1,217 research outputs found
Homm-sw. Networks-of-stories to value tangible and intangible heritage in museum: abstract, poster & e-poster
No full text1st International Conference on Digital Heritag
Book Review: The Quest for Postmodern Ethics: A Phenomenological Comparison of the Philosophies of Martin Heidigger and Sri Aurobindo Ghose
No full textA review of The Quest for Postmodern Ethics: A Phenomenological Comparison of the Philosophies of Martin Heidigger and Sri Aurobindo Ghose by R. Brad Bannon
Imaging and characterization of heterogeneous landfills using geophysical methods
No full textNowadays many countries use landfilling for the management of their waste or for treating old landfills. Emissions from landfills can be harmful to the environment and to human health, making the stabilization of landfills a priority for the landfill communities. Estimation of the emission potential for determination of the aftercare period and improvement of the treatment technologies for the minimization of the aftercare period are examples of problems landfill research groups are now facing. For handling these problems, the degradation processes inside the landfill, which highly depend on the heterogeneity of the landfill, must be well understood. Geophysical methods can be used to image and characterize the heterogeneity of the landfill body non-intrusively. Researchers have earlier used geophysical methods for landfills. However, till now, artifacts, uncertainties and low resolution remained problematic in imaging and characterizing the landfill body in detail. In addition, the results so far have been rather qualitative. In this thesis, we aim to improve the imaging and characterization of landfill bodies using seismic and electrical methods, by proposing new ways to deal with some major problems that were previously encountered. A landfill body is very heterogeneous with many high-density areas that act as obstructions to the fluid flow. Characterization of these high-density areas is important for the understanding of the preferential flow paths inside the landfill body and hence of the degradation processes. These high-density areas manifest themselves as scatterers in the recorded seismic wavefield. Till now, research works using the seismic method have had difficulties in imaging a landfill body mainly because of the presence of very strongly scattered seismic energy. We investigate the use of seismic interferometry (SI), by performing a number of modeling studies, to improve the imaging. The additional amount of traces and sources computed by SI provides more information, as an increased number of rays penetrate into the earth and are recorded. Furthermore, scatterers act as secondary sources illuminating the landfill from below, thus reducing possible artifacts due to the location of the seismic receivers and sources only at the earth's surface. We discuss in detail the concept of using SI for landfill application and its advantages. The SI approach is compared with the conventional reflection seismic survey (CRSS), considering different acquisition geometries and processing and acquisition errors. Our results have established the merits of SI in landfill applications. The next step was to test our modeling results on field data. For this, we acquire seismic datasets at two different landfill sites. Before applying SI to the CRSS data, we attempt to image the landfill body solely by CRSS. We have found that this is possible when special processing steps are adopted. Special care has been taken in velocity analysis. The developed methodology is proposed to be used for very heterogeneous subsurfaces in order to image the higher-density areas (scatterers) in detail. We apply this procedure in two fieeld datasets. We have succeeded to image higher-density areas, the top and bottom of the landfill, and the geological subsurface below the landfill body. The geometry used in acquiring the second field dataset was better for the purpose than the first one, resulting in an improved imaging of the landfill. SI is applied to the first acquired field dataset for validation of the modeling studies. Not only have we been able to improve the imaging of the landfill body, but we have also proposed a new method for the removal of surface waves that dominate the field seismic data. In our first field dataset, surface-wave signal from another source was recorded; that was not possible to be removed using conventional processing/filtering techniques. We use the method of adaptive subtraction (AS) involving SI to remove the surface waves and have, thereby, shown the improved imaging of reflections inside the landfill body. Finally, we explore the improvement of the characterization of the landfill body when using the velocity analysis results from all three approaches (CRSS, SI and AS). Besides imaging, the characterization of the higher-density areas and of the leachate- and gas/air-bearing zones inside the landfill is very important for understanding the degradation processes. Using a landfill-specific empirical relationship between the unit weight and shear (S)-wave velocity of the landfill materials, we have calculated the density distribution inside the landfill. These values can be used in models that predict the emission potential. For further characterization, we use electrical methods in conjunction with the seismic methods. In the first study, we are able to determine the heterogeneities (wet and dry pockets) through combined use of S-wave velocity and electrical resistivity (ER). S-wave velocity can resolve the high-density areas (scatterers) that act as an obstruction to the fluid flow. ER helps to identify the pockets that represent accumulation of water (low-resistivity values) above the high-density areas. In the second field study, we acquire S- and compressional (P)-wave reection seismic datasets. By jointly interpreting the results, leachate and gas/air bearing zones are distinguished. The conditions that must be met for interpreting leachate or gas/air (relatively dry) zones are thoroughly discussed, taking into account the P- and S-wave velocities. Interpreting results of ER and induced polarization (IP) measurements acquired at the same location as the seismic surveys, the structure of the