mass discontinuities. This paper presents a methodology for the identification and analysis of flat surfaces outcropping in a rocky slope using the 3D data obtained with LiDAR. This method identifies and defines the algebraic equations of the different planes of the rock slope surface by applying an analysis based on a neighbouring points coplanarity test, finding principal orientations by Kernel Density Estimation and identifying clusters by the Density-Based Scan Algorithm with Noise. Different sources of information —synthetic and 3D scanned data— were employed, performing a complete sensitivity analysis of the parameters in order to identify the optimal value of the variables of the proposed method. In addition, raw source files and obtained results are freely provided in order to allow to a more straightforward method comparison aiming to a more reproducible research.

Mechanical Properties and Durability of CNT Cement Composites

In the present paper, changes in mechanical properties of Portland cement-based mortars due to the addition of carbon nanotubes (CNT) and corrosion of embedded steel rebars in CNT cement pastes are reported. Bending strength, compression strength, porosity and density of mortars were determined and related to the CNT dosages. CNT cement paste specimens were exposed to carbonation and chloride attacks, and results on steel corrosion rate tests were related to CNT dosages. The increase in CNT content implies no significant variations of mechanical properties but higher steel corrosion intensities were observed.

Relationship between static and dynamic elastic modulus of calcarenite heated at different temperatures: the San Julián's stone

The San Julián’s stone is the main material used to build the most important historical buildings in Alicante city (Spain). This paper describes the analysis developed to obtain the relationship between the static and the dynamic modulus of this sedimentary rock heated at different temperatures. The rock specimens have been subjected to heating processes at different temperatures to produce different levels of weathering on 24 specimens. The static and dynamic modulus has been measured for every specimen by means of the ISRM standard and ultrasonic tests, respectively. Finally, two analytic formulas are proposed for the relationship between the static and the dynamic modulus for this stone. The results have been compared with some relationships proposed by different researchers for other types of rock. The expressions presented in this paper can be useful for the analysis, using non-destructive techniques, of the integrity level of historical constructions built with San Julián’s stone affected by fires.

Self-heating function of carbon nanofiber cement pastes

The viability of carbon nanofiber (CNF) composites in cement matrices as a self-heating material is reported in this paper. This functional application would allow the use of CNF cement composites as a heating element in buildings, or for deicing pavements of civil engineering transport infrastructures, such as highways or airport runways. Cement pastes with the addition of different CNF dosages (from 0 to 5% by cement mass) have been prepared. Afterwards, tests were run at different fixed voltages (50, 100 and 150V), and the temperature of the specimens was registered. Also the possibility of using a casting method like shotcrete, instead of just pouring the fresh mix into the mild (with no system’s efficiency loss expected) was studied. Temperatures up to 138 °C were registered during shotcrete-5% CNF cement paste tests (showing initial 10 °C/min heating rates). However a minimum voltage was required in order to achieve a proper system functioning.

Fire-resistance, physical, and mechanical characterization of particleboard containing Oceanic Posidonia waste

In this work, particleboards manufactured with Oceanic Posidonia waste and bonded with cement are investigated. The particleboards are made with 3/1.5/0.5 parts of cement per part of Posidonia waste. The physical properties of bulk density, swelling, surface absorption, and dimensional changes due to relative humidity as well as the mechanical properties of modulus of elasticity, bending strength, surface soundness, perpendicular tensile strength and impact resistance are studied. In terms of the above properties, the best results were obtained for particleboards with high cement content and when the waste “leaves” are treated (crushed) before board fabrication, due to internal changes to the board structure under these conditions. Based on the results of fire tests, the particleboard is non-flammable without any fire-resistant treatment.

Assessment of corrective measures for alleviating slope instabilities in carbonatic Flysch formations: Alicante (SE of Spain) case study

As is well known, in order to select remediation measures to correct or prevent slope instabilities, it is essential to identify and characterize the instability mechanisms. This task is especially complex for heterogeneous rock masses such as Flysch formations. This paper addresses the assessment of corrective measures used in carbonate Flysch formations by classifying and grouping field data reported in an available database in order to associate this data with various instability mechanisms and stratigraphic column types as well as with the corrective measures taken to stabilise them. For this purpose, 194 slopes have been geomechanically characterized, mainly by considering the observed instability mechanisms. The corrective measures that were applied have been evaluated for their suitability and performance, and, if applicable, the causes of their malfunction have been also studied. As a result, some guidelines based on the observed behaviour and the suitability of the correction measure as a function of instability type are proposed for similar slopes.

