Uso de nubes de puntos 3D para identificación y caracterización de familias de discontinuidades planas en afloramientos rocosos y evaluación de la calidad geomecánica

En este trabajo se estudia el uso de las nubes de puntos en 3D, es decir, un conjunto de puntos en un sistema de referencia cartesiano en R3, para la identificación y caracterización de las discontinuidades que afloran en un macizo rocoso y su aplicación al campo de la Mecánica de Rocas. Las nubes de puntos utilizadas se han adquirido mediante tres técnicas: sintéticas, 3D laser scanner y la técnica de fotogrametría digital Structure From Motion (SfM). El enfoque está orientado a la extracción y caracterización de familias de discontinuidades y su aplicación a la evaluación de la calidad de un talud rocoso mediante la clasificación geomecánica Slope Mass Rating (SMR). El contenido de la misma está dividido en tres bloques, como son: (1) metodología de extracción de discontinuidades y clasificación de la nube de puntos 3D; (2) análisis de espaciados normales en nubes de puntos 3D; y (3) análisis de la evaluación de la calidad geomecánica de taludes rocoso mediante la clasificación geomecánica SMR a partir de nubes de puntos 3D. La primera línea de investigación consiste en el estudio de las nubes de puntos 3D con la finalidad de extraer y caracterizar las discontinuidades planas presentes en la superficie de un macizo rocoso. En primer lugar, se ha recopilado información de las metodologías existentes y la disponibilidad de programas para su estudio. Esto motivó la decisión de investigar y diseñar un proceso de clasificación novedoso, que muestre todos los pasos para su programación e incluso ofreciendo el código programado a la comunidad científica bajo licencia GNU GPL. De esta forma, se ha diseñado una novedosa metodología y se ha programado un software que analiza nubes de puntos 3D de forma semi-automática, permitiendo al usuario interactuar con el proceso de clasificación. Dicho software se llama Discontinuity Set Extractor (DSE). El método se ha validado empleando nubes de puntos sintéticas y adquiridas con 3D laser scanner. En primer lugar, este código analiza la nube de puntos efectuando un test de coplanaridad para cada punto y sus vecinos próximos para, a continuación, calcular el vector normal de la superficie en el punto estudiado. En segundo lugar, se representan los polos de los vectores normales calculados en el paso previo en una falsilla estereográfica. A continuación se calcula la densidad de los polos y los polos con mayor densidad o polos principales. Estos indican las orientaciones de la superficie más representadas, y por tanto las familias de discontinuidades. En tercer lugar, se asigna a cada punto una familia en dependencia del ángulo formado por el vector normal del punto y el de la familia. En este punto el usuario puede visualizar la nube de puntos clasificada con las familias de discontinuidades que ha determinado para validar el resultado intermedio. En cuarto lugar, se realiza un análisis cluster en el que se determina la agrupación de puntos según planos para cada familia (clusters). A continuación, se filtran aquellos que no tengan un número de puntos suficiente y se determina la ecuación de cada plano. Finalmente, se exportan los resultados de la clasificación a un archivo de texto para su análisis y representación en otros programas. La segunda línea de investigación consiste en el estudio del espaciado entre discontinuidades planas que afloran en macizos rocosos a partir de nubes de puntos 3D. Se desarrolló una metodología de cálculo de espaciados a partir de nubes de puntos 3D previamente clasificadas con el fin de determinar las relaciones espaciales entre planos de cada familia y calcular el espaciado normal. El fundamento novedoso del método propuesto es determinar el espaciado normal de familia basándonos en los mismos principios que en campo, pero sin la restricción de las limitaciones espaciales, condiciones de inseguridad y dificultades inherentes al proceso. Se consideraron dos aspectos de las discontinuidades: su persistencia finita o infinita, siendo la primera el aspecto más novedoso de esta publicación. El desarrollo y aplicación del método a varios casos de estudio permitió determinar su ámbito de aplicación. La validación se llevó a cabo con nubes de puntos sintéticas y adquiridas con 3D laser scanner. La tercera línea de investigación consiste en el análisis de la aplicación de la información obtenida con nubes de puntos 3D a la evaluación de la calidad de un talud rocoso mediante la clasificación geomecánica SMR. El análisis se centró en la influencia del uso de orientaciones determinadas con distintas fuentes de información (datos de campo y técnicas de adquisición remota) en la determinación de los factores de ajuste y al valor del índice SMR. Los resultados de este análisis muestran que el uso de fuentes de información y técnicas ampliamente aceptadas pueden ocasionar cambios en la evaluación de la calidad del talud rocoso de hasta una clase geomecánica (es decir, 20 unidades). Asimismo, los análisis realizados han permitido constatar la validez del índice SMR para cartografiar zonas inestables de un talud. Los métodos y programas informáticos desarrollados suponen un importante avance científico para el uso de nubes de puntos 3D para: (1) el estudio y caracterización de las discontinuidades de los macizos rocosos y (2) su aplicación a la evaluación de la calidad de taludes en roca mediante las clasificaciones geomecánicas. Asimismo, las conclusiones obtenidas y los medios y métodos empleados en esta tesis doctoral podrán ser contrastadas y utilizados por otros investigadores, al estar disponibles en la web del autor bajo licencia GNU GPL.