landfill is better defined, wet and gas pockets are further characterized, and an indication for the type of the waste is obtained. The velocity analysis of extremely heterogeneous seismic data is challenging. We check the velocity distribution obtained from analysis of seismic reflection data by comparing it with the results of multichannel analysis of surface waves (MASW) and early-arrival waveform tomography. In the second field study, additional measurements (gas concentration and mechanical resistance to waste deformation) are used for validation of results from seismic and electrical methods. The methodology developed in this research presents a way for improved imaging and characterization of a heterogeneous landfill body through use of specially adapted seismic and electrical methods. New approaches are presented to overcome some problems that were encountered in the past and to provide more reliable, quantitative results.Geoscience & EngineeringCivil Engineering and Geoscience
Soil properties from seismic intrinsic dispersion
No full textTheoretical and experimental studies in the past have shown the sensitivity of seismic waves to soil/rock properties, such as composition, porosity, pore fluid, and permeability. However, quantitative characterization of these properties has remained challenging. In case of unconsolidated soils, the inherently loose and heterogeneous nature complicates the task of obtaining the in situ properties and spatial variations. In this thesis, we investigate the possibility of exploiting the information of seismic intrinsic dispersion in the low frequency band (10-200 Hz), which is relevant to onshore field data, in order to quantify these physical properties, with special focus on soil porosity and permeability. In situ values of these properties are crucial in many different projects. We first investigate the frequency-dependent seismic velocity and attenuation caused by inelastic losses at grain contacts and wave-induced fluid flow at different scales (from grain size to seismic wavelength), using the theory of poroelasticity first proposed by Biot and many subsequent extensions and modifications. Several pertinent models of poroelasticity are looked at in order to find out their applicability in explaining the observed seismic dispersion. The observed dispersion can vary greatly between various unconsolidated, fully-saturated soils. Further, we develop a stress-dependent Biot (SDB) model in order to study the behaviour of seismic waves propagating through a fully-saturated porous medium subjected to different stress conditions. This is achieved by combining the mechanics of granular soils with the effective-stress laws, finally coupling with Biot's theory. Careful analyses of the underlying soil/rock physics that relate geophysical observations to the physical properties reveal an interesting feature in the property domain among several different measurements. This is an extention to some recent work done by others. We have found that it is possible to find two or more measured quantities, showing contrasting (sometimes quasi-orthogonal) behaviour in the common parameter space, such that a combination of those measured quantities leads to a physics-based uniqueness in the property estimation. This quasi-orthogonality in the common property domain among different measured quantities is advantageously used for estimation of porosity, permeability, water saturation, and effective stress. Several numerical examples are presented where P- and S-wave velocity and attenuation are efficiently integrated in order to obtain soil properties. In addition to seismic waves, electromagnetic waves are briefly considered for extracting extra soil properties. In this research, considerable attention has been paid to the investigation of S waves travelling through a porous medium, since S waves have well-known significance in the context of shallow subsurface characterization. Twelve selected datasets of frequency-dependent S-wave velocity and attenuation from various soft-soil sites are used in this study. Data for fully-saturated, unconsolidated soils from land/onshore environment are only considered. It is found that the behaviour of seismic intrinsic dispersion can vary greatly with the soil-type. One of the main challenges in property estimation using intrinsic dispersion relates to reliable extraction of the information of intrinsic dispersion from the recorded seismic data. The difficulty lies in the quantification of scattering attenuation, the effect of which is always present in the recorded seismograms due to the wavelength-scale and smaller heterogeneities in the subsurface. Scattering has an absorption-like effect on the transmitted seismic energy. Accordingly, determining and subtracting the scattering attenuation from the total (or apparent) attenuation is critically important. We have discussed and successfully tested an approach, achieving this goal. Several shallow vertical seismic profiling (VSP) measurements are conducted in the field using a recently developed digital, array-seismic cone penetrometer (CPT) system. CPT provides information on cone-tip resistance, sleeve friction, and pore pressure, thus offering direct, additional knowledge on geological layering, that is used to calculate the scattering attenuation. To obtain the soil properties, an inversion algorithm is presented based on simulated annealing and the poroelasticity theory. We study the sensitivity of different parameters involved in the cost function to be minimized. The most and the least sensitive parameters are discriminated based on the eigenanalyses of the covariance matrix of the gradient of the cost function. The eigenvectors and the corresponding eigenvalues of the covariance matrix are used to navigate efficiently the search algorithm in the multidimensional space and find a relatively stable, global solution of the cost function. Finally, we apply the methodology developed in this research to a VSP dataset acquired in a layered sequence of siltstone, shale and sandstone. The porous sandstone contains hydrocarbon accumulations. The influence of fluid mobility (permeability-to-viscosity ratio) on the estimated P-wave intrinsic dispersion is distinctly observed. Using optimization by simulated annealing together with VSP and well-log measurements, the Biot and squirt flow (BISQ) model is found to provide one possible mechanism for the observed dispersion. The layer-specific fluid mobility values are estimated using our approach; they are found to be close to the independent measurements of mobility using Stoneley waves and from dynamic formation-tests carried out at the same borehole. The depth distribution of fluid mobility matches well between our estimate and the independent measurements. The methodology developed and the results obtained in this research pave the way to a new direction for in situ, quantitative soil/rock characterization using seismic waves.Geoscience & EngineeringCivil Engineering and Geoscience
