Tomographic inversion of time-domain resistivity and chargeability data for the investigation of landfills using a priori information

In this paper, we present a new code for the modelling and inversion of resistivity and chargeability data using a priori information to improve the accuracy of the reconstructed model for landfill. When a priori information is available in the study area, we can insert them by means of inequality constraints on the whole model or on a single layer or assigning weighting factors for enhancing anomalies elongated in the horizontal or vertical directions. However, when we have to face a multilayered scenario with numerous resistive to conductive transitions (the case of controlled landfills), the effective thickness of the layers can be biased. The presented code includes a model-tuning scheme, which is applied after the inversion of field data, where the inversion of the synthetic data is performed based on an initial guess, and the absolute difference between the field and synthetic inverted models is minimized. The reliability of the proposed approach has been supported in two real-world examples; we were able to identify an unauthorized landfill and to reconstruct the geometrical and physical layout of an old waste dump. The combined analysis of the resistivity and chargeability (normalised) models help us to remove ambiguity due to the presence of the waste mass. Nevertheless, the presence of certain layers can remain hidden without using a priori information, as demonstrated by a comparison of the constrained inversion with a standard inversion. The robustness of the above-cited method (using a priori information in combination with model tuning) has been validated with the cross-section from the construction plans, where the reconstructed model is in agreement with the original design

Hybrid approach for travel time seismic tomography in elliptical anysotropic media

Hybrid approach for seismic travel time tomography is proposed in the case of elliptical anisotropic media. A sequential scheme is presented that combines Simulating Annealing with Linearized Least Squares inversion: at first, Simulated Annealing is implemented to obtain a velocity model that can be used as initial guess for successive Linearized Least Square inversion; in the meantime Linear Traveltime Interpolation is diffusely used to trace raypaths and calculate traveltimes. The procedure was tested both for a synthetic model and a field study. Since the field study come from a previous study, uniquely solved by Linearized Least Squares inversion without suggestions for initial guess of the velocity model, we were interested in evaluating upgrades from hybrid approach compared with solutions coming from a single technique. We found hybrid approach able to individuate a better velocity model with respect to a ”single technique” approach but, as the improvement was slight despite of the big amount of computation time needed by simulated annealing, we had also an indirect validation of the previous results of the field study

Three-dimensional reconstruction of a masonry building through electrical and seismic tomography validated by biological analyses

In this paper, we present an integrated approach, for assessing the condition of an ancient Roman building, affected by rising damp and cracking phenomena. The combination of high-resolution geophysical methods, such as seismic and electrical tomography, with biological information, allowed a more detailed evaluation of the state of conservation of the masonry building. A preliminary three-dimensional electrical survey was conducted to detect the existing building foundations and to determine the variation of the resistivity in the ground. Then, electrical and seismic tomography investigations were carried out on an inner wall of opus caementicium, subjected to rising damp effects and cracks. This approach was adopted to obtain a high-resolution image of the wall, which allowed to identify the inner mortar and the outer brick component from resistivity and velocity contrasts. Furthermore, the geophysical results revealed evidence of wall fractures (indicated by low velocity and high resistivity values) and a significant volume where rising of damp was taking place (resulting in a low resistivity zone). Biological analyses validated the geophysical model: in fact, the biological proliferation occurred up to a height of 0.75 m, where the interface between high and low resistivity values was recovered. This approach can be employed to reconstruct a three-dimensional model of masonry structures in order to plan recovery actions

Pavement testing by integrated geophysical methods: Feasibility, resolution and diagnostic potential

This work is focused on the assessment of the diagnostic potential of several geophysical methods when applied to the investigation of a rigid airport pavement. The potential and limit of each technique are evaluated as well as the added value deriving from their integration. Firstly, we reconstruct a high-resolution image of the pavement by a large electromagnetic and georadar screening. An advanced processing of georadar data, implemented through the picking of the arrival times of reflections for each profile, provides a quantitative estimation of the deviation between the design and the as-built thickness of layers. Additionally, electrical tomography has been applied to unequivocally identify the anomalous zones, where higher values of resistivity would be associated to porous zones that are prone to degradation and failure. The seismic tomographic survey had the additional purpose to recover the mechanical properties of the pavement in terms of both P- and S-waves and consequently of elastic constants (Poisson's ratio), whose values were consistent with those recovered in literature. The anomalies detected by each technique are consistent in their indications and they can be correlated to failure phenomena occurring at layer interfaces within the pavement structure or to unexpected variations of the layer thicknesses. The cost-effective geophysical campaign has validated the four-layered system deduced from the original design and has been used to reconstruct a high-resolution map of the pavement in order to discriminate fractures, crack-prone areas or areas where the as-built differs from the original design

Engineering-geology model of the seismically-induced Cerda landslide

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3D tomography of some pillars of the Coliseum

A few years ago a 2D tomography survey was carried out (Bernabini et al., 1990) on some pillars of the >Coliseum. To cover a greater portion of the pillars and with the aim of clearly defining the velocity field and thus identifyining any evidence ov vertical variations, it was decided to enlarge the research by carrying outa 3D tomographic survey on the same pillars. The LSQR was the resolution algorithm utilized and the results obtained will be discussed and analysed

Seismic transmission tomography:determination of the elastic properties of building structures (some examples)

This paper is a general review on seismic transmission tomography considering data acquisition and processing. Some questions on linear and non linear inversions are tackled, and advice given on the choice of the best damping factor. Taking into account prediction matrices we show that it is possible to point out the best distribution of sensors and shot points in terms of resolution and stability of system. Then two examples in which seismic tomography was used are described concerning the determination of elastic characteristics of building structures