Regional subsidence modelling in Murcia city (SE Spain) using 1-D vertical finite element analysis and 2-D interpolation of ground surface displacements

Subsidence is a hazard that may have natural or anthropogenic origin causing important economic losses. The area of Murcia city (SE Spain) has been affected by subsidence due to groundwater overexploitation since the year 1992. The main observed historical piezometric level declines occurred in the periods 1982–1984, 1992–1995 and 2004–2008 and showed a close correlation with the temporal evolution of ground displacements. Since 2008, the pressure recovery in the aquifer has led to an uplift of the ground surface that has been detected by the extensometers. In the present work an elastic hydro-mechanical finite element code has been used to compute the subsidence time series for 24 geotechnical boreholes, prescribing the measured groundwater table evolution. The achieved results have been compared with the displacements estimated through an advanced DInSAR technique and measured by the extensometers. These spatio-temporal comparisons have showed that, in spite of the limited geomechanical data available, the model has turned out to satisfactorily reproduce the subsidence phenomenon affecting Murcia City. The model will allow the prediction of future induced deformations and the consequences of any piezometric level variation in the study area.

Application of multi-sensor advanced DInSAR analysis to severe land subsidence recognition: Alto Guadalentín Basin (Spain)

Multi-sensor advanced DInSAR analyses have been performed and compared with two GPS station measurements, in order to evaluate the land subsidence evolution in a 20-year period, in the Alto Guadalentín Basin where the highest rate of man-induced subsidence (> 10 cm yr−1) of Europe had been detected. The control mechanisms have been examined comparing the advanced DInSAR data with conditioning and triggering factors (i.e. isobaths of Plio-Quaternary deposits, soft soil thickness and piezometric level).

Evaluation of the potential of InSAR time series to study the spatio-temporal evolution of piezometric levels in the Madrid aquifer

The Tertiary detritic aquifer of Madrid (TDAM), with an average thickness of 1500 m and a heterogeneous, anisotropic structure, supplies water to Madrid, the most populated city of Spain (3.2 million inhabitants in the metropolitan area). Besides its complex structure, a previous work focused in the north-northwest of Madrid city showed that the aquifer behaves quasi elastically trough extraction/recovery cycles and ground uplifting during recovery periods compensates most of the ground subsidence measured during previous extraction periods (Ezquerro et al., 2014). Therefore, the relationship between ground deformation and groundwater level through time can be simulated using simple elastic models. In this work, we model the temporal evolution of the piezometric level in 19 wells of the TDAM in the period 1997–2010. Using InSAR and piezometric time series spanning the studied period, we first estimate the elastic storage coefficient (Ske) for every well. Both, the Ske of each well and the average Ske of all wells, are used to predict hydraulic heads at the different well locations during the study period and compared against the measured hydraulic heads, leading to very similar errors when using the Ske of each well and the average Ske of all wells: 14 and 16 % on average respectively. This result suggests that an average Ske can be used to estimate piezometric level variations in all the points where ground deformation has been measured by InSAR, thus allowing production of piezometric level maps for the different extraction/recovery cycles in the TDAM.

Self-heating and deicing conductive cement. Experimental study and modeling

This research studies the self-heating produced by the application of an electric current to conductive cement pastes with carbonaceous materials. The main parameters studied were: type and percentage of carbonaceous materials, effect of moisture, electrical resistance, power consumption, maximum temperature reached and its evolution and ice melting kinetics are the main parameters studied. A mathematical model is also proposed, which predicts that the degree of heating is adjustable with the applied voltage. Finally, the results have been applied to ensure that cementitious materials studied are feasible to control ice layers in transportation infrastructures.