Analysis of 9-component SCPT data to obtain shallow subsoil structure
No full textA 9-component seismic cone penetration test (SCPT) was conducted at a site near Delft. A sledge hammer striking horizontally a wooden plate was used to generate shear (S) waves polarized in the crossline and inline directions. A vertical hammer hitting a metal plate generated the P wave. The data were acquired using a recently developed array (7-level) 3-component SCPT tool. In addition to downhole SCPT data, surface seismic data were collected using 24 3-component geophones planted at 0.75 m interval on the ground. The most explicit layer boundaries are found at 4.5 m, 5.5 m and 10 m depths. The following velocity model for the shallow subsoil could be obtained. 2.5-4.5 m: Vs=82.23 m/s, Vp=951.77 m/s; 4.5-5.5 m: Vs=33.01 m/s, Vp=488.33 m/s; 5.5-10 m: Vs= 92, 52 m/s, Vp=1483.89 m/s; 10-14.5 m: Vs=221.80 m/s, Vp=796.58 m/s.Applied Geophysics and PetrophysicsGeoscience & EngineeringCivil Engineering and Geoscience
Crosswell nonlinear seismic waveform inversion without downhole sources and its application to time-lapse monitoring
No full textCrosswell seismic measurements enable obtaining high resolution, high accuracy images of the subsurface between boreholes. They are, however, generally expensive considering the need of deployment of special downhole sources. In this study, we develop a novel nonlinear waveform inversion to estimate velocity structures between two vertical boreholes using VSP data without downhole sources. Contrary to the conventional full waveform inversion (FWI), the effect of wave propagation between surface sources and one of the vertical boreholes is appropriately cancelled using representation theory. Furthermore, it enables us to calculate partial derivatives of the cost function without explicitly resolving the Green’s functions in seismic interferometry. We test numerically this new approach of time-lapse monitoring of a deeper target layer, considering also the effect of changes in the complex, shallow vadose zone. We assume that the temporal changes in velocity in the vadose zone are larger than those at the deeper target layer. Our results show that in contrast to conventional FWI, the newly developed approach has the advantages of expensive crosswell seismics involving downhole sources. The estimated velocity is robust against spatiotemporal changes in the near-surface. The approach will be very useful when accurate time-lapse seismic measurements are needed in a cost-effective manner. Accepted author manuscriptApplied Geophysics and Petrophysic
Time-lapse target-oriented crosswell full waveform inversion without downhole sources
No full textTime-lapse seismics has a wide range of application in different scales, from near-surface to resource exploration. Crosshole seismics is used to characterize fluid reservoirs and to obtain highly resolved rock/soil-dynamic parameters e.g., elastic moduli and Poisson ratio. Developments in distributed acoustic sensing shows the potential of deploying permanent downhole receivers at low costs. In order to achieve an efficient and accurate time-lapse seismic measurement in such scenarios, we have developed a nonlinear waveform inversion to reconstruct velocity structure between boreholes using VSP data with source located only at the surface, and no downhole sources. The new approach formulates the forward modelling using wavefield representation theorem, which enables directly estimating the velocity structure by minimizing data residuals and calculating the gradient from the adjoint state problem. We test the approach using numerical modelling of time-lapse VSP data to detect layer-specific temporal changes. A heterogeneous shallow vadose zone represents a low-velocity layer. The results show that the new approach provides more stable and more accurate temporal velocity profiles than conventional full waveform inversion, when the initial velocity model does not include the shallow low-velocity layer. The new approach is robust and highly advantageous as it does not require downhole seismic sources. Accepted author manuscriptApplied Geophysics and Petrophysic
A Novel Methacrylate Derivative Polymer That Resists Bacterial Cell-Mediated Biodegradation Data Sharing Archive
No full textFigure DataWe studied biodegradation resistance of a custom synthesized (by TDA Research Inc) novel ethylene glycol ethyl methacrylate (EGEMA) with ester bond linkages that are external to the central polymer backbone when polymerized. Experiments were designed to compare degradation resistance with Ethylene glycol dimethacrylate (EGDMA) with internal ester bond linkages. The data has been published in an article titled "A Novel Methacrylate Derivative Polymer That Resists Bacterial Cell-Mediated Biodegradation" in the Journal of Biomedical Materials Research: Part B - Applied Biomaterials. The data in this record supports the figures in the published manuscript.NIH/NIDCR 1R43DE024013Kumar, Dhiraj; Ghose, Debarati; Mutreja, Isha; Bolskar, Robert D; Jones, Robert S. (2021). A Novel Methacrylate Derivative Polymer That Resists Bacterial Cell-Mediated Biodegradation Data Sharing Archive. Retrieved from the Data Repository for the University of Minnesota (DRUM), https://doi.org/10.13020/jms8-pq47
Seismic interferometry as a tool for improved imaging of the heterogeneities in the body of a landfill
No full textAccepted Author ManuscriptGeo-engineeringApplied Geophysics and Petrophysic
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