Characterization of the instability mechanisms affecting slopes on carbonatic Flysch: Alicante (SE Spain), case study

The studied Flysch sequence of Alicante occupies a widely populated area crossed by main communication routes. The slopes existing on this area usually suffer slope instabilities that cause substantial damage and a very high maintenance cost. In order to assess the type of instability mechanisms affecting these heterogeneous carbonatic slopes, in this paper a wide inventory of 194 Flysch rock slopes has been performed, reporting the existing lithologies, their competence and their relative arrangement and the geometrical relationship between bedding and the slope and the associated instability mechanism. All these data have been jointly used for performing an instability mechanisms characterization. For systematically characterizing the wide type of complex rock exposures existing in the study area, they are divided into basic units referred as lithological pattern columns to which the different observed instability mechanisms are associated. Inventoried instability mechanisms are diverse and sometimes are combined with each other. Rockfalls are a very common instability mechanism associated to the differential weathering and sapping of the marly lithologies which are present in a wide number of geometrical combinations. The other instability mechanisms closely depend on the combination of the geometrical and lithological parameters. Therefore, this work provides a new basic tool which can be easily used during preliminary project stages for knowing the instability mechanisms which can affect rock slopes excavated on carbonatic Flysch heterogeneous geological formations.

Monitoring an earthfill dam using differential SAR interferometry: La Pedrera dam, Alicante, Spain

Surface displacement at the dykes of La Pedrera reservoir (SE Spain) has been measured by satellite differential Synthetic Aperture Radar (SAR) interferometry. At the main dyke, a displacement of about 13 cm along the satellite line of sight has been estimated between August 1995 and May 2010, from a dataset composed by ERS-1, ERS-2 and Envisat-ASAR images. Two independent short-term processing tasks were also carried out with ERS-2/Envisat-ASAR (from June 2008 to May 2010) and TerraSAR-X (from August 2008 to June 2010) images which have shown similar spatial and temporal displacement patterns. The joint analysis of historical instrument surveys and DInSAR-derived data has allowed the identification of a long-term deformation process which is reflected at the dam's surface and is also clearly recognizable in the inspection gallery. The plausible causes of the displacements measured by DInSAR are also discussed in the paper. Finally, DInSAR data have been used to compute the long-term settlement of La Pedrera dam, showing a good agreement with external studies. Consequently, this work demonstrates the integration of DInSAR with in-situ techniques which helps provide a complete spatial vision of the displacements in the dam thereby helping to differentiate the causal mechanisms.

Temperature influence on the physical and mechanical properties of a porous rock: San Julian's calcarenite

This work discusses the results from tests which were performed in order to study the effect of high temperatures in the physical and mechanical properties of a calcarenite (San Julian's stone). Samples, previously heated at different temperatures (from 105 °C to 600 °C), were tested. Non-destructive tests (porosity and ultrasonic wave propagation) and destructive tests (uniaxial compressive strength and slake durability test) were performed over available samples. Furthermore, the tests were carried out under different conditions (i.e. air-cooled and water-cooled) in order to study the effect of the fire off method. The results show that uniaxial compressive strength and elastic parameters (i.e. elastic modulus and Poisson's ratio), decrease as the temperature increases for the tested range of temperatures. A reduction of the uniaxial compressive strength up to 35% and 50% is observed in air-cooled and water-cooled samples respectively when the samples are heated to 600 °C. Regarding the Young's modulus, a fall over 75% and 78% in air-cooled and water-cooled samples respectively is observed. Poisson's ratio also declines up to 44% and 68% with the temperature in air-cooled and water-cooled samples respectively. Slake durability index also exhibits a reduction with temperature. Other physical properties, closely related with the mechanical properties of the stone, are porosity, attenuation and propagation velocity of ultrasonic waves in the material. All exhibit considerable changes with temperature.

Effect of aspect ratio on strain sensing capacity of carbon fiber reinforced cement composites

The electrical resistivity of carbon fiber reinforced cement composites (CFRCCs) has been widely studied, because of their utility as multifunctional materials. The percolation phenomenon has also been reported and modeled when the electrical behavior of those materials had to be characterized. Amongst the multiple applications of multifunctional cement composites the ability of a CFRCC to act as a strain sensor is attractive. This paper provides experimental data relating self-sensing function and percolation threshold, and studying the effect of fiber aspect ratio on both phenomena. Higher fiber slenderness permitted percolation at lower carbon fiber addition, affected mechanical properties and improved strain-sensing sensitivity of CFRCC, which was also improved if percolation had not been achieved.

Influence of using slag cement on the microstructure and durability related properties of cement grouts for micropiles

Today, the use of micropiles for different applications has become very common. In Spain, the cement grouts for micropiles are prepared using ordinary Portland cement and w:c ratio 0.5, although the micropiles standards do not restrict the cement type to use, provided that it reaches a certain compressive strength. In this study, the influence of using slag cement on the microstructure and durability related properties of cement grouts for micropiles have been studied until 90 hardening days, compared to an ordinary Portland cement. Finally, slag cement grouts showed good service properties, better than ordinary Portland cement ones.