A hydrological–economic model for sustainable groundwater use in sparse-data drylands: Application to the Amtoudi Oasis in southern Morocco, northern Sahara

A hydrological–economic model is introduced to describe the dynamics of groundwater-dependent economics (agriculture and tourism) for sustainable use in sparse-data drylands. The Amtoudi Oasis, a remote area in southern Morocco, in the northern Sahara attractive for tourism and with evidence of groundwater degradation, was chosen to show the model operation. Governing system variables were identified and put into action through System Dynamics (SD) modeling causal diagrams to program basic formulations into a model having two modules coupled by the nexus ‘pumping’: (1) the hydrological module represents the net groundwater balance (G) dynamics; and (2) the economic module reproduces the variation in the consumers of water, both the population and tourists. The model was operated under similar influx of tourists and different scenarios of water availability, such as the wet 2009–2010 and the average 2010–2011 hydrological years. The rise in international tourism is identified as the main driving force reducing emigration and introducing new social habits in the population, in particular concerning water consumption. Urban water allotment (PU) was doubled for less than a 100-inhabitant net increase in recent decades. The water allocation for agriculture (PI), the largest consumer of water, had remained constant for decades. Despite that the 2-year monitoring period is not long enough to draw long-term conclusions, groundwater imbalance was reflected by net aquifer recharge (R) less than PI + PU (G < 0) in the average year 2010–2011, with net lateral inflow from adjacent Cambrian formations being the largest recharge component. R is expected to be much less than PI + PU in recurrent dry spells. Some low-technology actions are tentatively proposed to mitigate groundwater degradation, such as: wastewater capture, treatment, and reuse for irrigation; storm-water harvesting for irrigation; and active maintenance of the irrigation system to improve its efficiency.

Geological risk assessment of Amtoudi Agadir in southern Morocco: a key case for sustainable cultural heritage

Medieval fortified granaries known as “agadirs” are very common in southern Morocco, being catalogued as world cultural heritage by United Nations. These Berber buildings (made of stones and tree trunks) usually located on rocky promontories, constitute historical testimonials related to the origin of Morocco, and, as tourist attractions, have a positive impact on the local economy. The sustainability of these ancient monuments requires geological-risk evaluations of the massif stability under the agadir with the proposal of stabilization measures, and an architectonic analysis with appropriate maintenance of the structural elements. An interdisciplinary study including climate, seismicity, hydrology, geology, geomorphology, geotechnical surveys of the massif, and diagnosis of the degradation of structural elements have been performed on the Amtoudi Agadir, selected as a case study. The main findings from this study are that the prevalent rocks used for construction (coming from the underlying substratum) are good-quality arkosic sandstones; the SW cliffs under the agadir are unstable under water saturation; some masonry walls are too thin and lack interlocking stones and mortar; and failures in the beams (due to flexure, fracture, and exhaustion in the resistance due to insect attacks or plant roots) are common. The basic risk assessment of ancient buildings of cultural heritage and their geologic substratum are needed especially in undeveloped areas with limited capacity to implement durable conservation policies. Therefore, recommendations have been provided to ensure the stability and maintenance of this important archaeological site.

An approach for characterising the weathering behaviour of Flysch slopes applied to the carbonatic Flysch of Alicante (Spain)

Various studies indicate that most of the slope instabilities affecting Flysch heterogeneous rock masses are related to differential weathering of the lithologies that make up the slope. Therefore, the weathering characteristics of the intact rock are of great importance for the study of these types of slopes and their associated instability processes. The main aim of this study is to characterise the weathering properties of the different lithologies outcropping in the carbonatic Flysch of Alicante (Spain), in order to understand the effects of environmental weathering on them, following slope excavation. To this end, 151 strata samples obtained from 11 different slopes, 5–40 years old, were studied. The lithologies were identified and their mechanical characteristics obtained using field and laboratory tests. Additionally, the slaking properties of intact rocks were determined, and a classification system proposed based on the first and fifth slake cycles (Id1 and Id5 respectively) and an Index of Weathering (IW5), defined in the study. Information obtained from the laboratory and the field was used to characterise the weathering behaviour of the rocks. Furthermore, the slaking properties determined from laboratory tests were related to the in-situ weathering properties of rocks (i.e., the weathering profile, patterns and length, and weathering rate). The proposed relationship between laboratory test results, field data, and in-situ observations provides a useful tool for predicting the response of slopes to weathering after excavation during the preliminary stages of design.

Morphological classification of microtidal sand and gravel beaches

A new classification of microtidal sand and gravel beaches with very different morphologies is presented below. In 557 studied transects, 14 variables were used. Among the variables to be emphasized is the depth of the Posidonia oceanica. The classification was performed for 9 types of beaches: Type 1: Sand and gravel beaches, Type 2: Sand and gravel separated beaches, Type 3: Gravel and sand beaches, Type 4: Gravel and sand separated beaches, Type 5: Pure gravel beaches, Type 6: Open sand beaches, Type 7: Supported sand beaches, Type 8: Bisupported sand beaches and Type 9: Enclosed beaches. For the classification, several tools were used: discriminant analysis, neural networks and Support Vector Machines (SVM), the results were then compared. As there is no theory for deciding which is the most convenient neural network architecture to deal with a particular data set, an experimental study was performed with different numbers of neuron in the hidden layer. Finally, an architecture with 30 neurons was chosen. Different kernels were employed for SVM (Linear, Polynomial, Radial basis function and Sigmoid). The results obtained for the discriminant analysis were not as good as those obtained for the other two methods (ANN and SVM) which showed similar success.

SMRTool

Este programa se encuentra disponible en Excel y en código MATLAB.

SMRTool (MATLAB)

Versión MATLAB.

Datasets and results of the research [Discontinuity spacing analysis in rock masses using 3D point clouds]

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SMR analysis using 3DPC datasets

Datasets and results of the paper: Characterization of rock slopes through slope mass rating using 3D point clouds, Riquelme et al 2016, IJRMMS.

Characterization of rock slopes through slope mass rating using 3D point clouds

Rock mass classification systems are widely used tools for assessing the stability of rock slopes. Their calculation requires the prior quantification of several parameters during conventional fieldwork campaigns, such as the orientation of the discontinuity sets, the main properties of the existing discontinuities and the geo-mechanical characterization of the intact rock mass, which can be time-consuming and an often risky task. Conversely, the use of relatively new remote sensing data for modelling the rock mass surface by means of 3D point clouds is changing the current investigation strategies in different rock slope engineering applications. In this paper, the main practical issues affecting the application of Slope Mass Rating (SMR) for the characterization of rock slopes from 3D point clouds are reviewed, using three case studies from an end-user point of view. To this end, the SMR adjustment factors, which were calculated from different sources of information and processes, using the different softwares, are compared with those calculated using conventional fieldwork data. In the presented analysis, special attention is paid to the differences between the SMR indexes derived from the 3D point cloud and conventional field work approaches, the main factors that determine the quality of the data and some recognized practical issues. Finally, the reliability of Slope Mass Rating for the characterization of rocky slopes is highlighted.

Proposal of a New Parameter for the Weathering Characterization of Carbonate Flysch-Like Rock Masses: The Potential Degradation Index (PDI)

The susceptibility of clay bearing rocks to weathering (erosion and/or differential degradation) is known to influence the stability of heterogeneous slopes. However, not all of these rocks show the same behaviour, as there are considerable differences in the speed and type of weathering observed. As such, it is very important to establish relationships between behaviour quantified in a laboratory environment with that observed in the field. The slake durability test is the laboratory test most commonly used to evaluate the relationship between slaking behaviour and rock durability. However, it has a number of disadvantages; it does not account for changes in shape and size in fragments retained in the 2 mm sieve, nor does its most commonly used index (Id2) accurately reflect weathering behaviour observed in the field. The main aim of this paper is to propose a simple methodology for characterizing the weathering behaviour of carbonate lithologies that outcrop in heterogeneous rock masses (such as Flysch slopes), for use by practitioners. To this end, the Potential Degradation Index (PDI) is proposed. This is calculated using the fragment size distribution curves taken from material retained in the drum after each cycle of the slake durability test. The number of slaking cycles has also been increased to five. Through laboratory testing of 117 samples of carbonate rocks, extracted from strata in selected slopes, 6 different rock types were established based on their slaking behaviour, and corresponding to the different weathering behaviours observed in the field.