Blending of industrial waste from different sources as partial substitution of Portland cement in pastes and mortars

Binary and ternary combinations of sewage sludge ash (SSA) with marble dust (MD), fly ash (FA) and rice husk ash (RHA) as replacement in Portland cement pastes, were assessed. Several tests were carried out at different curing ages: thermogravimetry, density, water absorption, ultrasonic pulse velocity and mechanical strengths. Pozzolanic effects of the mineral admixtures, densities similar to control sample and improved absorptions when combining waste materials were identified. In general, the compressive strength reaches or exceeds the cement strength class, and blending SSA, FA and RHA (30% cement replacement) increase of strength by 9%, compared to the control sample, was achieved.

Propiedades físicas y mecánicas de una calcarenita: la Piedra de San Julián

En este trabajo se estudian las características físico-mecánicas de la Piedra de San Julián y su comportamiento frente a procesos de calentamiento a temperaturas similares a las alcanzadas en un incendio, así como la puesta a punto y validación de métodos dinámicos no destructivos para el dictamen del estado de desgaste del material. El enfoque está orientado a los parámetros que más interesan en la utilización de la Piedra como material de construcción. Dado que esta Tesis se realiza por compendio de artículos, por razones prácticas y necesidades de publicación, el contenido de la misma está dividido en tres grandes bloques, como son: fluencia, exposición a altas temperaturas y relación entre módulos estáticos y dinámicos. Para el estudio de la fluencia o deformabilidad a largo plazo bajo carga constante se han realizado ensayos de carga estáticos de larga duración. Por otra parte, se ha efectuado un análisis del comportamiento reológico del hormigón en las distintas normativas, especialmente en el Código Modelo FIB (2010), y se ha buscado un paralelismo entre las previsiones del Código y los resultados obtenidos en los ensayos. Al mismo tiempo se han probado varios modelos reológicos que reproduzcan de forma precisa el comportamiento de la fluencia según el Código y los ensayos. Esto ha permitido ajustar una función, adaptando las especificaciones del Código modelo, que describe la deformación en el tiempo de la Piedra de San Julián. La validez teórica de esta ecuación alcanza períodos temporales similares a los existentes para los ensayos realizados con hormigón. El modelo reológico que se ha obtenido por ajuste de todo el período anterior, consta de cuatro celdas de Kelvin y predice igualmente la deformación por fluencia de la roca. La correcta evaluación de las deformaciones a largo plazo es necesaria siempre que se estudie la intervención en edificaciones históricas, bien sea variando la distribución de cargas, o simplemente realizando obras de mantenimiento de cierto calado. La influencia de la temperatura alcanzada y del proceso de enfriamiento utilizado, se ha analizado sobre 55 muestras de roca calentando a temperaturas de hasta 600 ºC y enfriando por dos métodos: al aire y mediante inmersión en agua, ambas a temperatura ambiente. Los parámetros controlados antes y después del proceso térmico han sido: porosidades abierta y total velocidad de propagación de ondas ultrasónicas, módulo de elasticidad, coeficiente de Poisson, resistencia a compresión uniaxial (UCS) y durabilidad según el ensayo de sequedad, humedad y desmoronamiento, Slake Durability Test (SDT). Como conclusiones más notables cabe destacar: la UCS disminuye en un 35% y en un 5O% según el enfriamiento se haya realizado al aire o por inmersión, mientras que el módulo de elasticidad se reduce entre un 75% y un 80%. Las conclusiones obtenidas son importantes para la determinación del daño estructural producido en un incendio, así como para evaluar la influencia del método de extinción. Por otra parte, pueden servir para estimar indirectamente la temperatura máxima alcanzada en un incendio, de cara a la determinación de los posibles efectos sobre otros elementos constructivos. Para la relación entre módulos estáticos y dinámicos se han estudiado 24 muestras con diferentes grados de deterioro. Con los datos obtenidos en los ensayos se han analizado estadísticamente quince modelos de relación con diferentes combinaciones de variables, y se ha construido la correspondiente matriz de correlación. El coeficiente de determinación más alto corresponde a una relación lineal entre ambos módulos. La determinación del módulo de elasticidad por medios no destructivos y de fácil implementación es muy útil cuando se trata de dictaminar sobre el envejecimiento de un material estructural de este tipo. El valor del módulo con respecto al de la roca intacta es un indicador de las características resistentes y grado de debilitamiento del material. Sin embargo, el módulo bajo cargas gravitatorias -estáticas- difiere en general del obtenido dinámicamente, de una manera diferente según el material que se analice. Aquí se ha obtenido una expresión, que correlaciona con un alto valor del coeficiente de determinación ambos módulos, para la roca estudiada. Los parámetros, relaciones y modelos estudiados y propuestos en esta tesis, suponen un importante avance científico de gran utilidad para la conservación y restauración del patrimonio de edificios y otras obras de carácter histórico-cultural construidas con la Piedra de San Julián. Asimismo, las conclusiones obtenidas y los medios y métodos empleados podrán ser extrapolados a otros materiales similares con las adaptaciones oportunas.